Homework 4 -- CAPE

(a) and (b) Due Monday 27 April 2010; (c) due Wednesday 29 April 2010.


(a) Plot the sounding for 12 UTC 21 April 2010 for Salt Lake City, Utah on the FSL interactive sounding site: http://www-frd.fsl.noaa.gov/mab/soundings/java/

i. Determine the elevation (in mb) of the LCL, LFC (if present) and EL (if present).

765 mb, 601 mb and 267 mb.

ii. What is the value of CAPE for this sounding? What is the value of CIN for this sounding? ~200 J/kg and -50 J/kg

(b) Examine the geographic plot of surface based CAPE for that is roughly coincident in time with the above sounding.

i. Describe whether the pattern shown in the Salt Lake City area is roughly consistent with your results above.

The pattern shows a CAPE maximum extending across Utah. Salt Lake City is in the area with just less than 250 J/kg. Thus, the pattern shown is consistent with value of CAPE I found in the sounding analysis above.

ii. What is the value of the vertical velocity at the Equilibrium Level for the CAPE value shown near Park City, Utah (that CAPE value is 450 J/kg)?

30 m/s

(c) The Day 1 Convective Outlook from SPC for 4/25/10 is given here. Note the red highlighted text in the discussion for the mid Missisippi River Valley.


Illustrate the point the forecaster was trying to make by doing the following:

(i) The 1400 UTC surface chart with two isobars drawn on it is given here.

  1. Isobars are drawn on standard synoptic charts at 4 millibar intervals. Draw the 1004, 1008, 1012, and 1016 isobars.
  2. Draw some streamlines on the 1400 UTC surface chart (arrows tangent to the instantaneous wind direction);

Here is my plot.

(ii) Here is the map showing surface-based CAPE and CIN for 1400 UTC. Using this chart and the surface chart you just analyzed, illustrate the statement the forecaster was making.

The surface plot shows streamlines extending from the Gulf of Mexico. The Gulf of Mexico is a warm water body, such that air masses coming from it have high mixing ratios and dew points. Since, for a given temperature, sbCAPE is greater the higher the dew point temperature, the wind circulating higher dew point air northward (air with higher mixing ratios), should be increasing the CAPE values in the Mississippi River Valley states. The chart that shows the instantaneous value of CAPE shows that the area of CAPE is coextensive with the area of high dew points shown on the surface plot.