Measurements and Data Analysis

Discussion Sections 302 and 303

Weather Discussion

NCEP NAM Model

Surface/Precip 1200Z 850 mb/Temp 1200Z 300 mb/Wind speed

1200Z 850-800 mb/Relative

Humidity 1200Z

Current Radar Loop Current Satellite Loop Current Water Vapor Loop

Radar/Satellite

Forecast

Observations and Measurements Station models

Observations taken at a particular weather station Observations are taken simultaneously across

the nation several times a day Ensures accuracy of forecast models

Now that we have our observations, what do we do? There are some missing points in-between the

observations Large variations in those observations from place

to place We need to contour!

Coordinated Universal Time (or Zulu Time) Atmospheric scientists use a coordinated

universal time (UTC) Z stands for Zulu

Examples 0800Z 1531Z 2130Z

Essentially the same as Greenwich Mean Time (GMT)

Converting from UTC Central Standard Time (CST)

November 7th 2010 - March 13th 2011 before 2 am Central Daylight Time (CDT)

March 13th 2011 after 2 am – November 6th 2011 How to convert to CST and CDT

CST Subtract 600 from the time

Ex. 1700Z – 600 = 1100 (which is 11 am)

CDT Subtract 500 from the time

Ex. 2100Z – 500 = 1700 (which is 5 pm)

Weather Maps Importance of contoured maps

Easy diagnosing and depicting weather features and variables Ex. Predicting atmospheric fronts, hurricanes, storms,

etc. Give easy-to-read, general information about

small to large areas

Contouring Contouring is the process of

drawing isopleths An isopleth is a line of equal

value iso – equal pleth – value

A contour analysis involves drawing multiple isopleths

Each isopleth has a different name depending on the contour analysis

Common Isopleths

Isopleth Name Isopleth Meaning

Isobar Pressure

Isotherm Temperature

Isotach Wind Speed

Isogon Wind Direction

Isopycnic Density

Isodrosotherm Dew Point

Isohyet Precipitation Accumulation

Isohume Humidity

Isoshear Wind Shear

Isohaline Salinity

Isoneph Cloudiness

Isohel Sunshine

How to Contour Interpolate between given values to correctly

place an isopleth Think about the contour as a line separating

the observations with higher values on one side of the line, and lower values on the other side

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How to Contour Locate regions of high

and low values first Example

Draw the 15 °F isotherm

15

15

How to Contour

Contour at evenly spaced increments

Example Draw the 75 °F and 80 °F

isotherms

75

75

80

80

Circlular Isopleths Sometimes, you

will find the values are localized In this case, you

would draw a circle

Draw the 20°F and 25 °F isotherms

20

20

25

25

20

How to Contour Isopleths cannot touch or cross Isopleths cannot branch or fork

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11

8 7

9

91111

1112

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10

8

8 7

7

7

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6 5

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9

9

10

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0

NO!

How to Contour Do not create contours where there is an

absence of data

Preparing to Contour Search for continuity (time and space) on the

weather map Eliminate what appears to be faulty or incorrect

data Ex: a 95 is found amongst 50s

Survey the map and look for: Areas of rapid change (large gradients) Steady areas (flat field)

Review data to determine isopleth spacing Will you need to squeeze isopleths tightly? Will you have room to label the isopleths?

Contouring Tips

Use a pencil Draw smooth lines Be neat and

accurate Label the isopleths

In-Class Examples

Draw the 25°F - 50°F isotherms at 5°F intervals.

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25

30

35

3540

45

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45

5050

In-Class ExamplesDraw the isobars at 4 mb intervals, starting at

1000 mb .

Station Pressure Example Only focus on the pressure

Convert 3 digit numbers to actual pressure Remember, 032 => 1003.2 mb

Remove stations that do not have a pressure reading There are two of them

Draw lines at 4 mb increments above 1000 mb 1004 mb, 1008 mb, 1012 mb, 1016 mb, etc.