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Mesoscale Discussion 1699
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   MESOSCALE DISCUSSION 1699
   NWS STORM PREDICTION CENTER NORMAN OK
   0506 PM CDT TUE SEP 09 2014

   AREAS AFFECTED...SRN NEB / NRN KS / SRN IA / NRN MO

   CONCERNING...TORNADO WATCH 499...

   VALID 092206Z - 092300Z

   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 499 CONTINUES.

   SUMMARY...A GROWING TORNADO THREAT APPEARS TO BE EVOLVING WITH A
   SUPERCELL NEAR NEBRASKA CITY NEBRASKA. EXTRAPOLATION OF THIS STORM
   AND AN EVOLVING SHORT-SEGMENT BOW JUST TO ITS NORTH SUGGEST A
   DOWNSTREAM WATCH OR LOCAL WFO EXTENSION MAY BE REQUIRED PRIOR TO
   00Z.

   DISCUSSION...21Z MESOANALYSIS INDICATED AN ELONGATED AREA OF LOW
   PRESSURE FROM NWRN KS INTO E-CNTRL CO WITH AN ASSOCIATED WARM FRONT
   EXTENDING ENEWD THROUGH S-CNTRL AND SERN NEB INTO FAR NWRN MO BEFORE
   CURVING MORE SEWD TO NEAR ST. LOUIS. RECENT TRENDS IN VOLUMETRIC
   RADAR DATA INDICATE THE EVOLUTION OF A SUPERCELL ALONG THE WARM
   FRONT NEAR NEBRASKA CITY AS OF 2145Z WITH A BOWING LINE SEGMENT
   EXTENDING NNEWD THROUGH MILLS AND POTTAWATTAMIE COUNTIES IN IA. 

   RAP-BASED GUIDANCE SUGGESTS THAT THE LOCAL ENVIRONMENT INVOF THE
   WARM FRONT IS QUITE FAVORABLE FOR SUPERCELLS WITH MLCAPE OF
   2000-3000 J/KG WHICH IS COINCIDENT WITH 40-50 KT OF EFFECTIVE BULK
   SHEAR. MOREOVER...LOW T-TD SPREADS AND ENHANCED LOW-LEVEL SHEAR
   ALONG AND JUST TO THE COOL SIDE OF THE BOUNDARY SHOULD ENHANCE
   TORNADO POTENTIAL WITH THE ABOVE-MENTIONED SUPERCELL. 

   LATEST MODEL GUIDANCE INDICATES THAT A SWLY LLJ SHOULD CONTINUE TO
   STRENGTHEN AND INCREASE IN BREADTH AS IT DEVELOPS NEWD THROUGH THE
   LOWER MO VALLEY THROUGH 03Z. THIS SHOULD SERVE TO ENHANCE THE
   POLEWARD FLUX OF HEAT AND MOISTURE ALONG THE ERN EXTENSION OF THE
   WARM FRONT NEAR THE IA-MO STATE LINE...AS WELL AS BOOST LOW-LEVEL
   SHEAR. AS SUCH...EXPECT THE THREAT FOR TORNADOES...DAMAGING
   WINDS...AND HAIL TO SPREAD EWD ALONG THIS BOUNDARY THIS EVENING.

   ..MEAD.. 09/09/2014


   ATTN...WFO...DMX...EAX...OAX...TOP...ICT...GID...LBF...GLD...

   LAT...LON   41050019 41049825 41279826 41389602 41859608 41869427
               41149425 41179402 40579397 40549413 39729419 39519458
               39559729 39319736 39149900 39139962 40049961 40050015
               41050019 

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Page last modified: September 09, 2014
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