SWODY1
SPC AC 031228
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0728 AM CDT FRI AUG 03 2007
VALID 031300Z - 041200Z
..THERE IS A SLGT RISK OF SVR TSTMS MUCH OF ERN NY INTO NRN NEW
ENGLAND...
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN PLAINS/HIGH
PLAINS...
..NERN STATES...
LARGE UPPER LOW CENTERED SRN HUDSON BAY. SEVERAL IMPULSES ROTATING
AROUND LOW CIRCULATION AS NOTED ON W/V IMAGERY. OF MOST INTEREST TO
NEW ENGLAND AREA TODAY IS THE S/WV CURRENTLY MOVING FROM SERN
ONTARIO INTO SRN QUEBEC. WHILE THE STRONGEST FLOW AND UPPER SUPPORT
EXPECTED TO REMAIN N OF INTERNATIONAL BORDER...THE SHEAR COUPLED
WITH EXPECTED INSTABILITY SUPPORTS SEVERE THUNDERSTORM THREAT MUCH
OF INTERIOR NEW ENGLAND TODAY.
WITH RELATIVELY COOL MID LEVEL TEMPERATURES SPREADING EWD ACROSS NEW
ENGLAND TODAY/LAPSE RATES FROM 7-7.5 C/KM/COMBINED WITH INCREASING
MOISTURE...THUNDERSTORMS WILL BECOME QUITE ACTIVE INTERIOR NEW
ENGLAND.
WHILE THE COLD FRONT ASSOCIATED WITH HUDSON BAY LOW IS STILL ACROSS
SRN ONTARIO AND NOT EXPECTED TO MAKE IT WEAKLY ACROSS THE LOWER
LAKES UNTIL THIS EVENING...THREAT OF SEVERE THUNDERSTORMS WILL
DEVELOP BY MID DAY ACROSS INTERIOR NRN NEW ENGLAND SWWD INTO ERN NY
IN RESPONSE TO SURFACE HEATING.
CINH DISSIPATES BY EARLY AFTERNOON AS TEMPERATURES WARM THRU THE 80S
AND SURFACE DEWPOINTS RISE TO NEAR 70F. RESULT WILL BE A VERY
UNSTABLE AIRMASS WITH MUCAPES RANGING FROM 2500-3500 J/KG INTERIOR
NEW ENGLAND.
S/WV TROUGH CROSSING SRN QUEBEC WILL ENHANCE BOTH LARGE SCALE ASCENT
AND SHEAR FOR POTENTIAL SUPERCELL DEVELOPMENT INTERIOR ME INTO NRN
NH. MODEL SOUNDINGS THIS AFTERNOON INDICATE MARGINAL DEEP LAYER
SHEAR FROM 30-35KT...HOWEVER WITH THE STEEP LAPSE RATES AND EXPECTED
INSTABILITY...FORECASTED LARGE HAIL POTENTIAL HAS BEEN INCREASED
WITH ISOLATED TORNADOS POSSIBLE ASSOCIATED WITH ANY SUPERCELL
DEVELOPMENT.
SHEAR WEAKENS ALONG WITH SOMEWHAT LESS INSTABILITY ACROSS ERN NY
INTO SRN NEW ENGLAND. HOWEVER WITH MUCAPES AOA 2000 J/KG AND LAPSE
RATES NEAR 7C/KM COMBINED WITH A RATHER DEEP SURFACE MIXED LAYER
WITH THE STRONG HEATING...A FEW SEVERE STORMS ARE EXPECTED SWD TO
NERN PA/NY BORDER.
..NORTHERN HIGH PLAINS...
UNLIKE NEW ENGLAND WHERE EARLY VISIBLE IMAGERY SUPPORTS STRONG
HEATING...THE SLIGHT RISK NRN HIGH PLAINS WILL HAVE TO DEAL WITH
INITIALLY EXTENSIVE CLOUD COVER. STRONG RETURN OF MOISTURE UNDERWAY
TO E OF LEE TROUGH THRU WRN NE/SD WITH THE 25-30KT LOW LEVEL JET.
THE APPROACH OF THE RATHER ILL-DEFINED UPPER WAVE NOW MOVING ACROSS
NRN INTERMOUNTAIN REGION INTO WY...WILL PROVIDE BOTH SOME INCREASE
IN SHEAR AND LARGE SCALE ASCENT EWD ACROSS WY INTO ADJACENT HIGH
PLAINS BY THIS EVENING.
WHILE LOW LEVEL MOISTURE AND POTENTIAL INSTABILITY WILL BE MORE THAN
SUFFICIENT TO SUPPORT STRONG/SEVERE THUNDERSTORMS LATER THIS
AFTERNOON...THE WARM AIR ALOFT...MARGINAL DEEP LAYER SHEAR AND
EFFECTS ON HEATING OF CURRENT CLOUD COVER...LEADS TO UNCERTAINTY AS
WHERE AND TO WHAT EXTENT OF TODAYS SEVERE THREAT.
LOW LEVEL JET DOES INCREASE TO 40-50KT ACROSS NE/SD THIS EVENING
WHICH NOT ONLY ENHANCES SHEAR BUT PROVIDES STRONG ASCENT ACROSS THE
FRONTAL BOUNDARY WHICH WILL EXTEND SEWD ACROSS SD INTO ERN NEB.
BOTH NAM AND GFS DEVELOP A STRONG CONVECTIVE PCPN SIGNAL BY THIS
EVENING FROM WRN SD INTO NRN NEB VICINITY FRONTAL ZONE AND LOW LEVEL
JET.
GIVEN THE MENTIONED UNCERTAINTIES WILL MAKE LITTLE CHANGES IN
OUTLOOK ATTM. THE LATER OUTLOOKS SHOULD HAVE A BETTER HANDLE ON
WHERE THE BEST FOCUS FOR PARTICULARLY SURFACE STORM DEVELOPMENT MAY
OCCUR.
.HALES/GRAMS.. 08/03/2007
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