Jul 20, 2018 1630 UTC Day 1 Convective Outlook
Updated: Fri Jul 20 16:28:09 UTC 2018 (20180720 1630Z Day 1 shapefile | 20180720 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180720 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MODERATE 37,841 5,747,168 Nashville, TN...Cincinnati, OH...Louisville, KY...Evansville, IN...Clarksville, TN...
ENHANCED 118,437 13,991,090 Indianapolis, IN...Memphis, TN...Lexington-Fayette, KY...Fort Wayne, IN...Huntsville, AL...
SLIGHT 147,033 21,246,426 Detroit, MI...Columbus, OH...Wichita, KS...Toledo, OH...Birmingham, AL...
MARGINAL 284,883 25,982,667 Chicago, IL...Tucson, AZ...Cleveland, OH...Atlanta, GA...Tulsa, OK...
Probabilistic Tornado Graphic
20180720 1630 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
10 % 31,362 4,683,992 Cincinnati, OH...Louisville, KY...Clarksville, TN...Jackson, TN...Hamilton, OH...
5 % 43,042 7,044,224 Memphis, TN...Nashville, TN...Fort Wayne, IN...Dayton, OH...Evansville, IN...
2 % 98,166 11,508,844 Indianapolis, IN...Toledo, OH...Lexington-Fayette, KY...Huntsville, AL...Lansing, MI...
Probabilistic Damaging Wind Graphic
20180720 1630 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 156,926 19,735,910 Indianapolis, IN...Memphis, TN...Nashville, TN...Cincinnati, OH...Louisville, KY...
15 % 146,931 21,226,912 Detroit, MI...Columbus, OH...Wichita, KS...Toledo, OH...Birmingham, AL...
5 % 285,421 25,884,541 Chicago, IL...Tucson, AZ...Cleveland, OH...Atlanta, GA...Akron, OH...
Probabilistic Large Hail Graphic
20180720 1630 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SIG SEVERE 62,638 9,001,901 Indianapolis, IN...Nashville, TN...Cincinnati, OH...Louisville, KY...Evansville, IN...
45 % 37,584 5,749,807 Nashville, TN...Cincinnati, OH...Louisville, KY...Evansville, IN...Clarksville, TN...
30 % 71,908 10,911,248 Indianapolis, IN...Memphis, TN...Lexington-Fayette, KY...Fort Wayne, IN...Dayton, OH...
15 % 142,958 16,284,906 Columbus, OH...Wichita, KS...Toledo, OH...Grand Rapids, MI...Little Rock, AR...
5 % 311,696 32,533,175 Chicago, IL...Detroit, MI...Cleveland, OH...Atlanta, GA...Birmingham, AL...
   SPC AC 201628

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1128 AM CDT Fri Jul 20 2018

   Valid 201630Z - 211200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   NORTHERN/WESTERN TENNESSEE...WESTERN/NORTHERN
   KENTUCKY...SOUTHERN/EASTERN INDIANA...AND SOUTHWESTERN OHIO...

   ...SUMMARY...
   The greatest threat for severe thunderstorms will develop across the
   Ohio and Tennessee Valley regions into the Mid-South today into
   early tonight, with damaging gusts, large hail and tornadoes
   possible.

   ...Mid MS/OH/TN Valleys...
   Morning water vapor loop shows a significant upper low tracking
   southeastward across southern WI.  A strong mid level jet lies to
   the south of the low, extending from the northern Plains into MO. 
   As this upper wind max overspreads the warm sector over parts of the
   Mid MS, OH, and TN Valleys, the risk of rather widespread severe
   thunderstorms will develop this afternoon into tonight.  A very
   moist and unstable air mass has developed across this region with
   pockets of MUCAPE in the 5000-6000 J/kg range.  Steep low and mid
   level lapse rates combined with strong effective shear values will
   result in a conditional risk of severe storms throughout the region.
   The primary forecast uncertainty is the timing and location of
   initiation.

   12z model guidance shows wide diversity in where/when the most
   intense convective clusters will occur later today.  Due to this
   uncertainty, few changes have been made to the ongoing outlook. 
   Discrete supercell development is possible along/ahead of the
   approaching cold front due to shear vectors orthogonal to the front
   and favorable shear magnitudes.  Any storms that remain discrete
   will pose a risk of very large hail and a tornado or two.  It
   appears likely that multiple clusters of storms will congeal into
   fast-moving bowing structures posing a risk of rather widespread
   damaging winds.  This threat will likely spread as far east as
   eastern KY/TN overnight.

   ...KS/MO/OK/AR this evening...
   A surface boundary will extend from western KS into southwest MO and
   northwest AR later today.  Given the intense heat to the south of
   boundary, and a corridor of high dewpoints immediately north of the
   boundary, a zone of high CAPE values will result.  There is
   relatively good consensus of 12z models that show clusters of storms
   forming over KS late this afternoon and tracking along this corridor
   though the evening.  Damaging winds and large hail will be possible
   if this scenario unfolds.

   ..Hart/Picca.. 07/20/2018

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z