Hail in Minnesota, July 30, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
220 PM CDT TUE JUL 30 2002

...FORECAST CONCERN CENTERS AROUND SEVERE WEATHER POTENTIAL TONIGHT
AND TOMORROW...

SYNOPSIS...MORNING SUBJECTIVE UPPER AIR ANALYSIS INDICATED STRONG
ZONAL FLOW AT H3. A COUPLE OF DIFFERENT SHORT WAVES WERE VISIBLE
THIS MORNING AT H5. THE FIRST WAS OVER CNTRL WY WITH THE SECOND AND
STRONGER WAVE...MOVING THROUGH THE PACIFIC NORTHWEST. LOW LEVEL
MOISTURE WAS LACKING WITH SFC RIDGE OVER THE OZARKS...BUT SOME
MOISTURE RETURN WITH 10 DEGREE DP AT KLBF AND A PERSISTANT 25 KNTS
LLJ. AT THE SFC...18Z MSAS ANALYSIS INDICATED LO PRESSURE OVR S
CNTRL SD WITH A WEAK BOUNDARY EXTENDING EAST INTO CNTRL MN.

FORECAST...ANOTHER DECENT SETUP FOR SVR WX ACROSS THE CWA FOR
TONIGHT. ATMOSPHERE HAS BECOME EXTREMELY UNSTABLE ACROSS MOST OF THE
CWA THIS AFTERNOON AS CAP CONTINUES TO WEAKEN. FRONT CONTINUES TO
SLOWLY SAG TO THE SOUTH THROUGH THE NORTHERN CWA. THIS WILL BECOME
STATIONARY AROUND THE I-90 CORRIDOR THIS EVENING. SHORT WAVE SEEN ON
MORNING UPPER AIR ANALYSIS WILL INTERACT WITH THE BOUNDARY TO
PRODUCE SCT TRW OVERNIGHT. DEEP LAYER SHEAR OF 40-50KNTS ACROSS THE
CWA WILL LEAD TO SUSTAINED SVR CONVECTION...INCLUDING SUPERCELLS.
WEB BULB HEIGHTS ARE RUNNING BELOW 12K...AND THUS SOME VERY LARGE
HAIL IS POSSIBLE. MID LEVEL DRYING AND DECENT 40KNT FLOW AT H5 WILL
ALSO LEAD TO A DECENT DAMAGING WIND POTENTIAL. WILL INCLUDE SVR IN
THE NORTHERN/CNTRL ZONES OVERNIGHT. LLJ THEN KICKS AFTR 03Z FROM
CNTRL NEB NE INTO SW MN. WITH CONVERGENCE FROM LOW LEVEL JET WILL
CONTINUE THUNDER THREAT FOR THE OVERNIGHT HOURS FOR OUR SW MN ZONES.
ADVECTION VECTOR SEEMS STRONGER THAN THE PROPAGATION VECTOR AND THUS
SOME BACKBUILDING OF THE STORMS SEEMS POSSIBLE.

STRONGER SHORT WAVE MOVES ACROSS THE NORTHERN US ON WEDNESDAY. THIS
WILL PUSH A REINFORCING COLD FRONT INTO THE NORTHWEST CWA BY
18Z...AND THEN EXIT THE SE CWA AFTER 03Z. SFC WNDS GO AROUND TO THE
SW DURING THE MORNING AND THIS IS PERFECT FOR DEEP MIXING ACROSS THE
CWA. WILL USE WINDY WORDING IN THE SOUTH AND GO WELL ABOVE GUIDANCE
FOR HIGHS. WILL HAVE TO WATCH THE FIRE DANGER OUT WEST. IF WE MIX TO
H7 WINDS WILL BE STRONGER THAN FORECAST...AND WITH DEWPOINTS MIXING
OUT...MAY BE IN THE RED FLAG CRITERIA. ALSO WILL HAVE TO MONITOR NW
IA FOR HEAT ADVISORY IF DEWPOINTS DONT MIX OUT.

ATMOSPHERE WILL ONLY BECOME MODERATELY UNSTABLE TOMORROW AFTERNOON
AHEAD OF THE FRONT WITH THE DECREASE IN LOW LEVEL MOISTURE FROM
MIXING. ALSO CAPPING INVERSION INCREASING THROUGH THE DAY WITH +16
AT H7 INDICATED BY ETA. THIS SHOULD EFFECTIVELY CAP WESTERN CWA ALL
DAY. WILL CONTINUE WITH THE PREVIOUS FORECAST OF A SLIGHT CHC JUST
BEHIND THE FRONT. WITH INVERTED V SOUNDINGS AND MODERATE INSTABILITY
MAY HAVE TO WORRY ABOUT SOME WIND IF STORMS CAN GET GOING.

FRONT THEN HANGS UP TO OUR SOUTH ON THURSDAY. SOME MID LEVEL
FRONTOGENESIS INDICATED BY THE AVN IN NORTHERN NEB...BUT FEEL WILL BE
TO WEAK TO MENTION SHOWERS. OTHERWISE A PARTLY CLOUDY AND COOLER DAY
IS IN STORE. LLJ GETS GOING OUT WEST THURSDAY NIGHT INTO FRIDAY
MORNING AND THE AVN BLOWS UP BIG MCS. FEEL MOST OF THIS IS
CONVECTIVE FEEDBACK SO WILL IGNORE IN THE ZONES. FRONT THEN SLATED TO
SLIDE THROUGH CWA AGAIN ON SATURDAY WILL EXPAND THE CHC FOR TRW TO
INCLUDE ENTIRE CWA.

NO CHANGES TO THE REST OF THE EXTENDED. OZF AND GRIDS OUT BY 300 PM.

.FSD...NONE

BOUSTEAD