SPC AC 051254
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0754 AM CDT FRI OCT 05 2007
VALID 051300Z - 061200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS CENTRAL MN AND W
CENTRAL WI...
...SYNOPSIS...
A BROAD/DEEP MID LEVEL TROUGH WILL PROGRESS EWD FROM CA TO THE GREAT
BASIN AS A DOWNSTREAM RIDGE AMPLIFIES OVER THE MS/OH VALLEY REGION.
THE NET RESULT WILL BE AN INCREASINGLY MERIDIONAL FLOW REGIME OVER
THE ROCKIES CENTRAL ROCKIES AND ADJACENT HIGH PLAINS...WITH
RESULTANT CYCLOGENESIS EXPECTED ACROSS ERN WY. MEANWHILE...A SHARP
BAROCLINIC ZONE WILL DRIFT SLOWLY NWD ACROSS SD/MN/WI TO THE E OF
THE DEVELOPING WY CYCLONE. THIS SLOW MOVING WARM FRONT...ALONG WITH
THE DEEP BAROCLINIC ZONE ASSOCIATED WITH THE GREAT BASIN
TROUGH...WILL PROVIDE THE PRIMARY FOCI FOR THUNDERSTORM DEVELOPMENT
THROUGH THE PERIOD.
...UPPER MS VALLEY THROUGH TONIGHT...
CLUSTERS OF PRIMARILY ELEVATED THUNDERSTORMS HAVE BEEN WEAKENING
SLOWLY THIS MORNING FROM WRN IA INTO SE MN/NW WI. THIS CONVECTION
HAS BEEN SUPPORTED BY LOW-LEVEL WAA ALONG THE LLJ AXIS...AS WELL AS
A MID LEVEL TROUGH EJECTING NEWD OVER NW IA/SW MN. EXPECT MID LEVEL
WAVE AND ASSOCIATED CONVECTION TO CONTINUE SPREADING NEWD OVER MN/NW
WI/WRN UPPER MI/LAKE SUPERIOR THROUGH THIS EVENING.
A PLUME OF STEEPER MID LEVEL LAPSE RATES OVERSPREADING NEB/SD WILL
EFFECTIVELY CAP THE PLAINS PORTION OF THE WARM FRONT. THE CAP AND
MID LEVEL LAPSE RATES WILL BE WEAKER FARTHER TO THE E ACROSS MN/WI
DURING THE AFTERNOON. THE PRIMARY CONCERN ACROSS MN/WI WILL BE THE
EARLY PASSAGE OF THE MID LEVEL WAVE...AS WELL AS A LARGER SCALE
BACKGROUND ENVIRONMENT OF MID LEVEL HEIGHT RISES. THESE FACTORS
SUGGEST THAT STORM COVERAGE SHOULD BE RATHER ISOLATED INVOF THE WARM
FRONT DURING THE AFTERNOON...WITH THE MAJORITY OF CONVECTION
EXPECTED N OF THE WARM FRONT WHERE ELEVATED INSTABILITY WILL BE
MARGINAL. IF SURFACE-BASED STORMS DO FORM...BOUNDARY LAYER
DEWPOINTS IN THE MID 60S AND SURFACE TEMPERATURES APPROACHING 80 F
WITHIN CLOUD BREAKS WILL SUPPORT MLCAPE VALUES NEAR 1000 J/KG.
LOW-LEVEL AND DEEP LAYER SHEAR WILL BE FAVORABLE FOR SUPERCELLS
ALONG THE WARM FRONT...WHERE A CONDITIONAL TORNADO/WIND/HAIL THREAT
WILL EXIST. STILL...THE OVERALL SEVERE STORM THREAT SHOULD BE
LIMITED BY MODEST INSTABILITY AND SPARSE STORM COVERAGE IN THE
SURFACE WARM SECTOR.
...CENTRAL/ERN UT INTO WRN WY THIS AFTERNOON/EVENING...
AN EXTENSIVE N-S BAND OF PRECIPITATION WITH EMBEDDED THUNDERSTORMS
IS EXPECTED TO DEVELOP THIS AFTERNOON ALONG THE DEEP BAROCLINIC ZONE
ACROSS CENTRAL UT AND THEN SPREAD QUICKLY NWD INTO WRN WY...WHILE
THE ENTIRE BAND SHIFTS SLOWLY EWD TONIGHT. VERTICAL SHEAR IS
FORECAST TO BE QUITE STRONG OVER THIS AREA...WITH THE POTENTIAL FOR
FAST-MOVING BOWING SEGMENTS...AND POSSIBLY EMBEDDED SUPERCELL
STRUCTURES. HOWEVER...WEAK INSTABILITY WILL TEND TO LIMIT THE
SEVERE STORM THREAT TO ISOLATED STRONG/DAMAGING GUSTS AND MARGINALLY
SEVERE HAIL.
...SRN HIGH PLAINS THIS AFTERNOON...
A SERIES OF DIFFUSE MID LEVEL TROUGHS WILL LIFT NEWD FROM NM/CO
TOWARD WRN NEB/SD THIS AFTERNOON WHILE GRADUALLY WEAKENING. THE
RICHER LOW-LEVEL MOISTURE WILL REMAIN E OF THE SURFACE LEE TROUGH
ACROSS KS/NEB...BUT SOMEWHAT RICHER MOISTURE IS EXPECTED ALONG THE
WEAK LEE TROUGH INTO THE WRN TX PANHANDLE AND ERN NM. WIDELY
SCATTERED THUNDERSTORMS MAY DEVELOP THIS AFTERNOON ALONG THE
MOISTURE GRADIENT ACROSS ERN NM...ALONG THE ERN PERIPHERY OF THE
STRONGER MID-UPPER LEVEL SWLY FLOW. AFTERNOON MLCAPE VALUES
APPROACHING 1500 J/KG AND MODEST DEEP LAYER SHEAR COULD SUPPORT
ISOLATED STORMS CAPABLE OF PRODUCING GUSTY WINDS AND MARGINALLY
SEVERE HAIL THIS AFTERNOON/EVENING.
...ERN MT/WRN ND TONIGHT...
SOME OF THE CONVECTION ORIGINATING IN WRN WY MAY SPREAD NEWD AS
ELEVATED THUNDERSTORMS ACROSS ERN MT TONIGHT. ADDITIONALLY...AN
INCREASE IN LOW-LEVEL MOISTURE IN A STRENGTHENING WAA REGIME IS
EXPECTED ACROSS WRN ND TONIGHT. ELEVATED THUNDERSTORMS MAY DEVELOP
WITHIN THIS REGIME AFTER ABOUT 06Z...AND MID LEVEL INSTABILITY COULD
BE SUFFICIENT FOR STORMS WITH MARGINALLY SEVERE HAIL.
..THOMPSON/CROSBIE.. 10/05/2007
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