May 13, 2018 1630 UTC Day 1 Convective Outlook
Updated: Sun May 13 16:29:56 UTC 2018 (20180513 1630Z Day 1 shapefile | 20180513 1630Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180513 1630 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 71,379 8,646,180 Fort Wayne, IN...Aurora, IL...Naperville, IL...Joliet, IL...Gary, IN...
MARGINAL 237,364 31,190,091 Chicago, IL...Indianapolis, IN...Baltimore, MD...Denver, CO...Washington, DC...
Probabilistic Tornado Graphic
20180513 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
2 % 19,154 4,511,536 Fort Collins, CO...Alexandria, VA...Thornton, CO...Greeley, CO...Centreville, VA...
Probabilistic Damaging Wind Graphic
20180513 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 % 65,163 6,321,369 Fort Wayne, IN...Aurora, IL...Naperville, IL...Joliet, IL...Gary, IN...
5 % 172,089 22,741,323 Chicago, IL...Indianapolis, IN...Wichita, KS...Aurora, CO...Des Moines, IA...
Probabilistic Large Hail Graphic
20180513 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
15 % 33,196 3,402,759 Centreville, VA...Dale City, VA...Reston, VA...Burke, VA...Chantilly, VA...
5 % 200,288 27,508,557 Chicago, IL...Baltimore, MD...Denver, CO...Washington, DC...Omaha, NE...
   SPC AC 131629

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CDT Sun May 13 2018

   Valid 131630Z - 141200Z


   Scattered severe storms appear most likely across parts of the
   central Appalachians to Mid-Atlantic States and northwest Texas to
   south-central Kansas during the late afternoon to early evening, and
   northern portions of Illinois and Indiana early morning Monday.

   ...Central Appalachians to Mid-Atlantic States...
   Quasi-stationary front runs west/east across central OH into far
   southwest PA before arcing southeast across northern/eastern VA.
   Robust diabatic heating will occur in the warm sector within the
   eastern extent of the massive EML plume emanating from the central
   states. While a mid-level speed max is passing east of the region,
   sufficient deep-layer shear will persist for a few supercells amid
   MLCAPE around 600-1200 J/kg. Severe hail and damaging wind will be
   the primary hazards, but a tornado is possible with any supercell
   moving along the SRH-enriched front. Have upgraded to Slight Risk to
   account for this potential.

   Influx of richer low-level moisture beneath very steep mid-level
   lapse rates associated with a massive EML should result in large
   warm-sector buoyancy to about 3000 J/kg to the east of the TX
   dryline and southeast of a quasi-stationary front in KS. Scattered
   storms (more numerous than previous days) should develop along the
   dryline in the late afternoon. Deep-layer shear will be modest
   (effective values around 20-30 kt) even with a veering wind profile
   with height. Even so, the impressive thermodynamic environment will
   favor large hail and severe wind gusts with multicells and a few
   embedded supercells. Convection should largely weaken as inhibition
   strengthens greatly east of the dryline after sunset. 

   Low-level warm advection will again be centered on the IA to
   northern IL area tonight resulting in widespread elevated convection
   north of the quasi-stationary front expected to lie along the IA/MO
   border east through central IL/IN. While elevated buoyancy will be
   sufficient for a severe hail risk, rapid evolution to a
   west/east-oriented cluster should marginalize this threat. However,
   some CAMs suggest that this elevated MCS will organize into a
   forward-propagating bow across parts of northern IL/IN by 09-12Z
   Monday morning where the surface front becomes increasingly diffuse.
   A risk for strong to isolated severe wind gusts may develop in spite
   of large inhibition for surface-based parcels.

   Repeated initiation of widely scattered storms is anticipated during
   the late afternoon and evening within a persistent upslope flow
   regime. Winds aloft and vertical shear along the eastern periphery
   of the Great Basin upper low will be sufficient for a couple
   supercells developing off the Front Range. Severe hail should be the
   primary hazard. Given a pervasive stratus deck across much of the
   central High Plains, the tornado/wind risk will likely be confined
   to where stronger diabatic heating can occur. This appears most
   probable near/north of the Denver cyclone where at least pockets of
   greater heating should occur along the Palmer Divide.

   ..Grams/Bunting.. 05/13/2018