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Ed. 1.0 Sept 2007

Fire Weather 1Meteorological Concepts


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Slide 1

Session Goal

This training session introduces several meteorologicalconcepts which will help you to understand weathercharts, forecasts and fire weather

A number of diagrams used in this presentation are takenfrom Bureau of Meteorology publications (copyrightCommonwealth of Australia) and are used with theirpermission. For more details see Fire Weather 1Learning Manual


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Slide 2

Learning Outcomes

This training session will cover two learning outcomes

After completing this session you should be able toexplain:

how weather originates in terms of global circulation airmass and frontal characteristics, and how these

may impact fire behaviour


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Slide 3

Outline

1. What is weather?

2. Fundamentals of meteorology

3. Global circulation

4. Weather associated with high or low pressure

5. Airmass characteristics

6. Ridges, troughs and fronts

7. Effect of weather on fire behaviour


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Slide 4

Scenario

CFA Public Affairs

(used with their permission)


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Slide 5

What is Weather and Climate?

Weather describes the state of the atmosphere andhow it varies over short time periods from hours to days

Climate refers to the long term weather conditions at a

location over months or years, or average weather


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Slide 6

What is Fire Weather?

Fire weather describes the atmospheric conditions ofweather and climate in which:

(a) a wildfire is likely to be ignited

(b) a wildfire is difficult to suppress


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Slide 7

Key Weather Components

Temperature

Humidity

Wind

Precipitation Pressure


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Slide 8

Composition of the Atmosphere

Water vapourvaries between0 and 4%


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Slide 9

Vertical Structureof the Atmosphere

The Troposphere

Generally the lowest 10-12 km inVictorian latitudes

75% of the overall mass of the

atmosphere Temperature drops with height

Where weather happens!

The Stratosphere

Stable, dry layer above the level ofsurface convective currents

Temperature no longer falls with height

Contains the ozone layer


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Slide 10

Global Circulation

Global circulation describes atmospheric motion over theearth but what causes this?


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Slide 11

Incoming Solar Radiation

Solar energy combined with the earths geometry drives theweather


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Slide 12

Warm Air Rises

Heating air causes it to expand andbecome less dense

A sample of (otherwise identical) air that

is warmer than its surroundingenvironment will rise because it is lessdense and therefore lighter than the airaround it

Warm


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Slide 13

Cool Air Sinks

Cooling air causes it to contract andbecome more dense

A sample of (otherwise identical) air that

is cooler than its surroundingenvironment will sink because it is moredense and therefore heavier than the airaround it

Cold


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Slide 14

Pressure at the Earths Surface

Variations in surface pressureresult from differential solarheating

Rising air creates a relative void,resulting in low surface pressure

Sinking air creates a pile-up ofmass and high surface pressure

Supporting airflow is needed inthe upper atmosphere to sustainthese changes


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Slide 15

Simplified AtmosphericCirculation

A uniform, non-rotating earth,warmed at the equator andcooled at the poles

In reality this does not occurbecause:

The earth spins on its axisonce every 24 hours

There are seasonal variations

in solar heating The earth does not posses a

uniform surface oratmosphere


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Slide 16

A Dynamic Earth

Daily and annualvariations in solarheating

Surface featuresmountains, oceans,cities

Variations in thecomposition of the

atmosphere


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Slide 17

Coriolis Force

Coriolis force is anapparent deflection of theair from its path asdictated by the pressure

gradient force whenviewed by an observer onthe earths surface


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Slide 18

A Real Atmosphere

Real global circulation isdue to:

Variations in solarheating

Variations in the earthssurface features andatmosphere

Coriolis force


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Slide 19

Typical Global Conditions -February

Global map ofaverage sea levelpressure showingsubtropical highs

and equatoriallow (ITCZ)


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Slide 20

Typical Global Conditions -August

Global map ofaverage sea levelpressure showingsubtropical highs

and equatoriallow (ITCZ)


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Slide 21

Pressure Gradient Force

The atmospheretries to push airfrom high to lowpressure

Pressure GradientForce

S i S l Wi d i h


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Slide 22

Synoptic Scale Winds in theMid-latitudes

Air moves from high to lowpressure and is deflectedto the left by CoriolisForce. Eventually the two

forces balance and thewind blows parallel to theisobars

If you stand with your

back to the wind inAustralia the low pressurewill be on your right

Wi d St th d P


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Slide 23

Wind Strength and PressureGradient

The closer togetherthe isobars, thestronger the wind!


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Slide 24

High and Low Pressure Centres

In the southernhemisphere, windsblow anticlockwisearound highs and

clockwise around lowsbecause of the balancebetween PressureGradient Force,Coriolis Force and

Centrifugal Force


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Slide 25

The Influence of Friction

Friction acts in theopposite direction tosurface winds thisreduces the wind

speed

A force balance isreached where windvelocity is seen to

veer towards thedirection of lowerpressure

Hi h d L P C t


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Slide 26

High and Low Pressure CentresUnder the Influence of Friction

The balance offorces causes air tobe deflected awayfrom the centre of

highs and deflectedtowards the centreof lows


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Slide 27

Wind and the Weather Map


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Slide 28

Weather and High Pressure

Subsiding air tends to create more stable conditions asubsidence inversion can occur

Temperature:

Dependent upon upstream airmass Tends to increase, especially if the high pressure centre

moves to the east of Victoria

Cloud:

Low likelihood of cloud and precipitation Low cloud may become trapped under a subsidence

inversion


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Slide 29

Weather and Low Pressure

Rising air tends to create less stable conditions asubsidence inversion will erode

Temperature:

Dependent upon upstream airmass Tends to decrease, especially following the passage of a

cold front or low pressure trough

Cloud:

High chance of mid-level and convective cloud High chance of precipitation


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Slide 30

Airmasses

Airmasses are classified according to their sourceorigin. Consider the air upstream:

Is it continental, maritime, polar or tropical?

