Wednesday, December 19, 2012

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 191631
SWODY1
SPC AC 191629

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1029 AM CST WED DEC 19 2012

VALID 191630Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE ARKLATEX AND LWR MS
VLY NNE INTO THE OZARKS/MID MS VLY...

...SYNOPSIS...
POTENT FOUR CORNERS SHORTWAVE TROUGH WILL CONTINUE E TO THE OK/TX
PANHANDLES THIS EVE AND INTO THE MO OZARKS BY 12Z THU. FURTHER
AMPLIFICATION APPEARS LIKELY AS THE SYSTEM PARTIALLY PHASES WITH NRN
STREAM JET STREAK NOW OVER ID/WY.

ASSOCIATED SFC LOW NOW EVOLVING OVER THE CO-NM BORDER SHOULD TRACK E
INTO NW OK LATER TODAY BEFORE TURNING NE TO NEAR ST LOUIS BY THE END
OF THE PERIOD. STRONG FRONTOGENESIS AHEAD OF THE LOW WILL YIELD A
WARM FRONT THAT BY 12Z THU SHOULD EXTEND WELL E/SE INTO THE MID
OH/TN VLYS. SOUTH OF THE LOW...A STRONG...FAST-MOVING COLD FRONT
ALSO WILL HAVE EVOLVED...EXTENDING BY THAT TIME THROUGH FAR SE
MO...WRN TN...WRN MS...AND CNTRL LA INTO THE WRN GULF OF MEXICO.

...OZARKS SWD INTO LWR MS VLY LATE TODAY THROUGH EARLY THU...
STRONG FORCING FOR ASCENT /PRIMARILY DCVA/ ON LEADING EDGE OF FOUR
CORNERS TROUGH LIKELY WILL SUPPORT DEVELOPMENT OF ISOLD TO SCTD
TSTMS NEAR STRENGTHENING COLD FRONT AND/OR ALONG WRN EDGE OF AXIS OF
RETURNING LOW-LVL MOISTURE FROM SW/S CNTRL MO SSW TO THE ARKLATEX.
THE BULK OF THIS ACTIVITY SHOULD FORM DURING MID TO LATE EVE GIVEN
AS UPR 50S F SFC DEWPOINTS REACH SW MO.

AREA HODOGRAPHS WILL APPRECIABLY LENGTHEN AS BAND OF 50-60 KT SSWLY
700 MB FLOW OVERSPREADS REGION AHEAD OF UPR TROUGH...FOSTERING
SUSTAINED STORMS/SUPERCELLS. DEEP WIND PROFILES WILL BE LARGELY
UNIDIRECTIONAL. SUFFICIENT LOW-LVL SHEAR WILL NEVERTHELESS EXIST
GIVEN EXPECTED HODOGRAPH LENGTHS FOR STORMS TO POSE A RISK FOR
TORNADOES IN ADDITION TO SMALL BOWING SEGMENTS WITH DMGG WIND.

THE STORMS SHOULD GRADUALLY EVOLVE INTO A LARGER-SCALE BROKEN
BAND/QLCS THAT CONTINUES E TO ROUGHLY A ST LOUIS-SW IL TO WRN
MS-CNTRL LA LINE BY 12Z THU. ALTHOUGH PLUME OF STEEP MID LVL LAPSE
RATES ACCOMPANYING THE UPR TROUGH WILL BE CONFINED TO AREAS FROM
CNTRL AR NWD...DESTABILIZATION FARTHER S WILL BE AUGMENTED BY
AVAILABILITY OF RICHER LOW-LVL MOISTURE AS SFC DEWPOINTS RISE INTO
THE MID 60S F...SUPPORTING A NARROW BELT OF 500-750 J/KG SBCAPE
AMIDST 250-400 M2/S2 SRH AND 50+ KT DEEP SHEAR. THE MAIN LIMITING
OFFSETTING A MORE INTENSE SVR WEATHER OUTBREAK AND HIGHER
PROBABILISTIC FCST IS RELATIVELY MODEST/NARROW NATURE OF BOUNDARY
LAYER MOISTURE RETURN WHERE FORCING FOR ASCENT AND SHEAR WILL BE
GREATEST...I.E. OVER THE NRN HALF OF THE OUTLOOKED AREA. SUFFICIENT
INSTABILITY WILL BE IN PLACE...HOWEVER...TO POSE A RISK FOR A STRONG
TORNADO GIVEN PRESENCE OF A LONGER-LIVED SUPERCELL AND

ORIENTATION OF UPR TROUGH SUGGESTS THAT THE STRONGEST DCVA WILL
REMAIN BEHIND THE SFC COLD FRONT...EXCEPT NEAR SFC LOW AND PERHAPS
OVER CNTRL/SRN MO. A NARROW OVERLAP OF STRONG LARGE-SCALE FORCING
FOR ASCENT/MID-LVL COOLING ON NW FRINGE OF MOIST AXIS MAY PROVE
SUFFICIENT TO YIELD ISOLD STRONG TO POSSIBLY SVR STORMS ALONG THE
STRENGTHENING COLD FRONT AS FAR N AS CNTRL MO. THESE WOULD OCCUR IN
A ZONE OF MOIST-NEUTRAL THERMODYNAMIC ENVIRONMENT...WHERE STRONG
FRONTAL UPLIFT MAY COMPENSATE FOR WEAK BUOYANCY TO YIELD A
CONDITIONAL RISK FOR DMGG WIND.

..CORFIDI/COHEN.. 12/19/2012

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