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Mesoscale Discussion 1709
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   MESOSCALE DISCUSSION 1709
   NWS STORM PREDICTION CENTER NORMAN OK
   0353 PM CDT TUE AUG 18 2015

   AREAS AFFECTED...EASTERN IA AND NORTHERN/NORTH-CENTRAL IL INTO
   SOUTHERN WI

   CONCERNING...TORNADO WATCH 494...

   VALID 182053Z - 182300Z

   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 494 CONTINUES.

   SUMMARY...THE POTENTIAL FOR A COUPLE OF TORNADOES AND DAMAGING WINDS
   WILL LIKELY INCREASE THROUGH LATE AFTERNOON ACROSS FAR EASTERN IA
   AND MUCH OF NORTHERN/NORTH-CENTRAL IL INTO SOUTHERN WI. TORNADO
   WATCH 494 CONTINUES UNTIL 03Z.

   DISCUSSION...A MCV/COMPACT VORT MAX...WITH A VERY STRONG WIND FIELD
   FOR THE SEASON AS PER DERIVED WIND DATA...CONTINUES TO STEADILY
   PROGRESS EAST-NORTHEASTWARD AT MID-AFTERNOON ACROSS SOUTHERN IA/FAR
   NORTHERN MO. WHILE THE PRIMARY SYNOPTIC SURFACE LOW IS LOCATED ALONG
   THE IA/MN BORDER AS OF 20Z...A WEAKER SECONDARY SURFACE LOW IS NOW
   EVIDENT NEAR THE IA/MO/IL BORDER VICINITY WHERE 2-HR SURFACE
   PRESSURE FALLS ARE MAXIMIZED. ALTHOUGH IT HAS MODIFIED/SOMEWHAT
   DECAYED...A REMNANT EARLY-DAY OUTFLOW BOUNDARY IS STILL READILY
   EVIDENT IN SURFACE/VISIBLE SATELLITE DATA FROM FAR EAST-CENTRAL IA
   SOUTHEASTWARD INTO NORTH-CENTRAL/EAST-CENTRAL IL. AS
   DEEP-LAYER/LOW-LEVEL WINDS CONTINUE TO STRENGTHEN ACROSS THE REGION
   THROUGH EARLY EVENING /A TREND ALREADY SEEN IN REGIONAL WSR-88D VWP
   DATA/...TORNADO POTENTIAL MAY ESPECIALLY EXIST WITH ANY
   SEMI-DISCRETE STORMS THAT SPREAD NORTHEASTWARD AND CROSS THE
   AFOREMENTIONED BOUNDARY ACROSS FAR EASTERN IA AND NORTH-CENTRAL IL
   AND/OR IN VICINITY OF THE NORTHEASTWARD-SPREADING SUB-SYNOPTIC LOW
   ACROSS FAR EASTERN IA INTO NORTHWEST IL/SOUTHERN WI...EACH CASES
   WHERE LOW-LEVEL SHEAR/SRH AND VORTICITY ARE MAXIMIZED. ISOLATED
   DAMAGING WINDS WILL OTHERWISE BE A COMMON RISK.

   ..GUYER.. 08/18/2015


   ATTN...WFO...LOT...ILX...MKX...DVN...ARX...

   LAT...LON   43279109 43719060 43898913 43498856 40718886 40759121
               42749115 43279109 

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Page last modified: August 18, 2015
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