[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 031240
SWODY1
SPC AC 031238

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0738 AM CDT SUN SEP 03 2006

VALID 031300Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF EXTREME ERN
NEB AND WRN IA...

...SYNOPSIS...
CUTOFF LOW OVER SERN SD IS FORECAST TO MOVE SLOWLY ESEWD AND ACROSS
IA LATER TODAY AND TONIGHT. A WEAK FRONT WILL ACCOMPANY THIS LOW AND
SHOULD EXTEND FROM CENTRAL WI SSWWD INTO SERN OK/CENTRAL TX BY LATE
AFTERNOON. HIGH PRESSURE ALOFT OVER NV AND SRN TX WILL RESULT IN A
WEAK UPPER LEVEL TROUGH OVER THE LOWER CO VALLEY.

...EXTREME ERN NEB/WRN IA...
LATEST RUC ANALYSIS AND MODEL FORECAST INDICATES A POCKET OF
RELATIVELY COLD MID-LEVEL TEMPERATURES /-18 TO -20 C AT 500 MB/ WILL
SHIFT SEWD FROM SERN SD INTO WRN IA THIS AFTERNOON. DAYTIME HEATING
COUPLED WITH THE COLD TEMPERATURES ALOFT WILL RESULT IN STEEP LOW TO
MID-LEVEL LAPSE RATES...WITH SBCAPES RANGING FROM 500 TO 1000 J/KG.
THE INCREASING INSTABILITY AND LIFT ASSOCIATED WITH THE UPPER LOW IS
EXPECTED TO AID THUNDERSTORM DEVELOPMENT ACROSS THE AREA THIS
AFTERNOON. THOUGH INSTABILITY WILL BE WEAK...30-50 KT MID LEVEL
WINDS ON THE SRN PERIPHERY OF THE UPPER LOW MAY SUPPORT BRIEF
UPDRAFT ROTATION. GIVEN THE STEEP MID LEVEL LAPSE RATES AND COLD
TEMPERATURES ALOFT...HAIL IS EXPECTED TO BE THE PRIMARY SEVERE
THREAT. HOWEVER...THE POTENTIAL WILL EXIST FOR A SHORT LIVED TORNADO
DUE TO THE STEEP LOW-LEVEL LAPSE RATES AND CONCENTRATED ZONE OF
VORTICITY.

...WRN WI/NWRN IL AND EXTREME ERN IA...
BAND OF SHOWERS/ISOLATED STORMS ARE CURRENTLY LOCATED NEAR THE FRONT
ACROSS SERN MN AND ERN IA AND SHOULD PUSH SLOWLY EWD INTO WI/NWRN IL
THIS AFTERNOON. IF ENOUGH SUNSHINE CAN OCCUR AND WARM TEMPERATURES
INTO THE LOWER/MID 70S...THESE READINGS ALONG WITH DEWPOINTS IN THE
UPPER 50S WILL YIELD 500-750 J/KG OF MLCAPE. THIS INSTABILITY
COMBINED WITH LOW LEVEL CONVERGENCE LIKELY WOULD BE SUFFICIENT FOR
SURFACE BASED THUNDERSTORMS TO DEVELOP JUST EAST OF THE
PRE-MENTIONED CONVECTIVE BAND. A COUPLE OF NON-SUPERCELL TORNADOES
DEVELOPED SATURDAY IN IA...DURING THE EARLY CONVECTIVE STAGES. A
SIMILAR ENVIRONMENT WILL BE PRESENT OVER THIS AREA TODAY AND AN
ISOLATED TORNADO IS POSSIBLE...THOUGH THE THREAT SHOULD BE TOO
ISOLATED AND BRIEF TO WARRANT MORE THAN A 2% TORNADO PROBABILITY.

...LOWER CO VALLEY...
LOW-LEVEL MOISTURE SURGE FROM THE GULF OF CA WILL BE MAINTAINED
ACROSS THE REGION AS TROPICAL STORM JOHN CONTINUES MOVING NWWD ALONG
THE BAJA PENINSULA. ALTHOUGH OVERNIGHT PRECIPITATION AND MORNING
CLOUDS ARE EXPECTED TO HOLD TEMPERATURES DOWN SOME FROM SATURDAY'S
HIGHS...THE MOIST ENVIRONMENT...DIURNAL HEATING AND PRESENCE OF A
WEAK TROUGH ALOFT SHOULD RESULT IN SCATTERED THUNDERSTORMS THIS
AFTERNOON AND EVENING. WEAK WINDS FROM THE SURFACE-500 MB WILL LIMIT
VERTICAL SHEAR...THOUGH STEEP LOW-LEVEL LAPSE RATES MAY SUPPORT
STRONG TO SEVERE WIND GUSTS. HOWEVER...THE STRONG CONVECTIVE
OVERTURNING DURING THE PAST 24 HOURS AND LESS WARMING THAN SATURDAY
SUGGESTS THE THREAT SHOULD BE TOO ISOLATED FOR A SLIGHT RISK.

..IMY/GRAMS.. 09/03/2006