Is it dry or moist, warm or cool? In some instances air from the Southern Ocean can be

very dry

Consider how rapidly or slowly the airmass is moving

Consider whether the air will be modified: How will diurnal changes influence the air?

Will the air be moving from water to land?


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Slide 31

Summer Airmass Characteristics

Tropical

Maritime Tropical

MaritimeTropical

Continental

Southern

MaritimeSouthern

Maritime

Southern

Maritimemodifiedby

TasmanSea


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Slide 32

Winter Airmass Characteristics

Tropical

Maritime

Southern

Maritime

Southern

MaritimePolar

MaritimePolar

Maritime

Southern

Maritime


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Slide 33

Ridges and Troughs

Ridge:

An elongated area of relatively higher pressure associatedwith anticyclonic flow

Commonly extend from a high pressure system

Typically bring light winds and warm, clear weather

Trough:

An elongated area of relatively lower pressure associatedwith cyclonic flow

Commonly extend from a low pressure system

Typically bring cool, unsettled weather and precipitation


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Slide 34

Fronts

The boundary between airmasses of different densitiesis referred to as a front

Four types of front are evident:

Cold Warm

Occluded

Stationary

Cold fronts are most common in SE Australia


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Slide 35

Cold Front

A cold front is the boundary between a cold airmassmoving towards a region of warmer air

A backward sloping face forms as the cool, dense airslides underneath the warmer, lighter air ahead

Warm air retains more moisture than cold air so as it israpidly forced upwards, any moisture condenses out toform cloud and precipitation

Strong and gusty winds, cloud, rainfall, thunderstormsand falling temperatures are typically experiencedduring the passage of a cold front


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Slide 36

Profile of a Cold Front


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Slide 37

Cold Fronts in Victoria

The typical weather changes associated with thepassage of a cold front in Victoria are:

Strengthening and gusty northeasterly to northwesterlywinds before the front

Increasing evidence of instability such as cumulus cloud ordeveloping thunderstorms

A west to southwesterly wind change which can be quiteabrupt and bring severe squalls

A moderation of the wind speed and a clearing of theweather behind the front


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Slide 38

Wind Changes

A wind change refers to a distinct shift of winddirection, greater than 30, where wind speeds beforeor after the change are 10 km/h or more

In Victoria, the passage of a cold front is often referredto as a wind change or just a change because theseconditions are generally met

Cold Fronts Wind Changes and


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Slide 39

Cold Fronts, Wind Changes andFire Behaviour

Cold fronts, or changes, have a major impact on firebehaviour:

Strong, gusty, hot and dry north to northwesterly windsprior to the change promote fast moving intense fires

Lighting may ignite new fires

It might be a dry change i.e. precipitation is not expected

The west to southwesterly wind change may turn the eastflank of the fire into the main fire front

Effect of a Wind Change on Fire


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Slide 40

Effect of a Wind Change on FireBehaviour


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Slide 41

Summary

The sun is the driving force behind the worlds weather

Changes in air density create regions of high and lowpressure

Air will tend to move from high to low pressure Air flows anticlockwise around highs (anticyclones) and

clockwise around lows (cyclones)


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Slide 42

Air will rise:

As it converges towards low pressure

If it is less dense than the surrounding air

If it is forced by a barrier or another airmass Airmass characteristics can be determined from

examination of the weather map.

Fronts are the boundaries between airmasses of

different densities Fire behaviour can alter dramatically during a wind

change event


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Ed. 1.0 Sept 2007

Fire Weather 1Understanding Weather Charts


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Slide 44

Session Goal

This training session will introduce and describe weathercharts and their application

A number of diagrams used in this presentation are takenfrom Bureau of Meteorology publications (copyrightCommonwealth of Australia) and are used by permission.For more details see Fire Weather 1 Learning Manual


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Slide 45

Learning Outcomes

This training session will cover five learning outcomes

After completing this session you should understand:

the basic features depicted in a weather chart

how to interpret a weather chart typical summer and winter weather patterns in Australia

how to identify a day of severe fire danger from thesynoptic map

the three-dimensional nature of the atmosphere


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Slide 46

Outline

1. Typical features of a weather chart

2. Interpreting a weather chart

3. Typical summer and winter weather patterns in

Australia4. Severe fire weather on the synoptic map

5. Three-dimensional nature of atmosphere


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Slide 47

The Value of a Weather Chart

Weather charts or synoptic charts are veryrecognisable to most people

Weather charts display past, current and forecastinformation for a particular region

A large amount of material is contained within aweather map


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Slide 48

Typical Features of a Weather Map


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Slide 49

Isobars

Isobars indicate areasof constantatmospheric pressurein the same way that

contours indicateareas of constantaltitude on a landmap

Rid d Hi h P


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Slide 50

Ridges and High Pressure

High pressure zonesare clearly visible

Ridge axes areidentified by a wavy

line

T h d L P


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Slide 51

Troughs and Low Pressure

Low pressure zonesare clearly visible

Trough axes areidentified by a

dashed line theseare less clearlydefined than ridgeaxes

F t W th M


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Slide 52

Fronts on a Weather Map

Cold fronts are indicated by a solid triangle (blue on acoloured map) in the direction of the movement

