DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 111301
SWODY1
SPC AC 111259

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 AM CDT THU OCT 11 2012

VALID 111300Z - 121200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF SRN KS INTO
CENTRAL OK EWD THROUGH SRN MO/NRN AR TO EXTREME WRN KY/TN...

...SYNOPSIS...
TRENDS IN EARLY MORNING SATELLITE IMAGERY SHOWED A GENERAL SEWD
MOVEMENT OF THE WELL-DEFINED CLOSED MID-UPPER LEVEL LOW LOCATED OFF
THE SRN CA COAST /100 MILES SW SBA/ AT 12Z. 06Z NAM/GFS AND 00Z
ECMWF ARE CONSISTENT WITH THE EARLIER FORECAST INDICATING THIS
FEATURE PROGRESSES ESEWD REACHING THE SRN CA COAST AT 12/00Z...AND
THEN TRACKS ENEWD TOWARD SRN NV/LOWER CO RIVER VALLEY THIS EVENING
THROUGH EARLY FRIDAY MORNING. MEANWHILE...A DOWNSTREAM UPPER RIDGE
CENTERED OVER SW TX TO CO THIS MORNING WILL SHIFT E TOWARD THE SRN
AND CENTRAL PLAINS THIS FORECAST PERIOD.

IN THE LOW LEVELS...SLY WINDS OVER TX VEERING TO WSWLY OVER OK/AR
HAVE SPREAD MOISTURE NWD PRIOR TO THE START OF DAY 1. THE 11Z
SURFACE ANALYSIS SHOWED A WARM FRONT HAD REACHED N TX NEAR THE RED
RIVER VALLEY TO THE ARKLATEX REGION AND NERN LA. THIS BOUNDARY WILL
CONTINUE TO ADVANCE NWD TODAY...THOUGH THE SPC SSEO AND 06Z NAM
SUGGEST THIS BOUNDARY DOES NOT REACH NERN OK/SERN KS BY 12/00Z AS
PREVIOUSLY FORECAST. THESE LATER MODELS INDICATE THE WARM FRONT
WILL PROGRESS NWD AND TEND TO STALL W-E FROM THE TX PANHANDLE ALONG
THE I-40 CORRIDOR THROUGH OK INTO CENTRAL AR BY LATE AFTERNOON/EARLY
EVENING. MEANWHILE...A COLD FRONT WILL ADVANCE SSEWD THROUGH THE
CENTRAL PLAINS AND MIDWEST. BY 12Z FRIDAY...THIS FRONT SHOULD
EXTEND FROM THE OH VALLEY WSWWD TO INVOF THE MO/AR BORDER TO ALONG
THE KS/OK BORDER.

...SRN KS INTO CENTRAL OK AND EWD TO EXTREME WRN PORTIONS KY/TN...
LATEST MODELS REMAIN CONSISTENT INDICATING SCATTERED TSTMS ARE
FORECAST TO DEVELOP DURING 12/03Z-12/12Z TIME FRAME IN A W-E ALIGNED
CORRIDOR PARALLEL TO AND NEAR SURFACE WARM FRONT. GIVEN THE
AFOREMENTIONED FORECAST OF THIS BOUNDARY BEING A LITTLE SWD INTO
CENTRAL OK...THE SLIGHT RISK/15 PERCENT SEVERE HAIL PROBABILITY HAVE
BEEN EXPANDED SWD. THIS ACTIVITY WILL BE SUPPORTED BY SWATH OF 30-40
KT 850-MB SWLYS AND WARM FRONTAL FORCING...ALONG WITH RELATED
MOISTURE TRANSPORT AND ISENTROPIC ASCENT TO LFC. THIS REGION ALSO
WILL EXPERIENCE LARGE-SCALE ASCENT BENEATH RIGHT-ENTRANCE REGION OF
ROUGHLY 100-KT 250-MB JET MAX SHIFTING ESEWD ACROSS NRN MO/IL/
INDIANA. FAVORABLY STEEP MIDLEVEL LAPSE RATES ATOP INCREASING THETAE
WILL YIELD MUCAPE VALUES 1000-2000 J/KG ACROSS THE SLIGHT RISK
AREA...AMIDST 35-45 KT EFFECTIVE SHEAR MAGNITUDES. INITIAL
DEVELOPMENT MAY OCCUR LATE EVENING OVER OZARKS REGION AND MOVE
EWD...WITH DISCRETE/ BACKBUILDING EVOLUTION FARTHER W ACROSS SRN KS
INTO NRN/CENTRAL OK REGION OVERNIGHT AS A SSWLY LLJ STRENGTHENS FROM
W TX INTO WRN/CENTRAL OK. ADDITIONAL ACTIVITY MAY MOVE INTO THIS
REGION FROM DIURNAL/DRYLINE CONVECTIVE REGIME...THOUGH THAT
POTENTIAL REMAINS MORE CONDITIONAL.

