SWODY1
SPC AC 161602
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1102 AM CDT SUN SEP 16 2007
VALID 161630Z - 171200Z
..THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR NRN
AZ...SRN AND ERN UT...AND WRN CO...
..AZ/UT/CO AREA THIS AFTERNOON/EVENING...
THE PERSISTENT MID LEVEL LOW INVOF NRN CA IS EVOLVING INTO AN OPEN
WAVE AND WILL TRANSLATE EWD OVER NV TO WRN UT/NW AZ BY EARLY MONDAY.
IN ADVANCE OF THIS SYSTEM...A PLUME OF RELATIVELY RICH MOISTURE
/LOW-LEVEL DEWPOINTS IN THE UPPER 40S TO MID 50S/ IS SPREADING NEWD
FROM AZ INTO SRN/ERN UT AND WRN CO. THE 12Z OBSERVED FGZ AND GJT
SOUNDINGS MODIFIED FOR DAYTIME HEATING...ALONG WITH NAM/RUC FORECAST
SOUNDINGS...SHOW THE POTENTIAL FOR AFTERNOON MUCAPE VALUES OF
750-1500 J/KG IN CLOUD BREAKS WITHIN THE MOISTURE PLUME.
ADDITIONALLY...DEEP LAYER VERTICAL SHEAR WILL GRADUALLY INCREASE
FROM W TO E WITH THE APPROACH OF THE MID LEVEL TROUGH FROM
CA/NV...RESULTING IN WIND PROFILES SUFFICIENT FOR SUPERCELLS AND
BOWING LINE SEGMENTS.
EXPECT SCATTERED THUNDERSTORMS TO FORM BY EARLY AFTERNOON FROM AZ
ACROSS SRN/ERN UT INTO WRN CO...WITH GRADUAL STORM INTENSIFICATION
BY MID AFTERNOON. THE STRONGEST STORMS WILL BE CAPABLE OF PRODUCING
ISOLATED LARGE HAIL AND DAMAGING GUSTS...MAINLY FROM MID AFTERNOON
INTO THIS EVENING.
..PLAINS/MS VALLEY THROUGH TONIGHT...
ELEVATED CONVECTION IS ONGOING OVER CENTRAL/ERN KS IN ASSOCIATION
WITH LOW-LEVEL WAA WITH A 40 KT WSWLY LLJ...AND OVER NEB IN
ASSOCIATION WITH A WEAK MID LEVEL WAVE CRESTING THE SRN PLAINS
RIDGE. THE CONVECTION IN KS WILL LIKELY DIMINISH THIS AFTERNOON AS
THE LLJ WEAKENS. MEANWHILE...A SURFACE WARM FRONT IN KS WILL LIFT
NWD IN RESPONSE TO PRESSURE FALLS ACROSS THE CENTRAL/NRN PLAINS
THROUGH TONIGHT. THE NWD PROGRESS OF THE LOW-LEVEL
MOISTENING...HOWEVER...WILL BE PRECEDED BY A WARM ELEVATED MIXED
LAYER THAT WILL OVERSPREAD MUCH OF THE CENTRAL/NRN PLAINS. IF
CONVECTION CAN DEVELOP TONIGHT...VERY STEEP MID LEVEL LAPSE RATES
AND EFFECTIVE BULK SHEAR IN EXCESS OF 35 KT WOULD SUPPORT A THREAT
FOR STORMS WITH LARGE HAIL. HOWEVER...THE CAP SHOULD BE QUITE
SUBSTANTIAL...AND THE PROBABILITY OF CONVECTIVE INITIATION APPEARS
TOO MARGINAL TO WARRANT INCLUSION OF SEVERE PROBABILITIES.
.THOMPSON/GRAMS.. 09/16/2007
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