Warm fronts are indicated by a solid semicircle (red ona coloured map) in the direction of the movement

Occluded fronts are indicated by alternating solidsemicircles and triangles (purple on a coloured map) inthe direction of movement

Stationary fronts are indicated by a solid line alternated

with triangles (blue on a coloured map) towards thewarmer air and semicircles (red on a coloured map)towards the colder air

Examples of Fronts on a


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Slide 53

Examples of Fronts on aWeather Map

Typical Summer Weather


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Slide 54

Typical Summer WeatherPatterns in Australia

The mean path ofsummer high pressurecentres across southern

Australia as a result of

global circulation

Summer Weather Pattern 1:


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Slide 55

Summer Weather Pattern 1:Easterly Dip

A high pressure centreover the Bight directssoutheasterly windsover Victoria and NSW,

whilst a low overQueensland reinforcesthose easterlies

Victoria is likely toexperience cool andmoist conditions

Summer Weather Pattern 2:


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Slide 56

Summer Weather Pattern 2:Summer Heatwave

The SummerHeatwave results froma ridge associated witha blocking high

pressure system overthe Tasman Sea

Victoria is likely toexperience fine and hotweather

Typical Winter Weather


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Slide 57

Typical Winter WeatherPatterns in Australia

The mean path of winterhigh pressure centresacross southern Australiaas a result of global

circulation

Winter Weather Pattern:


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Slide 58

Winter Weather Pattern:Winter High

A high pressure centreover eastern Australiawith an associated ridgeextending westwards

Stable, cold and clearconditions would beexperienced as frontalactivity is restricted

Fire Weather and the Synoptic


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Slide 59

Fire Weather and the SynopticMap

A day in which severe firedanger may occur can bepredicted when specificsynoptic patterns are

known and identified onthe forecast weather chart

A Th Di i l At h


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Slide 60

A Three-Dimensional Atmosphere

Most weather mapsdisplay sea levelpressure when in realitythe atmosphere is three-

dimensional Upper level charts are

available that showmeteorologicalinformation aboveground level

300 hPa map

Atmospheric Thickness


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Slide 61

Atmospheric Thickness

Thickness refers to theheight of the layer between1000 hPa (~sea level) and500 hPa in metres or

decametres If the column of air is

heated, it expands andthe height increases

If the column of air iscooled, it contracts andthe height decreases


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Slide 62

Thickness is therefore a measure of how warm or coldthe atmosphere is between 1000 hPa and 500 hPa thiscan be related to ground level conditions

The warmer the 1000 hPa to 500 hPa layer, the higherthe temperature is likely to be at ground level

Thickness on a Weather Chart


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Slide 63

Thickness on a Weather Chart

Thickness is indicated

by dashed lines in

metres

Summary


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Slide 64

Summary

Features of a weather map include areas of high andlow pressure, ridges, troughs, and fronts

Synoptic charts give an indication of the weatherthrough applying the concepts of global circulation and

airmass characteristics

Typical seasonal weather patterns exist in Australia

An day of severe fire weather can often be predictedfrom a synoptic map

Atmospheric thickness gives an indication of theexpected temperature at the earths surface


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Ed. 1.0 Sept 2007

Fire Weather 1Satellite and Radar Interpretation

Session Goal


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Slide 66

Session Goal

This session will introduce the use of satellite and radarimagery in meteorology and discuss its interpretation

A number of diagrams used in this presentation are takenfrom Bureau of Meteorology publications (copyright

Commonwealth of Australia) and are used with theirpermission

Satellite images are credited where appropriate

Learning Outcomes


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Slide 67

Learning Outcomes



the different types of satellite and radar images

what meteorological features are present on a satellite orradar image

Outline


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Slide 68

Outline

1. Introduction to remote sensing

2. Satellite imagery:

Infrared

Visible Water vapour

3. Other uses of satellite technology

4. Radar imagery

Remote Sensing in Meteorology


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Slide 69

Remote Sensing in Meteorology

Remote sensing is the art of obtaining informationabout an object without physical contact

Remote sensing techniques:

Allow data to be obtained from gaps between the fixedAutomatic Weather Stations

Provide data about the upper atmosphere

Provide holistic information i.e. complete weathersystems can be seen on a single image

Passive and active remote sensing is available

Satellite Imagery


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Slide 70

Satellite Imagery

Passive satellite imagery is available in three forms:

Infrared

Visible

Water vapourThese are viewable as a single image or as a continuousloop

Infrared Satellite Imagery


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Slide 71

Infrared Satellite Imagery

Infrared images are pictures of the earth andatmosphere taken in the infrared part of theelectromagnetic spectrum they measure heat leavingthe earth and atmosphere

In an infrared image, brighter areas represent colderfeatures - higher cloud is colder than lower cloud andwill therefore appear brighter

Colour enhancements aid interpretation

Infrared images are available 24 hours a day

Example of Infrared Satellite


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Slide 72

pImagery

Images originally processed by the Bureau ofMeteorology from a geostationary satellite operated bythe Japan Meteorological Agency

Visible Satellite Imagery


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Slide 73

Visible Satellite Imagery

Visible images are created by measuring the reflectedsolar radiation from the earth and atmosphere in thevisible spectrum i.e. like a normal photograph

