SWODY2
SPC AC 200555
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1155 PM CST THU FEB 19 2009
VALID 211200Z - 221200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
STG MID/UPPER TROUGHING SHOULD CONTINUE OVER NERN PACIFIC WITH
BROAD/PERSISTENT VORTEX CENTERED WELL OFFSHORE ORE/NRN CA...AND
DOWNSTREAM RIDGING OVER WRN NORTH AMERICA. FARTHER E...UPPER AIR
PATTERN WILL CONTINUE TO BE CHARACTERIZED BY MEAN TROUGHING FROM
HUDSON BAY TO NRN GULF...TRAVERSED BY STG SHORTWAVES. FIRST OF
THESE WAVES -- NOW MANIFEST AS UPPER LOW OVER LOWER GREAT LAKES --
WILL LIFT ENEWD ACROSS NEW ENGLAND TO CANADIAN MARITIMES DAY-1.
STG/UPSTREAM PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
OVER SASK -- WILL DIG SEWD AND AMPLIFY FURTHER THROUGH DAY-2.
RESULTING TROUGH SHOULD DEVELOP EMBEDDED MID-UPPER LOW EARLY IN
PERIOD...BETWEEN UPPER MS VALLEY AND SRN LM. TROUGH THEN WILL PIVOT
EWD OVER OH VALLEY TO CENTRAL/SRN APPALACHIANS...WHILE ACCOMPANYING
LOW LIFTS NEWD OVER LH TOWARD ADJOINING PORTIONS ONT.
AT SFC...COLD FRONT NOW OVER S FL WILL MOVE WELL OFFSHORE
PENINSULA...CROSSING MUCH OF BAHAMAS/CUBA AND GULF OF MEXICO DAY-1.
WRN SEGMENT OF THIS BOUNDARY IS FCST TO RETURN NWD FROM BAY OF
CAMPECHE...PERHAPS REACHING LOWER-MIDDLE TX COAST AROUND MIDDLE OF
DAY-2 PERIOD BEFORE BEING OVERTAKEN BY NEXT COLD FRONT. IN RESPONSE
TO APCH OF STG CANADIAN SHORTWAVE TROUGH ALOFT...CENTRAL PLAINS
CYCLOGENESIS IS FCST DAY-1...EVOLVING TO COMPACT/STG CYCLONE OVER
CHI REGION AROUND 21/12Z. THIS LOW THEN WILL OCCLUDE AND BECOME
BETTER COLLOCATED WITH MID-UPPER CYCLONE BY END OF PERIOD. TRAILING
SFC COLD FRONT SHOULD MOVE FROM 21/12Z POSITION OVER SRN IL...AR AND
W-CENTRAL TX...TO 22/12Z POSITION FROM COASTAL MID-ATLANTIC SWWD
ACROSS GA TO N-CENTRAL GULF.
...DEEP S TX TO LOWER MS VALLEY...
CONDITIONAL SVR POTENTIAL EXISTS OVER PORTIONS LOWEST RIO GRANDE
VALLEY OF DEEP S TX -- CLOSE TO COAST. FCST VERTICAL WIND PROFILES
VEER SUBSTANTIALLY WITH HEIGHT...LEADING TO CURVED LOW LEVEL
HODOGRAPHS AND POTENTIALLY 40-50 KT EFFECTIVE SHEAR MAGNITUDES.
MIDLEVEL LAPSE RATES -- ASSOCIATED WITH ELEVATED MIXED LAYER
PRODUCED ON NEARBY MEX PLATEAU -- SHOULD BE SUFFICIENTLY STEEP TO
SUPPORT MLCAPES IN 1000-2000 J/KG RANGE -- DEPENDING ON VARIABILITY
OF SFC DEW POINTS FROM LOWER-UPPER 60S F. WARMTH AT BASE OF THAT
EML...HOWEVER...WILL OFFER STG CAPPING AHEAD OF SFC COLD FRONT.
SMALLER SCALE BOUNDARIES...SUCH AS SEA BREEZE...MAY
DEVELOP...OTHERWISE LIFT APPEARS WEAK/DIFFUSE. ATTM...CAP STRENGTH
APPEARS STG...WITH CONVECTIVE INITIATION TOO DEPENDENT ON STRONG
MESOSCALE PROCESSES TO ASSIGN UNCONDITIONAL SVR PROBABILITIES.
UNCONDITIONAL TSTM PROBABILITIES ARE SOMEWHAT GREATER FARTHER NE --
BUT STILL MRGL FOR GEN THUNDER OUTLOOK -- AS LOW LEVEL COLD FRONT
MOVES ACROSS E TX...LA AND LOWER MS VALLEY REGION. ACCOMPANYING
CONVECTION SHOULD BE ROOTED ABOVE RELATIVELY STABLE BOUNDARY LAYER
-- N OF MARINE FRONT -- AND NOT SO STRONGLY HOWEVER...THIS ALSO
MEANS WEAKER VALUES OF BOTH LAPSE RATES AND INFLOW-LAYER
THETAE...WITH ELEVATED MUCAPE GENERALLY BELOW 400 J/KG. INHIBITED
BY CAPPING BECAUSE OF GREATER DISTANCE FROM EML. CONVECTION WILL BE
RELATIVELY SHALLOW...WITH FCST SOUNDINGS INDICATING THAT MUCH OF IT
WILL NOT REACH UPWARD INTO FAVORABLE ICING LAYERS FOR THUNDER.
..EDWARDS.. 02/20/2009
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