SWODY1
SPC AC 200433
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1133 PM CDT THU APR 19 2007
VALID 201200Z - 211200Z
..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL PLAINS...
..SYNOPSIS...
HIGHLY AMPLIFIED UPPER AIR PATTERN FCST TO CONTINUE ACROSS CONUS --
DOMINATED BY WRN MEAN TROUGH AND RIDGING FROM WRN GULF TO HUDSON
BAY. MID-UPPER LEVEL LOW INITIALLY OVER ERN MT IS FCST TO EJECT NWD
OVER SASK TOWARD NWRN MB. UPSTREAM LOW -- NOW EVIDENT IN MOISTURE
CHANNEL IMAGERY JUST OFFSHORE NRN CA -- IS FCST TO DIG SEWD OVER SRN
CA/NRN BAJA REGION...THEN PIVOT EWD ACROSS NRN GULF OF CA AND LOWER
CO RIVER VALLEY BY 21/12Z.
AT SFC...DIFFUSE WARM FRONT -- ANALYZED ATTM OVER PORTIONS SRN
MO...ERN KS AND CENTRAL NEB -- IS FCST TO LIFT NWD ACROSS NRN NEB
AND SWRN SD...AND LINK WITH DEVELOPING LEE CYCLONE OVER ERN WY BY
21/00Z. PACIFIC FRONT ASSOCIATED WITH EJECTING MT TROUGH -- AND NOW
ANALYZED FROM CENTRAL NEB TO SWRN KS -- ALSO MARKS WRN EDGE OF
PARTIALLY MODIFIED RETURN FLOW AIR MASS AND ASSOCIATED 50S F SFC DEW
POINTS. THIS BOUNDARY WILL BECOME DIFFUSE AND BACK WWD TOWARD LEE
TROUGH...WITH RESULTING COMBINATION FORMING DRYLINE BETWEEN WRN NEB
AND NRN TX PANHANDLE. DRYLINE ALSO WILL EXTEND SWD ACROSS W TX TO
NRN COAHUILA BY MID/LATE AFTERNOON. NE-SW ALIGNED ZONE OF LOW LEVEL
FRONTOGENESIS ALSO WILL OCCUR FROM SFC LOW OVER ERN ND...ESPECIALLY
AFTER DARK.
SUBTROPICAL/SRN STREAM PERTURBATION IS EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER SRN CHIHUAHUA/DURANGO REGION. DESPITE MISSING UPPER
AIR DATA INPUT FOR NGM/NAM OVER MEX...THIS FEATURE APPEARS TO BE
RESOLVED AND IS REASONABLY PROGGED TO MOVE NEWD ACROSS SWRN/CENTRAL
TX DURING THIS PERIOD. HOWEVER...ANTICYCLONIC FLOW/PRESSURE PATTERN
AT SFC AND ASSOCIATED LACK OF LOW LEVEL FORCING IN PATH OF MID-UPPER
TROUGH SHOULD PRECLUDE SIGNIFICANT CONVECTIVE POTENTIAL.
..CENTRAL/NRN PLAINS...AFTERNOON-EVENING...
ISOLATED TO WIDELY SCATTERED TSTMS ARE POSSIBLE BY LATE AFTERNOON
INVOF DRYLINE FROM WARM FRONTAL INTERSECTION SWD ACROSS WRN KS.
CAPPING BENEATH ROBUST ELEVATED MIXED LAYER SHOULD LIMIT OVERALL
COVERAGE/NUMBER OF TSTMS BY DAY. HOWEVER...ANY ACTIVITY THAT
DEVELOPS IN WARM SECTOR OR ALONG DRYLINE WILL BE IN FAVORABLE
KINEMATIC ENVIRONMENT TO ROTATE -- LARGE/DAMAGING HAIL BEING MAIN
THREAT...AND SVR GUSTS ALSO POSSIBLE. NON-NEGLIGIBLE TORNADO
POTENTIAL EXISTS FOR ANY SFC-BASED TSTMS THAT MAY INTERACT WITH WARM
FRONTAL ZONE OVER WRN/CENTRAL NEB BEFORE DIABATIC SFC COOLING
BECOMES TOO STG TO SUPPORT SFC-BASED EFFECTIVE INFLOW LAYER. SELY
SFC WINDS WILL CONTRIBUTE TO FAVORABLY VEERING WIND PROFILES WITH
HEIGHT AND ENLARGED LOW LEVEL HODOGRAPHS...WITH 0-3 KM SRH ROUGHLY
150-200 J/KG OVER WARM SECTOR PORTION OF CATEGORICAL SLGT RISK
AREA...AND 200-300 J/KG INVOF SFC WARM FRONT.
THERMODYNAMICALLY...MAIN QUESTIONS WILL CONCERN CAPPING AND BOUNDARY
LAYER MOISTURE. FAVORABLE MIDLEVEL LAPSE RATES OF 8-9 DEG C/KM --
OVER 50S F DEW POINTS -- WILL SUPPORT MLCAPES IN 1000-1500 J/KG
RANGE AND LOCALLY HIGHER DURING LATE AFTERNOON SFC THERMAL MAX.
WITH SWD EXTENT ALONG/AHEAD OF DRYLINE...EXPECT GEN INCREASE IN
SBCINH...AS WELL AS GRADUAL WEAKENING OF MIDLEVEL FLOW AND
ASSOCIATED DEEP-LAYER SHEAR. SVR POTENTIAL OVER SWRN KS SWD INTO
NRN TX PANHANDLE THEREFORE BECOMES MUCH MORE CONDITIONAL.
..CENTRAL/NRN PLAINS...AFTER 21/00Z...
CONVECTIVE COVERAGE IS FCST TO INCREASE NEAR AND N OF SFC WARM FRONT
FROM LATE EVENING INTO OVERNIGHT HOURS...SUPPORTED BY MOIST
ADVECTION AND ISENTROPIC ASCENT INVOF 40-50 KT LLJ. WITH EFFECTIVE
SHEAR REMAINING FAVORABLE AS ACTIVITY BUILDS NWD...LARGE HAIL
POTENTIAL LIKEWISE WILL SHIFT NWD OVER NRN NEB AND SD AFTER DARK.
THIS ALSO MAY INCLUDE ADDITIONAL/ELEVATED CONVECTIVE POTENTIAL LATE
IN PERIOD...IN ZONE OF ND FRONTOGENESIS.
.EDWARDS/GRAMS.. 04/20/2007
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