Land and water are generally dark grey to black

whereas clouds are typically white or light grey

Greater reflection is evident for thicker clouds and theyappear brighter on visible satellite images

It can be difficult to discern between clouds at different

altitudes

Visible images are unavailable during the night

Example of Visible Satellite


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Slide 74

pImagery

Image originally

processed by the Bureau

of Meteorology from a

geostationary satellite

operated by the JapanMeteorological Agency

Water Vapour Satellite Imagery


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Slide 75

Water Vapour Satellite Imagery

Water vapour images indicate moisture in the upperatmosphere (mainly upwards of 4 km above sea level)

They also provide information on upper level circulationthat may not be apparent on other satellite imagery

Dry air is typically shown by darker colours whereasmore moist conditions are lighter and brighter

Example of Water Vapour


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Slide 76

Satellite Imagery

Image originally processed

by the Bureau of

Meteorology from a

geostationary satellite

operated by the JapanMeteorological Agency

Other Uses of Satellite


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Slide 77

Technology

Satellites can detect morethan just meteorologicalinformation:

smoke plumes

dust storms

Victorian Alpine Fires 2003 smoke plume image

originally processed by the Bureau of Meteorology

from a polar orbiting satellite operated by the US

NOAA


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Slide 78

Visible dust storm over eastern Australiaon 23rd October 2002 image originally

processed by the Bureau of Meteorology

from a polar orbiting satellite operated by

the Chinese Meteorological Administration

Radar Imagery


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Slide 79

Radar Imagery

Radar works by a transmitter emitting a pulse of radiowaves into the atmosphere, part of which is scatteredback by rain droplets and other debris

The location and intensity of precipitation is determined

by the time taken for the scattered pulses to return tothe receiver and the power with which they return:quicker and more intensely returned pulses indicateheavier precipitation

A horizontal map is produced of where rain is fallingand an indication of how heavily it is falling

Example of Radar Imagery


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Slide 80

Example of Radar Imagery

Radar Interpretation


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Slide 81

Radar Interpretation

Radar interpretation can be difficult:

The radar beam widens and increases in altitude with increasingdistance from the source, and therefore echo intensity is reducedand it can miss rainfall at increasing distances from the radarinstallation. Rainfall detected at a high level may evaporate

before hitting the ground Radar reflectivity is strongly dependent on the diameter of

raindrops rather than the amount of raindrops

A shadow effect can occur e.g. a thunderstorm cell close to theinstallation can shield the area of atmosphere in its wake

A lack of large droplets may result in the underestimation of

drizzle intensity It is possible for the radar to pick up insect swarms or smoke

plumes from major fires

Summary


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Slide 82

Summary

Remotely sensed imagery fills the gaps between fixedAutomatic Weather Stations and is holistic

Infrared, visible and water vapour satellite imagery isavailable in single image or continuous loop format

Radar images are useful in identifying precipitation interms of location and intensity, however a number oflimitations can reduce the accuracy

Remotely sensed imagery assists in the identification of

features such as cold fronts, dry air, rainbands,showers and thunderstorms


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Ed. 1.0 Sept 2007

Fire Weather 1Local Weather Effects

Session Goal


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Slide 84

Session Goal

This session will introduce several local weather effectsthat need to be considered in conjunction with thesynoptic weather situation when analysing fire behaviour

A number of diagrams used in this presentation are taken

or adapted from Bureau of Meteorology publications(copyright Commonwealth of Australia) and are used withtheir permission. For more details see Fire Weather 1Learning Manual

Learning outcomes


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Slide 85

Learning outcomes

This training session will cover three learning outcomes


several local weather effects

situations in which local weather effects may develop

how local weather effects may affect a fire

Outline


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Slide 86

Outline

1. Sea/land influenced winds

2. Mountain and valley winds

3. Thunderstorm outflow

4. Fire induced effects5. Synoptic weather influences

Weather on a Local Scale


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Slide 87

Weather on a Local Scale

Small-scale meteorological phenomena that impact aparticular area in isolation are referred to as localweather effects

In many instances local weather effects can dominate

over large-scale conditions e.g. during light synopticwinds

Local weather effects can have a significant impact onfire behaviour wildfires often become erratic andunpredictable

Sea Breeze


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Slide 88

Sea Breeze

During the day the landwarms more quickly thanthe water

Air above the land

warms, expands andrises causing surface lowpressure

Cooler and more moist

air in the high pressureregion over the waterflows onshore

Land Breeze


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Slide 89

Land Breeze

At night the land coolsmore quickly than thewater

Air above the land cools,

and the dense air sinkscreating a surface highpressure region

Air flows from the land to

the low pressure regionover the water

Mountain and Valley Winds


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Slide 90

Mountain and Valley Winds

Mountain and valley winds are caused by threeprocesses:

Wind flow around and between obstacles

Wind flow over obstacles

Surface heating and cooling

Wind flow is very sensitive to topography and localweather effects in upland terrain can have a significantimpact on fire behaviour

Wind Flow Around and BetweenObstacles


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Slide 91

Obstacles

Air will attempt to flow around isolated obstacles ratherthan over them this is especially the case in stableatmospheric conditions as the air is unable to rise

Under such conditions the wind is strongest and most

turbulent on the lower mountain sides and is alsofunnelled through gaps in the ranges

