DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 080539
SWODY1
SPC AC 080537

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1137 PM CST SAT DEC 07 2013

VALID 081200Z - 091200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
MODELS SUGGEST THAT THE PREVAILING NORTHEASTERN PACIFIC BLOCKING
PATTERN MAY BEGIN TO WEAKEN DURING THE LATTER HALF OF THE FORECAST
PERIOD. THIS PROBABLY WILL BE ACCOMPANIED BY SLOW CHANGES TO THE
DOWNSTREAM PATTERN...BUT A MID-LEVEL SUBTROPICAL HIGH...CENTERED
NEAR/EAST OF THE BAHAMAS...IS EXPECTED TO REMAIN STRONG TODAY INTO
TONIGHT. GIVEN ITS PRESENCE...A SIGNIFICANT SHORT WAVE
IMPULSE...WITHIN BROADER SCALE UPPER TROUGHING OVER THE WESTERN
U.S...APPEARS LIKELY TO BE FORCED NORTHEASTWARD...AS A SPLITTING
UPSTREAM IMPULSE DIGS INTO PORTIONS OF THE NORTHERN PLAINS AND
INTERMOUNTAIN REGION. SIGNIFICANT DEFORMATION APPEARS LIKELY AS IT
PROGRESSES INTO AN INCREASINGLY CONFLUENT REGIME...WITH STRONGEST
ASSOCIATED 500 MB HEIGHT FALLS SHIFTING FROM THE CENTRAL PLAINS AT
12Z TODAY THROUGH THE GREAT LAKES REGION BY 12Z MONDAY.

IN RESPONSE TO THESE DEVELOPMENTS...AND WITH A COLD/STABLE BOUNDARY
LAYER ENTRENCHED ACROSS MUCH OF THE CENTRAL AND EASTERN U.S...A
MODEST SURFACE CYCLONE...FORECAST TO FORM NEAR OR TO THE EAST OF THE
CENTRAL ROCKIES EARLY TODAY...PROBABLY WILL WEAKEN WHILE MIGRATING
TOWARD THE GREAT LAKES REGION. IN ITS WAKE...MODELS INDICATE THAT
ANOTHER COLD SURFACE RIDGE WILL BUILD ACROSS THE PLAINS INTO THE
MISSISSIPPI VALLEY.

MEANWHILE...AS THE SHALLOW LEADING EDGE OF THE INITIAL STRONG COLD
INTRUSION STALLS IN THE VICINITY OF NORTHERN FLORIDA...A MODEST
SOUTHERLY RETURN FLOW OF MOISTURE IS EXPECTED TO PERSIST AROUND THE
NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE...OFF THE GULF OF
MEXICO...AND GENERALLY ABOVE/TO THE COOL SIDE OF THE FRONTAL ZONE.
THIS COULD CONTRIBUTE TO DESTABILIZATION SUPPORTIVE OF WEAK
THUNDERSTORM ACTIVITY ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY
INTO MID ATLANTIC TODAY AND TONIGHT...WHILE CONVECTIVE POTENTIAL
REMAINS NEGLIGIBLE ELSEWHERE ACROSS THE NATION.

...LWR MS VALLEY INTO THE TN VALLEY AND MID ATLANTIC COAST...
A BROAD PRECIPITATION SHIELD APPEARS LIKELY IN ASSOCIATION WITH THE
MOISTURE RETURN ABOVE THE COLD AIR BY EARLY TODAY. EMBEDDED
CONVECTION IS PROBABLE WITHIN ZONES OF STRONGER LOWER/MID
TROPOSPHERIC WARM ADVECTION...FROM PORTIONS OF THE LOWER MISSISSIPPI
VALLEY EAST NORTHEASTWARD INTO THE TENNESSEE VALLEY/SOUTHERN
APPALACHIANS AND SOUTHERN MID ATLANTIC COAST REGION. THE EXTENT TO
WHICH MID-LEVEL THERMODYNAMIC PROFILES MAY SUPPORT CHARGE SEPARATION
AND LIGHTNING REMAINS UNCLEAR BASED ON THE VARIOUS MODEL FORECAST
SOUNDINGS...BUT THUNDERSTORM PROBABILITIES APPEAR GENERALLY LOW AT
LEAST THROUGH MUCH OF THE DAY. SOME INCREASE IN THUNDERSTORM
PROBABILITIES...SUPPORTIVE OF A CATEGORICAL THUNDER AREA...DOES NOT
APPEAR OUT OF THE QUESTION AFTER 09/06Z...ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...PERHAPS AS MID-LEVEL
FLOW TRENDS MORE CYCLONIC WITH AT LEAST SUBTLE HEIGHT FALLS.

..KERR/BUNTING.. 12/08/2013

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