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Severe Weather Risk This Weekend


Jim Martin

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MESOSCALE DISCUSSION 0096  
NWS STORM PREDICTION CENTER NORMAN OK  
0532 PM CST SAT JAN 21 2017  
  
AREAS AFFECTED...PORTIONS OF FAR NORTHEAST TEXAS...NORTHERN  
LOUISIANA...SOUTHERN/CENTRAL ARKANSAS...AND WESTERN MISSISSIPPI  
  
CONCERNING...TORNADO WATCH 16...  
  
VALID 212332Z - 220130Z  
  
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 16 CONTINUES.  
  
SUMMARY...THE THREAT FOR TORNADOES, VERY LARGE HAIL, AND DAMAGING  
WIND GUSTS CONTINUES ACROSS MUCH OF WATCH 16. ADDITIONALLY,  
DOWNSTREAM WATCH ISSUANCE WILL LIKELY BE NEEDED ACROSS NORTHEASTERN  
LA, SOUTHEASTERN AR, AND WESTERN MS WITHIN 2-3 HOURS.  
  
DISCUSSION...MULTIPLE SUPERCELLS HAVE FORMED LATE THIS AFTERNOON  
ACROSS WEST-CENTRAL PORTIONS OF WATCH 16, IN RESPONSE TO LOW-LEVEL  
CONFLUENCE NEAR A SURFACE TROUGH/WARM FRONT AND MID/UPPER-LEVEL  
ASCENT ON THE NOSE OF AN IMPULSE OVER EASTERN TX. A SURFACE LOW WAS  
ANALYZED NEAR THE TX/LA BORDER AT 23Z, WITH A WARM FRONT EXTENDING  
TO ITS SOUTHEAST TOWARDS NEW ORLEANS. NEAR THIS BOUNDARY, BACKED  
SURFACE WINDS ARE ENHANCING STORM-RELATIVE HELICITY SUFFICIENTLY FOR  
LOW-LEVEL MESOCYCLOGENESIS. INDEED, A FAIRLY PROMINENT TORNADIC  
DEBRIS SIGNATURE WAS NOTED ACROSS FAR NORTHEAST MARION COUNTY / FAR  
SOUTHEAST CASS COUNTY IN TX OVER THE LAST 20-30 MINUTES AND ANOTHER  
RECENTLY OBSERVED OVER NORTHEAST BOSSIER PARISH.  
  
MORE SUPERCELLS ARE LIKELY TO FORM FARTHER SOUTH, WITH THE POTENTIAL  
FOR TORNADOES CONTINUING AS THEY PROGRESS NORTHEAST, ESPECIALLY WHEN  
THESE CELLS APPROACH THE AFOREMENTIONED SURFACE FRONT. MOREOVER,  
STEEP MID-LEVEL LAPSE RATES NOTED IN 18/20Z REGIONAL SOUNDINGS AND  
AMPLE EFFECTIVE SHEAR WILL MAINTAIN THE POTENTIAL FOR ROBUST  
ORGANIZED UPDRAFTS CAPABLE OF VERY LARGE HAIL. INDEED, RECENT KSHV  
DATA HAVE DEPICTED SEVERAL BROAD/DEEP ZDR COLUMN AND RING STRUCTURES  
ALOFT, SUGGESTING HAILSTONE GROWTH SHOULD BE QUITE EFFICIENT.  
  
..PICCA.. 01/21/2017  

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not to beat a dead horse but despite debris up 8-10k feet, a mention of debris by SPC, and pictures of several large tornadoes, the "strongest" warning or statement  out of SHV was a funnel cloud was reported.....and the rest radar indicated...

no mentions of radar confirmed or spotter confirmed....

if you just read the warnings/statements like most of the public does there are no tornado touchdowns and one funnel cloud

did I miss something

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4 minutes ago, janetjanet998 said:

not to beat a dead horse but despite debris up 8-10k feet, a mention of debris by SPC, and pictures of several large tornadoes, the "strongest" warning or statement  out of SHV was a funnel cloud was reported.....and the rest radar indicated...

no mentions of radar confirmed or spotter confirmed....

if you just read the warnings/statements like most of the public does there are no tornado touchdowns and one funnel cloud

did I miss something

Those photos were sent to them almost real time in NWS Chat too, they really haven't been saying much other then they're watching certain cells.

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   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Central and southern Alabama
     Western and central Florida Panhandle
     Small part of southeastern Mississippi
     Coastal Waters

   * Effective this Saturday night and Sunday morning from 650 PM
     until 300 AM CST.

   ...THIS IS A PARTICULARLY DANGEROUS SITUATION...

   * Primary threats include...
     Several tornadoes and a few intense tornadoes likely
     Scattered damaging winds and isolated significant gusts to 75
       mph possible
     Isolated very large hail events to 2.5 inches in diameter
       possible

   SUMMARY...A cluster of storms now moving into extreme southwestern
   Alabama is the first of what likely will be several areas of severe
   weather moving across this watch overnight.  As a warm front moves
   northward across the region, conditions will moisten and destabilize
   considerably amidst strong vertical shear.  The resulting parameter
   space is one often associated with long-lasting, intense tornadoes
   rated EF2 or greater.