Eddy Formation


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Slide 92

ddy o at o

If the terrain or obstacleis rough, airflowdownwind near groundlevel can become more

turbulent and a wakemay be created whereairflow is lighter butgustier in nature

An eddy can form in the

lee side of the hill, withflows opposite to thegeneral wind direction

Plan view

Plan view

Wind Channelling


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Slide 93

g

Wind can becomedirectionally channelledby ridges and valleysunder both light and

strong wind conditions Wind speed increases

due to funnelling

Plan view

Wind Flow Over Obstacles


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Slide 94

If air is unable to flow around an obstacle or theatmosphere is unstable it will be forced to rise andcross the obstacle in its path

Top acceleration and mountain waves can occur when

airflow passes over a region of steep topography If airflow encounters a large obstacle in its path (such

as a mountain):

1.The flow can remain as a single airflow (laminar flow) as

it passes over the obstacle, or2.The flow can become turbulent

Top Acceleration


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Slide 95

p

If the flow remainslaminar, and there is astable layer of air abovethe obstacle, wind speed

increases as the top ofthe obstacle isapproached this is topacceleration

Side view

Mountain Waves


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Slide 96

If airflow becomes turbulent, eddies and mountain wavescan form

Mountain waves typically occur when the wind forced overa mountain increases in speed with height in a mildly

unstable atmosphere In such cases, the air is forced up and the disturbance on

the lee side forms a series of wavelike troughs and peaksthat are sometimes recognisable by lenticular clouds

Rotors also occur due to mountain waves and are a closedparcel of air rotating along an axis parallel to the mountainrange but somewhat downwind


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Slide 97

In complex terrain, adecoupling between theair within and above thevalley rim can occur two

separate flow systemscan become evident

Side view

Up-Slope and Down-Slope Winds


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Slide 98

p p p

A number of up-slope and down-slope local weathereffects can occur in regions of undulating terrain due toheating or cooling of the air

These include:

Foehn

Katabatic

Anabatic

Under these conditions erratic and unpredictable fire

behaviour is likely, especially for up-slope winds wherepreheating effects to fuel upstream can increase fireintensity and rate of spread

Foehn Wind


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Slide 99

As a moist air parcel movesup-slope it cools andcontracts

Water vapour will condense

and is released. This processadds heat to the environment latent heat of condensation

Air that descends is warmerand drier a Foehn wind

Typically requires moist windsthat increase in speed withheight

Side view

Katabatic Wind


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Slide 100

The earth cools at night as it emitslongwave radiation

The layer of air directly above the groundalso cools and is then cooler than a layerof air at higher altitudes or a layer at the

same altitude but away from the slope This cooler and denser slab of air moves

down-slope under the influence of gravityforming a katabatic wind or drainage flow

Katabatic winds are strongest when the

sky is clear, in steep terrain wherevegetation is sparse, and when synopticwinds are light

Anabatic Winds


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Slide 101

During the day incoming solar radiationwarms the earths surface

The layer of air directly above this warmsmore than a layer of air at higher altitudes ora layer at a similar altitude but further fromthe slope

The warmer and less dense air rises andcreates a void that tends to draw in air fromlower down the slope

Anabatic winds are strongest when the sky isclear, in steep terrain where vegetation is

sparse, in areas that receive greater amountsof sunlight and when synoptic winds are light

Anabatic winds are typically stronger thanKatabatic flows

Anabatic/Katabatic ValleySystems


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Slide 102

Systems

A decoupling betweenthe air within and abovethe valley can occur

In some instances up-

valley anabatic winds candominate during the dayand down-valleykatabatic winds candominate during the

evening despite a strongsynoptic flow above

The Influence of Cloud on LocalWeather Effects


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Slide 103

Weather Effects

Many local weather effects result from differential solarheating

Increased daytime cloud density will reduce theintensity of incoming solar radiation, and will impede

the development of local weather effects driven byheating such as the sea breeze or anabatic wind

Increased nocturnal cloud levels will reduce thepotential for katabatic and land breeze effects to occur

as the earths surface will cool at a lower rate

Thunderstorm Outflow


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Slide 104

If moist air rises to great heightsin an unstable atmosphere dueto convection, it will condense.If it continues to rise, toweringcumulonimbus clouds will formcreating a thunderstorm cell

Accompanying the columnformation is strong up and downdrafts

Cool dense air that sinks out of

a thunderstorm (a down draft)diverges rapidly when it hits theground thunderstorm outflow

Exercise I


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Slide 105

Consider what local effects maytake place here:

Morwell

Yarram

McAllister River Valley

Mt Baw Baw

Exercise II


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Slide 106

Topographic maps canbe used to identifypossible local effects

What local effects might

take place around theGrampians?

Fire Induced Effects


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Slide 107

A fire itself can impact on the local weather if it is ofsufficient size. Smoke columns typically carry moremoisture than the surrounding air and this is mainly dueto the effects of combustion

The rising plume of smoke can act as an immoveableobject to the synoptic wind flow and this can causeerratic fire behaviour in its wake

Fires can also generate thunderstorms and lightning onsome occasions lightning activity can cause newstarts downwind, making suppression even moredifficult

Synoptic Weather InfluencesWeak Pressure Gradients


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Slide 108

Weak Pressure Gradients

A weak pressuregradient with clearskies will allow whichlocal effects todevelop?

Synoptic Weather InfluencesStrong Pressure Gradients


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Slide 109

Strong Pressure Gradients

A strong pressuregradient will allowwhich local effects todevelop?

