DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 081933
SWODY1
SPC AC 081931

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0131 PM CST FRI MAR 08 2013

VALID 082000Z - 091200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SRN HIGH PLAINS
REGION...

...DISCUSSION...
LITTLE CHANGE APPEARS NECESSARY TO THE ONGOING FORECAST...WITH
LATEST DATA SUGGESTING THAT CURRENT EXPECTATIONS REMAIN ON TRACK.
THE ONLY CHANGE INSERTED THIS FORECAST WILL BE INCLUSION OF A
MARGINAL /5% PROBABILITY/ FOR HAIL POSSIBLY APPROACHING SEVERE
LEVELS IN A STRONGER CELL OR TWO THIS AFTERNOON ACROSS SRN AZ JUST
AHEAD OF THE UPPER LOW APPROACHING SRN CA ATTM. FOR ADDITIONAL
SHORT-TERM INFORMATION ON THIS AREA...PLEASE REFER TO SWOMCD #0251.

..GOSS.. 03/08/2013

.PREV DISCUSSION... /ISSUED 1046 AM CST FRI MAR 08 2013/

CORRECTED FOR NDFD GRID GENERATION

...SYNOPSIS...
UPPER-AIR PATTERN ACROSS CONUS IS DOMINATED BY TWO PRIMARY CYCLONES
-- ONE OVER ATLC S OF NOVA SCOTIA WITH STG VORTICITY LOBE EXTENDING
WWD OVER MID-ATLC REGION...AND ANOTHER LOCATED OVER CHANNEL ISLANDS
AREA OFFSHORE SRN CA. AS MID-ATLC PERTURBATION MOVES
OFFSHORE...SYNOPTIC-SCALE RIDGING WILL SHIFT EWD ACROSS MS VALLEY TO
UPPER GREAT LAKES...LOWER OH VALLEY AND TN VALLEY REGIONS.
MEANWHILE...MAIN PAC LOW WILL TURN EWD ACROSS SRN CA...REACHING NEAR
AZ/NM BORDER BY END OF PERIOD. BROAD BELT OF CYCLONIC FLOW --
INCLUDING ROUGHLY 120-KT 250-MB JET MAX AND ELONGATED RIBBON OF
80-90 KT 500-MB WINDS -- WILL SHIFT EWD OVER PORTIONS SRN AZ AND NRN
MEX..IN STEP WITH PROGRESS OF CA CYCLONE. SMALLER MID-UPPER LEVEL
CIRCULATION IS EVIDENT IN MOISTURE CHANNEL IMAGERY OVER WRN ORE.
THIS FEATURE WILL WEAKEN...LOSING IDENTITY WITH TIME AS ITS
VORTICITY FIELD IS ENTRAINED INTO TRAILING PORTION OF CA
PERTURBATION. WEAK SHORTWAVE TROUGH IS EVIDENT IN SATELLITE IMAGERY
AND VWP/PROFILER DATA OVER SRN HIGH PLAINS ATTM...AND IS FCST TO
DEAMPLIFY AS IT EJECTS NEWD OVER MO/AR THIS EVENING.

AT SFC...15Z CHART SHOWED CYCLONE OVER SRN PORTION KS/CO BORDER
REGION...WITH SYNOPTIC WARM FRONT ENEWD ACROSS N-CENTRAL/NERN KS AND
WELL-DEFINED LEE TROUGH SSWWD OVER ERN NM. DRYLINE SHOULD BECOME
BETTER DEFINED TODAY FROM BIG-BEND REGION GENERALLY NNEWD ACROSS WRN
TX/OK PANHANDLES...RETREATING WWD SOMEWHAT OVERNIGHT. SECONDARY SFC
LOW...INITIALLY MORE CLOSELY RELATED TO MID-UPPER CYCLONE -- WAS
EVIDENT OVER SRN NV IN DRA-LAS AREA...WITH PAC COLD FRONT ARCHING
GENERALLY SWD OVER NRN BAJA. INTERMOUNTAIN LOW AND LEE LOW SHOULD
BEGIN TO MERGE OVER ERN CO AROUND END OF PERIOD. BY THAT TIME...PAC
COLD FRONT SHOULD CATCH UP TO RETREATED DRYLINE OVER PORTIONS TX
PANHANDLE/SOUTH-PLAINS AND PERMIAN BASIN REGIONS.

