Saturday, October 3, 2009

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 031247
SWODY1
SPC AC 031244

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT SAT OCT 03 2009

VALID 031300Z - 041200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...

UPPER PATTERN TODAY WILL REMAIN DOMINATED BY A LARGE CYCLONE
CENTERED OVER THE GREAT LAKES AND ANOTHER ONE DROPPING INTO THE
PACIFIC NW. GREAT LAKES CYCLONE IS FORECAST TO LIFT SLOWLY NWD INTO
SRN ONTARIO WHILE THE UPPER LOW OVER WA WILL DROP SWD...REACHING NRN
CA LATE TONIGHT. SURFACE PATTERN IS CHARACTERIZED BY AN OCCLUDED
FRONT THAT EXTENDS THROUGH CNTRL NY FROM AN OCCLUDED LOW OVER THE
GREAT LAKES. THIS BOUNDARY TRANSITIONS TO A COLD FRONT THAT
STRETCHES THROUGH THE MID ATLANTIC AREA INTO THE WRN
CAROLINAS...SERN STATES THEN WWD INTO S TX WHERE IT BECOMES
STATIONARY. A WARM FRONT EXTENDS ACROSS SRN NEW ENGLAND.

...NERN STATES...

UPPER JET MAX LOCATED IN BASE OF UPPER LOW ACROSS KY AND WV WILL
ROTATE NEWD INDUCING A WEAK SURFACE WAVE ON THE COLD FRONT OVER THE
MID-ATLANTIC REGION. THIS PROCESS WILL RESULT IN THE FRONT ADVANCING
EWD THROUGH THE REMAINDER OF THE MID-ATLANTIC AND OFFSHORE LATER
TODAY. AS THIS OCCURS...THE WARM FRONT WILL LIFT A LITTLE FARTHER
NWD THROUGH SRN NEW ENGLAND. WV IMAGERY INDICATES A BAND OF DEEP
MOISTURE ALONG THE ATLANTIC SEABOARD...AS WELL AS AN UPPER IMPULSE
LIFTING NWD JUST OFF THE NC COAST. THE MOIST PLUME WILL BEGIN TO
SHIFT EWD AS OH VALLEY IMPULSE ROTATES NEWD ALONG ERN PERIPHERY OF
UPPER TROUGH. CONVECTION WITH EMBEDDED THUNDERSTORMS WILL PERSIST
WITHIN MOISTURE PLUME ALONG LOW LEVEL WARM CONVEYOR BELT AND TRAIN
NWD THROUGH NEW ENGLAND. AS A RESULT OF WIDESPREAD ONGOING CLOUDS
AND RAIN...DESTABILIZATION POTENTIAL WILL BE LIMITED AND DUE
PRIMARILY TO A MODEST INCREASE IN BOUNDARY LAYER MOISTURE OVER SRN
NEW ENGLAND...SOUTH OF RETREATING WARM FRONT. MLCAPE WILL BE
GENERALLY AOB 500 J/KG. THE LARGER 0-2 KM HODOGRAPHS WILL REMAIN
CONFINED TO THE STABLE BOUNDARY LAYER NORTH OF WARM FRONT WHERE
WINDS ARE BACKED TO ELY. MOSTLY UNIDIRECTIONAL DEEP LAYER WINDS WILL
EXIST FARTHER SOUTH IN WARM SECTOR BUT WITH 0-6 KM SHEAR OF 40-50 KT
SUFFICIENT FOR A THREAT OF BOWING SEGMENTS AND EMBEDDED UPDRAFT
ROTATION WITH THE STRONGER STORMS.

POTENTIAL WILL EXIST FOR THE BOUNDARY LAYER TO DESTABILIZE IN A
NARROW CORRIDOR BEHIND DEEP MOISTURE PLUME AND EAST OF COLD FRONT
ACROSS ERN PA...SERN NY AND NJ. HOWEVER...WEAK MID-LEVEL LAPSE RATES
WILL LIKELY RESULT IN MARGINAL INSTABILITY. STORMS MAY DEVELOP ON
THE EWD ADVANCING FRONT DURING THE AFTERNOON. WITH BULK SHEAR OF 50
KT...POTENTIAL WILL EXIST FOR A FEW UPDRAFTS TO ROTATE AND DEVELOP
BOWING STRUCTURES WITH ISOLATED DAMAGING WIND THE MAIN THREAT.

DUE TO THE EXPECTED MARGINAL THERMODYNAMIC ENVIRONMENT...ONLY LOW
SEVERE PROBABILITIES APPEAR WARRANTED AT THIS TIME...BUT AREA WILL
CONTINUE TO BE MONITORED.


...S TX...

ONE OR TWO CLUSTERS OF STG...PERHAPS MRGL SVR TSTMS ARE POSSIBLE
ACROSS PORTIONS CENTRAL/S TX EARLY IN PERIOD. THIS ACTIVITY IS
EXPECTED AS ISENTROPIC ASCENT TO LFC OCCURS N OF SFC FRONT...IN
REGIME OF INCREASING LOW LEVEL MOISTURE AND FAVORABLE EFFECTIVE
SHEAR ALOFT. PRIMARY FACTOR PRECLUDING CATEGORICAL OUTLOOK ATTM
INCLUDE PRESENCE OF RELATIVELY WEAK MIDLEVEL LAPSE RATES THAT WILL
LIMIT BUOYANCY AND POTENTIAL FOR LARGER HAIL.

MID-UPPER LEVEL CLOUDS AND MOISTURE STREAMING OFF PACIFIC TS OLAF
MAY SOMEWHAT RESTRAIN DIABATIC HEATING WITHIN AND ALONG WARM SIDE OF
FRONTAL ZONE DURING AFTERNOON...AND MOST LIKELY WILL YIELD WEAK
UPPER LEVEL LAPSE RATES. HOWEVER...MODEST DIFFERENTIAL HEATING
ACROSS BOUNDARY MAY CONTRIBUTE TO ADDITIONAL/SFC-BASED/DIURNAL
DEVELOPMENT INVOF FRONTAL ZONE. ANY STG-SVR GUSTS SHOULD OCCUR IN
AND S OF FRONTAL ZONE...WHILE HAIL SIZE SHOULD BE MRGL SVR...AT
BEST...ANYWHERE OVER REGION.

..DIAL/SMITH.. 10/03/2009

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