tilman tues 130pm tusc iiiandiv

8/12/2019 Tilman Tues 130pm Tusc Iiiandiv

1/47

Climate, Weather and Property Risk

Presentation to Cat Modeling 2014February 11, 2014

Craig TillmanDave Bachiochi

David Hamilton


2/47

Presentation Outline

Weather Scales, Variability and Volatility

Climate Processes and Weather Outcomes

Severe Convective Storm (SCS) Phenomenology

2

Physical CharacteristicsAssociated Hazards

Recent trends in SCS activity


3/47

Highlights

US SCS activity has increased during the last decade

Increased activity mainly linked to decadal climate variability:

Jet stream modification related to variability in Pacific sea-surfacetemperatures associated with the Pacific Decadal Oscillation (PDO),ENSO and other factors

3

WPC expects key climate signals to continue to favor increased severeconvective storm activity.


4/47

Climate is what we expect,

weather is what we get.

4

Andrew John Herbertson

Modified Version by Robert Heinlein

Also Inspired by Mark Twain


5/47

Natural Sciences Scales of Climate Variability

The atmosphere-ocean system is naturally variable in time and space

Variability in time is apparent in a range of scales from days to many years

Short-term weather and long-term climate impact each other to defineboth the present risk and its future evolution

5

TornadicSupercells

Transient WeatherSystems

(e.g., Cold Front)

Large-Scale,Slow Moving

Patterns(e.g., Polar Jet)

Severe WeatherOutbreak Example

Long-Term NaturalVariability/Global

Warming


6/47

Complex Physical Problem

Changes in the atmosphere and/or ocean can trigger change in the variabilityand overall state of the system locally in time and space

ty

6

RemoteForcing

ChangingVariab

ili

C

hangingRisk


7/47

Volatility Vs. Variability

Weather volatility is a measure of variability, dependent on the time andspace scales of interest.

High weather volatility (i.e., extreme variability) can lead to unexpectedresults.

Volatility on smaller space and time scales may have limited impacts

Short-term temperature spikes

7

Localized severe weather Volatility on larger scales can lead to significant, negatively impactful events:

Extended droughts

Large-scale floods

Severe weather outbreaks


8/47


9/47

Managing the Volatility Property Risk Perspective

Changing ExposureChanging Exposure

Increasing UncertaintyDecreased Quality

Synoptic Variability

Short-Term Intermediate-Term Long-Term

Natural VariabilityClimate Change

9

Adaptive StrategiesAdaptive Strategies

Historical RecordHistorical Record

Short-term: Day to Day Variability Intermediate: Global Climate Indices Alter Variability

Long-term: Global warming Shifted Patterns/Strength

Blocked FlowsTropical EventsDry SpellsRain EventsSevere WeatherOutbreaks

ENSONAOAtlantic SSTSnow-coverMJO

Pattern Shifts

Additional CO2Sea Ice Melt

Natural Variability"A New Normal"


10/47

Severe Convective Storms (SCS)Phenomenology


11/47

What is Convection? Convection the movement of a fluid

In Meteorology, convection is the vertical overturning of the atmosphere

Deep Convection is a thunderstorm, whereas

Hot, moist air near the surface rises rapidly in an Updraft

Precipitation falls back to the ground, generating a Downdraft

Updrafts and Downdrafts are responsible for all SCS Perils!!!

11


12/47

What Causes Convection?

The 3 Ingredients for Thunderstorm Development

Source of Moisture

Gulf of Mexico is the primary source of moisture for US SCS development

Instability

In thunderstorms, unstable air refers to vertical air motion, i.e.

12

warm, moist air rising

cold air descending

Source of Lift

Surface HeatingTerrain

Fronts


13/47

What Sustains Convection? Long-lived or organized thunderstorms require vertical wind shear,

i.e. change in wind speed and direction with altitude

Allows for a sustained updraft and downdraft

Delivers abundant low level moisture to fuel the storm

Provides an avenue for depositing precipitation without choking the updraft

Enables storm rotation and motion

13

Cold Front liftswarm moist air.

