SWODY1
SPC AC 230552
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT SAT MAY 23 2009
VALID 231200Z - 241200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
IN MID-UPPER LEVELS...HIGH-AMPLITUDE RIDGING IS FCST TO CONTINUE
OVER WRN CANADA. MEAN RIDGE WILL BE PENETRATED OVER NRN ROCKIES BY
RELATIVELY TIGHT/QUASI-ZONAL HEIGHT GRADIENT EXTENDING FROM COASTAL
BC AND PAC NW EWD ALONG CANADIAN BORDER TO GREAT LAKES AND NRN NEW
ENGLAND. S OF RELATED BELT OF ENHANCED FLOW ALOFT...VERY LOOSE
HEIGHT GRADIENTS AND WEAK DEEP-LAYER FLOW WILL PREVAIL IN MOST
AREAS...EXCEPT OVER PORTIONS SERN CONUS AS NOTED BELOW. MOST
PROMINENT FEATURES ALOFT WILL BE BROAD CYCLONE OVER SWRN CONUS AND
LOW MOVING INLAND FROM NERN GULF. SWRN LOW -- NOW EVIDENT IN
MOISTURE CHANNEL IMAGERY OVER SRN/CENTRAL AZ...IS FCST TO
MOVE/REDEVELOP NWD ACROSS UT THEN AND CONNECT WITH SRN FRINGE OF WLY
FLOW BELT. THIS FEATURE SHOULD REACH WRN WY OVERNIGHT AHEAD OF WEAK
PACIFIC SHORTWAVE TROUGH...BASED ON STG CONSENSUS OF OPERATIONAL
SPECTRAL/NAM AND SREF MEAN. MEANWHILE...GULF LOW IS EXPECTED TO
MOVE INLAND OVER GULF COAST BETWEEN SIL-PNS EARLY IN PERIOD AND
PROCEED SLOWLY NWWD ACROSS MS.
AT SFC...COLD FRONT -- ANALYZED INITIALLY FROM NRN MN OVER
E-CENTRAL/SWRN SD AND NEB PANHANDLE -- IS FCST TO MERGE WITH
WEAKER/OLDER FRONTAL ZONE TO ITS S AND DECELERATE. RESULT BY 24/00Z
SHOULD BE QUASISTATIONARY FRONT FROM W-CENTRAL IL WWD INVOF KS/NEB
BORDER TO NERN CO...RETURNING NWD OVERNIGHT ACROSS CENTRAL HIGH
PLAINS AS WARM FRONT.
...ERN GULF COAST REGION...
NERN GULF LOW MAY BECOME TROPICAL IN CHARACTER BEFORE LANDFALL...REF
NHC OUTLOOK UNDER WMO HEADER ABNT 20 KNHC FOR DETAILS. BELT OF
ENHANCED LOW LEVEL FLOW ABOVE SFC -- I.E. LLJ WITH 30-40 KT WIND
BETWEEN .5-4 KM AGL -- REASONABLY IS SHOWN IN FCST SOUNDINGS ESE-NE
OF CENTER AS IT TRACKS INLAND...AND WILL CONTRIBUTE TO ENHANCED LOW
LEVEL SHEAR. WHETHER OR NOT THIS SYSTEM ACQUIRES TROPICAL CHARACTER
BEFORE MOVING INLAND...NET EFFECT FOR LOW LEVEL HODOGRAPHS IN
MIDDLE-OUTER PORTION OF CIRCULATION ENVELOPE WILL BE SIMILAR TO THAT
OFTEN SEEN WITH LANDFALLING TROPICAL DEPRESSIONS OR INLAND DECAY
PHASES OF INITIALLY STRONGER SYSTEMS...E.G. 0-1 KM SRH 150-300 J/KG
OVER BROAD AREA. THIS INDICATES SOME POTENTIAL FOR STORM
ROTATION...DESPITE WEAKER WINDS IN MID-UPPER LEVELS...AS LONG AS
SUFFICIENT POCKETS OF FAVORABLE LOW LEVEL DESTABILIZATION CAN
DEVELOP AND CONVECTIVE MODE IS DISCRETE/ORGANIZED ENOUGH TO SUPPORT
SFC-BASED SUPERCELLS. ATTM RISK IS TOO MRGL AND CONDITIONAL ON
MESOBETA AND SMALLER SCALE PROCESSES FOR CATEGORICAL OUTLOOK.
