Thursday, September 6, 2007

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 061954
SWODY1
SPC AC 061951

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0251 PM CDT THU SEP 06 2007

VALID 062000Z - 071200Z

..THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CENTRAL
PLAINS AND MIDWEST STATES...

..CENTRAL PLAINS AND MIDWEST STATES...
UPPER TROUGH...CURRENTLY LOCATED OVER ERN WY/NRN CO/WRN NEB AND SD
PER WATER VAPOR IMAGERY...WILL CONTINUE TO MOVE EWD THIS FORECAST
PERIOD TOWARD THE MID MO TO UPPER MS VALLEYS THIS EVENING AND
TONIGHT. SURFACE ANALYSES INDICATED A NEARLY STATIONARY BOUNDARY
EXTENDING FROM NERN-NORTH CENTRAL MN SWWD THROUGH SERN SD TO CENTRAL
NEB TO WRN KS. ALTHOUGH SLY LOW LEVEL FLOW CONTINUES TO ADVECT
MOISTURE NWD IN ADVANCE OF THIS BOUNDARY...INCREASING CLOUDINESS
WITHIN THIS MOIST AXIS IS EXPECTED TO FURTHER LIMIT SURFACE HEATING
AND DEVELOPMENT OF GREATER INSTABILITY.

THUS FAR...TSTM ACTIVITY HAS BEEN RATHER LIMITED IN COVERAGE. LOW
LEVEL WAA ALONG NRN EXTENT OF THE SURFACE BOUNDARY EXTENDING INTO
NERN MN IS EXPECTED TO MAINTAIN ONGOING BACKBUILDING CLUSTER OF
TSTMS WITH WEAK INSTABILITY SUPPORTING A THREAT FOR ISOLATED HAIL
AND STRONGER WIND GUSTS. MEANWHILE...ONGOING TSTM COMPLEX
APPROACHING SERN SD/NERN NEB APPEARS TO BE ASSOCIATED WITH ANAFRONT
CONVECTIVE DEVELOPMENT WHERE DEEP LAYER SHEAR IS STRONGER WITHIN
POST-FRONTAL ENVIRONMENT. FARTHER W...ISOLATED TSTMS HAVE DEVELOPED
MAINLY ACROSS ERN WY TO FAR WRN NEB/NRN CO ATTENDANT WITH UPPER
TROUGH.

ADDITIONAL TSTM DEVELOPMENT IS LIKELY ACROSS WRN NEB AND POTENTIALLY
INTO WRN SD AS STRONGER FORCING SPREADS EWD. DESPITE WEAKER
INSTABILITY LOCATED WITHIN THIS POST-FRONTAL AIR MASS...STEEP LOW
LEVEL LAPSE RATES SUGGEST A POTENTIAL FOR ISOLATED DAMAGING WIND
GUSTS WITH THE STRONGER CORES AND ISOLATED HAIL. PRESENT
INDICATIONS CONTINUE TO SUGGEST THAT THESE TSTMS WILL SPREAD EWD
INTO MORE MOIST/UNSTABLE AIR MASS OVER CENTRAL NEB AND INTENSIFY
FURTHER DURING THE EVENING. STRENGTH OF FORCING AND DEGREE OF
INSTABILITY SUGGEST THE LIKELIHOOD OF ORGANIZATION INTO A LINEAR MCS
EXTENDING FROM SOUTHEAST SD INTO NORTHERN KS...MOVING INTO PARTS OF
MN/IA/MO DURING THE NIGHT. THIS LINE OF STORMS WILL LIKELY MAINTAIN
A RISK OF DAMAGING WINDS AND HAIL THROUGH AT LEAST 06Z.

..MO/IL...
ASCENT ATTENDANT WITH REMNANT UPPER LOW...NOW CENTERED OVER ERN
MO...WILL SUPPORT ADDITIONAL TSTMS...SOME WITH STRONGER CORES...
THROUGH THE REMAINDER OF THIS AFTERNOON INTO THE EARLY EVENING.
MODEST INSTABILITY ATTRIBUTED TO WEAK LAPSE RATES COMBINED WITH WEAK
DEEP LAYER SHEAR WILL CONTINUE TO LIMIT STORM ORGANIZATION.
HOWEVER...LOW LEVEL DIRECTIONAL SHEAR WITHIN THE MOIST/TROPICAL AIR
MASS AND ADDITIONAL SURFACE HEATING SUGGESTS THE POTENTIAL FOR
ADDITIONAL TRANSIENT LOW LEVEL CIRCULATIONS. THE POTENTIAL FOR A
BRIEF TORNADO OR TWO IS MOST LIKELY FROM SRN MO/FAR NERN AR/FAR WRN
TN INTO WEST-CENTRAL IL ALONG AND WEST OF THE STRONGER LOW LEVEL
WINDS.

.PETERS.. 09/06/2007

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