Jun 23, 2018 1300 UTC Day 1 Convective Outlook
Updated: Sat Jun 23 12:56:45 UTC 2018 (20180623 1300Z Day 1 shapefile | 20180623 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180623 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 254,840 41,430,901 Philadelphia, PA...Dallas, TX...Memphis, TN...Fort Worth, TX...Baltimore, MD...
MARGINAL 473,140 38,439,596 Charlotte, NC...Nashville, TN...Virginia Beach, VA...Raleigh, NC...Norfolk, VA...
Probabilistic Tornado Graphic
20180623 1300 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
2 % 115,650 14,377,586 Philadelphia, PA...Baltimore, MD...Washington, DC...Oklahoma City, OK...Arlington, VA...
Probabilistic Damaging Wind Graphic
20180623 1300 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 % 254,341 41,427,644 Philadelphia, PA...Dallas, TX...Memphis, TN...Fort Worth, TX...Baltimore, MD...
5 % 425,271 37,914,569 Nashville, TN...Virginia Beach, VA...Raleigh, NC...Norfolk, VA...Greensboro, NC...
Probabilistic Large Hail Graphic
20180623 1300 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 % 94,927 18,989,302 Dallas, TX...Fort Worth, TX...Baltimore, MD...Washington, DC...Oklahoma City, OK...
5 % 393,900 22,677,445 Memphis, TN...Virginia Beach, VA...Norfolk, VA...Chesapeake, VA...Shreveport, LA...
   SPC AC 231256

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0756 AM CDT Sat Jun 23 2018

   Valid 231300Z - 241200Z


   Scattered severe thunderstorms are expected especially this
   afternoon and evening from the southern Plains to the lower
   Mississippi Valley and a portion of the Southeast States. Other
   severe storms are expected over the Middle Atlantic region. More
   isolated strong to severe storms might occur over a portion of the
   central and northern Plains.

   ...Southern Plains...
   Persistent regenerative convection and its related cold pool across
   Oklahoma into far north Texas has continued to reinforce a roughly
   west/east-oriented frontal zone across the region. This effective
   front may transition a little northward later today although its
   latitudinal location later today is a bit uncertain given the
   persistence of early day convection. Along/south of this boundary,
   and as far west as a weak surface wave and dryline/surface trough
   across west-central/western north Texas, the air mass should become
   moderately unstable by peak heating with 2000-4000 J/kg MLCAPE
   possible. Owing to hot surface temperatures and modest convergence,
   isolated to widely scattered thunderstorm development around late
   afternoon appears most probable across the Low Rolling Plains
   vicinity of west/north Texas and possibly into southwest Oklahoma,
   with greater uncertainties for surface-based/diurnally driven
   development north/northeastward into other parts of Oklahoma given
   unclear air mass characteristics/recovery.

   Additional storms may develop farther east-northeast within the
   frontal zone during the evening as the southerly low-level jet
   strengthens. A belt of modest winds aloft with 25-30 kt at 500 mb
   will result in 35-40 kt effective bulk shear near/north of the front
   where surface winds will remain backed to easterly. Weaker shear
   will reside in warm sector. Both multicell and some supercell
   structures will be possible with damaging wind and large hail the
   main threats from late afternoon into the evening.

   ...Deep South from the Mississippi River to Georgia/South
   A MCV appears to be aiding the eastward-persistence of an MCS from
   eastern Arkansas into northern Mississippi/southwest Tennessee early
   this morning, while MCS-preceding storms have also increased across
   northeast Mississippi into northern Alabama. For short-term details,
   see Mesoscale Discussion 835. The MCV and the modest outflow-related
   cold pool that accompanies it should focus additional development
   during the day within a destabilizing boundary layer with up to 2500
   J/kg MLCAPE possible. A belt of stronger winds aloft accompanying
   the MCV/shortwave trough will aid storm organization and the
   environment appears supportive of sub-regional corridors of damaging
   winds through the afternoon into early/mid evening, perhaps as far
   east as parts of South Carolina.

   ...Mid-Atlantic States...
   A warm front will lift north through Virginia into Pennsylvania
   during the day ahead of a cold front accompanying a shortwave
   trough. Diabatic warming of the moist warm sector will result in
   moderate instability with upwards of 2000-2500 J/kg MLCAPE possible
   especially from southeast Virginia through the Delmarva into
   southern New Jersey. A belt of stronger winds aloft will accompany
   the upper low as it shifts northeast and transitions to an open
   wave. Storms are expected to develop over the higher terrain with a
   lee trough across central Virginia also a focus for development. A
   few splitting supercells will be possible as effective bulk shear
   increases to 30-40 kt, with storms also organizing into broken bands
   as they develop east-northeastward. Damaging wind will be the main
   threat, but some hail will also be possible and a brief tornado
   cannot be ruled out, particularly with any storms interacting with
   the warm front where low-level/deep-layer shear will be regionally

   ...Wyoming/central High Plains to Middle Missouri River Valley...
   Ascent accompanying a shortwave trough moving southeast through the
   northern Rockies and diabatic heating will promote increasing
   thunderstorm development over the higher terrain of Wyoming into the
   broader north-central High Plains this afternoon. High based storms
   capable of downburst winds and severe hail appears to be the main

   Farther east across South Dakota into eastern Nebraska, a surface
   trough accompanying a lead shortwave trough will provide a focus for
   storm development during the afternoon. Modest winds aloft will
   support multicell storm modes with a few instances of marginally
   severe hail and gusty winds possible.

   ..Guyer/Marsh.. 06/23/2018