   The tornado watch area is approximately along and 100 statute miles
   north and south of a line from 80 miles north of Mobile AL to 50
   miles south of Columbus GA. For a complete depiction of the watch
   see the associated watch outline update (WOUS64 KWNS WOU7).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Tornado Watch means conditions are favorable for
   tornadoes and severe thunderstorms in and close to the watch
   area. Persons in these areas should be on the lookout for
   threatening weather conditions and listen for later statements
   and possible warnings.

 

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AY 1 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
0655 PM CST SAT JAN 21 2017  
  
VALID 220100Z - 221200Z  
  
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN  
ARKANSAS TO NORTHERN LOUISIANA INTO WESTERN MISSISSIPPI...  
  
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST  
MISSISSIPPI INTO SOUTHERN AND SOUTH CENTRAL ALABAMA AND SOUTHWEST  
GEORGIA...  
  
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER  
MISSISSIPPI VALLEY INTO MUCH OF THE GULF COASTAL STATES...  
  
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER  
MISSISSIPPI VALLEY INTO MUCH OF THE SOUTHEAST STATES...  
  
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE LOWER  
AND MIDDLE MISSISSIPPI VALLEY INTO MOST OF THE SOUTHEAST STATES...  
   
..SUMMARY  
  
SEVERE STORMS ARE WILL PERSIST THIS EVENING AND INTO THE OVERNIGHT  
FROM PARTS OF THE LOWER MISSISSIPPI VALLEY INTO THE GULF COAST  
STATES.  SOME OF THE STORMS WILL BE CAPABLE OF PRODUCING SIGNIFICANT  
SEVERE WEATHER INCLUDING A STRONG TORNADOES AND VERY LARGE HAIL.  
   
..LOWER MISSISSIPPI VALLEY THROUGH THE GULF COAST STATES  
  
EARLY THIS EVENING A WARM FRONT EXTENDS FROM THE GULF COAST THROUGH  
LA, SOUTHWEST AR AND OK. THIS BOUNDARY WILL CONTINUE TO ADVANCE  
NORTH INTO THE GULF COAST STATES AND SERVE AS A FOCUS FOR SEVERE  
STORMS TONIGHT. SEVERE THUNDERSTORMS INCLUDING A FEW SUPERCELLS ARE  
UNDERWAY FROM NORTHERN LA INTO SOUTHERN AR AND ARE DEVELOPING IN  
ASSOCIATION WITH ASCENT ATTENDING A PROGRESSIVE VORTICITY MAXIMUM  
LOCATED IN THE EXIT REGION OF A STRONG UPPER JET. THESE STORMS ARE  
EMBEDDED WITHIN 45-50 KT EFFECTIVE BULK SHEAR, AND 0-1 KM HODOGRAPHS  
ARE SUFFICIENT FOR LOW-LEVEL MESOCYCLONES. THE CAPE/SHEAR PARAMETER  
SPACE WILL CONTINUE TO SUPPORT THE RISK FOR VERY LARGE HAIL AND  
TORNADOES THIS EVENING.   
  
THE ATMOSPHERE HAS DESTABILIZED IN VICINITY OF THE WARM FRONT WITH  
STEEP LAPSE RATES AND A CORRIDOR OF MLCAPE FROM 1000-1500 J/KG FROM  
THE LOWER MS VALLEY INTO THE GULF COASTAL AREA. ADDITIONAL STORMS  
ARE DEVELOPING ALONG AND JUST NORTH OF THE WARM FRONT FROM THE  
CENTRAL GULF COAST INTO SOUTHERN LA. THE LOW-LEVEL JET SHOULD  
UNDERGO A SIGNIFICANT INCREASE OVER THE GULF COAST STATES TONIGHT IN  
RESPONSE TO MASS ADJUSTMENTS WITHIN EXIT REGION OF APPROACHING UPPER  
JET. THIS PROCESS WILL PROMOTE ADDITIONAL THUNDERSTORM DEVELOPMENT  
ALONG AND JUST NORTH OF THE WARM FRONT WITH THETA-E ADVECTION  
BENEATH STEEP MID-LEVEL LAPSE RATE PLUME CONTRIBUTING TO MODERATE  
INSTABILITY. THE COUPLED JET STRUCTURE WILL RESULT IN VERY FAVORABLE  
VERTICAL WIND PROFILES FOR SUPERCELLS WITH LOW-LEVEL MESOCYCLONES.  
MIXED MODES WITH BOTH DISCRETE CELLS AND CLUSTERS ARE LIKELY. GIVEN  
THE SHEAR/INSTABILITY PARAMETER SPACE, SOME SUPERCELLS WILL BECOME  
CAPABLE OF PRODUCING STRONG TORNADOES IN ADDITION TO LARGE HAIL AND  
DAMAGING WIND.  
  

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