Summary


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Slide 110

A number of different local weather effects exist thatencourage unpredictable fire behaviour

Fires can influence the local environment by generatingtheir own weather

Understanding the relationship between synopticconditions and local weather effects is essential tosuccessful fire management


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Ed. 1.0 Sept 2007

Fire Weather 1Weather and Fire Danger Indices

Session Goal


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Slide 112

This session will discuss how to interpret the fire dangerrating system used in Bureau of Meteorology fire weatherforecasts


from Bureau of Meteorology publications (copyrightCommonwealth of Australia) and are used by permission.For more details see Fire Weather 1 Learning Manual

Learning Outcomes


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Slide 113



the inputs into the Fire Danger Index (FDI)

the FDI / Fire Danger Rating (FDR) system and how it isused

Outline


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Slide 114

1. What is fire danger?

2. Forest Fire Danger Index

3. Grassland Fire Danger Index

4. Weather associated with an extreme FDI day

What is Fire Danger?


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Slide 115

Fire danger is a measure of the difficulty in controllingor suppressing a wildfire and is a function of fuel stateand weather

Fire danger is quantified using a numerical FDI to

which a descriptive FDR is attached, where highervalues represent a higher level of danger

FDI values are typically calculated in two situations:

As part of routine fire weather forecasting

To predict the behaviour of a going wildfire

Fire Danger Index


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Slide 116

FDI is calculated with the following input variables:

Fuel state

Temperature

Humidity

Wind speed

For the following environments:

Forests

Grassland

McArthur Forest Fire DangerIndex (FFDI)


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Slide 117

Index (FFDI)

McArthur FFDI determines the difficulty of firesuppression due to:

Drought Factor (a measure of forest fuel availability)

Temperature

Relative humidity

Average wind speed (at 10m height)

Drought Factor


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Slide 118

DF estimates the proportion (in tenths) of the fine fuels(


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Slide 119

The descriptive forest fire danger system is defined as follows:

FDR FFDI

Low 0 4

Moderate 5 11

High 12 23

Very high 24 49

Extreme 50 +

The value for FFDI is capped at 100, however higher values arepossible on rare occasions

Fires with an FFDI above 50 typically become weather dominated

How Variables Impact FFDI


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Slide 120

Drought Factor = FFDI

Temperature = FFDI

Relative humidity = FFDI

Wind speed = FFDI

Diurnal Variation of FFDI


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Slide 121

FFDI Assumptions


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Slide 122

Terrain aspect or slope is not taken into account

An available fuel amount of 12.5 tonnes per hectare isassumed (indicated on the back of the meter) and fuelloads can be heavier than this

The FFDI model assumes moderate instability. Firebehaviour in elevated fuels may be underestimated, andextreme days will often be more unstable than the modelassumes

The FFDI model assumes a uniform canopy interceptionof sunlight

The FFDI model assumes full sunlight

McArthur Grassland FireDanger Index (GFDI)


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Slide 123

g ( )

McArthur GFDI determines the difficulty of fire suppressiondue to:

Curing (a measure of forest fuel availability)

Temperature

Relative humidity

Average wind speed (at 10m height)

Curing


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Slide 124

Most grasses have a natural life cycle in which plantsmature annually, and die or become dormant

The moisture content of the grass is lost seasonally inthe drying or curing process

Values for curing are expressed as the percentage ofdry (dead) grass 0% cured (completely green) to100% cured (completely dead)

GFDI System


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Slide 125

The descriptive grassland fire danger system is as follows:

FDR GFDI

Low 0 2

Moderate 3 7

High 8 19

Very high 20 49

Extreme 50 +

GFDI values can reach over 100 on rare occasions, particularlyif wind speed and curing is high

Fires with an GFDI above 50 typically become weather dominated

How Variables Impact GFDI


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Slide 126

Curing = GFDI

Temperature = GFDI

Relative humidity = GFDI

Wind speed = GFDI

Diurnal Variation of GFDI


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Slide 127

GFDI Assumptions


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Slide 128

Aspect or slope is not taken into account

Atmospheric instability is not taken into account

Extreme FDI Conditions


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Slide 129

In many instances, days where fire danger is severewill experience FFDI or GFDI values of 50 or more i.e.fire danger will reach extreme on the McArthur scale

If the synoptic chart implies a day of severe or

extreme fire danger, then this will often be confirmedupon examination of the FDI values

Forecast values of extreme FDI are the strongestreason for a Total Fire Ban declaration

Weather Associated With anExtreme FDI Day


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Slide 130

y

Extreme FDI values are associated with a number ofsynoptic situations including:

A dry low pressure system directing strong and gustynorth, west or northwesterly winds across the state

A high pressure system directing hot and dry northerlywinds over the state

A vigorous cold front approaching a strong high pressureregion directing hot and dry northerly winds across thestate before a gusty southwesterly wind change

Summary


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Slide 131

Fire danger is a measure of the difficulty in controllingor suppressing a fire

There are two fire danger indices used in Victoria:

FFDI and GFDI

Fire danger is used as a basis for fire agencypreparedness, fire behaviour prediction, and publicsafety awareness

FDI / FDR varies hourly and daily

An extreme FDI day can occur under a number ofsynoptic conditions


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Ed. 1.0 Sept 2007

Fire Weather 1

Bureau of Meteorology Productsand Services

Session Goal


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Slide 133

This session will discuss how to access and interpretBureau of Meteorology fire weather products andservices


from Bureau of Meteorology publications (copyrightCommonwealth of Australia) and are used with theirpermission. For more details see Fire Weather 1Learning Manual

Learning Outcomes


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Slide 134

This training session will cover three learning outcomes.


how to access the Bureau of Meteorology Registered Userwebpage

how to access numerous weather products and servicesavailable on the Bureau of Meteorology Registered Userwebpage

the information contained in the various fire weatherproducts issued by the Bureau of Meteorology

Outline


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Slide 135

1. Accessing the Bureau of Meteorology public website

2. Registered User page

3. Fire weather products

4. Other information available on the website

Weather on the Web


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Slide 136

The Bureau ofMeteorology (Bureau)public website isaccessed throughwww.bom.gov.au

To access theRegistered Userwebpage click on thelink.

