Saturday, May 23, 2009

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 231254
SWODY1
SPC AC 231250

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT SAT MAY 23 2009

VALID 231300Z - 241200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
THE PRIMARY BELT OF WLYS WILL BE CONFINED TO THE CANADIAN BORDER
REGION AS A SERIES OF EMBEDDED SHORTWAVE TROUGHS ROTATE EWD FROM
ONTARIO TO WRN QUEBEC. FARTHER S...A MORE DIFFUSE FLOW REGIME
PERSISTS ACROSS THE MAJORITY OF THE CONUS...WITH RELATIVELY WEAK
FLOW ASSOCIATED WITH SUBTROPICAL MID LEVEL TROUGHS OVER THE GULF
COAST AND NRN MEXICO/SRN AZ AND NM.

A BROAD PLUME OF LOW-MID LEVEL MOISTURE EXTENDS NWD OVER THE
SRN/CENTRAL ROCKIES...WHERE SEVERAL DAYS OF PRIOR CONVECTION HAVE
ADJUSTED MID LEVEL LAPSE RATES TO LARGELY MOIST ADIABATIC.
SCATTERED MAINLY DIURNAL THUNDERSTORMS WILL LIKELY FORM AGAIN THIS
AFTERNOON IN CONJUNCTION WITH SURFACE HEATING OVER THE ELEVATED
TERRAIN...BUT THE POTENTIAL FOR STRONG DOWNDRAFTS WILL BE LIMITED BY
THE POOR LAPSE RATES AND SUBSTANTIAL CLOUD COVER.

...SRN AL/FL PANHANDLE/ERN MS TODAY...
THE BROAD SUBTROPICAL LOW OVER THE GULF OF MEXICO FROM PREVIOUS DAYS
HAS CONSOLIDATED OVERNIGHT INTO TIGHTER CYCLONE THAT IS NOW
APPROACHING THE AL COAST. SEVERAL PERSISTENT CONVECTIVE
CLUSTERS...AND ASSOCIATED/FOCUSED LATENT HEAT RELEASE...APPEAR TO
HAVE AIDED IN THE DEVELOPMENT OF QUASI-TROPICAL CHARACTERISTICS WITH
THIS SYSTEM AS LARGER SCALE VERTICAL SHEAR HAS RELAXED SOMEWHAT
COMPARED TO PRIOR DAYS. THE CONSOLIDATION OF THE CYCLONE HAS ALSO
RESULTED IN STRENGTHENING OF ELY/SELY LOW-LEVEL FLOW TO 30-40 KT TO
THE N/NE OF THE CYCLONE...AND CURVED LOW-LEVEL HODOGRAPHS FROM MOB
AND EVX THAT APPEAR SUPPORTIVE OF EMBEDDED ROTATING STORMS.

THERE WILL BE THE POTENTIAL FOR A BRIEF TORNADO OR TWO AND GUSTY
WINDS WITH THE STRONGER EMBEDDED STORMS TODAY ALONG THE COAST. THE
PRIMARY LIMITING FACTOR FOR SUPERCELLS/TORNADOES WILL BE THE SMALL
SIZE OF THE SYSTEM AND ITS ASSOCIATED FAVORABLE WIND FIELD...AS WELL
AS GRADUAL WEAKENING THAT IS EXPECTED TODAY AS THE CYCLONE MOVES
NNWWD/INLAND AND AWAY FROM THE PRIMARY MOISTURE/INSTABILITY FEED
ORIGINATING OVER THE LOOP CURRENT.

