Jul 21, 2017 0100 UTC Day 1 Convective Outlook
Updated: Fri Jul 21 00:55:49 UTC 2017 (20170721 0100Z Day 1 shapefile | 20170721 0100Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170721 0100 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 83,057 2,451,679 Des Moines, IA...Cedar Rapids, IA...Davenport, IA...Iowa City, IA...Rapid City, SD...
MARGINAL 371,206 24,705,522 Chicago, IL...Indianapolis, IN...Denver, CO...Omaha, NE...Aurora, CO...
Probabilistic Tornado Graphic
20170721 0100 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
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20170721 0100 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
15 % 83,139 2,442,581 Des Moines, IA...Cedar Rapids, IA...Davenport, IA...Iowa City, IA...Rapid City, SD...
5 % 313,118 23,748,851 Chicago, IL...Indianapolis, IN...Denver, CO...Omaha, NE...Aurora, CO...
Probabilistic Large Hail Graphic
20170721 0100 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
15 % 57,581 400,254 Rapid City, SD...Minot, ND...Gillette, WY...Dickinson, ND...Spearfish, SD...
5 % 374,238 26,701,797 Chicago, IL...Indianapolis, IN...Denver, CO...Omaha, NE...Aurora, CO...
   SPC AC 210055

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 PM CDT Thu Jul 20 2017

   Valid 210100Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHERN HIGH PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM IOWA INTO
   WESTERN ILLINOIS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   NORTHERN HIGH PLAINS INTO THE MIDWEST...

   ...SUMMARY...
   A few severe storms producing wind or hail remain possible from the
   western Dakotas into Iowa and Illinois. Isolated strong storms
   remain possible for an hour or two across Maine with marginal hail
   or wind.

   ...Northern Plains into Illinois...
   Scattered storms currently exist across the western Dakotas near a
   cold front, with  more widely spaced storms farther east across Iowa
   and southeastern Nebraska near a quasi-stationary front. A very
   moist air mass exists across the region, with storms coinciding with
   peak heating. Sporadic near-severe wind gusts have been reported,
   along with marginally severe hail as well. 

   As a low-amplitude upper trough continues eastward across the
   northern Plains, a southerly low-level jet will enhance warm
   advection across the region, with additional development possible
   through the evening. Hail or wind will be possible within a narrow
   corridor. 

   For more information see mesoscale discussion 1373.

   ...Northeast...
   A few strong cells remain over Maine with marginal hail or wind
   threat. However, with loss of heating, further weakening is
   expected. 

   To the south, a small bow with a history of severe wind over PA is
   weakening across NJ, and will soon exit the coast. Therefore, have
   removed severe probs for this area. For more information see
   mesoscale discussions 1371 and 1372.

   ..Jewell.. 07/21/2017

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z