Measurements and Data Analysis
Discussion Sections 302 and 303
Weather Discussion
NCEP NAM Model
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Surface/Precip 1200Z
850 mb/Temp 1200Z
300 mb/Wind speed 1200Z
850-800 mb/Relative Humidity
1200Z
Radar/Satellite
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Current Radar Loop
Current Satellite Loop
Current Water Vapor Loop
Forecast
Observations and Measurements
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Station models
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Observations are taken simultaneously across the nation
several times a day
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Observations taken at a particular weather station
Ensures accuracy of forecast models
Now that we have our observations, what do we do?
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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)
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Atmospheric scientists use a coordinated universal time (UTC)
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Z stands for Zulu
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Examples
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0800Z
1531Z
2130Z
Essentially the same as Greenwich Mean Time (GMT)
Converting from UTC
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Central Standard Time (CST)
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Central Daylight Time (CDT)
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November 7th 2010 - March 13th 2011 before 2 am
March 13th 2011 after 2 am – November 6th 2011
How to convert to CST and CDT
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CST
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Subtract 600 from the time
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Ex. 1700Z – 600 = 1100 (which is 11 am)
CDT
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Subtract 500 from the time
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Ex. 2100Z – 500 = 1700 (which is 5 pm)
Weather Maps
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Importance of contoured maps
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Easy diagnosing and depicting weather features and variables
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Ex. Predicting atmospheric fronts, hurricanes, storms, etc.
Give easy-to-read, general information about small to large
areas
Contouring
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Contouring is the process of
drawing isopleths
An isopleth is a line of equal value
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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
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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
5
5
How to Contour
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Locate regions of high and
low values first
Example
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15
Draw the 15 °F isotherm
15
How to Contour
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Contour at evenly spaced
increments
Example
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75
Draw the 75 °F and 80 °F
isotherms
75
80
80
Circlular Isopleths
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Sometimes, you will
find the values are
localized
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20
In this case, you 20
would draw a circle
Draw the 20°F and
25 °F isotherms
20
25
25
How to Contour
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Isopleths cannot touch or cross
Isopleths cannot branch or fork
10
9
7
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9
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5
8
11
10
6
9
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7
11
11
9
10
12
11
7
10
10
10
9
7
10
NO!
How to Contour
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Do not create contours where there is an absence of data
Preparing to Contour
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Search for continuity (time and space) on the weather
map
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Survey the map and look for:
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Eliminate what appears to be faulty or incorrect data
Ex: a 95 is found amongst 50s
Areas of rapid change (large gradients)
Steady areas (flat field)
Review data to determine isopleth spacing
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Will you need to squeeze isopleths tightly?
Will you have room to label the isopleths?
Contouring Tips
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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.
25
30
35
40
25
30
35
40
45
45
50
50
In-Class Examples
Draw the isobars at 4 mb intervals, starting at 1000 mb .
Station Pressure Example
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Only focus on the pressure
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Remove stations that do not have a pressure reading
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Convert 3 digit numbers to actual pressure
Remember, 032 => 1003.2 mb
There are two of them
Draw lines at 4 mb increments above 1000 mb
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1004 mb, 1008 mb, 1012 mb, 1016 mb, etc.