SWODY1
SPC AC 172000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT WED AUG 17 2011
VALID 172000Z - 181200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL HIGH
PLAINS AND NRN PLAINS...
THE FIRST CHANGE TO THE OUTLOOK AT 20Z IS TO ADD A 5 PERCENT WIND
DAMAGE AND HAIL PROBABILITY ACROSS ERN UPPER MI AND NRN LAKE MI
WHERE A LINE OF STRONG TO SEVERE THUNDERSTORMS IS ONGOING. THE
SECOND CHANGE IS TO TRIM THE FAR WRN EDGE OF THE SLIGHT RISK AREA
ALONG THE WRN EDGE OF THE INSTABILITY AXIS. THE THIRD CHANGE IS TO
CONNECT THE 5 PERCENT WIND DAMAGE PROBABILITY FROM OK TO IL ALONG AN
AXIS OF STRONG INSTABILITY. THUNDERSTORMS THAT INITIATE ALONG THIS
AXIS MAY HAVE A MARGINAL WIND DAMAGE THREAT MAINLY DUE TO THE STEEP
LOW-LEVEL LAPSE RATES IN PLACE. OTHERWISE...THE ONLY OTHER CHANGES
ARE MINOR ADJUSTMENTS TO THE THUNDER-LINES.
..BROYLES.. 08/17/2011
.PREV DISCUSSION... /ISSUED 1127 AM CDT WED AUG 17 2011/
...CENTRAL HIGH PLAINS THIS AFTERNOON INTO EARLY TONIGHT...
A MOIST UPSLOPE FLOW REGIME IS NOW ESTABLISHED FROM ERN CO NWD TO
WRN NEB. 12Z REGIONAL SOUNDINGS SHOWED STEEP LAPSE RATES IN THE
700-500 MB LAYER ABOVE THE MOIST UPSLOPE...SUCH THAT AFTERNOON
TEMPERATURES NEAR 90 WITH BOUNDARY LAYER DEWPOINTS IN THE LOW 60S
WILL RESULT IN MLCAPE APPROACHING 2500 J/KG. 50-70 KT WLY FLOW
ALOFT IS ALSO PRESENT OVER THE CENTRAL HIGH PLAINS...WHICH COMBINED
WITH THE WEAK UPSLOPE FLOW WILL RESULT IN FAVORABLE DEEP-LAYER
VERTICAL SHEAR FOR SUPERCELLS. PRESENT INDICATIONS ARE THAT A FEW
STORMS WILL FORM AROUND MID AFTERNOON ALONG THE MOISTURE GRADIENT
FROM THE NEB/WY BORDER SWD INTO NE CO AS CONVECTIVE INHIBITION
DIMINISHES.
LARGE HAIL IS EXPECTED TO BE THE MAIN THREAT THIS
AFTERNOON/EVENING...WITH ISOLATED VERY LARGE HAIL POSSIBLE GIVEN THE
EXPECTED SUPERCELL STRUCTURES AND MODERATE INSTABILITY. AN ISOLATED
TORNADO OR TWO CANNOT BE RULED OUT...THOUGH THE TORNADO THREAT MAY
BE TEMPERED BY TEMPERATURE-DEWPOINT SPREADS APPROACHING 30 F AND
RELATIVELY WEAK LOW-LEVEL SHEAR NEAR AND JUST E OF THE LEE TROUGH
WHERE STORMS WILL LIKELY FORM. OTHERWISE...A FEW DAMAGING GUSTS
WILL BE POSSIBLE...ESPECIALLY THIS EVENING IF STORM MERGERS LEAD TO
SOME UPSCALE GROWTH INTO A CLUSTER OR TWO. A NOCTURNAL INCREASE IN
LOW-LEVEL SLY FLOW AND WAA SHOULD HELP SUSTAIN THE CONVECTION INTO
THE OVERNIGHT HOURS WITH AT LEAST A MARGINAL HAIL/WIND THREAT.
...NW IL/ERN MO THIS AFTERNOON...
A WEAK SURFACE COLD FRONT WILL MOVE SEWD FROM NRN MO/ERN IA/SRN WI
TO NW IL AND ERN MO BY LATE THIS AFTERNOON/EVENING. A BAND OF
MID-UPPER 60S DEWPOINTS ALONG THE FRONT AND SURFACE HEATING IN CLOUD
BREAKS WILL SUPPORT MLCAPE RANGING FROM 1500 J/KG ACROSS NW IL TO
2000 J/KG ACROSS E CENTRAL MO. THOUGH LOW-LEVEL FLOW WILL REMAIN
WEAK...WNWLY MIDLEVEL FLOW OF 35-50 KT WILL CONTRIBUTE TO SUFFICIENT
DEEP-LAYER SHEAR FOR SOME ORGANIZED/POSSIBLY SUPERCELLULAR STORM
STRUCTURES. A FEW STORMS ARE EXPECTED TO DEVELOP ALONG THE FRONT
THIS AFTERNOON...WITH THE POTENTIAL FOR ISOLATED LARGE HAIL AND
DAMAGING WINDS.
...CENTRAL AND EAST CENTRAL FL THIS AFTERNOON...
DAYTIME HEATING INLAND OVER THE FL PENINSULA WILL RESULT IN
MODERATE-STRONG INSTABILITY THIS AFTERNOON. REMNANT OUTFLOW
BOUNDARIES FROM MORNING CONVECTION NEAR TAMPA BAY WILL CONTINUE TO
MOVE INLAND INVOF OF A DIFFUSE REMNANT FRONT...WHERE NEW
THUNDERSTORM DEVELOPMENT IS LIKELY EARLY THIS AFTERNOON. OTHER
STORMS WILL ALSO FORM ALONG THE E COAST SEA BREEZE WHICH WILL REMAIN
CLOSE TO THE COAST IN A WEAK WLY LOW-LEVEL FLOW REGIME S OF THE
REMNANT FRONT. MLCAPE APPROACHING 3000 J/KG AND PW NEAR 2 INCHES
WILL SUPPORT STRONG UPDRAFTS AND PRECIPITATION LOADING...WHILE DCAPE
NEAR 1000 J/KG WILL BE SUPPORTIVE OF STRONG DOWNDRAFTS AND THE
POTENTIAL FOR ISOLATED DAMAGING GUSTS THIS AFTERNOON.
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