SWODY2
SPC AC 200557
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT WED OCT 20 2010
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SRN HIGH PLAINS...
...SYNOPSIS...
OVER WRN CONUS...REX PATTERN FCST TO PREVAIL IN MIDDLE-UPPER LEVELS
THROUGH EARLY PART OF PERIOD...WHEREUPON STG HEIGHT FALLS WILL OCCUR
OVER PAC COAST REGION IN ADVANCE OF PROGRESSIVE SHORTWAVE TROUGH.
THIS WILL LEAD TO EJECTION OF CYCLONE NOW EVIDENT IN MOISTURE
CHANNEL IMAGERY OVER COASTAL NWRN BAJA. SREF MEMBERS AND
OPERATIONAL WRF/SPECTRAL MODELS ARE IN UNANIMOUS AGREEMENT ON
POSITIONING OF THIS LOW OVER WRN/SWRN AZ BY 21/12Z...WITH STG
CONSENSUS OF THESE PROGS REGARDING TRACK OF PRIMARY VORTICITY LOBE
TOWARD NERN NM OVER ENSUING 24 HOURS...WITH SOME OPENING OF HEIGHT
CONTOURS TO ITS NW. PRONOUNCED NEGATIVE TILT IS FCST WITH
ACCOMPANYING SHORTWAVE TROUGH...LEADING TO REGIME OF STG UPPER
DIFLUENCE SPREADING EWD FROM ERN NM ACROSS SRN PLAINS DURING DAY-3.
UPPER TROUGH WILL BE PRECEDED BY LOW-LEVEL CONVERGENCE/FRONTAL ZONE
ACROSS ERN NM AND W TX.
FARTHER NE...DEEP BUT PROGRESSIVE MID-UPPER LEVEL TROUGHING IS FCST
ACROSS GREAT LAKES REGION SWD OVER CENTRAL/NRN APPALACHIANS.
INITIALLY LOW-AMPLITUDE PERTURBATION -- NOW EMBEDDED IN NW FLOW OVER
PORTIONS SK/MB -- IS FCST TO MOVE SEWD AND EWD ACROSS NRN ONT TO WRN
QUE DAY-1...EVOLVING INTO 500-MB LOW THAT SHOULD MOVE ENEWD TO NEWD
OVER CENTRAL/NRN QUE THIS PERIOD. AS THIS OCCURS...COLD FRONT WILL
MOVE EWD/SEWD FROM INTERIOR MID-ATLANTIC REGION AT 21/12Z ACROSS
MOST OF NEW ENGLAND BY 22/00Z...EXCEPT FOR PORTIONS MAINE.
FRONTAL-WAVE LOW MAY DEVELOP DURING AFTERNOON OVER VT/NH OR ADJACENT
PORTIONS SRN QUE...AND MOVE EWD ACROSS MAINE.
...PORTIONS SRN HIGH PLAINS...
SCATTERED-NUMEROUS TSTMS ARE EXPECTED FROM LATE MORNING/EARLY
AFTERNOON OVER CENTRAL/ERN NM ACROSS PORTIONS TX
PANHANDLE/SOUTH-PLAINS REGION DURING AFTERNOON-EVENING...SHIFTING
EWD OVER PORTIONS NW TX...WRN OK AND PERHAPS SWRN KS OVERNIGHT.
VERTICAL SHEAR PROFILES WILL SUPPORT POTENTIAL FOR SUPERCELLS AND/OR
BOWS. ATTM IT IS TOO SOON TO JUDGE DOMINANT CONVECTIVE STRUCTURE
AND THEREFORE PRIMARY SVR MODE...ESPECIALLY GIVEN FAIRLY DENSE
AGGREGATE COVERAGE OF TSTMS EXPECTED THROUGH MOST OF PERIOD.
CONVECTIVE AND MID-UPPER LEVEL RH PROGS FOR EARLY IN PERIOD
REASONABLY INDICATE LIMITED PACE/STRENGTH OF SFC DIABATIC HEATING
ACROSS MUCH OF ERN NM AND PANHANDLE REGION...BENEATH DENSE CLOUD
COVER ALOFT. MODIFIED FCST SOUNDINGS STILL SUGGEST...HOWEVER...
THAT EVEN MUTED INSOLATION WITH SFC DEW POINTS 50S F WILL WEAKEN
CINH SUFFICIENTLY TO SUPPORT ABUNDANT CONVECTION...IN TANDEM WITH
CONVERGENCE NEAR FRONT. FLOW IS FCST TO VEER WITH HEIGHT BENEATH
SUFFICIENTLY STG MIDLEVEL WINDS TO SUPPORT 35-45 KT EFFECTIVE SHEAR
MAGNITUDES. BOTH HEATING AND CAPPING ARE FCST TO STRENGTHEN WITH
SWD EXTENT ACROSS W TX...LEAVING COVERAGE AND INTENSITY OF
CONVECTION MORE UNCERTAIN...HENCE DECREASING UNCONDITIONAL SVR
PROBABILITIES. CONVECTION SHOULD MOVE EWD OVERNIGHT INTO GRADUALLY
MORE STABLE SFC AIR MASS WITH EWD EXTENT...ALTHOUGH DIABATICALLY
COOLED LAYER MAY REMAIN SHALLOW ENOUGH TO PERMIT STG-SVR GUSTS TO
REACH SFC IN SOME LOCALES.
...SRN/ERN NEW ENGLAND...
ISOLATED TO WIDELY SCATTERED TSTMS MAY BE ONGOING EARLY IN PERIOD
INVOF FRONT...OVER INTERIOR MID-ATLANTIC REGION...IN REGIME OF COLD
AIR ALOFT AND STEEP LOW-MIDDLE LEVEL LAPSE RATES. AS BOUNDARY LAYER
AIR MASS E OF MOUNTAINS DESTABILIZES WITH LATE MORNING/EARLY
AFTERNOON SFC HEATING...ALREADY-WEAK CINH WILL BE
REMOVED...SUPPORTING EITHER INTENSIFICATION OR REDEVELOPMENT OF
CONVECTION ALONG/AHEAD OF FRONT IN QUASI-LINEAR FASHION...AMIDST
NEARLY UNIDIRECTIONAL DEEP-TROPOSPHERIC WINDS. MAIN LIMITING FACTOR
WILL BE PRESENCE OF MRGL MOISTURE...WITH SFC DEW POINTS GENERALLY
UPPER 40S TO MID 50S F PROGGED. NONETHELESS...ACCORDINGLY MODIFIED
ETA-KF SOUNDINGS YIELD SFC-BASED BUOYANCY WITH 100-800 J/KG
MLCAPE...EXTENDING INTO ICING LAYERS FAVORABLE FOR TSTMS. ACTIVITY
SHOULD BE RATHER FAST-MOVING...I.E. 35-45 KT...WITH POTENTIAL FOR
STG-DAMAGING GUSTS IN MOST PERSISTENT/INTENSE CELLS.
..EDWARDS.. 10/20/2010
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