METR 361 Spring 2016

Composite Chart Lab

Assignment (due Friday):

On a U.S. base map, you will construct a composite chart using weather maps for a real case in which severe thunderstorms were reported. For each (paper) map, analyze for the “ingredients” favorable for a severe thunderstorm outbreak. For example, on the surface map, you would draw fronts, pressure troughs, and drylines. Then assign symbols to each and transfer only the symbols to a blank base map. When you have transferred all symbols from the plotted maps to the base map, the areas with the most ingredients, i.e., symbols, are the areas most likely to experience severe thunderstorms. Col. R.C. Miller and his group pioneered this technique and called it a composite chart. We still use the technique today.

For this lab you have 00Z April 3 maps from an outbreak last year, since the current pattern is mostly unfavorable for severe thunderstorms. Normally, you wouldn’t have the luxury of observed maps at the time of the severe weather. In real time, you would need to use forecast maps. But for this lab, we can hindcast the severe weather and you can look at the SPC storm report page to find the verification. This lab is about the technique.

You decide which features are favorable on each map. In my example from the first paragraph, I used the surface fronts, pressure troughs, and dryline because they provide lift. There are other features on the MSLP map that you must find, analyze, and transfer to the base map so I have given you three MSLP plots of the same time. Your rough analyses will not be turned in. You get to devise your own symbols. Make them similar in design to the ones used by Miller, shown in the example below. For example, Miller used different kinds of arrows for jet streams and you should also. You must use arrows that are different colors for different levels so they can be distinguished from each other. In the sample composite chart below, a red arrow is the 850 hPa jet axis while a blue arrow is the jet axis from 300 hPa.

You should devise different symbols to represent the other favorable features you find. Use the sample chart below for ideas and think of others on your own. You can also read Maddox and Doswell’s paper from the 12^th Conference on Severe Local Storms on our course home page. You must figure out how to represent in symbols all the important ingredients on each map. Don’t miss any and even though you know where the severe weather occurred, you must find the favorable ingredients even in areas of no severe thunderstorms. The symbols can be fanciful, and you must include a key showing all your symbols and the ingredients they represent. You must also write a severe weather discussion specifically explaining why severe weather occurred where it did. Write the discussion in a text or Word file and send it to me.

You have three US surface plots, the 850 hPa, 700 hPa, 500 hPa, 300 hPa, and 200 hPa maps.