DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 260451
SWODY1
SPC AC 260449

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1149 PM CDT SAT AUG 25 2012

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER SRN/CNTRL FL AND THE FL
KEYS...

...SYNOPSIS...
TROPICAL STORM ISAAC WILL APPROACH THE FL KEYS AND ERN GULF LATER
TODAY...WITH EVENTUAL INTENSIFICATION TO A HURRICANE FORECAST TO
OCCUR. PLEASE REFER TO OFFICIAL TRACK AND INTENSITY FORECAST
GUIDANCE FROM THE NATIONAL HURRICANE CENTER FOR MORE INFORMATION.

AN UPPER RIDGE WILL AMPLIFY OVER THE CNTRL/NRN ROCKIES...IN THE WAKE
OF AN UPPER TROUGH MOVING ACROSS SRN CANADA. THE SRN EXTENSION OF
THIS UPPER TROUGH WILL TRAVERSE EWD NEAR THE INTERNATIONAL BORDER
AND OVER THE UPPER GREAT LAKES. AN ASSOCIATED WEAK COLD FRONT WILL
MOVE EWD ACROSS WI/MI...WITH A MUCH DRIER AIR MASS OVERSPREADING THE
NRN PLAINS AND PARTS OF THE UPPER MIDWEST.

A WEAKENING MIDLEVEL CYCLONIC CIRCULATION AND ASSOCIATED SHEAR AXIS
WILL EXTEND FROM THE SRN PLAINS NEWD TOWARDS THE MID-MS RIVER
VALLEY...AND WILL SUPPORT ANOTHER ROUND OF SCATTERED THUNDERSTORM
DEVELOPMENT THIS AFTERNOON. FARTHER E...A PERSISTENT MIDLEVEL
CIRCULATION OVER THE MID-ATLANTIC REGION WILL WEAKEN AND SHIFT
N/NEWD IN ADVANCE OF THE AFOREMENTIONED SRN CANADA UPPER TROUGH.

...SRN/CNTRL FL AND THE FL KEYS...
LOW-LEVEL FLOW IS EXPECTED TO STRENGTHEN OVER SRN/CNTRL FL TODAY
WITHIN THE NRN SEMI-CIRCLE OF APPROACHING TROPICAL STORM ISAAC.
FORECAST MODEL SOUNDINGS DEPICT A WIDE SWATH OF 0-1 KM SHEAR
MAGNITUDES OF 30-40 KTS OVERSPREADING THE SRN HALF OF THE FL
PENINSULA BY THIS AFTERNOON. ALTHOUGH WIDESPREAD CONVECTION IS
CURRENTLY OCCURRING DOWNSTREAM FROM THE CENTER OF ISAAC /PER IR
LOOP/...SUFFICIENT INSTABILITY SHOULD STILL DEVELOP OVER THE FL
PENINSULA TO SUPPORT ISOLATED CONVECTION WITHIN/OUTSIDE THE OUTER
RAIN BANDS OF ISAAC...WITH MLCAPE VALUES POSSIBLY AS HIGH AS
500-1000 J/KG DURING PEAK HEATING. GIVEN THE PRESENCE OF LOW LCL
HEIGHTS AND FAVORABLY STRONG LOW-LEVEL SHEAR...A TORNADO THREAT MAY
ACCOMPANY DISCRETE STORMS DEVELOPING ALONG THE N/NERN PERIPHERY OF
ISAAC...AND PERHAPS WITHIN EMBEDDED CONVECTION IN OUTER RAIN BANDS.
A THREAT FOR CONVECTIVE WIND GUSTS MAY ALSO OCCUR...ESPECIALLY IN
AREAS WHERE RELATIVELY STRONGER DAYTIME HEATING RESULTS IN
STEEPENING LOW-LEVEL LAPSE RATES AND/OR WITHIN ORGANIZED LINE
SEGMENTS.

