SPC AC 230523
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1223 AM CDT WED MAR 23 2011
VALID 241200Z - 251200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODELS CONTINUE TO INDICATE THAT BLOCKING WILL REMAIN PROMINENT
WITHIN THE LARGE-SCALE UPPER FLOW IMPACTING MUCH OF NORTH AMERICA
THROUGH THIS FORECAST PERIOD. AN UPPER HIGH CENTERED OVER THE
CENTRAL CANADIAN PROVINCES APPEARS LIKELY TO MAINTAIN
STRENGTH...WHILE THE CENTER OF A BROAD CLOSED LOW DEEPENS OVER THE
LOWER ST. LAWRENCE VALLEY. IT APPEARS THAT TROUGHING NEAR THE
PACIFIC COAST MAY LOSE SOME AMPLITUDE...BUT STRONG FLOW IS EXPECTED
TO PERSIST FROM THE CREST OF AN EAST CENTRAL PACIFIC RIDGE THROUGH A
BROADLY CYCLONIC BELT ACROSS THE CALIFORNIA COAST AND INTERMOUNTAIN
WEST. SEVERAL VIGOROUS SHORT WAVE IMPULSES ARE EMBEDDED WITHIN THIS
REGIME...ONE OF WHICH IS PROGGED TO LIFT ACROSS THE CENTRAL ROCKIES
INTO THE PLAINS BY LATE THURSDAY NIGHT...AS ANOTHER TURNS INLAND
ACROSS THE OREGON AND NORTHERN CALIFORNIA COAST. THESE FEATURES MAY
CONTRIBUTE TO SOME THUNDERSTORM ACTIVITY THURSDAY.
HOWEVER...CONVECTIVE POTENTIAL ACROSS MUCH OF THE NATION IS EXPECTED
TO BE GENERALLY LOW...IN THE WAKE OF A STRONG SHORT WAVE TROUGH
ACCELERATING EAST OF THE MID ATLANTIC COAST...ACCOMPANIED BY STRONG
OFFSHORE CYCLOGENESIS.
...MID ATLANTIC COAST...
LIFT AND DESTABILIZATION WITHIN THE LEFT EXIT REGION OF A 100 KT 500
MB JET STREAK MAY STILL BE CONTRIBUTING TO A RISK FOR THUNDERSTORM
ACTIVITY ACROSS PARTS OF SOUTHEAST VIRGINIA/EASTERN NORTH CAROLINA
AT THE BEGINNING OF THE PERIOD. HOWEVER...THIS FORCING IS EXPECTED
TO RAPIDLY SHIFT EAST OF THE COAST BY LATE MORNING...ENDING ANY
LINGERING CONVECTIVE POTENTIAL.
...PLAINS...
22/21Z NCEP SREF APPEARS CONSIDERABLY WEAKER THAN 24 HOURS AGO WITH
THE SHORT WAVE IMPULSE PROGRESSING OUT OF THE GREAT BASIN INTO THE
CREST OF AN UPPER RIDGE OVER THE CENTRAL PLAINS.
IN TURN...LOW-LEVEL SURFACE CYCLOGENESIS TO THE LEE OF THE CENTRAL
ROCKIES IS MUCH WEAKER...WITH MOISTURE RETURN ALSO MUCH SLOWER TO
DEVELOP THURSDAY. THIS IS LOWERING CONFIDENCE CONCERNING THE
CONVECTIVE POTENTIAL THAT COULD DEVELOP. HOWEVER...ISOLATED STORM
DEVELOPMENT ROOTED IN A DEEPLY MIXED BOUNDARY LAYER STILL APPEARS
POSSIBLE DURING THE LATE AFTERNOON ACROSS PARTS OF THE PECOS VALLEY
INTO THE TEXAS SOUTH PLAINS. AND THUNDERSTORM PROBABILITIES WITHIN
A STRENGTHENING LOWER/MID TROPOSPHERIC WARM ADVECTION REGIME MAY NOT
BE COMPLETELY NEGLIGIBLE NEAR/NORTH OF THE RED RIVER VALLEY.
...NORTHERN CALIFORNIA...
GUIDANCE ALSO APPEARS GENERALLY FASTER WITH THE INLAND PROGRESSION
OF ANOTHER VIGOROUS CLOSED LOW...WHICH COULD BE ACCOMPANIED BY
STRONG MID-LEVEL COOLING /500 MB TEMPS BELOW -30C/ AND STRENGTHENING
VERTICAL SHEAR AS EARLY AS LATE THURSDAY AFTERNOON. SHEAR PROBABLY
WILL BECOME SUPPORTIVE OF UPDRAFT ROTATION AND THE POTENTIAL FOR LOW
TOPPED SUPERCELLS WITH EVEN WEAK BOUNDARY LAYER DESTABILIZATION.
THIS REMAINS UNCERTAIN... BUT THE THREAT FOR HAIL AND LOCALLY
DAMAGING WIND GUSTS...PERHAPS A TORNADO...MAY NOT BE COMPLETELY
NEGLIGIBLE...PARTICULARLY ACROSS NORTHERN PORTIONS OF THE SACRAMENTO
VALLEY.
..KERR.. 03/23/2011
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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