SPC AC 081250
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT MON JUN 08 2009
VALID 081300Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE REGION FROM THE
SRN GREAT LAKES/MIDWEST SOUTHWEST TO OK AND NWRN TX...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE HIGH
PLAINS...
...SYNOPSIS...
MODEST WSWLY FLOW OF 35-50KT EXISTS IN A BROAD BELT ACROSS THE
CENTRAL CONUS BETWEEN DEEP UPPER LOW CENTERED ACROSS THE CANADIAN
PRAIRIES AND SUBTROPICAL RIDGE AXIS ACROSS NRN MEXICO...SOUTH
TX...AND ADJACENT GULF WATERS. A WELL-DEFINED SHORT WAVE TROUGH WAS
EMBEDDED WITHIN THE LARGER SCALE FLOW AND WAS CROSSING THE MID
MISSOURI RIVER VALLEY THIS MORNING. THIS DISTURBANCE...AND
ASSOCIATED SURFACE LOW/WAVE...WILL CONTINUE TO TRACK ENEWD TOWARD
THE SRN GREAT LAKES TODAY WHILE TRAILING COLD FRONT...PRECEEDED BY
NUMEROUS CONVECTIVE OUTFLOW BOUNDARIES...MOVES EWD/SEWD TOWARD THE
OH VALLEY. THE TRAILING SEGMENT OF THE COLD FRONT....FROM SERN KS
ACROSS WRN OK TO THE TX PNHDL...WILL LIKELY STALL ALONG OR NEAR THIS
AXIS AS STRONGER UPPER FORCING FOR ASCENT LIFTS AWAY FROM THESE
AREAS DURING THE DAY.
...MIDWEST/SRN GREAT LAKES...
THERE IS SUBSTANTIAL UNCERTAINTY REGARDING AIRMASS DESTABILIZATION
AND FOCUS FOR SUSTAINED STORM DEVELOPMENT ACROSS PARTS OF THIS
REGION TODAY DESPITE THE APPROACH OF SHORT WAVE TROUGH EJECTING FROM
THE PLAINS. INITIAL SURGE OF MODERATE TO LOCALLY HEAVY RAIN AND
TSTMS WILL MOVE ACROSS LOWER MI THIS MORNING AIDED BY A LEADING
SMALL-SCALE MID LEVEL CIRCULATION AND STRONG MOISTURE TRANSPORT ON
THE NOSE OF 50KT LOW LEVEL JET. WARM FRONT EXPECTED TO MAKE SOME NWD
PROGRESS ACROSS NRN IL AND LOWER MI IN THE WAKE OF THIS FIRST ROUND
OF PCPN AND AHEAD OF SURFACE LOW WHICH IS EXPECTED TO TRACK ENEWD
THROUGH THE AFTERNOON.
ABUNDANT LOW LEVEL MOISTURE /DEWPOINTS IN THE MID AND UPPER 60S F/
AND POCKETS OF SURFACE HEATING IN THE WAKE OF MORNING CLOUDS AND
RAIN SHOULD ALLOW FOR MODEST SURFACE-BASED DESTABILIZATION ACROSS
THE WARM SECTOR TODAY. GIVEN SUPPORTIVE UPPER FORCING FOR ASCENT
WITH THE SHORT WAVE TROUGH AND DIURNAL DESTABILIZATION... EXPECT
SOME CONVECTION TO INCREASE NEAR THE WARM FRONT AND ALONG/AHEAD OF
RESIDUAL OUTFLOWS INTO THE AFTERNOON. BELT OF FASTER WLY MID LEVEL
FLOW AROUND 50KT WILL EXIST COINCIDENT WITH THIS RENEWED CONVECTIVE
DEVELOPMENT AND SHOULD SUPPORT AN INCREASE IN STORM ORGANIZATION AND
SEVERE WEATHER POTENTIAL IN THE FORM OF STRONG WINDS AND SOME HAIL.
ATTM...PRESENCE OF WIDESPREAD CLOUDINESS AND PRECIPITATION MAKES IT
DIFFICULT TO ACCURATELY PINPOINT THOSE AREAS WHERE THE GREATER
DESTABILIZATION WILL OCCUR...ESPECIALLY FROM IL INTO LOWER MI. IT IS
POSSIBLE THAT MORE SUPPORTIVE LARGE SCALE ASCENT WITH THE SHORT WAVE
AND LOW MAY OUTRUN GREATER AIR MASS DESTABILIZATION ACROSS THESE
AREAS AND RESULT IN LIMITED STORM COVERAGE/DEVELOPMENT.
HOWEVER...THERE APPEARS TO BE AT LEAST A NARROW CORRIDOR FROM IL
INTO SWRN LOWER MI WHERE FRONTAL BOUNDARY MAY BE SITUATED AND
DIABATICALLY ENHANCED THIS AFTERNOON. SHEAR...MOISTURE...AND
POTENTIAL FOR A FEW SUSTAINED STORMS/SUPERCELLS ALONG THIS BOUNDARY
SUPPORT SLIGHTLY HIGHER TORNADO PROBABILITIES AND PERHAPS THE CHANCE
FOR SOME LARGER HAIL AS WELL.