...CENTRAL/SRN HIGH PLAINS...
ISOLATED TSTMS ARE POSSIBLE BEFORE DARK NEAR DRYLINE...BUT
POTENTIALLY SUPERCELLULAR IN CHARACTER. SCATTERED TSTMS SHOULD FORM
AFTER DARK...INCREASING IN COVERAGE THROUGH MUCH OF OVERNIGHT HOURS
AS PAC COLD FRONT AND LARGE-SCALE ASCENT ALOFT CATCH UP TO DRYLINE.
GREATEST UNCONDITIONAL SVR THREAT IS OVER SRN HIGH PLAINS...BUT
ISOLATED SVR DEVELOPMENT IS POSSIBLE AS FAR N AS ERN CO/WRN KS INVOF
SFC LOW AND NEAR WARM FRONT.

AS LEADING/WEAK SHORTWAVE TROUGH EJECTS AWAY FROM REGION...
1. SUBTLE SHORTWAVE RIDGING WILL OCCUR...ACTING TO TEMPORARILY
REINFORCE ELEVATED MIXED LAYER THROUGH WEAK DAVA/DVM WHILE EWD
ADVECTION OF REMAINING EML CONTINUES.
2. ASSOCIATED CLOUD COVER WILL MOVE AWAY...LEAVING BROAD GAP OF
RELATIVELY CLEAR SKIES FOR REMAINDER DAYLIGHT HOURS PRIOR TO ARRIVAL
OF NEXT UVV PLUME...NOW EVIDENT IN VIS/IR IMAGERY OVER AZ.
3. DRYLINE WILL SHARPEN FROM COMBINATION OF MOIST ADVECTION FARTHER
E AND STRENGTHENING MIXING ALONG AND W OF BOUNDARY. W TX MESONET
DATA INDICATES LOW-50S F SFC DEW POINTS HAVE REACHED AREA BETWEEN
CDS-LBB. THOUGH MOISTENING VIA ADVECTION WILL BE OFFSET SOMEWHAT BY
HEATING/MIXING...EXPECT MID-UPPER 50S DEW POINTS IN NARROW CORRIDOR
E OF DRYLINE BY 00Z...FROM ERN PANHANDLES/WRN OK SWD.

MODIFIED RAOBS AND FCST SOUNDINGS SUGGEST 500-1000 J/KG MLCAPE
POSSIBLE E OF CAPROCK OVER SRN PLAINS...SOMEWHAT LESS OVER HIGHER
TERRAIN NEARER TO DRYLINE. BUOYANCY ALSO SHOULD WEAKEN NWD OVER WRN
KS WHERE MOISTURE WILL BE LESS. ROBUST MID-UPPER LIFT IS NOT FCST
TO REACH OUTLOOK AREA UNTIL OVERNIGHT -- LIKELY AFTER 03Z. AS
SUCH...EML-RELATED CAPPING SHOULD REMAIN STG...DELAYING ONSET OF
SUBSTANTIAL CONVECTION WHILE LIMITING BOTH ITS SWD EXTENT AND
DIURNAL COVERAGE. STILL...A FEW TSTMS MAY DEVELOP BEFORE DARK INVOF
DRYLINE...IN ENVIRONMENT CHARACTERIZED BY STRENGTHENING DEEP-LAYER
AND AT LEAST ADEQUATE LOW-LEVEL SHEAR FOR SUPERCELLS. EXPECT RISK
OF DAMAGING GUSTS AND HAIL WITH ANY SUCH TSTMS...SUPPORTED BY
INITIALLY HIGH LCL AND DEEP SUBCLOUD LAYER.

LOW-LEVEL MOISTURE...DEEP SHEAR AND LOW-LEVEL SHEAR EACH SHOULD
STRENGTHEN FROM LATE AFTN THROUGH EVENING AS MOIST ADVECTION
CONTINUES E OF DRYLINE...TROUGH ALOFT APCHS...AND BROAD/45-55 KT LLJ
TAKES SHAPE FROM W TX TO SERN NEB. RELATED HODOGRAPH ENLARGEMENT
SHOULD YIELD 250-450 J/KG EFFECTIVE SRH IN SUPPORT OF STORM-SCALE
ROTATION. DAMAGING GUSTS ARE POSSIBLE...THREAT DIMINISHING AFTER
ABOUT 06Z...WITH INCREASING HAIL RISK INTO EVENING. TORNADO
POTENTIAL...WHILE NON-ZERO...IS MITIGATED BY LACK OF ROBUST
MOISTURE...AND BY LIMITED TEMPORAL WINDOW BETWEEN EVENING LOWERING
OF LCL AND LOSS OF SFC-BASED EFFECTIVE INFLOW.

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