DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 041925
SWODY1
SPC AC 041923

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0223 PM CDT WED SEP 04 2013

VALID 042000Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS INTERIOR NORTHWEST...

ONLY VERY MINOR ADJUSTMENTS HAVE BEEN MADE TO 1630Z OUTLOOK.
OTHERWISE...PREVIOUS OUTLOOK REMAINS.

STRONG HEATING ACROSS THE INTERIOR NW WILL SOON FORCE READINGS TO
CONVECTIVE TEMPERATURES. LATEST VIS IMAGERY SUPPORTS THIS WITH
EXPANDING BOUNDARY LAYER CU FIELD...ESPECIALLY OVER THE HIGHER
TERRAIN. ADDITIONALLY...A WEAK MID LEVEL DISTURBANCE IS LIFTING
NNEWD ACROSS NERN ORE. THIS FEATURE MAY ENHANCE THE PROSPECT FOR
ROBUST CONVECTION ACROSS THE SLGT RISK REGION THIS AFTERNOON.

..DARROW.. 09/04/2013

.PREV DISCUSSION... /ISSUED 1127 AM CDT WED SEP 04 2013/

...SYNOPSIS...
LITTLE OVERALL CHANGE TO THE UPPER FLOW PATTERN IS FORECAST THIS
PERIOD...AS AN EXPANSIVE UPPER RIDGE -- CENTERED OVER THE CENTRAL
HIGH PLAINS -- PERSISTS. MEANWHILE...TWO TROUGHS FLANKING THE RIDGE
WILL REMAIN STEADY-STATE FROM A LARGE-SCALE PERSPECTIVE...WITH ONLY
MINOR SHIFTS IN POSITION/INTENSITY EXPECTED THROUGH THE PERIOD.

MINOR EWD SHIFT IN THE UPPER LOW OFF THE PAC NW COAST WILL RESULT IN
SOME SHARPENING OF A SURFACE BAROCLINIC ZONE...WHICH SHOULD LOOSELY
FOCUS A ZONE OF CONVECTION THIS PERIOD. OTHER STORMS ARE EXPECTED
INVOF A WEAK SURFACE LOW FORECAST OVER THE CENTRAL HIGH PLAINS --
PARTICULARLY N AND NE OF THIS FEATURE WHERE UPSLOPE FLOW AND WARM
ADVECTION PROVIDE ENHANCED ASCENT.

...INTERIOR PAC NW...
WEAK LAPSE RATES THROUGH THIS AFTERNOON ACROSS THE REGION PER LATEST
MODEL RUNS SUGGEST THAT EVEN WITH DIURNAL HEATING...CAPE WILL REMAIN
LIMITED ACROSS THE AREA. WHILE SHOWERS AND ISOLATED/STRONGER STORMS
WILL LIKELY DEVELOP -- AIDED BY MODERATELY STRONG MID-LEVEL
SSWLYS...SEVERE THREAT IS PROGGED TO REMAIN ISOLATED.

SOMEWHAT GREATER POTENTIAL COULD EVOLVE OVERNIGHT...AS THE OFFSHORE
UPPER LOW DRIFTS EWD. RESULTING COOLING AT MID-LEVELS -- AND THUS
MODEST STEEPENING OF LAPSE RATES -- MAY SUPPORT CONTINUATION OF
STORMS THROUGH THE SECOND HALF OF THE PERIOD. WHILE WIND THREAT
SHOULD DIMINISH AS THE BOUNDARY LAYER STABILIZES...HAIL POTENTIAL
COULD INCREASE A BIT WITH THE INCREASE IN ELEVATED INSTABILITY.
THUS...WITH ISOLATED AFTERNOON WIND POTENTIAL AND THEN A POSSIBLE
UPTICK IN OVERNIGHT HAIL RISK...ENOUGH EVIDENCE APPEARS TO EXIST TO
RULE OUT DOWNGRADING FROM SLIGHT RISK TO SEE TEXT/5% SEVERE
PROBABILITY.

...NRN HIGH PLAINS VICINITY...
WEAK CONVECTION IS ONGOING ATTM ACROSS CENTRAL SD...INVOF A WEAK
SURFACE LOW AND ASSOCIATED WARM FRONT EXTENDING ENEWD. THIS ZONE --
AND A WEAK LOW-LEVEL UPSLOPE FLOW REGIME INTO THE BLACK HILLS AND
HIGHER ELEVATIONS OF ERN WY/SERN MT -- WILL LIKELY SUPPORT
CONTINUED/ISOLATED STORM DEVELOPMENT...PARTICULARLY LATER THIS
AFTERNOON AND EARLY EVENING THROUGH THE PEAK DIURNAL
HEATING/DESTABILIZATION CYCLE. THOUGH MID-LEVEL WLY FLOW SHOULD
REMAIN MODEST /AROUND 25 KT/ THROUGH THE PERIOD...LOW-LEVEL ELY
COMPONENT WILL RESULT IN SUFFICIENT VEERING/SHEAR FOR UPDRAFT
ORGANIZATION AND ASSOCIATED RISK FOR ISOLATED HAIL/WIND.

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