METR 361 Spring
2019
Composite Chart Lab
Assignment (due next Wednesday):
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 could 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 maps from an unspecified but real
outbreak. Something happened. It’s up to
you to determine where the severe thunderstorms have a likelihood of occurring.
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. 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 favorable ingredients which you must identify. 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. 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 mb jet axis while a blue arrow is the jet axis from 300 mb.
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. To get ideas, you can also read Maddox and Doswell’s paper
from the 12th Conference on Severe Local Storms or Miller’s 1972
report (last 2 pages). Both are 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 you must find the favorable ingredients even in areas which
seem to have no severe thunderstorms. The symbols can be fanciful so you must
include a key showing all your symbols and the ingredients they
represent. You must also draw a second map in SPC convective outlook format,
showing the area where and how likely your maps show this outbreak to have been.
Do not show the area of ordinary thunderstorms. Use the SPC probability
nomenclature of MRGL, SLGT, ENH, MDT, and HIGH.
Finally, you must write a short discussion in which you discuss which
ingredients were present in your area and what they contributed to the
outbreak.
You have the 00Z US surface plot, the 850 mb, 500 mb, 300
mb, and 200 mb maps.