Downdraft acts

to reinforcefront


14/47

What Causes Convective Outbreaks?The Basic SCS Model

SCS Outbreaks are dictated by jet stream amplification

Jet Stream amplification is a bending and strengthening of upper level flow, leading to: Large scale cold air mass intruding over continent from the north

Surface low pressure that draws gulf air into the countrys midsection

14

,

Which is sustained by vertical wind shear organized by the jet stream


15/47

Severe Convective Storms: Large-to-Small Scale

15

Vertical wind shear on the large scale dictates storm evolution on small scale

Abundant low-level moisture provides thunderstorm cells with fuel


16/47

What is a Severe Convective Storm?

A thunderstorm is considered Severe if at least one of these exist1:

Hail that is at least 1 inch in diameter

Wind gusts to 58 mph or higher

A tornado

16

Courtesy of : The Storm PredictionCenter of the US National Weather

Service

1As defined by NOAAs NWS


17/47

Hail

Precipitating ice pellets ranging from pea to grapefruit size

Updraft strength and freezing altitude govern hail production

Damage dependent on hail size, density, concentration and air motion

Easily detected by Doppler radar

Typically falls in swaths (or hailstreaks)

17Hailstreak from 10 April 2001: Changnon and Burroughs, MWR, 2003


18/47

Hail Video

18


19/47

Downbursts

A downburst is a strong downdraft and is a localized phenomenon:

Rain-cooled air accelerates downward, hits the ground, and spreads

Strong surface winds create straight-line wind damage

Microburst: a downburst with a diameter of less than 4 km

19


20/47

Downbursts (cont.)

Macrobursts:

Downdraft diameter > 4 km

Create gust fronts

propagate hundreds of miles

winds recorded up to 130 mph

20

SCSs can produce hail streaks or swaths. On April 10, 2001, aparticular strong hail storm produced a hail swath over the entirestate of Missouri.

Times of hail are LST, and locations with hailstones >1 inch indiameter are shown as dots.


21/47

Downburst Video

21


22/47

Tornadoes

Violently rotating column of air in contact with the surface

Typically only a few hundred meters in diameter and last for only 5-10 min.

Average forward speed of 25-30 mph (40-50 kph)

Damage is localized but often devastating

caused by high winds within and near tornado core, as well as from

22


23/47

Tornado Ratings Enhanced Fujita Scale

Classifies damage on a six-point scale, with input from engineers & scientists

Considers 28 different damage indicators including construction strength

23


24/47


Examples of Damage associated with the 6 classes of tornado intensity

24


25/47



25


26/47



26


27/47

Severe Convective Storm TypesPerils associated with the following storm types, in decreasing intensity

Supercells Tornadoes, Straight Line Winds, Hail

Multi-cell Line Straight Line Winds, Hail, and to a lesser extent, tornadoes

Multi-cell Clusters Localized Wind Damage and Hail

Ordinary Cells typically non-severe

Photo by Sean Heavey

27

SCS Nomenclature

Supercells

Squall line/Derecho

Micro/Macroburst


28/47

Severe Convective Storm Types Supercells

A persistent, rotating thunderstorm lasting several hours

Strong / tilted / rotating updraft

Sustained downdraft displaced from the updraft

High likelihood of severe weather (hail, high winds, tornadoes)

Typically responsible for the strongest tornadoes

28


29/47

Severe Convective Storms Derecho

Definition: a convective system producing a wind damage swath over 240miles in length from winds of at least 58 mph

Can travel hundreds of miles over several hours to a couple of days.

Propagate analogously to an ocean wave either ahead of a cold front oralong a stationary front

Squall line expands with broad and intense gust front

29

Lyndon State University Course Notes, met130, Ch 14


30/47

Derecho Animation

30


31/47

Super-Derecho of 2012

31

24 Hour Maximum Radar Reflectivity field reveals Derecho path and

expansion after developing from a single cell in southwest Iowa.


32/47

Severe Convective Storms Scale Comparison

Tornado

32

Hail

Wind

Increased Size/Impact Potential


33/47

Severe Convective Storms Scale Example

33


34/47

Severe Convective Storms Climatology


35/47

Climatology: What is expected thunderstorm activity?

Thunderstorms can occur during any month and at any time of day

Typically, greatest risk for SCSs is during spring and early summer

In the daily cycle, storms typically peak in the late afternoon and evening

Climatologies (average arrivals) of tornado and hail are quite similar whilederechos have a peak frequency slightly later in season.

35


36/47

Monthly Severe Hail Climatology (Hail Days)

January February July August

36Cintineo, John L., Travis M. Smith, Valliappa Lakshmanan, Harold E. Brooks, Kiel L. Ortega, 2012: An ObjectiveHigh-Resolution Hail Climatology of the Contiguous United States. Wea. Forecasting, 27, 12351248.

