SWODY2
SPC AC 221730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CST SAT DEC 22 2007
VALID 231200Z - 241200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MID ATLANTIC
REGION...
..SYNOPSIS...
ADDITIONAL DEEPENING OF THE NRN STREAM CLOSED LOW...INITIALLY
LOCATED OVER THE UPPER MS VALLEY AT 12Z SUNDAY...IS EXPECTED ON DAY
2 AS THIS SYSTEM BECOMES MORE NEGATIVELY TILTED AND TRACKS EWD INTO
THE GREAT LAKES REGION AND THEN NEWD TO SRN QUEBEC BY 12Z MONDAY. A
LEAD SRN STREAM SHORT WAVE TROUGH IS EXPECTED TO TRACK NWD FROM IND/
LOWER MI INTO ONTARIO WHILE THE UPPER MS VALLEY CLOSED LOW MOVES
INTO GREAT LAKES/OH VALLEY REGION. THE NEXT IMMEDIATELY UPSTREAM
SRN STREAM IMPULSE IS FORECAST TO TRACK FROM THE ARKLATEX REGION
THROUGH THE TN VALLEY AND PHASE WITH THE CLOSED LOW OVER THE UPPER
OH VALLEY INTO THE LOWER GREAT LAKES/NERN STATES SUNDAY AFTERNOON
INTO SUNDAY NIGHT. AS THIS PHASING TAKES PLACE...ALREADY STRONG
WIND FIELDS WILL CONTINUE TO RESPOND WITH A 110+ KT 500 MB WLY JET
TRANSLATING FROM THE OH VALLEY TO NERN STATES SUNDAY AFTERNOON TO
END OF FORECAST PERIOD.
AT THE SURFACE...990 MB SURFACE LOW IS EXPECTED TO OCCLUDE AS IT
SHIFTS SLOWLY NWD FROM NEAR MKE INTO THE UPPER GREAT LAKES REGION. A
SECONDARY LOW WILL LIKELY FORM NEWD INTO ONTARIO AND TRACK TO NRN
QUEBEC BY 12Z MONDAY. TRAILING COLD FRONT...INITIALLY EXTENDING SWD
ALONG THE OH/IND BORDER AREA AND THROUGH ERN AL TO THE CENTRAL GULF
IS EXPECTED MOVE QUICKLY EWD SUNDAY AND SHOULD EXTEND FROM ERN NY/PA
SWD THROUGH THE ERN PART OF THE MID ATLANTIC REGION TO NRN FL. THIS
FRONT IS FORECAST EXIT MUCH OF THE ERN SEABOARD BY 12Z MONDAY...
ASIDE FROM CENTRAL FL.
..MID ATLANTIC REGION...
THERE IS SOME CONCERN WITH RESPECT TO THE DEGREE OF MOISTURE RETURN
OFF OF THE ATLANTIC AS SLY WINDS STRENGTHEN ON SUNDAY AHEAD OF THE
DEEPENING UPPER LOW ACROSS THE GREAT LAKES REGION. HOWEVER...
SURFACE DEWPOINTS IN THE LOWER 60S RESIDE AT THIS TIME ABOUT 100-130
MILES OFF THE SRN ATLANTIC COAST. THIS MOISTURE SHOULD ADVECT NWD
TO AT LEAST NRN NC BY SUNDAY AFTERNOON WITH UPPER 50S DEWPOINTS INTO
VA/DELMARVA REGION. COOLING ALOFT ATTENDANT TO HEIGHT FALLS WITH
APPROACHING UPPER SYSTEM/ASCENT WITHIN ENTRANCE REGION OF UPPER
LEVEL JET COMBINED WITH LOW LEVEL WARM AIR/MOISTURE ADVECTION WILL
SUPPORT MARGINAL INSTABILITY...BELOW 500 J/KG.
DYNAMIC LIFT ASSOCIATED WITH THE ARKLATEX/TN VALLEY SHORT WAVE
TROUGH...COUPLED WITH LOW LEVEL WAA...SHOULD SUPPORT DEVELOPMENT OF
A LOW-TOPPED SQUALL LINE WITH RAPIDLY MOVING/BOWING LINE SEGMENTS.
MAGNITUDE OF FORCING/LIFT ALONG THE ADVANCING FRONT WITH WEAK
INSTABILITY SHOULD SUPPORT SPORADIC LIGHTNING. GREATEST POTENTIAL
FOR BOUNDARY LAYER MODIFICATION/COUPLING WILL EXIST EAST OF THE
APPALACHIANS WHERE DEVELOPMENT OF A NARROW COLD FRONTAL RAIN BAND
APPEARS LIKELY DURING THE AFTERNOON. KINEMATICS AS CURRENTLY
FORECAST APPEAR MORE THAN SUFFICIENT FOR CONVECTIVE DAMAGING WINDS
TO SPREAD EAST THROUGH EARLY EVENING GIVEN FORECAST STORM MOTION OF
50-60KT...AND MEAN WIND IN EXCESS OF 70KT. A BRIEF/ISOLATED TORNADO
CANNOT BE COMPLETELY RULED OUT GIVEN INTENSE EFFECTIVE SRH IN EXCESS
OF 400-500 M2/S2 OVER SOME PARTS OF ERN VA TO THE DELMARVA/SERN PA
AREA THROUGH EARLY EVENING.
..NRN PA/SRN NY...
GIVEN DYNAMIC SYSTEM WITH STRONG SLY LLJ /70-80+ KT/ EXTENDING INTO
PA/NY TO QUEBEC THROUGH THE DAY SUNDAY...A FORCED LINE OF CONVECTION
WILL BE POSSIBLE ALONG THE FRONT THAT MOVES THROUGH THIS REGION
SUNDAY AFTERNOON/EVENING. VERY WEAK INSTABILITY IS EXPECTED TO
PRECLUDE ACTIVITY FROM BECOMING DEEP ENOUGH FOR CHARGE
SEPARATION/LIGHTNING PRODUCTION. HOWEVER...STRENGTH OF WIND FIELDS
COULD SUPPORT A FEW STRONG CONVECTIVE WIND GUSTS.
.PETERS.. 12/22/2007
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