SPC AC 181731
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1231 PM CDT WED JUL 18 2007
VALID 191200Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF HUDSON
VALLEY...NEW ENGLAND AND THE MID ATLANTIC STATES WWD INTO THE CNTRL
PLAINS...
...SYNOPSIS...
ERN U.S. LONG WAVE TROUGH IS EXPECTED TO AMPLIFY DURING THE DAY TWO
PERIOD AS STRONG SHORT WAVE TROUGH TRANSLATES SEWD THROUGH THE GREAT
LAKES. MEANWHILE IN THE W...ANOTHER STRONG SHORT WAVE TROUGH WILL
PIVOT NNEWD THROUGH THE PACIFIC NW INTO ERN BC/AB. IN THE
LOW-LEVELS...PRIMARY SURFACE LOW ATTENDANT TO GREAT LAKES UPPER
SYSTEM WILL DEEPEN SLIGHTLY AS IT DEVELOPS FROM LOWER MI INTO NEW
ENGLAND BY FRIDAY MORNING. TRAILING COLD FRONT WILL PUSH SWD/SEWD
THROUGH THE MID ATLANTIC STATES AND OH VALLEY...LIKELY FOCUSING MUCH
OF THE STRONG TO SEVERE STORM DEVELOPMENT THROUGH THE FORECAST
PERIOD. IN THE W...PACIFIC COLD FRONT WILL SLOWLY SHIFT EWD THROUGH
THE NRN ROCKIES...EVENTUALLY OCCLUDING WITH NRN PORTION OF
QUASI-STATIONARY BOUNDARY WHICH WILL STRETCH FROM WRN MT SEWD INTO
CNTRL WY.
...NERN STATES WWD INTO THE OH VALLEY...
LATEST SHORT TERM MODEL GUIDANCE REMAINS CONSISTENT IN SUGGESTING
THAT MULTIPLE TSTM CLUSTERS WILL BE ONGOING THURSDAY MORNING WITHIN
PRE-FRONTAL WARM SECTOR OVER THE OH VALLEY. THE STRONGEST AIR MASS
DESTABILIZATION IS FORECAST TO OCCUR TO THE S OF THIS PRE-EXISTING
ACTIVITY FROM THE MID ATLANTIC STATES WWD ALONG THE OH RIVER.
HERE...DAYTIME HEATING COUPLED WITH DEWPOINTS IN THE 60S TO LOWER
70S WILL CONTRIBUTE TO MLCAPES APPROACHING 2000-2500 J/KG....WITH
INSTABILITY DECREASING TO 500-1000 J/KG WITH NWD EXTENT WHERE
CLOUDS/PRECIPITATION WILL LIKELY PERSIST.
IT APPEARS THAT REMNANT NOCTURNAL STORMS WILL LIKELY PERSIST THROUGH
THE MORNING...EVENTUALLY RE-INTENSIFYING BY AFTERNOON OVER THE OH
VALLEY WITH ADDITIONAL DEVELOPMENT OCCURRING ALONG COLD FRONT AS
STRONGER HEIGHT FALLS ATTENDANT TO UPPER TROUGH OVERSPREAD REGION.
FORECAST SOUNDINGS EXHIBIT LARGELY UNIDIRECTIONAL WLY FLOW WITH
35-50 KT OF DEEP LAYER SPEED SHEAR...SUPPORTIVE OF EMBEDDED
SUPERCELL AND/OR BOWING STRUCTURES CAPABLE OF MAINLY DAMAGING WINDS.
A COUPLE OF TORNADOES AND SOME HAIL WILL ALSO BE
POSSIBLE...ESPECIALLY WITH ANY SUPERCELLS THAT CAN BECOME
ESTABLISHED.
SYNOPTIC SYSTEM WILL REMAIN RELATIVELY PROGRESSIVE WITH SEVERE
POTENTIAL INCREASING INTO THE MID ATLANTIC STATES...THE HUDSON
VALLEY AND PERHAPS PARTS OF SRN NEW ENGLAND THURSDAY NIGHT. A
CORRIDOR OF STRONGER LOW-LEVEL SHEAR WILL DEVELOP EWD INTO THE
HUDSON VALLEY AND EVENTUALLY NEW ENGLAND...IN CONJUNCTION WITH THE
MIGRATORY SURFACE LOW. HOWEVER...THE DEGREE OF AIR MASS INSTABILITY
REMAINS IN QUESTION WHICH COULD POTENTIALLY LIMIT MORE SIGNIFICANT
SEVERE WEATHER POTENTIAL. STILL...THE THREAT WILL EXIST FOR
DAMAGING WINDS AND SOME HAIL WITH STORM CLUSTERS WHICH ARE EXPECTED
TO BE ONGOING AHEAD OF COLD FRONT.
...LOWER MO VALLEY INTO KS...
BOTH LARGE-SCALE FORCING FOR ASCENT AND VERTICAL SHEAR WILL REMAIN
WEAKER THAN POINTS TO THE E...THOUGH STEEPER LAPSE RATES AND
COMPARABLE BOUNDARY LAYER MOISTURE WILL CONTRIBUTE AFTERNOON MLCAPES
APPROACHING 2000-3000 J/KG. TSTMS ARE EXPECTED TO BECOME
INCREASINGLY NUMEROUS THROUGH THE AFTERNOON AS FRONT PROGRESSES SWD
AND INTERACTS WITH DESTABILIZING ENVIRONMENT. THE MARGINAL VERTICAL
SHEAR SUGGESTS THAT MULTICELLULAR CLUSTERS WILL BE THE PRIMARY
CONVECTIVE MODE WITH THE MAIN SEVERE THREATS BEING LARGE HAIL AND
DAMAGING WINDS.
...NRN ROCKIES INTO CNTRL HIGH PLAINS...
LATEST MODEL GUIDANCE REMAINS CONSISTENT IN SUGGESTING A MORE
CONCENTRATED SEVERE WEATHER THREAT WILL LIKELY REMAIN N OF THE
INTERNATIONAL BORDER WHERE STRONGER LARGE-SCALE FORCING FOR ASCENT
WILL INTERACT WITH UNSTABLE...PRE-FRONTAL AIR MASS. WHILE SOME
DESTABILIZATION IS FORECAST ALONG COLD FRONT WHERE DEEP LAYER
VERTICAL SHEAR WILL BE THE STRONGEST...IT APPEARS THAT THE STRONGER
INSTABILITY /MLCAPES OF 1000-1500 J PER KG/ WILL EXIST ALONG
QUASI-STATIONARY BOUNDARY FROM CNTRL MT INTO CNTRL/ERN WY WHERE
VERTICAL SHEAR IS WEAKER.
ISOLATED/SCATTERED STORMS ARE LIKELY TO DEVELOP DURING THE
AFTERNOON/EVENING HOURS ALONG QUASI-STATIONARY BOUNDARY WITH SOME
THREAT OF SEVERE HAIL WITH THE MORE INTENSE STORMS. ALONG THE COLD
FRONT...UNCERTAINTY EXISTS WITH REGARD TO EVENTUAL CONVECTIVE
COVERAGE AND THEREFORE ONLY LOW PROBABILITIES WILL BE INCLUDED ATTM.
..MEAD.. 07/18/2007
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0800Z
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