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  Tuesday December 6, 2016

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SPC - No watches are valid as of Tue Dec 6 13:30:03 UTC 2016

No watches are valid as of Tue Dec  6 13:30:03 UTC 2016.


No Mesoscale Discussions are in effect as of Tue Dec 6 13:30:03 UTC 2016.

SPC Dec 6, 2016 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook
      
Day 1 Outlook Image
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0645 AM CST TUE DEC 06 2016

VALID 061300Z - 071200Z

...THERE IS A MRGL RISK OF SVR TSTMS OVER PARTS OF SOUTHERN GEORGIA
AND NORTHERN FLORIDA....

...SUMMARY...
ISOLATED SEVERE STORMS WITH DAMAGING WIND AND POSSIBLY A TORNADO ARE
POSSIBLE THE NEXT FEW HOURS ACROSS SOUTHERN GEORGIA AND NORTHERN
FLORIDA.

...SYNOPSIS...
IN MID/UPPER LEVELS...A LARGE-SCALE TROUGH WILL PERSIST OVER CENTRAL
NORTH AMERICA...WITH SEVERAL SHORTWAVES AND SMALL CYCLONES EMBEDDED
IN A BROAD FIELD OF CYCLONIC FLOW COVERING MOST OF THE CONTIGUOUS
U.S.  A STRONG SHORTWAVE TROUGH -- FORMERLY A CLOSED CYCLONE OVER
NORTHERN MEXICO AND NOW AN INCREASINGLY PROGRESSIVE OPEN-WAVE
PERTURBATION OVER MISSISSIPPI -- WILL ACCELERATE TO VIRGINIA AND
NORTH CAROLINA BY 00Z...THEN QUICKLY OFFSHORE.  IN THE PROCESS...THE
TROUGH WILL WEAKEN...ITS 500-MB VORTICITY FIELD CONTRACTING
NORTHWARD. 

AT THE SURFACE...11Z ANALYSIS SHOWED AN OCCLUDED LOW OVER
NORTHEASTERN MISSISSIPPI...NEARLY STACKED VERTICALLY WITH THE
MID/UPPER PERTURBATION.  THIS LOW WILL EJECT NORTHEASTWARD TOWARD
THE UPPER OHIO VALLEY TODAY AND WEAKEN...BEFORE BEING OVERTAKEN BY
THE NORTHERN LIMB OF AN ARCTIC COLD FRONT NOW PLUNGING SOUTHWARD AND
SOUTHEASTWARD ACROSS IOWA...MISSOURI AND THE SOUTHERN PLAINS.  A
SEPARATE COLD FRONT EXTENDED FROM A TRIPLE POINT OVER SOUTHERN
ALABAMA SOUTHWARD OVER THE WESTERN FLORIDA PANHANDLE THEN
SOUTHWESTWARD ACROSS THE WESTERN GULF.  THIS FRONT SHOULD MOVE TO
NORTHERN FLORIDA BY 00Z...THEN STALL NEAR LAKE OKEECHOBEE NEAR THE
END OF THE PERIOD AND THROUGH MUCH OF DAY 2.  MEANWHILE A WAVY...
WARM/STATIONARY FRONTAL ZONE EXTENDS EASTWARD FROM THE TRIPLE POINT
ACROSS SOUTHERN GEORGIA TO A WEAK LOW OVER THE ATLANTIC OFF
SAVANNAH.  PORTIONS OF THIS BOUNDARY HAVE MOVED LITTLE THE PAST
SEVERAL HOURS...WHILE OTHER SEGMENTS ARE DRIFTING NORTHWARD.  THE
GEORGIA SEGMENT OF THIS FRONT SHOULD UNDERGO SLOW NET NORTHWARD
MOTION THE NEXT COUPLE HOURS UNTIL BEING OVERTAKEN FROM WEST TO EAST
BY A CONVECTIVE BAND DISCUSSED BELOW. 

