Forecast Discussion
SPC AC 130536
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT TUE MAR 13 2007
VALID 141200Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS WED/WED NIGHT ACROSS PARTS OF
THE SRN GREAT LAKES/LWR OHIO VALLEY....
...THERE IS A SLGT RISK OF SVR TSTMS WED ACROSS THE LWR MS VLY/CNTRL
GULF COAST....
THE DETAILS OF THE UPPER FLOW EVOLUTION OVER THE NEXT FEW DAYS
REMAIN A POINT OF CONSIDERABLE UNCERTAINTY AMONG MODEL GUIDANCE.
BUT...IT STILL APPEARS PROBABLE THAT THE LARGE-SCALE PATTERN WILL
BECOME INCREASINGLY DOMINATED BY THE AMPLIFICATION OF AN UPPER
TROUGH WITHIN THE STRONG BELT OF WESTERLIES NOW ALONG THE
CANADIAN/U.S. BORDER. THIS DEVELOPMENT MAY BE A BIT SLOWER THAN
PREVIOUSLY THOUGHT...AND IT NOW SEEMS PROBABLE THAT ASSOCIATED WAVE
DEVELOPMENT ALONG THE POLAR FRONT MAY BE GRADUAL. HOWEVER...IT
APPEARS INCREASINGLY LIKELY THAT THE PROGRESSION OF THE SURFACE
FRONT SOUTH OF THE UPPER MISSISSIPPI VALLEY AND UPPER GREAT LAKES
REGION WILL BE ACCOMPANIED BY SUBSTANTIAL CONVECTIVE DEVELOPMENT
DURING THE DAY 2 FORECAST PERIOD.
A RETURN FLOW OF 55-60F SURFACE DEW POINTS IS EXPECTED AROUND THE
WESTERN PERIPHERY OF A RETREATING WESTERN ATLANTIC SURFACE
RIDGE...THROUGH MUCH OF THE LOWER/MID MISSISSIPPI VALLEY INTO THE
OHIO VALLEY...BEFORE THE REMNANTS OF A SOUTHERN BRANCH CLOSED LOW
PROGRESSES THROUGH THE CENTRAL GULF COAST REGION. MID 60S DEW
POINTS APPEAR PROBABLE NEAR CENTRAL GULF COASTAL AREAS. AND...
MODEL FORECAST SOUNDINGS /PARTICULARLY THE NAM AND NAMKF/ ARE NOW
INDICATING A BIT MORE SUBSTANTIAL DESTABILIZATION WILL OCCUR IN
ASSOCIATION WITH THIS PRE-FRONTAL MOISTENING.
FARTHER WEST...LOWER/MID TROPOSPHERIC WARMING WEST/NORTH OF THE
LOWER MISSISSIPPI VALLEY AND WEST OF THE MIDDLE MISSISSIPPI VALLEY
IS EXPECTED CONTRIBUTE TO SUBSTANTIAL INHIBITION. THIS IS EXPECTED
TO LIMIT CONVECTIVE POTENTIAL ACROSS MUCH OF THE CENTRAL/ SOUTHERN
PLAINS.
...SOUTHERN GREAT LAKES/LOWER OHIO VALLEY...
SEASONABLY STRONG SURFACE HEATING IS ANTICIPATED AHEAD OF THE COLD
FRONT ACROSS MUCH OF THE LOWER OHIO VALLEY. AND...THE SURFACE
BOUNDARY WILL PROBABLY PROVIDE THE MAIN FOCUS FOR CONVECTIVE
DEVELOPMENT AS IT ADVANCES SOUTH OF THE SOUTHERN GREAT LAKES REGION
LATE WEDNESDAY AFTERNOON INTO WEDNESDAY NIGHT.
HOWEVER...MODEL FORECAST SOUNDINGS SUGGEST MID-LEVEL CAPPING MAY BE
WEAK ENOUGH FOR THE DEVELOPMENT OF SCATTERED STORMS DURING THE
AFTERNOON AS FAR SOUTH AS THE OHIO RIVER. DEEP LAYER SHEAR TO THE
SOUTH OF THE FRONTAL ZONE IS GENERALLY PROGGED TO BE MODERATE AT
BEST...BUT 30-40 KT WESTERLY MEAN ENVIRONMENT FLOW WILL ENHANCE
STORM MOTION AND DAMAGING WIND POTENTIAL...IN ADDITION TO SOME
MARGINALLY SEVERE HAIL.
IN CLOSER PROXIMITY TO THE FRONT...FORCING MAY SUPPORT AN ORGANIZING
LINE OF STORMS BY LATE AFTERNOON...IN MORE FAVORABLY SHEARED REGIME
ON SOUTHERN FRINGE OF WESTERLIES. ISOLATED SUPERCELLS WILL BE
POSSIBLE...ALONG WITH SOME RISK FOR TORNADOES...BUT IT APPEARS A
TENDENCY TOWARD UNIDIRECTIONAL SHEAR MAY FAVOR DAMAGING WIND/HAIL AS
PRIMARY THREATS. ACTIVITY IS EXPECTED TO DEVELOP SOUTHWARD TOWARD
THE OHIO RIVER WITH CONTINUING SEVERE POTENTIAL THROUGH AT LEAST
LATE WEDNESDAY EVENING.
...LOWER MISSISSIPPI VALLEY/CENTRAL GULF COAST...
SOUNDINGS ACROSS THIS REGION APPEAR LIKELY TO BE CHARACTERIZED BY
WEAK LAPSE RATES AND SOMEWHAT SATURATED...WHICH WILL TEND LIMIT
INSTABILITY AHEAD OF CLOSED LOW AS IT FINALLY PROGRESSES EAST OF
TEXAS. HOWEVER...STRENGTHENING OF SOUTHERLY LOW-LEVEL FLOW IS
EXPECTED TO CONTRIBUTE TO SIZABLE LOW-LEVEL HODOGRAPHS...WHICH WILL
PROVIDE POTENTIAL FOR ISOLATED TORNADOES/WIND DAMAGE WITH CONVECTION
LIKELY TO OVERSPREAD THE REGION DURING THE DAYTIME HOURS WEDNESDAY.
MODELS ARE SUGGESTIVE THAT UPPER FORCING MAY SUPPORT AN ORGANIZED
CONVECTIVE CLUSTER ACROSS PARTS OF UPPER TEXAS COASTAL AREAS THROUGH
SOUTHERN LOUISIANA...BEFORE STRONGEST CONVECTION DEVELOPS OFFSHORE
SOMETIME WEDNESDAY NIGHT.
..KERR.. 03/13/2007
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