DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 231629
SWODY1
SPC AC 231627

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CDT THU AUG 23 2012

VALID 231630Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF NWRN KS AND
SWRN NEB...

...SYNOPSIS...

A SPLIT FLOW REGIME WILL BE MAINTAINED THROUGH THE D1
PERIOD...FEATURING A PROGRESSIVE WAVE TRAIN ACROSS SRN CANADA AND
THE NRN TIER OF STATES...AND SUB-TROPICAL BRANCH DISTURBANCES FROM
THE SWRN DESERTS TO SERN ATLANTIC COAST. MORE SPECIFICALLY...A
SHORTWAVE TROUGH FROM THE UPPER MS VALLEY TO ERN SASKATCHEWAN/WRN
MANITOBA WILL TRANSLATE EWD INTO THE UPPER GREAT LAKES AND WRN
ONTARIO. THIS SYSTEM WILL PRECEDE A MORE INTENSE SHORTWAVE TROUGH
AMPLIFYING OVER BRITISH COLUMBIA/ALBERTA INTO THE PACIFIC NW AND NRN
INTERMOUNTAIN REGION. FARTHER S...A VORTICITY MAXIMUM OVER THE
LOWER CO VALLEY WILL MOVE SLOWLY EWD THROUGH THE FOUR CORNERS
REGION.

IN THE LOW LEVELS...A WEAK COLD FRONT FROM NWRN MN TO A SURFACE LOW
OVER ERN SD WILL CONTINUE TO UNDERGO FRONTOLYSIS AS IT PROGRESSES
SLOWLY EWD INTO THE UPPER MS VALLEY. FARTHER S...A LEE TROUGH WILL
PERSIST OVER THE CNTRL/SRN HIGH PLAINS...ANCHORED BY A LEE LOW ALONG
THE CO/KS BORDER.

...CNTRL HIGH PLAINS THIS AFTERNOON INTO TONIGHT...

12Z REGIONAL SOUNDINGS OBSERVED THE OVERLAP OF A MOIST BOUNDARY
LAYER /LOWEST 100-MB MEAN-MIXING RATIOS OF 13-14 G PER KG/ BENEATH
STEEP MIDLEVEL LAPSE RATES WHICH WILL CONTRIBUTE TO MODERATE
INSTABILITY /MLCAPE OF 1000-2000 J PER KG/ E OF LEE TROUGH AND S OF
DENSER MID AND HIGH-CLOUDS OVER WRN/CNTRL NEB. THOUGH LARGE-SCALE
FORCING WILL REMAIN RATHER WEAK THROUGH THE PEAK OF THE DIURNAL
HEATING CYCLE...LATEST MESOSCALE AND CONVECTION-ALLOWING MODEL
GUIDANCE ARE IN GOOD AGREEMENT IN SUGGESTING THAT THE LEE TROUGH
WILL FOCUS SURFACE-BASED STORM DEVELOPMENT OVER NWRN KS BY MID
AFTERNOON.

MODEST /25-30 KT/ DEEP-LAYER SHEAR WILL COINCIDE WITH THE MODERATE
INSTABILITY TO SUPPORT MULTICELL STORM MODES CAPABLE OF DAMAGING
WINDS AND SOME HAIL. BY LATE EVENING...THE INTERACTION OF ONGOING
STORMS AND THEIR ASSOCIATED COLD POOLS WITH A DEVELOPING NOCTURNAL
LOW-LEVEL WIND MAXIMUM SUGGESTS THE POTENTIAL FOR UPSCALE GROWTH
INTO AN MCS WITH A RISK OF ISOLATED DAMAGING WINDS PERSISTING INTO
TONIGHT.

..UPPER MS VALLEY THIS AFTERNOON AND EVENING...

STRONGER FORCING FOR ASCENT ASSOCIATED WITH SRN SEGMENT OF SHORTWAVE
TROUGH APPEARS TO BE PROGRESSING WELL TO THE E OF SURFACE FRONT THIS
MORNING...CASTING SOME UNCERTAINTY ON AREAL COVERAGE OF TSTMS
ALONG/AHEAD OF THE BOUNDARY LATER TODAY. IT DOES APPEAR THAT
DAYTIME HEATING WILL AUGMENT MODEST BOUNDARY LAYER MOISTURE AND
MIDLEVEL LAPSE RATES OF 7.0-7.5 C/KM TO FOSTER AFTERNOON MLCAPE
VALUES OF 1000-2000 J/KG.

BASED ON LATEST MODEL GUIDANCE...IT APPEARS THAT ONGOING STORMS ESE
OF VVV MAY INCREASE IN COVERAGE AND INTENSITY THIS AFTERNOON AS
AMBIENT AIR MASS DESTABILIZES...AND AREA IS GLANCED BY
SASKATCHEWAN/MANITOBA PORTION OF SHORTWAVE TROUGH. PROFILER AND VAD
DATA FROM WOODLAKE MN AND SIOUX FALLS SD...RESPECTIVELY HAVE SHOWN A
GENERAL WEAKENING TREND OF THE LOW TO MID-TROPOSPHERIC WIND FIELD
OWING TO THE EWD PASSAGE OF LEAD MIDLEVEL IMPULSE AND GRADUAL
CESSATION OF NOCTURNAL LOW-LEVEL WIND MAXIMUM. AS SUCH...VERTICAL
SHEAR IS EXPECTED TO REMAIN MARGINALLY SUPPORTIVE OF ORGANIZED STORM
MODES WITH A RISK FOR LOCALLY DAMAGING WINDS AND PERHAPS SOME HAIL
INTO THIS EVENING.

..MEAD/SMITH.. 08/23/2012

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