Jun 20, 2018 1630 UTC Day 1 Convective Outlook
Updated: Wed Jun 20 16:34:19 UTC 2018 (20180620 1630Z Day 1 shapefile | 20180620 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180620 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 49,646 7,113,878 Des Moines, IA...Richmond, VA...Newport News, VA...Hampton, VA...Lynchburg, VA...
MARGINAL 303,585 37,665,315 Indianapolis, IN...Columbus, OH...Washington, DC...Virginia Beach, VA...Raleigh, NC...
Probabilistic Tornado Graphic
20180620 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
5 % 11,195 1,186,643 Des Moines, IA...Ames, IA...West Des Moines, IA...Ankeny, IA...Urbandale, IA...
2 % 16,090 663,775 Cedar Rapids, IA...Waterloo, IA...Iowa City, IA...Cedar Falls, IA...Marion, IA...
Probabilistic Damaging Wind Graphic
20180620 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
15 % 49,760 7,152,070 Des Moines, IA...Richmond, VA...Newport News, VA...Hampton, VA...Cedar Rapids, IA...
5 % 300,037 38,065,409 Indianapolis, IN...Columbus, OH...Washington, DC...Virginia Beach, VA...Raleigh, NC...
Probabilistic Large Hail Graphic
20180620 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
5 % 86,755 3,027,069 Des Moines, IA...Cedar Rapids, IA...Columbia, MO...Waterloo, IA...Bend, OR...
   SPC AC 201634

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1134 AM CDT Wed Jun 20 2018

   Valid 201630Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
   THE MIDDLE ATLANTIC AND IOWA...

   ...SUMMARY...
   Scattered strong to severe thunderstorms are expected to affect
   parts of the Mid Atlantic region and Iowa today.  Other more sparse
   strong storms are possible over the Ohio Valley, Central Plains, and
   portions of Oregon.

   ...Iowa...

   Objective analysis indicates the atmosphere has become moderately
   unstable (1000-1500 J/kg MLCAPE) across central IA. Vorticity
   maximum rotating through base of an upper low circulation will
   result in a surface low developing north through west-central IA
   today. East of this feature a warm front will lift slowly north
   while a cold front advances east through southern IA into MO.
   Despite weak shear through a deeper layer, low-level hodographs and
   vertical vorticity in vicinity of the warm front may become
   sufficient for transient low-level mesocyclones. A few brief
   tornadoes are possible as storms move northeast and interact with
   the warm front this afternoon. Storms may eventually congeal into a
   line along the front with a threat for a few damaging wind gusts. 

   ...Middle Atlantic region...

   Isolated storms moving off the higher terrain as well as storms
   developing farther north along pre-frontal boundaries and advancing
   southeast into the moderately unstable atmosphere will pose a risk
   for isolated wet downbursts this afternoon. 

   ...Oregon...

   A fast-moving shortwave trough is just west of the northern CA
   coastline.  This feature will move inland later today, helping to
   initiate scattered thunderstorms along the eastern slopes of the
   Cascades where moisture is sparse but sufficient for development.
   Forecast soundings suggest favorable wind fields for severe storms
   capable of large hail and damaging winds.  Dewpoints only in the 40s
   appear to be the main limiting factor to a more organized event.

   ..Dial/Nauslar.. 06/20/2018

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