STORM2K

MESOSCALE DISCUSSION 0407
NWS STORM PREDICTION CENTER NORMAN OK
1258 PM CDT WED APR 21 2004

AREAS AFFECTED...OKLAHOMA

CONCERNING...SEVERE THUNDERSTORM POTENTIAL

VALID 211758Z - 212000Z

...TORNADIC SUPERCELLS ARE EXPECTED TO DEVELOP LATER THIS AFTERNOON
ACROSS MUCH OF OKLAHOMA...

COMPLEX ARRAY OF LOW LEVEL BOUNDARIES FROM OVERNIGHT
CONVECTION...AND ONGOING DAYTIME HEATING WILL PROVIDE THE FOCUS FOR
THUNDERSTORM DEVELOPMENT LATER THIS AFTERNOON. LATEST SATELLITE
IMAGERY SUGGEST MASS FIELDS ARE FOCUSING OVER WRN/CNTRL OK AHEAD OF
APPROACHING UPPER SPEED MAX. LEADING EDGE OF BOUNDARY LAYER CU THAT
IS STREAMING WNWD APPEARS LOOSELY CORRELATED WITH 60F SFC DEW
POINTS. THIS MOISTURE INCREASE WILL PROVE INSTRUMENTAL IN SUPERCELL
DEVELOPMENT BY 21Z. MID LEVEL TEMPERATURES ARE SIGNIFICANTLY COLDER
THAN TUESDAY RESULTING IN SBCAPE VALUES IN EXCESS OF 2000J/KG AT 17Z
OVER MUCH OF THE SURGING WARM SECTOR. LATEST THINKING IS STEEPENING
LAPSE RATES ALONG WRN EDGE OF MOISTURE RETURN WILL BE ONE ZONE FOR
INITIATION AS EXIT REGION OF UPPER SPEED MAX APPROACHES. OTHER
SUPERCELLS SHOULD DEVELOP ALONG DRY LINE...OR OLD OUTFLOW BOUNDARY
BY LATE AFTERNOON. TORNADOES IN ADDITION TO VERY LARGE HAIL WILL
ACCOMPANY AN EVER INCREASING CONVECTIVE THREAT INTO THE EVENING
HOURS.

A TORNADO WILL BE ISSUED BY 20Z FOR MUCH OF OK.

..DARROW.. 04/21/2004


ATTN...WFO...SHV...TSA...FWD...OUN...AMA...

http://www.spc.noaa.gov/products/md/md0407.html shows the area of concern across most of Oklahoma. A tornado watch will be issued by 4 pm eastern, 3 pm central to affect most of central and eastern Oklahoma. Supercells producing huge hail and destructive tornadoes are likely as we head through the evening. Red Rock, Oklahoma City, and Tulsa will likely see these destructive storms and a tornado outbreak once again could commence this afternoon and evening.

Stay safe today and tonight as these storms will survive into Arkansas too with large hail, destructive winds, and possibly more damaging tornadoes.

Jim