March April

May June

September October

November December


37/47

Severe Convective Storms Tornado Climatology

37

Courtesy of Dr. Greg Forbes, The Weather Channel


38/47

Derecho Climatology

Most common in late spring and summer

Most active locations, on average, see more than one derecho per year

38


39/47

lim P rn n Th ir Im n

Are we in a new norm?


40/47

Large Scale: Jet Stream

Jet streams are the dominant atmospheric force on weather systems

Jet wave patterns often modified by global climate signals

ENSO and PDO are significant climatic modulators of North American weather

Arctic Signals

NAO

40

BUT, during any given year or period there are other wildcard signals such as AOor NAO that could reduce or enhance the severe convective storm activity.

ENSO

PDOAMO

Antarctic Signals

Indian-PacificSignals

ENSO

PDO


41/47

Pacific Decadal Oscillation (PDO)

Anomalous sea surface temperatures in North Pacific

Cold or warm phases last about 20 to 30 years.

ENSO events typically persist for 6 18 months

Negative PDO brings stronger northwesterly winds to the Northwest UScoast as well as cold Pacific coastal ocean temperatures.

4141

Cooler water in theNortheast Pacific

2008 La Nina coolerwater in the equatorialPacific

Negative (cold) PDO and La Niaillustrated in sea surface

temperature anomaly field onMarch 6, 2008

Warm water in theNorth Central Pacific


42/47

Estimated Uptick in SCS Activity

0

1

2

3

0

1

2

3

dizedSevereWeath

er

EF2+ Count EF2+ Smoothed Radar 55 dBz

Radar Smoothed DPI DPI Smoothed

Average Smoothed

El NioLa Nia

5.4

Large scale climate factors and SCSsare correlated

Enhanced risk indicated in radarand tornado count analyses

Evidence for a cycle tied to PDO

Year-to-year variations tied toENSO

42

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

192

2

192

4

192

6

192

8

193

0

193

2

193

4

193

6

193

8

194

0

194

2

194

4

194

6

194

8

195

0

195

2

195

4

195

6

195

8

196

0

196

2

196

4

196

6

196

8

197

0

197

2

197

4

197

6

197

8

198

0

198

2

198

4

198

6

198

8

199

0

199

2

199

4

199

6

199

8

200

0

200

2

200

4

200

6

200

8

201

0

201

2

PDO

Smooth PDO

Warm Epoch Warm EpochCold Epoch Cold

-2

-1

-2

-1

1970

1972

1974

197

197!

19!0

19!2

19!4

19!

19!!

1990

1992

1994

199

199!

2000

2002

2004

200

200!

2010

2012

Standar

COLD PDOCOLD PDO WARM PDO

nce , ac v y as

increased to levels to that of the priorcold PDO epoch


43/47

43La Nia + Negative PDO

o a a

Strength and position of jets criticalto the location and amount ofsevere weather activity potential.


44/47

EU Idealized Pattern Plots

Generally Mild

POLAR JET

Arctic Air Mass

LLLLLLLLLLLLLLLL

44

Generally

Mild

SUB-TROPCAL JET

HHHHHHHHHHHHHHHH

Lo! le"el #et$

%ot layer o& air &ro'

A&rican Sa%ara and

S(anis% Platea)*

T%e S(anis% +Pl)'e,


45/47

What Does Heightened Activity Mean?

Large-scale climate factors favor increase in:

Upper-level (jet stream) energy

Atmospheric instability

Subsequently increasing the probability of SCS outbreaks

45

Higher number of intense supercells

Long-track tornadoes


46/47

Recent Trends In Spatial Pattern

Stormdays

Stormdays

Tornado Days Hail Days

Change in Number of Average Days: 2008-2012 minus 1983-2007

46

Atmospheric ingredients conducive to SCS have expanded eastward in recent years.

Eastward expansion in SCS potential coincides primarily with negative PDO and La Nina


47/47

Recent increased likelihood in SCS activity in the US

Changes to atmosphere driven by jet stream changes

Jet stream modulation driven by large-scale patterns

Climate factors expected to persist and influence severe convective stormactivity for at least the next 5 years

Severe Convective Storms

47

tilman tues 130pm tusc iiiandiv

Documents