...MO SWWD TO OK/NWRN TX...
SYNOPTIC COLD FRONT WILL REMAIN WEST/NORTH OF THESE AREAS BUT
NUMEROUS OUTFLOW BOUNDARIES AND DIFFERENTIAL HEATING AROUND
RESIDUAL/DECAYING CIRRUS CANOPIES WILL OCCUR BENEATH PRONOUNCED EML
AND VERY MOIST BOUNDARY LAYER. THIS PROCESS SHOULD LEAD TO AN AXIS
OF VERY STRONG INSTABILITY FROM NWRN TX ACROSS OK AND INTO MO.
MLCAPE IN THIS CORRIDOR IS FORECAST TO CLIMB TO AT LEAST 2500 J/KG
BUT INHIBITION WILL ALSO REMAIN QUITE STRONG...ESPECIALLY ACROSS SRN
PORTIONS OF THE AREA. EXPECT THE COMBINATION OF SURFACE HEATING AND
LIFT/MIXING ALONG THE RESIDUAL BOUNDARIES TO LEAD TO AT LEAST
ISOLATED STORM DEVELOPMENT WITHIN MODERATELY SHEARED FLOW INTO THE
EVENING.
WHILE GREATER LARGE SCALE SUPPORT FOR ASCENT ACROSS THE NW TX AREA
WILL BE QUITE WEAK...STRONG HEATING/MIXING ALONG THE DRYLINE MAY BE
SUFFICIENT FOR A FEW STORMS IN THIS AREA BENEATH 35-40KT WLY 500MB
FLOW. AS IN PRIOR DAYS...ONE OR TWO SUPERCELLS APPEAR POSSIBLE INTO
THE EVENING HOURS.
...HIGH PLAINS...
WITH HEATING...MARGINALLY MOIST POST-FRONTAL AIR MASS PUSHED INTO
ERN/SERN PARTS OF WY/CO PLAINS MAY SUPPORT THE DEVELOPMENT OF MODEST
INSTABILITY /MLCAPE 500-800 J/KG/ LATER THIS AFTERNOON. REGION LIES
BENEATH COLD CYCLONIC FLOW ALOFT AND EXPECT TERRAIN AND LARGE SCALE
INFLUENCES TO CONTRIBUTE TO STORM DEVELOPMENT ACROSS THE AREA INTO
THE EVENING. DEEP-LAYER SHEAR AND LOWER LEVEL HELICITY ENHANCED BY
ELY COMPONENT OF THE LOWER LEVEL FLOW WILL RESULT IN GENERALLY
LOW-TOPPED SUPERCELLS WITH THE POTENTIAL FOR HAIL/HIGH WINDS AND
PERHAPS A BRIEF/WEAK TORNADO.
...DELMARVA/PA/NJ...
SURFACE CONVERGENCE ON WEAK LEE/THERMAL TROUGH...AND INTERSECTION OF
THIS TROUGH WITH STALLED FRONT ACROSS PA/NJ COULD AID STORM
DEVELOPMENT IN INCREASINGLY UNSTABLE AIR MASS THROUGH LATE
AFTERNOON. THIS DEVELOPMENT COULD BE FURTHER SUPPORTED/SUSTAINED BY
LARGE SCALE HEIGHT FALLS SPREADING EAST FROM THE OH VALLEY LATER
TODAY. MODELS DO FORECAST AN INCREASE IN THE MID LEVEL FLOW FROM
25-30KT LATER TODAY AND THIS COULD FAVOR STORM
ORGANIZATION/PERSISTENCE. HOWEVER...GENERALLY WEAK LAPSE RATES WILL
PROBABLY LIMIT PARCEL ACCELERATIONS WITHIN STORM UPDRAFTS AND EXPECT
ONLY A FEW CLUSTERS OF MULTICELLULAR CONVECTION WITH MARGINAL
POTENTIAL TO PRODUCE A FEW TSTM WIND EVENTS.
...CNTRL/SRN PLAINS LATE...
LIFT AND DESTABILIZATION ARE EXPECTED TO INCREASE ACROSS THIS AREA
LATER IN THE PERIOD AND RESULT IN AN INCREASING CHANCE FOR STRONG
CONVECTION INTO TUESDAY MORNING. THERE ARE MODEL DIFFERENCES WITH
STORM DEVELOPMENT ALONG/ATOP RETREATING WARM FRONT FROM NWRN OK TO
WRN KS AS NEXT IMPULSES EMANATING FROM SIGNIFICANT UPPER TROUGH
MOVING OVER SRN CA MOVE EAST. NONETHELESS...ANY DEVELOPMENT IN THIS
AREA WILL LIKELY OCCUR WITHIN VERY STEEP LAPSE RATE REGIME WITH
SUFFICIENT SHEAR FOR POTENT AND PERSISTENT UPDRAFTS. THUS...AT LEAST
A LOW PROBABILITY HAIL THREAT MAY EVOLVE INTO EARLY TUESDAY.
..CARBIN/HURLBUT.. 06/08/2009
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