Severe Weather Risk 12-9-2012 (TN, MS, AR, LA)

[Jim Martin]

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1200 AM CST SAT DEC 08 2012

VALID 091200Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE SUN AFTN AND SUN EVE

ACROSS PARTS OF CNTRL/SRN AND ERN AR...NE TX...NRN LA...NW MS AND

WRN TN...

..SYNOPSIS

WITHIN LARGE-SCALE UPPER TROUGHING ENCOMPASSING MUCH OF INTERIOR

NORTH AMERICA...IT STILL APPEARS THAT SOME PHASING OF EMBEDDED SHORT

WAVE IMPULSES WILL LEAD TO SHARPENING ALONG A POSITIVELY TILTED AXIS

EXTENDING FROM NORTHWESTERN ONTARIO THROUGH THE TEXAS BIG BEND

REGION BY 12Z MONDAY. SIZABLE SPREAD PERSISTS AMONG THE MODELS AND

MODEL ENSEMBLES CONCERNING THE DETAILS OF THE SHORT WAVE

DEVELOPMENTS...BUT IT APPEARS THAT THE LEAD IMPULSE SHIFTING EAST OF

THE NORTHERN PLAINS EARLY IN THE PERIOD MAY REMAIN MOST PROMINENT AS

IT CONTINUES EAST NORTHEASTWARD ACROSS THE UPPER MIDWEST AND GREAT

LAKES REGION. THIS FEATURE IS EXPECTED TO SUPPORT PRIMARY SURFACE

CYCLOGENESIS...MAINLY EAST OF THE MIDDLE MISSISSIPPI VALLEY INTO

SOUTHERN ONTARIO LATE IN THE PERIOD.

A SIGNIFICANT COLD INTRUSION PROBABLY WILL SURGE MORE RAPIDLY

SOUTHWARD THROUGH THE SOUTHERN PLAINS THAN EASTWARD INTO THE LOWER

MISSISSIPPI VALLEY...AS A SOUTHERLY RETURN FLOW OFF THE WESTERN GULF

OF MEXICO CONTRIBUTES TO PRE-FRONTAL MOISTENING. A NARROW CORRIDOR

OF PRECIPITABLE WATER IN EXCESS OF 1 INCH MAY REACH THE UPPER OHIO

VALLEY/LOWER GREAT LAKES REGION BY LATE SUNDAY NIGHT...WITH VALUES

OF 1.25 TO 1.5 INCHES ACROSS THE WESTERN GULF COAST INTO THE LOWER

MISSISSIPPI VALLEY. COUPLED WITH INCREASING FORCING FOR UPWARD

VERTICAL MOTION...DESTABILIZATION PROBABLY WILL BE SUFFICIENT TO

SUPPORT CONSIDERABLE THUNDERSTORM ACTIVITY FROM PORTIONS OF THE

SOUTHERN PLAINS INTO THE LOWER OHIO AND TENNESSEE VALLEYS...AND

PERHAPS PARTS OF THE LOWER GREAT LAKES REGION.

..CNTRL/SRN AND ERN AR...NE TX...NRN LA...NWRN MS...WRN TN

ALTHOUGH SOUTH/SOUTHWESTERLY LOW-LEVEL JET STRENGTHENING LIKELY WILL

BE STRONGEST TO THE NORTHEAST OF THE REGION LATE IN THE

PERIOD...MODEST STRENGTHENING OF 850 MB FLOW TO 30-40 KT STILL

APPEARS POSSIBLE ACROSS PARTS OF THE ARKLATEX REGION INTO UPPER

PORTIONS OF THE LOWER MISSISSIPPI VALLEY SUNDAY EVENING. THIS IS

EXPECTED TO OCCUR AS A SHORT WAVE IMPULSE /LIKELY DIGGING UPSTREAM

THROUGH MUCH OF THE DAY SUNDAY/ FINALLY BEGINS TO ACCELERATE EAST OF

THE SOUTHERN ROCKIES. THIS MAY ALSO CONTRIBUTE TO AN INCREASINGLY

DIVERGENT UPPER FLOW FIELD ACROSS SOUTHERN/EASTERN ARKANSAS AND

ADJACENT STATES...WHERE VERTICAL SHEAR AND FORCING FOR UPWARD

VERTICAL MOTION MAY SUPPORT SQUALL LINE EVOLUTION. A WINDOW OF

OPPORTUNITY APPEARS TO EXIST FOR POTENTIALLY DAMAGING WIND

GUSTS...AS WELL AS LARGE HAIL...BEFORE ACTIVITY SPREADS INTO A LESS

STABLE ENVIRONMENT TO THE EAST AND WEAKENS OVERNIGHT.

PEAK BOUNDARY LAYER DESTABILIZATION IS EXPECTED DURING THE LATE

AFTERNOON AND EARLY EVENING HOURS ALONG A PRE-FRONTAL CORRIDOR

ACROSS THE ARKLATEX INTO CENTRAL ARKANSAS. BEFORE STRONGER FORCING

DEVELOPS...SCATTERED DISCRETE STORM DEVELOPMENT IS POSSIBLE IN THE

PRESENCE OF 500-1000 J/KG OF MIXED LAYER CAPE. FORECAST SOUNDINGS

ARE SUGGESTIVE OF STRONG...BUT MOSTLY UNIDIRECTIONAL VERTICAL SHEAR.

HOWEVER...LOW-LEVEL HODOGRAPHS MAY BECOME SUFFICIENTLY LARGE TO

SUPPORT AT LEAST SOME TORNADIC POTENTIAL.

[Disc]

HOWEVER...LOW-LEVEL HODOGRAPHS MAY BECOME SUFFICIENTLY LARGE TO

SUPPORT AT LEAST SOME TORNADIC POTENTIAL.

Yeah, hodos look kinda "meh" right now. (Monticello, AR)

[Jim Martin]

Here are a few more soundings for tomorrow evening across central and eastern Arkansas...

Little Rock...

Pine Bluff...

Stuggart...