SPC AC 161959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT SUN AUG 16 2009
VALID 162000Z - 171200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF ERN CO...KS AND
NRN OK...
ONE CHANGE TO THE DAY 1 OUTLOOK IS TO REMOVE THE 5 PERCENT WIND
PROBABILITY FROM MN AND WI AND EXTEND THE LINE NEWD INTO SRN LOWER
MI. RUC ANALYSIS INDICATES THAT LOW-LEVEL LAPSE RATES ARE VERY STEEP
IN NW IND AND FAR SRN LOWER MI WITH WSR-88D VWPS HAVE 20-25 KT OF
FLOW AT 1 KM SUGGESTING A FEW OF THE THUNDERSTORMS COULD HAVE
MARGINALLY SEVERE WIND GUSTS.
FURTHER WEST IN THE WRN PART OF THE SLIGHT RISK AREA...ISOLATED
THUNDERSTORMS MAY DEVELOP IN NCNTRL CO THIS AFTERNOON WHERE VISIBLE
SATELLITE CURRENTLY SHOWS CUMULUS GROWTH. THE MAIN CLUSTER OF
THUNDERSTORMS IS EXPECTED TO INITIATE EARLY THIS EVENING AS
LARGE-SCALE ASCENT INCREASES DUE TO AN APPROACHING UPPER-LEVEL
TROUGH. RUC ANALYSIS CURRENTLY INDICATES STRONG VERTICAL SHEAR AND
STEEP MID-LEVEL LAPSE RATES ARE IN PLACE ALONG THE FRONT RANGE
FAVORABLE FOR HAIL. A THREAT FOR LARGE HAIL MAY DEVELOP AS
CONVECTIVE CLUSTERS AND POSSIBLY ISOLATED SUPERCELLS MOVE EWD INTO
WRN KS DURING THE OVERNIGHT PERIOD SUPPORTED BY INCREASING ELEVATED
INSTABILITY AND A STRENGTHENING LOW-LEVEL JET.
..BROYLES.. 08/16/2009
.PREV DISCUSSION... /ISSUED 1128 AM CDT SUN AUG 16 2009/
...OK/KS NEWD TO THE UPPER MS VALLEY THROUGH TONIGHT...
THE PRIMARY SYNOPTIC CYCLONE IS IN THE PROCESS OF DEVELOPING NEWD
FROM NRN MN TO WRN ONTARIO...IN ADVANCE OF A PRONOUNCED LEAD
SHORTWAVE TROUGH ROTATING NEWD AROUND THE CLOSED LOW CENTERED NEAR
THE MT/ND/SK BORDER. A SURFACE COLD FRONT TRAILING SWD FROM THE
CYCLONE WILL CONTINUE TO PROGRESS EWD ACROSS MN/WI/IA THROUGH
TONIGHT...WHILE THE SWRN EXTENSION OF THE FRONT WILL GRADUALLY STALL
FROM NW OK INTO ERN KS.
A BAND OF PRE-FRONTAL THUNDERSTORMS PERSISTS FROM SE IA ACROSS NRN
MO INTO SE KS/EXTREME N CENTRAL OK...AND THIS CONVECTION APPEARS TO
BE ASSOCIATED WITH A WEAK SHORTWAVE TROUGH EJECTING NEWD OVER THE
SAME AREA. THE WIDESPREAD CLOUDS AND POOR MID LEVEL LAPSE RATES
FROM ROUGHLY THE KANSAS CITY AREA NEWD WILL LIMIT THE MAGNITUDE OF
THE INSTABILITY THROUGH THE AFTERNOON...AND KEEP ANY THREAT FOR
DAMAGING WINDS/LARGE HAIL MARGINAL ALONG OR E OF THE COLD FRONT.
SOMEWHAT STRONGER INSTABILITY IS EXPECTED TO DEVELOP THIS AFTERNOON
ACROSS ERN KS IN THE WAKE OF THE MORNING CONVECTION AND SE OF THE
COLD FRONT...AS WELL AS ALONG THE SERN FRINGE OF THE THICKER
CLOUDS/ONGOING CONVECTION FROM MO SWWD INTO SE KS/NE OK.
