SWODY2
SPC AC 090526
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 AM CDT SAT AUG 09 2008
VALID 101200Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID ATLANTIC COAST
INTO CNTRL NY...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN AND CNTRL HIGH
PLAINS...
...SYNOPSIS...
DEEP...UPPER LOW CENTERED OVER SWRN ONTARIO WILL MOVE SLOWLY EWD
THROUGH THE LOWER GREAT LAKES DURING THE DAY TWO PERIOD.
MEANWHILE...UPSTREAM LOW OVER BRITISH COLUMBIA WILL PROGRESS EWD
INTO ALBERTA WITH A RATHER STRONG SHORT WAVE TROUGH ROTATING AROUND
THIS FEATURE ACROSS THE PACIFIC NW AND NRN INTERMOUNTAIN REGION. IN
THE LOW LEVELS...SURFACE LOW ATTENDANT TO THE GREAT LAKES SYSTEM
WILL DEVELOP EWD ACROSS NY WITH A PRE-FRONTAL TROUGH STRENGTHENING
FROM THE DE RIVER VALLEY SSWWD THROUGH THE PIEDMONT REGION. A COLD
FRONT WILL PUSH EWD THROUGH THE LOWER GREAT LAKES TOWARD THE MID
ATLANTIC COAST BY MONDAY MORNING. FARTHER W...A LEE LOW WILL
PERSIST OVER ERN MT WITH ATTENDANT TROUGH EXTENDING SWD INTO THE
CNTRL HIGH PLAINS. WITH TIME...THE NRN EXTENSION OF THE LEE TROUGH
WILL BE OVERTAKEN BY A COLD FRONT MOVING EWD THROUGH THE NRN HIGH
PLAINS.
...LOWER GREAT LAKES INTO MID ATLANTIC STATES...
SOME CONCERN STILL EXISTS THAT PERSISTENT CLOUDS AND/OR
PRECIPITATION MAY TEND TO LIMIT STRONGER DIABATIC HEATING AND
RESULTANT DESTABILIZATION ACROSS THE REGION SUNDAY.
HOWEVER...LATEST MODEL GUIDANCE IS RELATIVELY CONSISTENT IN
SUGGESTING THAT AN AXIS OF STRONGER INSTABILITY /MLCAPES OF
1000-1500 J PER KG/ WILL DEVELOP ALONG PRE-FRONTAL TROUGH FROM THE
MID ATLANTIC COAST NWWD INTO CNTRL NY.
DEEP ASCENT IN LEFT EXIT REGION OF UPPER JET STREAK OVER THE CNTRL
APPALACHIANS COMBINED WITH HEIGHT FALLS/DYNAMIC COOLING AHEAD OF
UPPER LOW ARE EXPECTED TO CONTRIBUTE TO AN INCREASE IN STORM
COVERAGE ALONG TROUGH AND COLD FRONT DURING THE AFTERNOON. WHILE
ANY STRONGER STORMS WILL BE CAPABLE OF SOME HAIL GIVEN THE
RELATIVELY COOL MIDLEVEL TEMPERATURES /-15 TO -20 C AT 500 MB/...THE
MORE ORGANIZED SEVERE THREAT WILL EXIST ACROSS SLIGHT RISK AREA
WHERE LOCALLY STRONGER INSTABILITY SHOULD PROMOTE MORE
INTENSE/LONGER-LIVED UPDRAFTS. ADDITIONALLY...A BELT OF STRONGER
MIDLEVEL FLOW WILL OVERSPREAD THE DELMARVA INTO LOWER HUDSON VALLEY
WITH SUFFICIENT DEEP-LAYER SHEAR DEVELOPING TO SUPPORT SOME UPDRAFT
ROTATION. LARGE HAIL AND DAMAGING WIND GUSTS APPEAR TO BE THE
PRIMARY HAZARDS WITH THE MOST INTENSE STORMS.
...NRN/CNTRL HIGH PLAINS...
MODEST BOUNDARY LAYER MOISTURE /DEWPOINTS IN THE 50S/ WILL EXIST
INVOF LEE TROUGH WHERE AFTERNOON TEMPERATURES WILL WARM THROUGH THE
80S INTO THE LOWER 90S. WHEN COMBINED WITH MIDLEVEL LAPSE RATES OF
7-7.5 C/KM...AIR MASS WILL BECOME MODERATELY UNSTABLE WITH MLCAPES
APPROACHING 1000-1500 J/KG. DAYTIME HEATING COUPLED WITH FRONTAL
CONVERGENCE AND INCREASED FORCING FOR ASCENT IN ADVANCE OF NRN
ROCKIES SHORT WAVE TROUGH ALL WILL CONTRIBUTE TO AN INCREASE IN
STORM COVERAGE AND INTENSITY BY MID/LATE AFTERNOON FROM ERN PORTIONS
OF MT/WY/CO INTO THE WRN DAKOTAS AND NEB PNHDL.
AS MENTIONED IN PREVIOUS DISCUSSIONS...STRONGER MID AND HIGH-LEVEL
WIND FIELDS WILL LAG SURFACE WARM SECTOR TO THE NW. BUT...FORECAST
HODOGRAPHS DO SHOW NOTABLE VEERING WINDS WITH HEIGHT WITH AROUND 30
KT OF DEEP-LAYER SHEAR. STORMS SHOULD BE RELATIVELY HIGH-BASED
GIVEN 30-35+ F TEMPERATURE/DEWPOINT SPREADS WITH THE POTENTIAL FOR
MARGINAL SUPERCELL STRUCTURES CAPABLE OF DAMAGING WINDS AND HAIL.
...SRN PLAINS INTO LOWER MS VALLEY...
MIDLEVEL LAPSE RATES ARE FORECAST TO REMAIN RATHER WEAK...BUT
BOUNDARY LAYER DEWPOINTS IN THE 60S TO LOWER 70S COMBINED WITH
STRONG DAYTIME HEATING WILL RESULT IN THE DEVELOPMENT OF A
MODERATELY UNSTABLE AIR MASS /MLCAPES OF 1000-2000 J PER KG/ AHEAD
COLD FRONT BY AFTERNOON. VERTICAL SHEAR WILL REMAIN RATHER
WEAK...THOUGH A FEW STRONG MULTICELL CLUSTERS ARE POSSIBLE WITH THE
THREAT FOR MAINLY DAMAGING WINDS DURING THE AFTERNOON AND EVENING
HOURS.
..MEAD.. 08/09/2008
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