Lab 12 - Earth Science

WEATHER MAP INTERPRETATION

This exercise is designed to help you interpret weather maps prepared by the National Weather Service, part of the National Oceanographic and Atmospheric Agency (NOAA).  You will be given a copy of an official weather map, together with an explanation sheet for the symbols and terminology to which you can refer to answer the questions.

I.  Weather observations are routinely made every 6 hours at stations around the world.  From this data, maps are made showing surface weather conditions and conditions in the troposphere.

1.  What is the date of your weather map?
 
 February 15, 1987

2.  At what time were the observations valid?
 
 a.  Surface and 500-millibar maps: 7:00 AM
 b.  Temperature and precipitation maps    1:00 AM

II.  Using the smaller maps printed on the lower right portion of the weather map, answer the following questions:

1.  What were the highest and lowest temperatures recorded at Chicago for a 24-hour period ending at 1:00 a.m.?
 
Highest:   35oF. Lowest:  23oF.

2.  Which weather station recorded the highest amount of precipitation for a 24-hour period, and what the amout?
 
Station Name:  Springfield, Missouri Amount in inches:  1.33 inches

3.  At approximately what altitude above Chicago was the barometric pressure 500 millibars?  (If not 500-millibar height contour is located directly above Chicago on the map, select a contour that is nearby, or interpolate a value.)
 
Altitude of 500-millibar height contour above or near Chicago:            552                                    feet

4.  What was the approximate wind speed at this altitude?
 
      The station symbol nearest and "on its way towards" Chicago is located over Wisconsin; 44 to 49 MPH

5.  What was the air temperature at this altitude?
 
     The dashed line over Springfield, IL is -20oC.   The dashed line over Green Bay, WI reads -25oC.


 
III.  The following questions refer to the large surface weather map.  Notice the surved black lines which are closed or go off to the edge of the map.

1.  These lines are called           isobars                                 and connect point having the same   atmospheric pressure                                        .

2.  Notice the numbers (such as "996," "1000," etc.) on these lines or at the ends of them.  What do these numbers represent?

Those numbers represent atmospheric pressure, in millibars.
 

3.  What is meant by the words "HIGH" and "LOW" and the letters "L" and "H" on the weather map?  (All of these may not be shown on your map)

HIGH (or "H" if there isn't room to write all the letters) represents a high pressure center where the isobars increase in value towards the center.

LOW (or "L" if there isn't room to write all the letters) represents a low pressure center where the isobars decrease in value towards the center.

The standard isobar interval is 4 millibars.

4.  Give the geographic location of one HIGH and one LOW shown on your map.
 
HIGH location:  north of Armstrong, Ontario in Canada LOW location:  Centered in Fort Worth, Texas

5.  What conclusion can you draw about the amount of area on the earth's surface, covered by these?
 
 These pressure centers cover areas larger than entire states (i.e., thousands of square miles)

6.  What is the barometric pressure at the center of the HIGH and the center of the LOW?
 
HIGH:  Armstrong, Ontario = "376" which is 1037.6 millibars LOW:  Fort Worth, TX = "936" which is 993.6 millibars

7.  What conclusion can you draw about the pressure requirement for an area to be marked "HIGH"?

 The isobars must increase in value towards the center.
 

8.  What is the highest value of barometric pressure shown on your weather map?   What is the lowest?
 
Highest:  Armstrong, Ontario = "376" which is 1037.6 millibars Lowest:  NW of Seattle, in the Pacific Ocean, "892" = 989.2 millibars

9.  Does precipitation seem to occur in association with the HIGHs or with the LOWs?
 
 LOW pressure centers indicate bad weather.  Notice how the rainfall maps coincides with the LOWs.


 
IV.  Masses of air are classifified to indicate their origin and basic characteristics.  For example, the letter P (Polar) denotes relativedly cold air from northern regions, and the letter T (Tropical) denotes relatively warm air from southerly regions.  Letters placed before P and T indicate air of maritime characteristics (m) or continental characteristics (c).  Letters placed after P and T show that the air mass is cooler (k) or warmer (w) than the surface over which it is moving.  A plus sign (+) between 2 air mass symbols indicates a transitional air mass changing from one type to the other.  Two air mass symbols, one above the other and separated by a line, indicate one air mass aloft and another at lower levels.  Air mass symbols are formed by combinations of the following letters:
 
m = Maritime

c = Continental

A = Arctic

P = Polar

T = Tropical

 E = Equatorial

S = Superior (a warm, dry air mass having its origin aloft)

k = colder than the surface over which the air mass is moving

w = warmer than the surface over which the air mass is moving

1.  What is meant by the following air mass symbols?
 
cP =
mP =
mT =
cA =
mTk =
cPw =

2.  Draw the symbols used for each of the following events (look up in your booklet "Daily Weather Maps")
 
a.  cold front symbol = 
b.  warm front symbol =
c.  stationary front symbol =
d.  occluded front symbol =

3.  What kinds of weather fronts are shown on your map?
 
 

4.  For each of the fronts on your maps, what type of air mass lies on each side of the front?
 
 


 
V.   Interpret the sample station model below, use your "Daily Weather Maps" guide booklet (Page 2) to decipher the weather information as required:
Sky coverage:   "Completely overcast"
Wind Direction (dd) of wind source:   "from Northeast"
Wind Velocity (ff) in miles per hour:  "21-25 mph"
Air Temperature TT) in Fahrenheit degrees:  "45 oF."
Visibility (VV) in miles: "2.5 miles"
Present Weather (ww) description:  "continuous rain"
Dew Point Temperature (TdTd):  "45 oF."
Cloud Type, Low Altitude (CL):  "Fractostratus and/or Fractocumulus of bad weather"
Sky Coverage of Low and/or Middle Clouds (Nh):  "completely overcast"
Barometric Pressure (PPP) in millibars:  "1022.0 millibars"
Pressure Change (pp):  "zero"
Pressure Tendency (a):  "steady - same as 3 hours ago"
Past Weather (W):  "thunderstorm, without or without precipitation"
Time Precipitation Began or Ended (Rt):  "6 to 12 hours ago"
Amount of Precipitation (RR) in inches:  "0.30"  (anything much smaller is unmeasureable)