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Wednesday, April 27, 2011

Severe Weather Expected Across Carolinas Today And Tonight

**5.50am** I just noticed this statement from the National Weather Service, issued at 5am this morning:

THUNDERSTORMS WILL GRADUALLY INCREASE IN COVERAGE ACROSS THE
WESTERN CAROLINAS AND NORTHEAST GEORGIA TODAY...ESPECIALLY THIS
AFTERNOON AND EVENING. AS THE ATMOSPHERE BECOMES MORE UNSTABLE
THROUGH THE DAY...THE THUNDERSTORMS WILL GAIN THE POTENTIAL TO
PRODUCE LARGE HAIL...DAMAGING WIND GUSTS...AND LOCALLY VERY HEAVY
RAINFALL.


A MORE SOLID LINE OF THUNDERSTORMS WILL DEVELOP FROM CENTRAL
TENNESSEE THROUGH THE DEEP SOUTH TODAY AND MOVE EASTWARD ACROSS
THE FORECAST AREA LATE THIS EVENING THROUGH THE OVERNIGHT HOURS.
IT IS LIKELY THAT SEVERE...DAMAGING WINDS WILL ACCOMPANY THIS
LINE AS IT MOVES INTO THE REGION. SOME OF THE THUNDERSTORMS ALONG
THE LINE COULD PRODUCE LARGE HAIL AS WELL...AND ISOLATED TORNADOES
WILL BE POSSIBLE.


KEEP ABREAST OF THE LATEST WEATHER CONDITIONS THROUGHOUT TODAY AND
TONIGHT. SEVERE THUNDERSTORM OR TORNADO WATCHES ARE VERY LIKELY
FOR PART OR ALL OF THE AREA LATE TODAY THROUGH TONIGHT. MAKE PLANS
NOW FOR WHERE YOU WILL TAKE SHELTER WHEN THE THUNDERSTORMS ARRIVE.
KEEP AN ALERTING NOAA WEATHER RADIO NEARBY IN CASE WARNINGS ARE
ISSUED WHILE YOU ARE SLEEPING TONIGHT.



The Carolinas will be at extreme high for severe weather today and tonight as the weather system that has spawned numerous tornadoes, severe thunderstorms, 5" hailstones and heavy flooding is expected to traverse our area by tomorrow morning. It is possible that we could see supercells move into our area from Alabama, Georgia and Tennessee ahead of the front this afternoon until the early morning hours tomorrow.  My main concern is that we could see multiple Derecho events that would knock over trees and power lines, and have some large hail. I will refer you back to the post I wrote Saturday morning for links that will help you prepare for these storms.

For up to date information on the progress of this storm system, please visit the GSP weather forecast office of the National Weather Service. If you have a weather radio, please keep it with you today and tonight, especially if it one of those types that can receive weather alerts from the National Weather Service.

I will add additional posts today and tonight about this potentially dangerous storm system as conditions warrant.

Here is the 1am CDT forecast discussion regarding this storm from the Storm Prediction Center:



 SPC AC 270610
   
   DAY 1 CONVECTIVE OUTLOOK CORR 1
   NWS STORM PREDICTION CENTER NORMAN OK
   0110 AM CDT WED APR 27 2011
   
   VALID 271200Z - 281200Z
   
   ...THERE IS A HIGH RISK OF SVR TSTMS OVER PORTIONS OF NRN
   MS...AL...FAR NWRN GA AND SRN MIDDLE TN...
   
   ...THERE IS A MDT RISK OF SVR TSTMS OVER MUCH OF CNTRL AND NRN MS
   AND AL...NWRN GA...MUCH OF TN AND KY...WRN CAROLINAS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER MS VALLEY/GULF
   COAST STATES NWD TO THE CANADIAN BORDER...
   
   CORRECTED FOR SPELLING ERROR
   
   ...SYNOPSIS...
   AN UPPER TROUGH AXIS WILL BE CENTERED ACROSS THE SRN PLAINS AT 12Z
   WED...WITH A 100 KT MID LEVEL JET ACROSS N TX. THIS FEATURE WILL
   STRENGTHEN THROUGH 00Z AS IT EJECTS NEWD ACROSS THE LOWER MS AND
   INTO THE TN/OH VALLEYS DURING THE DAY. AT THE SURFACE...LOW PRESSURE
   IS FORECAST TO BE OVER W CNTRL AR AT 12Z...WITH A DEVELOPING COLD
   FRONT TRAILING SWWD INTO ERN TX. THESE FEATURES WILL MOVE RAPIDLY
   ENEWD...WITH THE SURFACE LOW NEARING SRN INDIANA BY 00Z AND A SHARP
   LOW PRESSURE TROUGH EXTENDING SWD INTO CNTRL KY...MIDDLE TN...ERN MS
   AND WRN AL.
   