Login to the Registered UserWebpage
http://www.bom.gov.au/http://www.bom.gov.au/


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Slide 137

Enter Username and Password


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Slide 138

Four different RegisteredUser pages exist:

Username bomw0025:CFA HQ and regions

Username bomw0026:CFA volunteers

Username bomw0027:DSE HQ and regions

Username bomw0028:

General fire weather

Registered User webpage


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Slide 139

The Registered User webpage contains a large amountof data under the following headings:

Synoptic Charts

Forecasts and Warnings

Observations Satellite Imagery

Radar

Computer Model Diagnostics

Climate InformationForecasts and Warnings includes products prepared forfire management agencies.

Fire Weather Products


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Slide 140

The Bureau produces a number of fire weather productsspecifically for fire management agencies:

Fire Weather Estimates

Extended Fire Weather Estimates

Fire Weather Briefing Fire Weather Outlook

Spot Fire Forecast / Prescribed Burn Forecast

Wind Change Chart

Thunderstorm Forecast

Fire Weather Estimates


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Slide 141

Fire Weather Estimates areissued twice daily during the fireseason at:

0630h for the current dayand,

1645h for the following day

Fire Weather Estimates areissued for 25 representativelocations around Victoria in nine

weather districts


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Slide 142

For each of the 25 locations the following fields arepredicted for maximum temperature time:

Maximum temperature (C)

Relative humidity (%)

Wind direction Wind speed and gust (km/h)

FFDI (using a calculated Drought Factor)

GFDI (using an observed Curing value)

Wind change time and wind strength (if appropriate)


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Slide 143

For each of the nine districts the following fields are predicted formaximum temperature time:

Lightning Activity Level (LAL; 0 = nil, 1 = one or two, 2 = a few, 3= numerous strikes over a district)

Rain (No = less than 5mm, Yes = greater than 5mm over an

entire district during the 24 hour period from 0900h on theforecast day)

Height of the mixing depth above sea level (mix, metres)

Upper level wind direction and strength (at 1000 to 2000 metresabove mean sea level; km/h)

FDI above 35 (approximate time when FDI is above 35, for *locations if occurring four hours or more before or after maximumtemperature time)


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Slide 144

Summary comments are also provided to complementthe numerical predictions

Mallee district sample

Extended Fire WeatherEstimates


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Slide 145

At 1715h each day during the fire season a set ofExtended Fire Weather Estimates (with a reducednumber of locations and meteorological parameters) isissued for an additional three days beyond the next-dayforecast

Fire Weather Briefing


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Slide 146

At 1045h each day during the fire season a written FireWeather Briefing is issued

The Fire Weather Briefing:

Outlines any variations to the estimates issued earlier that

day at 0630hrs Provides more detail about the days weather

Gives a summary of the expected weather over the nextfew days

Fire Weather Outlook


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Slide 147

At 1650h each day during the fire season the FireWeather Outlook is issued which provides synopticcharts and comments regarding the expected weatherconditions for the following four days

Spot Fire / Prescribed BurnForecast


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Slide 148

A Spot Fire / Prescribed Burn Forecast for the localweather conditions associated with a fire can berequested at any time during the year

Spot Fire/Prescribed Burn Forecasts cover a short-term

forecast period and include: Predictions for temperature, RH and wind speed at ground

and upper levels in three hourly time steps for a nine hourperiod, and an outlook for the following 12 hours

A written description and alternative scenarios

Spot Fire/Prescribed Burn Forecasts have the highestpriority behind Wind Change Charts

Thunderstorm Forecast


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Slide 149

A Thunderstorm Forecast isissued for the state ofVictoria by 1130h each dayindicating areasof likely thunderstorm activity

This chart is updated whenapplicable

Wind Change Chart


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Slide 150

A Wind Change Chart is issued on days where asignificant wind change is expected to cross the stateand the fire danger is expected to be very high orextreme

This chart plots the current position of the wind changeand the predicted position in three-hour increments,and indicates the wind speed and direction before andbehind the change

The chart is updated every three hours until the change

either moves out of the state or has weakened, to suchan extent, that it is no longer considered to be a threat

Additional website information


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Slide 151

The Registered User webpage also containssupplementary weather information, including:

Synoptic charts

Observations

Satellite imagery Radar

Computer Model Diagnostics (model data and predictedmeteograms for selected locations across Victoria)

Climate information Links

Summary


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Slide 152

The Bureau public website provides access to a range ofweather products and services:

Detailed products for fire management agencies can beaccessed from the Registered User section

A number of products are regularly issued to firemanagement agencies during the fire season

