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Mesoscale Discussion 1675
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   MESOSCALE DISCUSSION 1675
   NWS STORM PREDICTION CENTER NORMAN OK
   0601 PM CDT THU AUG 13 2015

   AREAS AFFECTED...PORTIONS W-CNTRL NEB.

   CONCERNING...SEVERE THUNDERSTORM WATCH 487...

   VALID 132301Z - 132330Z

   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 487
   CONTINUES.

   SUMMARY...THUNDERSTORM COVERAGE HAS INCREASED IN A VERY MOIST AND
   UNSTABLE  ENVIRONMENT SUITABLE FOR CONTINUED UPSCALE GROWTH...WITH
   MULTIPLE SEVERE STORMS POSSIBLE THROUGH AT LEAST EARLY EVENING. 
   ACTIVITY SHOULD MOVE GENERALLY SOUTHWARD DOWN THE WATCH AREA AND
   OFFER LARGE HAIL.  DAMAGING WIND MAY BECOME MORE PREVALENT AS
   WELL...BEFORE STORMS WEAKEN LATE THIS EVENING.

   DISCUSSION...SFC MESOANALYSES AND REFLECTIVITY ANIMATIONS CONTINUE
   TO SHOW WELL-DEFINED CYCLONIC VORTEX OVER SANDHILLS...CENTERED OVER
   SRN CHERRY COUNTY NW TIF.  SFC TROUGH EXTENDS SSWWD FROM THAT LOW
   NEAR AN IML-GLD-SPD AXIS...AND SHOULD MOVE LITTLE THROUGH EVENING. 
   THAT TROUGH ALSO ACTS AS MESOBETA-SCALE CONVERGENCE MAX AND
   EFFECTIVE DRYLINE...WITH SFC DEW POINTS DECREASING FROM NEAR 70 ON E
   SIDE TO 50S AND LOW 60S TO ITS W.  ANOTHER TROUGH AND CONVERGENCE
   ZONE EXTENDED GENERALLY ENEWD FROM LOW TO NEAR ONL...ALONG WHICH
   STORMS HAVE DEVELOPED AND MULTIPLIED DURING PAST 1-2 HOURS.  MAIN
   FACTOR DRIVING WW IS CONVECTIVE COVERAGE...GIVEN SUITABILITY OF
   ENVIRONMENT ALONG AND E OF FIRST TROUGH...AND S OF SECOND.

   REMNANT DIURNAL HEATING AND 15-16 G/KG MEAN MIXING RATIOS IN MOIST
   SECTOR OFFSET MODEST MIDLEVEL LAPSE RATES ENOUGH TO YIELD MLCAPE
   2000-3000 J/KG...WHICH WILL DIMINISH MOST SLOWLY INVOF MOIST AXIS
   LOCATED FROM NEAR ANW SWD TO NEAR LINCOLN/DAWSON COUNTY LINE. 
   THOUGH LOW-LEVEL WINDS AND HODOGRAPH SIZES WILL REMAIN
   WEAK...VEERING WITH HEIGHT...FCST SWD STORM MOVEMENT AND DOMINANT
   SLY BOUNDARY-LAYER WIND COMPONENT SUGGEST SUFFICIENT STORM-RELATIVE
   INFLOW TO MAINTAIN CONVECTION FOR A FEW HOURS AT LEAST...WHILE
   FORECAST SWD STORM MOTIONS INTO 15-20 KT 850-MB WINDS MAY YIELD
   30-40 KT STORM-RELATIVE INFLOW...DEPENDING ON SPEED OF FORWARD
   PROPAGATION.  WHILE IT REMAINS UNCLEAR HOW FAR S CONVECTION WILL GO
   BEFORE DISSIPATING...MAINLY DUE TO CONVECTIVE-MODE
   UNCERTAINTIES...DECREASING LOW-LEVEL THETAE AND INCREASING CINH ARE
   EXPECTED S OF ABOUT I-80 -- BOTH WITH SWD EXTENT AND WITH TIME THIS
   EVENING.

   ..EDWARDS.. 08/13/2015


   ATTN...WFO...GID...LBF...

   LAT...LON   40669941 40690125 41370128 42080141 42290138 42500134
               42690101 42730059 42790015 42799926 42779925 42429923
               42089922 41739920 41399920 41289919 41039919 41049942
               40669941 40669941 

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Page last modified: August 13, 2015
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