...SOUTHERN GEORGIA...NORTHERN FLORIDA...
THE GREATEST SEVERE POTENTIAL...SUCH THAT IT IS...APPEARS TO BE IN THE
NEXT 2-3 HOURS WHILE HODOGRAPHS REMAIN SOMEWHAT FAVORABLY ENLARGED
PER 12Z TLH RAOB AND SOME VWPS IN THE AREA.  THEREAFTER...AS THE
MID/UPPER-LEVEL PERTURBATION WEAKENS AND MOVES AWAY FROM THIS
REGION...ALONG WITH RELATED SURFACE ISALLOBARIC FORCING...
BOUNDARY-LAYER FLOW WILL VEER FURTHER.  THIS...IN TURN...SHOULD
GRADUALLY REDUCE BOTH CONVERGENCE AND SRH IN THE BOUNDARY LAYER...
LEADING TO PROGRESSIVELY LOWER CONVECTIVE COVERAGE AND STRENGTH.  IN
THE MEANTIME...HOWEVER...AN ISOLATED DAMAGING GUST OR BRIEF TORNADO
CANNOT BE RULED OUT...ESPECIALLY IN ONE OF TWO REGIMES:

1.  A WARM-SECTOR CONVERGENCE ZONE OVER NORTHERN FLORIDA...SOUTH OF
WHICH FLOW IS RELATIVELY BACKED FOR A SHORT TIME BEFORE
AFOREMENTIONED...SYNOPTICALLY FORCED VEERING OCCURS AND WEAKENS THE
KINEMATIC SUPPORT.  HOWEVER...DIABATIC SURFACE HEATING SHOULD BOOST
INFLOW-LAYER MLCAPE AND HELP TO MAINTAIN GENERAL THUNDER POTENTIAL
OVER MUCH OF PRE-COLD-FRONTAL FLORIDA THROUGH AFTERNOON. 

2.  NEAR THE SOUTHERN GEORGIA FRONTAL SEGMENT...WHERE A CORRIDOR OF
FAVORABLE REGION-WIDE DEEP SHEAR (E.G....EFFECTIVE-SHEAR MAGNITUDE
AROUND 50-60 KT) AND LOW-LEVEL SRH WILL BE JUXTAPOSED WITH RICH
LOW-LEVEL MOISTURE (SURFACE DEW POINTS LOW 70S F) AND THE NORTHERN
RIM OF A RELATED FIELD OF 500-1200 J/KG MLCAPE.  THE CURRENT
SOUTHWEST-NORTHEAST BAND OF CONVECTION OVER SOUTHERN GEORGIA AND THE
FLORIDA COASTAL BEND APPEARS TO REPRESENT THE WESTERN BOUND OF ANY
SUBSTANTIAL CONVECTIVE POTENTIAL...GIVEN THE LESS-UNSTABLE AIR MASS
FROM THERE WESTWARD TO THE COLD FRONT...AND THE EXPECTED KINEMATIC
TRENDS MENTIONED ABOVE.  THE TLH PROXIMITY SOUNDING LIKELY
REPRESENTED THE MOST UNSTABLE AVAILABLE THERMODYNAMIC PROFILE
OVERALL...BUT ALSO CONTAINED A WELL-DEFINED STABLE LAYER NEAR 700 MB
THAT MAY BE RESTRICTING UPDRAFT VIGOR.

..EDWARDS/LEITMAN.. 12/06/2016

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SPC Dec 6, 2016 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
      
Day 4-8 Outlook Image
DAY 4-8 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CST TUE DEC 06 2016

VALID 091200Z - 141200Z

...DISCUSSION...
THE LARGE-SCALE TROUGH MOVING INTO THE EASTERN U.S. ON THURSDAY
SHOULD MOVE OFF THE EASTERN SEABOARD ON FRIDAY...WHILE UPSTREAM FLOW
BECOMES ZONAL.  MEDIUM-RANGE MODELS ARE IN GENERAL AGREEMENT
SUGGESTING A BROAD...LOW-AMPLITUDE UPPER FLOW PATTERN WILL DEVELOP
ACROSS THE CONTIGUOUS U.S. THIS WEEKEND INTO EARLY NEXT WEEK /DAYS
5-8/.  ALTHOUGH SOME MOISTURE MAY RETURN POLEWARD INTO THE NORTHWEST
GULF COAST REGION ON DAY 6/SUNDAY...THE TRACK OF MID-LATITUDE
SHORTWAVE TROUGHS ARE EXPECTED TO REMAIN NORTH OF THIS REGION.  THE
LACK OF STRONGER FORCING FOR ASCENT AND RELATIVELY MARGINAL
INSTABILITY PRECLUDE THE INCLUSION OF A SEVERE-WEATHER RISK AREA. 
THE OTHER DAYS SHOULD HAVE OFFSHORE FLOW INTO THE GULF OF MEXICO
LIMITING THE DEVELOPMENT OF DEEP-MOIST CONVECTION INLAND.

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