SPC AC 030556
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT MON AUG 03 2009
VALID 041200Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDDLE MS/OH RIVER
VALLEYS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NORTH CENTRAL HIGH
PLAINS...
...SYNOPSIS...
TUESDAY WILL BE CHARACTERIZED BY A FAIRLY PROGRESSIVE UPPER TROUGH
OVER EASTERN CANADA...WITH MULTIPLE LOW AMPLITUDE DISTURBANCES
EMBEDDED WITHIN NORTHWESTERLY FLOW ALOFT FROM THE NORTHERN ROCKIES
TO THE APPALACHIANS. PERSISTENT UPPER LOW OFF THE NORTHERN CA COAST
WILL ONLY MOVE SLOWLY EASTWARD...WITH AN UPPER RIDGE OTHERWISE
PERSISTING OVER THE CENTRAL/SOUTHERN ROCKIES.
...LOWER MO/MIDDLE MS VALLEYS TO OH/TN VALLEYS...
COLD FRONT WILL CONTINUE TO GRADUALLY SPREAD SOUTH-SOUTHEASTWARD
OVER THE MIDWEST/OH VALLEY ON TUESDAY...AS BRUNT OF UPPER TROUGH
PIVOTS EAST-NORTHEASTWARD OVER ONTARIO/QUEBEC AND THE ADJACENT GREAT
LAKES REGION. IT APPEARS THAT SCATTERED TSTMS /PERHAPS SOME STRONG/
WILL BE ONGOING ACROSS THE MIDDLE MS/LOWER OH VALLEYS TUESDAY
MORNING. AIDED BY A POTENTIAL MID LEVEL IMPULSE EMBEDDED WITHIN
NORTHWESTERLY FLOW ALOFT...THE REMNANTS OF THIS ACTIVITY AND/OR
PERIPHERAL STRONG/SEVERE DEVELOPMENT SHOULD OCCUR EASTWARD ACROSS
THE OH VALLEY/TN VALLEY THROUGH THE AFTERNOON AMIDST A WESTERLY LOW
LEVEL MOISTURE/INSTABILITY FEED.
FARTHER NORTH/WEST ACROSS THE REMAINDER OF THE MIDWEST/LOWER MO
VALLEY...THE DETAILS OF THE SEVERE THREAT ARE DIFFICULT TO PORTEND
IN ADVANCE LARGELY OWING TO UNCERTAINTIES REGARDING EARLY DAY
CONVECTION...BUT AT LEAST A CONDITIONAL CATEGORICAL SLIGHT RISK
APPEARS WARRANTED. PRESUMING A RELATIVELY
UNPERTURBED/NON-CONVECTIVELY OVERTURNED AIRMASS...ADDITIONAL
STRONG/SEVERE DEVELOPMENT WOULD ALSO BE POSSIBLE FARTHER NORTH IN
VICINITY OF THE ROUGHLY WEST-EAST SURFACE FRONT...ALTHOUGH A BOUT OF
POTENTIAL LARGE SCALE SUBSIDENCE IN THE WAKE OF THE EARLY DAY MID
LEVEL IMPULSE AGAIN COMPLICATES THE DETAILS OF DIURNAL
REDEVELOPMENT.
WITH THE NOCTURNAL REDEVELOPMENT OF A MODEST WESTERLY LOW LEVEL JET
ACROSS THE LOWER MO VALLEY...STRONG/SEVERE DEVELOPMENT COULD BECOME
MORE LIKELY BY EVENING AND/OR CONTRIBUTE TO ANOTHER ROUND OF STRONG
STORMS ACROSS THE LOWER MO/MIDDLE MS VALLEYS TUESDAY NIGHT.
OVERALL...DAMAGING WINDS/SEVERE HAIL WILL BE THE PRIMARY HAZARDS
ACROSS THE REGION...AND ULTIMATELY SOMEWHAT HIGHER CALIBER SEVERE
PROBABILITIES COULD LATER BE WARRANTED.
...NORTH CENTRAL HIGH PLAINS...
EARLY DAY REINFORCING FRONTAL PASSAGE WILL CONTRIBUTE TO INCREASING
MOIST UPSLOPE TRAJECTORIES WITHIN THE POST-FRONTAL ENVIRONMENT
ACROSS THE NORTH CENTRAL HIGH PLAINS ON TUESDAY. UPPER HEIGHTS MAY
GRADUALLY RISE DIURNALLY ACROSS THE REGION WITH LIMITED BACKGROUND
FORCING FOR ASCENT...HOWEVER BY LATE AFTERNOON/EARLY EVENING...TSTM
DEVELOPMENT WILL BECOME MORE PROBABLE GIVEN COMBINATION OF A WEAKLY
CAPPED/MOIST AIRMASS...LOW LEVEL UPSLOPE/HEATING OVER THE HIGHER
TERRAIN...AND POTENTIALLY ONE OR MORE MID LEVEL DISTURBANCES
CRESTING THE SOUTHERN ROCKIES UPPER RIDGE DURING THE EVENING. VEERED
WIND PROFILES THROUGH THE LOW TO MID TROPOSPHERE AND 40-45 KT OF
EFFECTIVE BULK SHEAR WILL SUPPORT BOTH SUPERCELLS AND WELL ORGANIZED
MULTICELLS CAPABLE OF SEVERE HAIL/DAMAGING WINDS AND PERHAPS A
TORNADO...MAINLY ACROSS PORTIONS OF EASTERN WY/SOUTHWEST SD/WESTERN
NEB TUESDAY LATE AFTERNOON/NIGHT.
...KS/FAR NORTHERN OK...
CONVERGENCE/STRONG HEATING IN VICINITY OF SURFACE LOW/TRIPLE POINT
MAY CONTRIBUTE TO ISOLATED STRONG/SEVERE TSTM DEVELOPMENT TUESDAY
AFTERNOON ACROSS KS INTO FAR NORTHERN OK. LIMITED FORCING ON THE
LARGE SCALE MAY LIMIT THE COVERAGE OF TSTMS...BUT STEEP LAPSE RATE
ENVIRONMENT/AMPLE INSTABILITY MAY YIELD A FEW BOUTS OF SEVERE
HAIL/WIND GUSTS THROUGH SUNSET.
...SOUTHWEST/CENTRAL MT AND ADJACENT ID...
THE COMBINATION OF THE STALLING SURFACE FRONT AND DIFFERENTIAL
HEATING OVER THE HIGHER TERRAIN...ALONG WITH A RELATIVELY MOIST
AIRMASS AND MODERATELY STRONG WESTERLY FLOW ALOFT...MAY PROVE
SUFFICIENT FOR STORMS CAPABLE OF ISOLATED SEVERE HAIL/WIND TUESDAY
AFTERNOON/EARLY EVENING.
...ORE...
UPPER HEIGHTS WILL LIKELY FALL OVER WESTERN/CENTRAL ORE ON TUESDAY
AS PERSISTENT UPPER LOW MIGRATES SLOWLY EASTWARD TOWARD THE NORTHERN
CA COAST. WITH LITTLE CHANGE IN THE OVERALL PATTERN...A
MOIST/UNSTABLE AIRMASS AND MODERATE SOUTHERLY FLOW ALOFT WILL AGAIN
FAVOR THE POSSIBILITY OF DAMAGING WINDS/HAIL WITH THE STRONGEST
STORMS TUESDAY AFTERNOON/EARLY EVENING.
..GUYER.. 08/03/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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