Wind Change Charts and Spot Fire Forecasts assume thehighest priority

Spot Fire / Prescribed Burn Forecasts and Thunderstorm

Forecasts are issued all year


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Ed. 1.0 Sept 2007

Fire Weather 1Weather Observations on the FireGround

Session Goal


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Slide 154

This training session will introduce the importance ofbeing aware of local weather conditions as well asproviding guidance on how to obtain a simple weatherobservation

A number of diagrams used in this presentation are takenfrom Bureau of Meteorology publications (copyrightCommonwealth of Australia) and are used by permission.For more details see Fire Weather 1 Learning Manual

Learning Outcomes


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Slide 155

This training session will cover three learning outcomes


the suitable environmental conditions in which to take

weather observations how to undertake and interpret basic sky observations

how to undertake and interpret observations of wind speedand direction

Outline


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Slide 156

1. Being aware of the weather

2. Taking a weather observation cloud

3. Taking a weather observation visibility

4. Taking a weather observation wind speed anddirection

5. Taking a weather observation precipitation andhumidity

6. Weather Observation Activity assessed componentof Fire Weather 1

Being Aware of the Weather


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Slide 157

Weather has a major impact on fire behaviour, and fireground safety can be dependent on interpreting visualweather clues

A lack of awareness of the weather can have a serious

and detrimental effect on fire management andsuppression activities, and can jeopardise firefightersafety

Taking a Weather Observation


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Slide 158

Local weather observations need to be taken of thegeneral environmental conditions unaffected by a fireotherwise the data recorded may not be representativeof the surrounding area

Weather observations must be taken to a set standardin order for them to be referenced and compared topast and future observations


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Slide 159

When taking a weather observation on a fire ground: Take the observation away from the fire line

Take the observation upwind of the fire and smoke plumein an unburnt area

Take the observation in a clear and well exposed areaaway from trees or the forest canopy

Ideally take the observation in an elevated location

However, the observation site should reflect the type ofterrain in which the fire is currently burning

A fire ground weather observation should include cloud,wind and visibility

Cloud Observations


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Slide 160

Cloud observations should include the cloud type andamount as a minimum

Cloud type:

Stratiform or Cumuliform

Stratiform Clouds


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Slide 161

Stratiform clouds: Are generally flat in appearance

and of low to medium height

Typically display extensivehorizontal rather than vertical

development

Can give rise to precipitation thatis more continuous rather thanshowery

Stratiform clouds can be a precursorto a coming weather change e.g. anapproaching frontal passage

Cumuliform Clouds


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Slide 162

Cumuliform clouds: Are generally heaped in

appearance and of low to mediumheight; however cumulonimbus canstretch the height of the

troposphere Display greater vertical rather than

horizontal development indicatingconvective activity and an unstableatmosphere

Showers and thunderstormsare more likely to occur fromcumuliform clouds

Cloud Amount


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Slide 163

Cloud amount is estimated in eighths (or oktas) althoughit is perhaps simpler to record on the fire ground as:

Clear (no cloud)

Partly cloudy (cloud cover of less than 50%)

Mostly cloudy (50% to less than full cloud cover) Overcast (full cloud cover)

Visibility


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Slide 164

Visibility can be determined by comparing visualestimations with a map indicating the distance to knownpoints

Wind Speed Observations -Mechanical


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Slide 165

1. Obtaining wind speedobservations with ananemometer is typicallydone at about two metres,with the anemometer held

into the wind it can thenbe converted to a 10m windspeed

2. The anemometer should be

held for ten minutes to getan average wind speed andalso a maximum gust

Wind Speed Observations -Visual


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Slide 166

Wind speed is typically measured using an instrumentsuch as an anemometer, however visual indicators canalso be used if instrumentation is not available

Visual indicators include:

Watching cloud movement as the behaviour of cloudswill give an indication of wind conditions at that particularaltitude

Noting the speed of fire / smoke movement

Watching the movement of trees and vegetation usethe Beaufort Scale

Beaufort scale


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Slide 167

Wind Direction


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Slide 168

Wind direction can be estimated using a vane Without using specialist equipment wind direction can be

obtained using a compass or map and the followingmethods:

Analysing the direction of fire, smoke or cloud movement Analysing the directional movement of trees and other

foliage

Factors to Consider WhenTaking Wind Observations


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Slide 169

Convection: Any high based cumuliform cloud has the potential to

produce gusty and erratic wind behaviour

Inversion:

A dramatic increase in wind speed can result from thebreakdown of the overnight inversion

Diurnal variations in wind speed behaviour:

Wind speed and direction fluctuates significantlythroughout the day - take an observation over a ten

minute time period Height of observation:

Try and take the observation at a height of 10m

Precipitation and Humidity


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Slide 170

It is quite straightforward to detect precipitation but itmust not be assumed that the presence of rain meansthat relative humidity has reached 100%

Relative humidity only reaches 100% in clouds, and the

presence of fog is the only clear indicator that humidityat ground level has reached 100%

Weather Observation Activity


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Slide 171

This is an assessed component of the FW1 course1. Use the Bureau Registered User webpage to access

the forecast and current weather conditions, and anycurrent warnings for the local area

2. Go outside and take a local weather observationusing the assessment sheet estimate:

Temperature and humidity

Wind direction and speed using the Beaufort scale

Height, amount and type

Evidence of an approaching wind change

3. Complete the worksheet

Summary


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The safety of fire management personnel on the fireground is dependent on an awareness andunderstanding of the local weather conditions

Fire behaviour can be predicted through understanding

local meteorological conditions by taking a weatherobservation

fw1 full presentation_0

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