MEANWHILE...VERTICAL SHEAR WILL BE RELATIVELY STRONGER ALONG THE
FRONT IN KS...AND WEAKEN WITH EWD/SEWD EXTENT ACROSS MO/OK. THE NET
RESULT WILL BE AN ENVIRONMENT SUPPORTIVE OF PRIMARILY MULTICELL
CLUSTERS WITH AN ATTENDANT THREAT FOR ISOLATED DAMAGING WINDS AND
LARGE HAIL INTO THIS EVENING.
...NRN CO FRONT RANGE THIS EVENING INTO WRN KS OVERNIGHT...
THE SURFACE COLD FRONT CONTINUES TO SURGE SWD ACROSS THE TX
PANHANDLE /FASTER AND FARTHER THAN SHORT TERM MODEL
FORECASTS/...WITH THE SURFACE RIDGE ACROSS ERN CO. A LOW-LEVEL
UPSLOPE FLOW REGIME WILL BECOME ESTABLISHED THIS AFTERNOON ALONG THE
FRONT RANGE AND THIS EVENING INTO TONIGHT ACROSS E/NE CO AS THE
SURFACE RIDGE DEVELOPS EWD. HOWEVER...THE RICHER LOW-LEVEL MOISTURE
IS SHUNTED WELL TO THE E/SE IN KS/OK...AND THERE IS SOME QUESTION
REGARDING HOW SOON THE MOISTURE WILL BEGIN TO RETURN NWWD IN A WAA
REGIME FORECAST TO DEVELOP TONIGHT.
A SHORTWAVE TROUGH NOW OVER ID/NV WILL ROTATE EWD AND BEGIN TO
IMPACT NRN CO THIS EVENING IN THE ZONE OF LOW-LEVEL UPSLOPE
FLOW...WHERE THUNDERSTORM DEVELOPMENT IS EXPECTED INITIALLY.
AFTERNOON SURFACE TEMPERATURES IN THE 70S...BOUNDARY LAYER DEWPOINTS
IN THE MID 40S...AND SLIGHT MID LEVEL COOLING WILL CONTRIBUTE TO
MLCAPE OF 500-750 J/KG OVER THE FOOTHILLS. DESPITE THE MARGINAL
INSTABILITY...DEEP LAYER VERTICAL SHEAR WILL BE FAVORABLE FOR
SUPERCELLS CAPABLE OF PRODUCING ISOLATED LARGE HAIL AND DAMAGING
GUSTS. OVERNIGHT...ELEVATED CONVECTION SHOULD PERSIST AND SPREAD
EWD OVER THE HIGH PLAINS OF NE CO INTO WRN KS IN CONJUNCTION WITH
STRENGTHENING LOW-LEVEL WAA.
...NE GULF COAST THROUGH TONIGHT...
TROPICAL STORM CLAUDETTE IN THE EXTREME NE GULF OF MEXICO /NOW
LOCATED ABOUT 45 MILES SSE OF APALACHICOLA/ IS FORECAST TO MAKE
LANDFALL ALONG THE FL PANHANDLE THIS EVENING INTO EARLY TONIGHT.
THE CIRCULATION ENVELOPE IS RATHER SMALL AND THE AREA OF ENHANCED
LOW-MID LEVEL FLOW/SHEAR IS CONFINED TO A NARROW BELT IMMEDIATELY
N-E OF THE CIRCULATION CENTER...NEAR AND JUST OFF THE COAST OF THE
FL BIG BEND. ISOLATED SUPERCELLS AND BOWING SEGMENTS MAY OCCUR
WITHIN THE OUTER NERN CONVECTIVE BAND...BUT THE OVERALL TORNADO
THREAT APPEARS TO BE RATHER LIMITED AND WILL MAINTAIN ONLY LOW
PROBABILITIES IN THIS UPDATE.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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