Thursday, April 17, 2008

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 170549
SWODY1
SPC AC 170546

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1246 AM CDT THU APR 17 2008

VALID 171200Z - 181200Z

..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS S-CENTRAL TX NNEWD
ACROSS PORTIONS CENTRAL/NERN OK....

..SYNOPSIS...
SYNOPTIC PATTERN ALOFT FEATURES BROAD CYCLONIC GYRE CENTERED
OFFSHORE CAROLINAS...POSITIVELY TILTED RIDGE FROM SERN CANADA TO
N-CENTRAL GULF OF MEXICO...AND TROUGHING FROM HUDSON BAY SWWD ACROSS
AZ TO NWRN MEX. STG SHORTWAVE PERTURBATION -- EVIDENT IN MOISTURE
CHANNEL IMAGERY OVER 4-CORNERS REGION -- IS MOVING THROUGH BASE OF
LARGER SCALE TROUGH...AND SHOULD EJECT ENEWD TO NEWD ACROSS
S-CENTRAL PLAINS AS CLOSED LOW THIS PERIOD. OPERATIONAL
SPECTRAL/WRF AGREE WITH EACH OTHER ON 500 MB LOW POSITION NEAR MHK
BY 18/12Z...BUT THIS IS ABOUT 200 NM NE OF CONSENSUS SREF POSITION
OVER NWRN ON NEAR KS BORDER....LATTER BEING PREFERRED FOR THIS FCST
BASED ON CURRENT SATELLITE TRENDS.

AT SFC...FRONTAL ZONE INITIALLY WAS ANALYZED FROM LS SWWD ACROSS SRN
IA...NWRN MO...S-CENTRAL/SWRN KS...AND N-CENTRAL-W-CENTRAL TX
PANHANDLE...INTO SFC LOW LOCATED ROUGHLY BETWEEN CAO-TCC. THIS LOW
IS EXPECTED TO EJECT EWD THEN NEWD ALONG SFC FRONT...MOVING FROM
NWRN OK AROUND 17/12Z TO SERN KS DURING EVENING. AS THIS
OCCURS...SFC COLD FRONT SHOULD MOVE SWD OVER SRN HIGH PLAINS.
WEAK/SECONDARY LOW MAY DEVELOP INVOF COLD FRONT/DRYLINE INTERSECTION
THIS AFTERNOON ACROSS NW TX...WITH DRYLINE EXTENDING SSWWD INTO SFC
LOW OVER NRN COAHUILA.

..CENTRAL/SRN PLAINS...
SCATTERED TSTMS ARE EXPECTED TO DEVELOP DURING AFTERNOON INVOF SFC
FRONTAL ZONE OVER OK...GENERALLY BECOMING MORE LINEAR AND
BACKBUILDING SWD WITH TIME THROUGH EVENING AS REGIME SHIFTS EWD
ACROSS OK AND N-CENTRAL TX. DEEP-LAYER SHEAR PROFILES WILL BE
FAVORABLE FOR SUPERCELLS....ALTHOUGH DISCRETE STORM MODES MAY NOT BE
MAINTAINED FOR VERY LONG GIVEN STRONGLY PARALLEL COMPONENT OF MEAN
FLOW ALOFT WITH RESPECT TO FRONTAL FORCING ZONE. ANY SUSTAINED
SUPERCELLS MAY PRODUCE LARGE HAIL AND SVR GUSTS...ALONG WITH SLGT
TORNADO THREAT. AS SOURCE REGION RETURN FLOW AIR MASS CONTINUES TO
MODIFY SLOWLY...MOISTURE WILL ADVECT NWD ACROSS CENTRAL/NRN TX AND
OK...TO BE MODULATED SOMEWHAT DURING AFTERNOON BY VERTICAL MIXING
PROCESSES. EXPECT SFC DEW POINTS MID-UPPER 50S ACROSS MOST OF SERN
KS AND ERN OK...LOW 60S S-CENTRAL/SERN OK AND MID 60S CENTRAL/SRN TX
BY 17/21Z. MLCAPES TO NEAR 1500 J/KG ARE POSSIBLE AS A RESULT.

INITIALLY SEPARATE AREA OF TSTMS....AND SVR POTENTIAL...MAY DEVELOP
LATE AFTERNOON INTO EARLY EVENING OVER HILL COUNTRY AND ERN EDWARDS
PLATEAU REGIONS OF TX. THIS AREA WILL BE CHARACTERIZED BY FAVORABLE
LOW LEVEL MOISTURE AND STRONGEST SFC HEATING WITHIN OUTLOOK
AREA...SUPPORTING MLCAPES 1500-2000 J/KG E OF DRYLINE. SOMEWHAT
DRIER AND MORE WELL MIXED BOUNDARY LAYER NEAR DRYLINE WILL SUPPORT
AROUND 1000 J/KG MLCAPE DURING MOST PROBABLE TIME OF INITIATION --
22-01Z. HOWEVER...MOIST ADVECTION AND LOSS OF MIXING SHOULD LOWER
LCL DURING EARLY EVENING...SUCH THAT EFFECTIVE INFLOW PARCELS STAY
SFC-BASED FOR ROUGHLY 3-4 HOUR TIME WINDOW UNTIL SFC LAYER
SUFFICIENTLY COOLS TO ELEVATE THEM.

..LOWER MO VALLEY REGION...
BY MID-LATE AFTERNOON...NARROW PLUME OF AT LEAST MRGLLY FAVORABLE
LOW LEVEL MOISTURE -- E.G. SFC DEW POINTS LOW-MID 50S F -- SHOULD
CHARACTERIZE PROSPECTIVE STORM INFLOW REGION S OF FRONTAL ZONE
FARTHER NE OVER LOWER MO VALLEY. NEGATIVE FACTORS WILL INCLUDE
POTENTIAL FOR DIABATIC HEATING TO BE LIMITED BY CLOUD COVER...ANVIL
MATERIAL STREAMING FROM ANY NEAR-FRONTAL CONVECTION OVER SRN/CENTRAL
PLAINS...AS WELL AS LACK OF SIGNIFICANT UPPER SUPPORT BENEATH
SHORTWAVE RIDGING.

.EDWARDS/SMITH/COOK.. 04/17/2008

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