...N CENTRAL/NE PA AND S CENTRAL NY THIS AFTERNOON/EVENING...
A REMNANT BAROCLINIC ZONE WILL RETREAT NWD ACROSS CENTRAL/NRN PA AND
SRN NY THROUGH THE DAY WHILE BECOMING DIFFUSE...IN ADVANCE OF
ANOTHER COLD FRONT WHICH WILL MOVE SEWD ACROSS THE LOWER GREAT LAKES
OVERNIGHT. LOW-MID LEVEL ASCENT WILL REMAIN WEAK AND MID LEVEL
LAPSE RATES AOB 7 C/KM OVER THIS REGION WITH THE PRIMARY STORM TRACK
WELL TO THE N...BUT DAYTIME HEATING AND BOUNDARY LAYER DEWPOINTS
NEAR 60 F WILL SUPPORT AFTERNOON MLCAPE VALUES OF 500-1000 J/KG.
WIDELY SCATTERED THUNDERSTORMS SHOULD FORM DURING THE AFTERNOON
ACROSS PA/NY AND PERSIST INTO THE EVENING...WITH THE ERN EXTENT OF
THE THREAT LIMITED INTO SRN NEW ENGLAND BY TRAJECTORIES OFF THE COOL
WATER.

DEEP LAYER VERTICAL SHEAR WILL BE SUFFICIENT FOR ORGANIZED MULTICELL
CLUSTERS...AND AT LEAST MARGINALLY FAVORABLE FOR SUPERCELLS GIVEN
SPEED INCREASES WITH HEIGHT AND RELATIVELY STRAIGHT HODOGRAPHS.
RELATIVELY WEAK LOW-LEVEL FLOW AND MODEST INSTABILITY SUGGEST THAT
THE THREAT FOR HAIL AND STRONG OUTFLOW WINDS WILL REMAIN SOMEWHAT
LIMITED...THUS WILL MAINTAIN LOW SEVERE PROBABILITIES IN THIS
UPDATE.

...SRN MT LATE AFTERNOON/EVENING...
GRADUAL LOW-MID LEVEL MOISTENING IS EXPECTED ON THE NRN FRINGE OF
THE MONSOONAL MOISTURE PLUME ACROSS SRN MT TODAY INTO TONIGHT...AND
DOWNSTREAM FROM A WEAK MID LEVEL LOW MOVING SLOWLY NNEWD FROM UT.
THOUGH FORCING FOR ASCENT WILL BE WEAK OVER MT TODAY...A FEW STORMS
SHOULD FORM OVER THE MOUNTAINS THIS AFTERNOON AND MOVE EWD INTO S
CENTRAL MT THIS EVENING. 0-6 KM BULK SHEAR OF 30-40 KT ALONG THE
SRN FRINGE OF THE WLYS...AND IN ASSOCIATION WITH SELY LOW-LEVEL
FLOW...WILL SUPPORT ORGANIZED STORMS AND PERHAPS SOME SUPERCELL
STRUCTURES. MARGINALLY SEVERE HAIL AND STRONG OUTFLOW WINDS WILL BE
THE PRIMARY THREATS...THOUGH ONLY ISOLATED STORM COVERAGE AND MODEST
INSTABILITY WILL TEMPER THE OVERALL THREAT.

...SW NEB BORDER REGION THIS AFTERNOON/EVENING...
A STALLED BAROCLINIC ZONE WILL PROVIDE A FOCUS FOR SCATTERED
THUNDERSTORM DEVELOPMENT TODAY INTO TONIGHT FROM NE CO INTO NEB.
MOIST PROFILES/POOR MID LEVEL LAPSE RATES WILL LIMIT THE MAGNITUDE
OF INSTABILITY...WHILE DEEP LAYER VERTICAL SHEAR WILL REMAIN WEAK.
HOWEVER...THERE MAY BE A SMALL WINDOW OF OPPORTUNITY FOR SOMEWHAT
ORGANIZED STORMS THIS AFTERNOON AS LOW-LEVEL ELY/SELY FLOW GRADUALLY
INCREASES ALONG AND N OF THE FRONT. HAIL AND GUSTY OUTFLOW WINDS
MAY OCCUR...BUT THESE THREATS APPEAR RATHER MARGINAL ATTM.

..THOMPSON/SMITH.. 05/23/2009

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