...SRN HIGH PLAINS...
DIABATIC HEATING...STEEP LOW-LEVEL LAPSE RATES...DRYLINE LIFT...AND
INCREASING BOUNDARY-LAYER MOISTURE SHOULD LEAD TO WEAKENING CINH AND
INCREASING TSTM POTENTIAL THROUGH AFTERNOON. ACTIVITY ALSO MAY
DEVELOP OVER MOUNTAINS OF SRN NM AND MOVE NEWD INTO REGIME OF
INCREASING LOW-LEVEL MOISTURE WITH EWD EXTENT AND WITH TIME.
LOW-LEVEL FLOW WILL BE RELATIVELY WEAK BENEATH RIDGING ALOFT WHICH
SHOULD RESULT IN WEAKER CONVERGENCE ALONG THE DRY LINE/LEE
TROUGH...AND THUS TEND TO LIMIT THE OVERALL CONVECTIVE COVERAGE.
BUOYANCY MAY BE LIMITED SOMEWHAT BY EFFECTS OF CLOUD COVER
ALOFT...BOTH IN TERMS OF MID-UPPER LEVEL LAPSE RATES AND SOMEWHAT
MUTED PACE OF SURFACE HEATING. WITH THE STORMS THAT DO FORM...30-40
KT EFFECTIVE SHEAR MAGNITUDES WILL SUPPORT SOME STORM
ORGANIZATION...WITH MULTICELLULAR MODES BEING DOMINANT AND TRANSIENT
SUPERCELL EVOLUTION POSSIBLE. LOW SEVERE PROBABILITIES CONTINUE TO
BE WARRANTED FOR THIS REGION...GIVEN THE UNCERTAINTY IN THE TSTM
COVERAGE.

...PORTIONS AZ/SERN NV/SRN UT...
ONGOING STORMS OVER SERN CA/SRN NV MAY DEVELOP EWD THIS MORNING AS
LARGE SCALE ASCENT SPREADS SLOWLY EWD AHEAD OF THE UPSTREAM CLOSED
LOW. WIDELY SCATTERED TO SCATTERED TSTMS SHOULD ALSO DEVELOP OVER
PORTIONS NRN AZ...SRN UT AND SRN NV...AND PERHAPS OVER PARTS OF
E-CENTRAL/SERN AZ...DURING AFTERNOON. ACTIVITY MAY PERSIST INTO
EVENING. ISOLATED LARGE HAIL AND STRONG-SVR GUSTS MAY OCCUR FROM
MOST INTENSE CELLS. STRENGTHENING DEEP-LAYER ASCENT IS FORECAST
ACROSS MUCH OF THIS CORRIDOR...IN TERMS OF BOTH LOW-LEVEL FORCING
NEAR EWD-MOVING PACIFIC FRONT AND LARGE-SCALE LIFT/COOLING ALOFT
AHEAD OF INCREASINGLY PROGRESSIVE CYCLONE. MOIST ADVECTION AND
SURFACE DIURNAL HEATING WILL CONTRIBUTE TO AFTERNOON BUOYANCY.
WELL-MIXED SUBCLOUD LAYERS WILL SUPPORT GUSTY TSTM WINDS...BENEATH
SUFFICIENTLY STRONG FLOW ALOFT FOR 35-40 KT EFFECTIVE SHEAR
MAGNITUDES.

...SRN CA COAST...
ONGOING TSTMS...MAINLY ALONG AND JUST OFF THE SRN CA COAST...ARE
BEING SUPPORTED BY LOW LEVEL CONVERGENCE INVOF AN AREA OF LOW
PRESSURE LOCATED OFF THE SRN CA COAST AND SWD EXTENDING WIND SHIFT.
DEEP LAYER FORCING FOR ASCENT IMMEDIATELY AHEAD OF THE CLOSED LOW
CENTERED TO THE WNW OF THE SURFACE LOW WILL SPREAD EWD SUPPORTING
ADDITIONAL SUSTAINED UPDRAFTS. COLD MIDLEVEL TEMPERATURES AND
RELATIVELY WARM SEA SURFACE TEMPERATURES WILL CONTINUE TO BOOST
INSTABILITY WITH MUCAPE UP TO 500 J/KG POSSIBLE POTENTIALLY
EXTENDING INLAND ALONG THE COAST. DESPITE WEAK BULK SHEAR...
SUSTAINED CONVECTION MAY PRODUCE ISOLATED SVR HAIL APPROACHING 1
INCH IN DIAMETER...WHILE AMBIENT SURFACE VORTICITY COULD RESULT IN A
BRIEF WATERSPOUT MOVING INLAND AS A TORNADO.

..PETERS/JIRAK.. 10/11/2012

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