Wednesday, October 19, 2011

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 191944
SWODY1
SPC AC 191942

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0242 PM CDT WED OCT 19 2011

VALID 192000Z - 201200Z

...NO SVR TSTM AREAS FORECAST...

...20Z OUTLOOK UPDATE...

...MID ATLANTIC STATES INTO UPPER OHIO VALLEY/LWR GREAT LAKES...
SHOWERS ARE CURRENTLY DEVELOPING/INCREASING ALONG THE COLD FRONT AS
IT BEGINS TO ADVANCE EASTWARD/NORTHEASTWARD TO THE LEE OF THE
SOUTHERN APPALACHIANS. THE MOST VIGOROUS ACTIVITY APPEARS TO BE
OCCURRING WHERE THE COLD FRONT IS OVERTAKING A WEAK LINGERING
FRONTAL ZONE NEAR THE WESTERN EDGE OF THE MID ATLANTIC COASTAL
PLAIN. WHILE LOW-LEVEL MOISTENING ON STRENGTHENING PRE-FRONTAL
SOUTHERLY LOW-LEVEL FLOW ACROSS EASTERN NORTH CAROLINA INTO EASTERN
VIRGINIA AND THE DELMARVA PENINSULA IS STILL POSSIBLE THROUGH THIS
EVENING...MODEL FORECAST SOUNDINGS INDICATE CONSIDERABLE MID/HIGH
LEVEL WARMING WILL OCCUR EAST OF AN INTENSIFYING CYCLONIC UPPER JET
TO THE LEE OF THE APPALACHIANS. IT IS SEEMING INCREASINGLY LESS
LIKELY THAT CONVECTIVE DEVELOPMENT WILL BE DEEP ENOUGH TO REACH THE
FAVORABLE MIXED PHASE LAYER FOR CHARGE SEPARATION...AND THUNDERSTORM
ACTIVITY. HOWEVER...PRE-FRONTAL SHOWERS COULD STILL ENHANCE THE
DOWNWARD TRANSPORT OF MOMENTUM FROM ALOFT...PARTICULARLY ACROSS THE
MID ATLANTIC COASTAL PLAIN LATER THIS EVENING...WHERE/WHEN 850 MB
FLOW MAY STRENGTHEN TO 40-50+ KT.

HIGHEST THUNDERSTORM PROBABILITIES OVER INLAND AREAS THROUGH THE
REMAINDER OF THE PERIOD APPEAR TO EXIST LATER THIS EVENING AND
OVERNIGHT...ACROSS PARTS OF WESTERN PENNSYLVANIA INTO WESTERN NEW
YORK STATE. THIS IS WHERE FORCING IN THE EXIT REGION OF THE
INTENSIFYING UPPER JET MAY ENHANCE LIFT AND DESTABILIZATION
NORTHEAST OF THE DEEPENING OHIO VALLEY SURFACE CYCLONE...NEAR AND
NORTH OF AN ASSOCIATED OCCLUDING FRONTAL ZONE.

..KERR.. 10/19/2011

.PREV DISCUSSION... /ISSUED 1107 AM CDT WED OCT 19 2011/

...MID ATLANTIC STATES...
THE DEEP UPPER LOW CENTERED OVER THE MID MS VALLEY WILL BEGIN
LIFTING NORTHEASTWARD DURING THIS FORECAST PERIOD...WHILE THE
PRIMARY SURFACE COLD FRONT SWEEPS INTO THE WESTERN ATLANTIC. TWO
PERIODS OF SEVERE WEATHER THREAT ARE ANTICIPATED TODAY.

THE FIRST PERIOD IS NOW ONGOING ALONG THE COAST OF EASTERN NC.
INTENSE THUNDERSTORMS ARE OCCURRING JUST OFFSHORE ALONG SURFACE
BOUNDARY AND IN REGION OF LOW LEVEL WARM ADVECTION. THESE STORMS
MAY THREATEN THE OUTER BANKS OF NC THIS AFTERNOON...AS WELL AS THE
NEAR-SHORE AREAS OF EASTERN MD AND NJ. STRONGER CELLS IN THIS
CORRIDOR WILL BE CAPABLE OF DAMAGING WINDS OR A TORNADO/ WATERSPOUT.
THIS THREAT SHOULD END BY MID-LATE AFTERNOON AS THE PRIMARY LIFT
MOVES OUT TO SEA.

THE SECONDARY POTENTIAL THREAT WILL DEVELOP THIS AFTERNOON AS A
SHORTWAVE TROUGH NOW OVER NORTHERN GA ROTATES INTO NC/VA. ENHANCED
ASCENT AHEAD OF THIS FEATURE IS LIKELY TO GENERATE SCATTERED SHOWERS
AND A FEW THUNDERSTORMS. ONE OF THE MAIN FORECAST PROBLEMS INVOLVES
THE WEDGE FRONT THAT IS IN PLACE OVER THE REGION...AND IS NOT LIKELY
TO BE SCOURED AWAY EXCEPT FOR EASTERN VA/NC. THERE APPEARS TO BE A
CORRIDOR FROM NORTH CENTRAL NC INTO NORTHEAST VA WHERE A COMBINATION
OF SURFACE-BASED STORMS AND FAVORABLE TIMING OF THE UPPER WAVE WILL
SUPPORT A THREAT OF DAMAGING WINDS AND PERHAPS HAIL. EVEN IN THIS
AREA HOWEVER...UNCERTAINTY EXISTS REGARDING THE AMOUNT OF DAYTIME
HEATING MAY OCCUR AND THE RESULTANT LOW LEVEL LAPSE RATE PROFILE.
NEVERTHELESS...WILL MAINTAIN THE SLIGHT RISK FOR THIS SCENARIO.

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