   AHEAD OF THE FRONT...A VERY WARM AND MOIST AIR MASS WILL ALREADY BE
   IN PLACE BY MIDDAY WITH 68-72 BOUNDARY LAYER DEWPOINTS LIKELY FROM
   THE GULF COAST INTO MS/AL...AND MID TO UPPER 60S F OVER TN AND SRN
   KY WHERE SUBSTANTIAL MORNING CONVECTION WILL LIKELY BE ONGOING. WITH
   RELATIVELY COOL TEMPERATURE PROFILES ALOFT...AN EXTREMELY UNSTABLE
   ATMOSPHERE WILL RESULT ACROSS THE WARM SECTOR. WIND FIELDS
   THROUGHOUT THE TROPOSPHERE WILL STRENGTHEN WITH THE APPROACHING
   TROUGH/JET MAX...AND THE COMBINATION OF THE TWO IS EXPECTED TO
   RESULT IN A TORNADO OUTBREAK...WITH LONG-TRACKED STRONG TO VIOLENT
   TORNADOES POSSIBLE OVER THE HIGH RISK AREA.
   
   TO THE E...THE BROAD SLY FLOW ACROSS THE WARM SECTOR WILL EXTEND
   INTO THE MID ATLANTIC REGION...WITH A SECONDARY MOIST PLUME OFF THE
   ATLANTIC NWD INTO THE CAROLINAS AND WRN VA BY AFTERNOON.
   
   --- AN OUTBREAK OF TORNADOES AND DAMAGING WINDS IS EXPECTED TODAY
   THROUGH EVENING OVER PORTIONS OF NRN MS...NRN AL...TN AND KY. ---
   
   ...LOWER MS VALLEY INTO TN/OH VALLEYS...
   A COMPLICATED FORECAST SCENARIO WILL UNFOLD TODAY...BEGINNING RATHER
   EARLY IN THE PERIOD OVER SRN AND ERN AR AND NRN LA. MODELS ARE IN
   RELATIVELY GOOD AGREEMENT WITH THE PLACEMENT OF THE SURFACE LOW OVER
   AR BETWEEN 12-15Z...THEN DEVELOPING IT NEWD ACROSS TN/KY BY 00Z.
   NUMEROUS THUNDERSTORMS WILL BE ONGOING...AND SOME WILL BE
   SEVERE...FROM NRN LA/SRN AR EWD ACROSS NRN MS...WRN AND MIDDLE TN
   AND KY. DESPITE TIME OF DAY...PRESENCE OF RICH LOW LEVEL MOISTURE
   WILL RESULT IN LITTLE CAPPING AND SURFACE BASED EFFECTIVE PARCELS. 
   THUS...A TORNADO AND DAMAGING WIND THREAT WILL BE PRESENT WITH THIS
   ACTIVITY.
   
   SOUTH OF THE ONGOING ACTIVITY...STRONG DAYTIME HEATING WILL OCCUR.
   WITH BOUNDARY LAYER DEWPOINTS IN THE LOW 70S F...THIS WILL CREATE
   STRONG TO EXTREME INSTABILITY OVER MS AND AL NWD TO THE ONGOING
   CONVECTION. A CAPPING INVERSION WILL LIKELY KEEP MUCH OF THE WARM
   SECTOR S OF THE EARLY STORMS CAPPED...ALLOWING A BUILD UP OF
   INSTABILITY TO BE RELEASED WHEN LARGE SCALE FORCING ARRIVES DURING
   THE AFTERNOON ALONG THE COLD FRONT AND ESPECIALLY NEAR THE
   FRONT/OUTFLOW BOUNDARY INTERSECTION. THE RESULT WILL BE FAST MOVING
   TORNADIC SUPERCELLS CAPABLE OF STRONG TO VIOLENT TORNADOES. GIVEN
   THE FAST STORM MOTIONS AND RELATIVELY WIDE WARM SECTOR...SOME
   TORNADOES COULD BE LONG LIVED. THE GREATEST THREAT FOR THESE TYPES
   OF STORMS WILL BE OVER THE HIGH RISK AREA...OVER NRN MS AND
   AL...INTO EXTREME NWRN GA AND SRN MIDDLE TN. THIS ACTIVITY WILL
   PERSIST TO THE E...BUT CELLS MAY EVENTUALLY MERGE INTO MORE OF A
   QLCS STRUCTURE CAPABLE OF PARTICULARLY DAMAGING WINDS AND A FEW
   TORNADOES.
   
   ...WRN NC/VA...
   A CONDITIONAL SEVERE THREAT WILL EXIST BY LATE AFTERNOON OVER WRN
   NC/VA.  STRONG  HEATING WILL RESULT IN STEEP LOW LEVEL LAPSE
   RATES...BUT FORECAST SOUNDINGS SHOW A CAPPING INVERSION AROUND 700
   MB...WHICH SHOULD KEEP THE AIR MASS CAPPED. HOWEVER...MOISTURE
   ADVECTION...AS WELL AS SELY UPSLOPE FLOW MAY RESULT IN ISOLATED
   THUNDERSTORMS DURING THE AFTERNOON OVER THE HIGHER TERRAIN. WIND
   PROFILES WOULD FAVOR SUPERCELLS...CAPABLE OF PRODUCING TORNADOES
   HAIL AND WIND. WILL MAINTAIN LOW PROBABILITIES FOR THE DAYTIME
   CONVECTION.
   
   ..JEWELL.. 04/27/2011





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