January 18, 2008

 

Introduction to 500 mb maps

n     Pass out copies of 500 mb map handout

n     Read over the 1st paragraph on web page as an introduction.

o      Units for pressure are millibars

 

n     Skip where to get maps.  Go on to the how the “pattern of contours” on 500 mb maps can be used to estimate the “large scale temperature patterns”.  The analysis that I present will not be able to explain differences in weather between nearby cities (such as Tucson and Phoenix), but it can be used to see things like “relatively cold weather” in the Eastern United States and “relatively warm weather” in the western United States.

 

n     These are contour maps (like topographic maps the show surface elevation).  You should understand how to read them, so that if I pick a point on the map, you should be able to closely estimate the height of what is called the 500 mb pressure.  Demonstrate this using handout.  Highlight a particular contour.  Then pick a point on map.  Point out these heights are 5-6 km above sea level … that is around 3-4 miles above sea level … But as we will see this map can tell us a lot about what is going on with the weather pattern at the ground.

 

n     1st thing we are going to use these maps for is to estimate air temperature.  Basically, the higher the 500 mb height, the higher the air temperature between the ground and 500 mb.  If it helps, you can remember this by understanding that as air is warmed it expands, conversely when it is cooled it contracts.  Observations on the map:

·       higher heights (or contour values) are generally found toward the south.  Why? Sun’s heating is stronger toward the tropics and decreases toward the north.  You might expect to see straight lines across the map.  BUT as you know winter weather is quite changeable, cold fronts move in dropping temperature below average, followed by several days of warming before the next round of cold air. 

o      Draw picture of average heights (With North/South labeled) and how troughs/ridges develop (called “zonal” pattern).

o      Time 1 zonal, Later Time, cold air trough warm air ridge.

 

·       Show trough/ridge drawing on web page.  (have you heard terminology?) sometimes called upper level troughs and upper level ridges.

 

·       Compare with climatology or average heights for how much above or below average temperatures expected.

o      Point out difference between January (5680), April (5725), and May (5780) over Tucson

 

n     Go through note of caution.

n     Go over the sample maps at the bottom of the page

 

 

n     Go over where to get maps

o      How to read Z time on maps and forecast hour (00 hour is initialization from measured data, 12 hour is 12 hour forecast, etc.)

 

n     Go through an example relating one of forecast maps or handout map with the forecast temperature pattern

 

Reading Surface Station Models

n     Use the U. of IL site

o      Only need to know the fields shown here.  Not the others shown in appendix B

o      Go through each field’s link

§       For weather symbols, only need to know (Draw better symbols)

·       Rain, snow, freezing rain, thunderstorm, fog

 

n     Go through a reverse example, (Air Temp = 28° F, Dew Point = 23° F, Cloudy with moderate snow, Air pressure = 994.7 mb, northwest winds at 25 knots)

n     Take a quick look at the Arizona surface plot (in review section)

 

Reading Upper level Station Models (Use 500 mb as examples)

n     Use U. of IL site

o      Only need to know fields shown here.  Not all from appendix B.

o      Go through each link

§       For geopotential height, point out the last digit is often dropped.

n     Take a quick look at the upper air station model (in review section)

 

Use remaining time to look at some examples of current weather or forecasts