STORM2K

MESOSCALE DISCUSSION 1740
NWS STORM PREDICTION CENTER NORMAN OK
0216 PM CDT TUE JUL 20 2004

AREAS AFFECTED...SERN SD...NERN NEB...NWRN IA...EXTREME SWRN MN

CONCERNING...SEVERE THUNDERSTORM POTENTIAL

VALID 201916Z - 202115Z

SEVERE THUNDERSTORMS WILL DEVELOP BY LATE AFTERNOON AND A WW APPEARS
LIKELY BY 21Z. VERY LARGE HAIL WILL BE THE MAIN THREAT. A FEW
DAMAGING WIND GUSTS WILL BE POSSIBLE AS WELL ALONG WITH AN ISOLATED
TORNADO.

VISIBLE IMAGERY INDICATES CU FIELD BECOMING BETTER ORGANIZED OVER N
CENTRAL NEB FROM BLAINE INTO ROCK COUNTIES. OTHER CU FIELDS WERE
DEVELOPING FARTHER N BETWEEN PIR AND HON. ENVIRONMENT IS BECOMING
VERY UNSTABLE WITH MLCAPE NOW 2000-3000 J/KG E OF DRYLINE AND ALONG
WARM FRONT WHERE DEWPOINTS REMAIN IN THE 70S F.

FORECAST SOUNDINGS INDICATE TEMPERATURES IN THE UPPER 90S F ARE
REQUIRED TO ERASE CIN. THEREFORE...MOST LIKELY AREA OF INITIATION
WILL BE ALONG DRYLINE AND IN VICINITY OF SURFACE LOW WHERE HOTTEST
TEMPERATURES ARE LOCATED. ENHANCED CONVERGENCE AS WELL AS RICHER
LOW LEVEL MOISTURE ALONG WARM FRONT WILL FURTHER STRENGTHEN FORCING
AND POTENTIAL FOR SEVERE STORMS.

PRESENCE OF MID 70S F DEWPOINTS OVER SERN SD / ERN NEB AND WRN IA
ALONG WITH COOLER TEMPERATURES IN THE UPPER 80S F / LOWER 90S F
SUGGEST SOME TORNADO POTENTIAL AS BOUNDARY LAYER RH WILL NOT BE
PARTICULARLY LOW.

Looks like it might stay north of you NEweatherguy. Are you going to be headin out, because it won't be too far north of ya. I know Todd Heithkamp (spell??) it talking tennis ball sized hail, he is the warning coordinator out of NWS Sioux Falls.

Forget about 4pm, SPC went ahead and put the watch up!
I leave chasing to the pros, sort of speak. However, now that I can drive, I may eventually begin to check out some cloud structure, of course with common sense. Tonight, I will be cyber chasing.

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 657
NWS STORM PREDICTION CENTER NORMAN OK
240 PM CDT TUE JUL 20 2004


THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF


NORTHEAST NEBRASKA
SOUTHEAST SOUTH DAKOTA


EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 240 PM UNTIL 900
PM CDT.


TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.


THE TORNADO WATCH AREA IS ALONG AND 75 STATUTE MILES EAST AND WEST
OF A LINE FROM 25 MILES NORTHEAST OF HURON SOUTH DAKOTA TO 40
MILES WEST SOUTHWEST OF NORFOLK NEBRASKA.


REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA.
PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING
WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE
WARNINGS.


DISCUSSION...VERY UNSTABLE AIR MASS IN PLACE ACROSS WATCH AREA WITH
CAP BECOMING VERY WEAK WRN PORTION. RAPID DEVELOPMENT OF SEVERE
THUNDERSTORMS EXPECTED IN AREA OF BEST LOW LVL CONVERGENCE VICINITY
NEB/SD BORDER W OF YKN. VEERING SHEAR PROFILES SUPPORT SUPERCELLS
WHICH WILL ENHANCE POTENTIAL FOR VERY LARGE HAIL AND ISOLATED
TORNADOES.


AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 70 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 600.
MEAN STORM MOTION VECTOR 27025.