SPC MESOSCALE DISCUSSION 1620 FOR SWRN IL...ERN/SRN MO...CENTRAL
AR...NRN LA
CONCERNING...SEVERE THUNDERSTORM POTENTIAL...HEAVY RAINFALL...

VALID 221909Z - 222200Z

ISOLATED TO SCATTERED THUNDERSTORMS WILL CONTINUE TO DEVELOP THIS
AFTERNOON FROM AROUND STL THROUGH CENTRAL AR TO NRN LA WITH THE
POTENTIAL FOR VERY ISOLATED STRONG/DAMAGING WIND GUSTS.  RAINFALL
RATES OF 1 TO 1.5 INCH PER HOUR ARE LIKELY WITH THE STRONGEST
STORMS.

SATELLITE IMAGERY SHOWS AN AREA OF TCU/CBS DEVELOPING FROM AROUND
STL SSWWD INTO NRN LA WHICH IS WITHIN A REGION OF WEAK DEEP LAYER
CONVERGENCE PER VAD WINDS.  A VERY UNSTABLE AIRMASS EXISTS OVER
THIS REGION WITH 100 MB MLCAPE VALUES RANGING FROM 2500-3000 J/KG. 
AREA VAD WINDS INDICATE A WEAKLY SHEARED ENVIRONMENT WHICH COMBINED
WITH THE VERY UNSTABLE AIRMASS WILL SUPPORT PULSE-TYPE STORMS WITH
THE POTENTIAL FOR ISOLATED MARGINALLY SEVERE WIND GUSTS.  RICH
MOISTURE /PRECIPITABLE WATER VALUES IN EXCESS OF 1.8 INCHES/ AND
SLOW STORM MOVEMENT TO THE S AT 10-15 KT WILL RESULT IN RAINFALL
RATES FROM 1 TO 1.5 INCH PER HOUR WITH THE STRONGEST STORMS.

..PETERS.. 07/22/01