...CENTRAL PLAINS...
SCATTERED TSTMS AGAIN MAY DEVELOP ALONG AND N OF FRONTAL
ZONE...STRONGLY TIED TO COMBINATION OF SFC DIABATIC HEATING...WEAK
BOUNDARY LAYER UPSLOPE WINDS AND FRONTAL LIFT. SUFFICIENT HEATING
AGAIN SHOULD OCCUR TO OFFSET SEASONALLY WEAK UPPER LEVEL LAPSE RATES
ORIGINATING FROM QUASI-MONSOONAL SWRN REGIME. MID-UPPER WINDS ARE
FCST TO REMAIN WEAK...LEADING TO QUICKLY PRECIP-CONTAMINATED UPDRAFT
REGIONS AND OUTFLOW-DOMINANT CHARACTER OF STORMS. BEFORE THAT
HAPPENS...HOWEVER...PRONOUNCED VEERING OF WINDS WITH HEIGHT IN
LOWEST FEW KM AGL MAY CONTRIBUTE TO STRONGLY CURVING...IF RATHER
SMALL...LOW LEVEL HODOGRAPHS AND TRANSIENT SUPERCELL CHARACTER.
STRONGEST STORMS MAY PRODUCE MRGL SVR HAIL.
...NRN HIGH PLAINS...
ALTHOUGH LOW LEVEL WINDS ARE FCST TO BE WEAK...STG TURNING WITH
HEIGHT AND ELY SFC WINDS ARE FCST OVER PORTIONS CENTRAL/SRN MT
BENEATH 50-60 KT UPPER JET. MODIFIED FCST SOUNDINGS SUGGEST
RATHER MEAGER LOW LEVEL MOISTURE WILL KEEP MLCAPES UNDER 1000
J/KG...BUT SFC HEATING MAY BE STG ENOUGH TO RENDER WEAK MLCINH.
LACK OF EVIDENCE OF DISTINCT LOW LEVEL FOCI -- OTHER THAN OROGRAPHIC
-- INDICATES CONVECTIVE COVERAGE SHOULD BE ISOLATED.
ACCORDINGLY...MOST OPERATIONAL AND SREF PROGS BEAR THIS OUT...WITH
LACK OF CONVECTIVE PRECIP FCST ACROSS THIS AREA. GIVEN CONDITIONAL
RISK FOR SVR...BUT UNCERTAINTIES REGARDING LOW LEVEL FORCING AND
STORM COVERAGE...UNCONDITIONAL RISK APPEARS TOO LOW FOR CATEGORICAL
OUTLOOK.
...NERN CONUS...
DIURNAL HEATING IS FCST TO WEAKEN CINH ACROSS THIS REGION...WITH
SUFFICIENT LOW LEVEL MOIST ADVECTION TO OFFSET MIXING AND MAINTAIN
SFC DEW POINTS MID 50S TO LOW 60S F IN MOST AREAS. MODIFIED ETA-KF
FCST SOUNDINGS SUGGEST THIS WILL SUPPORT MLCAPE IN 500-1000 J/KG
RANGE. WELL-DEFINED N-S BOUNDARY IS EXPECTED TO DEVELOP DURING
DAY...ACROSS PORTIONS ERN NY SWD TO NJ OR NERN PA -- DEMARCATING
RELATIVELY COLD/STABLE MARINE AIR TO ITS E FROM MORE STRONGLY
HEATED...HIGHER THETAE INLAND REGIME OVER PA AND CENTRAL NY. NEARLY
UNIDIRECTIONAL FLOW WITH HEIGHT WILL PREVAIL W OF THIS
BOUNDARY...FLOW STEADILY STRENGTHENING WITH HEIGHT TO AROUND 60-65
KT AT 250 MB. ISOLATED STG/DAMAGING GUSTS MAY OCCUR WITH ACTIVITY
ALONG AND W OF BOUNDARY...AND LOCALLY BACKED WINDS IN BAROCLINIC
ZONE MAY CONTRIBUTE TO BRIEF SUPERCELLULAR ORGANIZATION IN ANY
RELATIVELY DISCRETE ACTIVITY TRAVERSING IT.
..EDWARDS/GRAMS.. 05/23/2009
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