THE OFFICIAL INTENSITY/TRACK FORECAST FROM THE NATIONAL HURRICANE
CENTER INDICATES TROPICAL STORM ISAAC WILL STRENGTHEN TO A HURRICANE
LATER TONIGHT AS IT APPROACHES SERN GULF. AS THIS OCCURS...ATTENDANT
BELT OF STRONGER LOW-LEVEL FLOW WILL SHIFT TOWARDS THE W COAST OF
THE FL PENINSULA...WITH THE FAVORABLE NE QUADRANT OF ISAAC
POSITIONED FROM NEAR TAMPA BAY SWD AFTER 00Z. DESPITE THE LOSS OF
SFC HEATING AND WEAKER INSTABILITY...LOW-LEVEL SHEAR WILL BE
ADEQUATE FOR ISOLATED TORNADOES IN STRONGER UPDRAFTS INTO EARLY MON
MORNING.

...SRN/CNTRL PLAINS NEWD INTO THE MID/UPPER MS RIVER VALLEY...
CONVECTION IS FORECAST TO BE ONGOING EARLY IN THE PERIOD ACROSS
PARTS OF CNTRL/ERN OK INTO NRN MO. A GRADUAL SEWD SHIFT OF A
SUBTLE/WEAK UPPER TROUGH AND SHEAR AXIS...AND ASSOCIATED SFC
TROUGH...IS FORECAST TO OCCUR...BECOMING JUXTAPOSED WITH AN AXIS OF
RICH MOISTURE /PW NEAR 1.8-2 INCHES/. ALTHOUGH IT IS UNCERTAIN TO
WHAT DEGREE EARLY MORNING CLOUD DEBRIS WILL AFFECT
HEATING...SUFFICIENT DESTABILIZATION SHOULD OCCUR WITHIN A VERY
MOIST BOUNDARY LAYER TO SUPPORT REDEVELOPMENT OF SFC-BASED
THUNDERSTORMS DURING THE AFTERNOON...AS FAR N AS PARTS OF NRN IL.
VERY WEAK DEEP-LAYER FLOW AND RESULTANT EFFECTIVE SHEAR /10-20 KTS/
WILL LIKELY LIMIT THUNDERSTORM ORGANIZATION AND PRECLUDE A
WIDESPREAD SVR THREAT...BUT A BRIEF/ISOLATED THREAT FOR STRONG WIND
GUSTS AND HAIL COULD ACCOMPANY THE STRONGEST STORMS.

...CNTRL HIGH PLAINS...
ISOLATED THUNDERSTORMS MAY DEVELOP DURING PEAK HEATING ALONG A
DEVELOPING LEE SFC TROUGH. MIDLEVEL HEIGHT RISES ARE FORECAST TO
OCCUR THROUGHOUT THE DAY...WHICH WILL LIKELY LIMIT AREAL
COVERAGE...BUT THERE IS SOME HINT OF AN UPSTREAM UPPER IMPULSE OVER
THE GREAT BASIN MOVING ACROSS WY INTO THE NEB PANHANDLE DURING THE
LATE AFTERNOON. STRONG HEATING WILL RESULT IN A WELL-MIXED BOUNDARY
LAYER...BUT MARGINAL MLCAPE VALUES AOB 500 J/KG GIVEN THE PRESENCE
OF MEAGER LOW-LEVEL MOISTURE. MODERATELY STRONG MIDLEVEL WLYS AND
STEEP LOW-LEVEL LAPSE RATES COULD SUPPORT A FEW ISOLATED STRONG WIND
GUSTS.

...MID-ATLANTIC REGION...
A LONG-LIVED MID/UPPER VORTICITY MAXIMUM WILL SLOWLY DRIFT E/NEWD
AND APPROACH THE ATLANTIC COAST. FORECAST MODEL GUIDANCE IS
CONSISTENT IN SHOWING SCATTERED THUNDERSTORMS DEVELOPING OVER PARTS
OF THE MID-ATLANTIC REGION DURING THE AFTERNOON. E-SELY SFC WINDS
BENEATH S-SWLY MIDLEVEL FLOW WILL RESULT IN KINEMATIC PROFILES
MARGINALLY SUPPORTIVE FOR ISOLATED STRONG WIND GUSTS AND PERHAPS A
BRIEF/WEAK TORNADO...WITH THE LATTER THREAT PRIMARILY OVER THE
DELMARVA PENINSULA INTO SRN NJ.

..ROGERS/PETERS.. 08/26/2012

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