May 13, 2018 0600 UTC Day 1 Convective Outlook
Updated: Sun May 13 06:00:36 UTC 2018 (20180513 1200Z Day 1 shapefile | 20180513 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180513 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 44,649 10,621,759 Chicago, IL...Aurora, IL...Rockford, IL...Naperville, IL...Joliet, IL...
MARGINAL 240,640 29,901,669 Indianapolis, IN...Columbus, OH...Washington, DC...Omaha, NE...Wichita, KS...
Probabilistic Tornado Graphic
20180513 1200 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 % 15,492 1,408,208 Aurora, CO...Fort Collins, CO...Thornton, CO...Greeley, CO...Longmont, CO...
Probabilistic Damaging Wind Graphic
20180513 1200 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 % 45,246 10,678,716 Chicago, IL...Aurora, IL...Rockford, IL...Naperville, IL...Joliet, IL...
5 % 239,729 29,653,580 Indianapolis, IN...Columbus, OH...Washington, DC...Omaha, NE...Wichita, KS...
Probabilistic Large Hail Graphic
20180513 1200 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 % 31,778 1,772,501 Rockford, IL...Cedar Rapids, IA...Davenport, IA...Iowa City, IA...Dubuque, IA...
5 % 144,994 13,402,828 Omaha, NE...Wichita, KS...Aurora, CO...Lincoln, NE...Des Moines, IA...
   SPC AC 130600

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Sun May 13 2018

   Valid 131200Z - 141200Z


   A few strong to severe thunderstorms are possible today from parts
   of the Midwest to the Mid Atlantic, the southern/central Plains, and
   a portion of the Colorado Front Range into the Laramie Mountains
   vicinity of Wyoming. Damaging wind and hail will be the primary


   A synoptic blocking pattern will persist today with cutoff upper low
   over the Great Basin and Intermountain West and a downstream upper
   ridge over the Southeast States. At the surface a quasi-stationary
   front will persist from eastern VA through the OH Valley and west
   into KS where it will intersect a dryline extending south through
   west TX.


   Richer low-level moisture with mid-upper 60s F surface dewpoints
   will advect through the warm sector to the south of a
   quasi-stationary front currently situated from the OH Valley through
   northern MO. A warm elevated mixed layer will expand east above the
   moistening warm sector and frontal zone contributing to very strong
   instability (2000-3000 J/kg MUCAPE) and a strong cap. Shortwave
   ridging and strong convective inhibition should limit thunderstorm
   development over much of this region during the day. However
   vorticity maximum currently approaching the southern Rockies will
   crest upper ridge this evening and tonight which, along with a
   strengthening low-level jet, should contribute to sufficient
   isentropic ascent for storms to initiate along/north of the front.
   Most CAM solutions suggest this activity will eventually grow
   upscale, possibly becoming a forward propagating MCS. Initial threat
   will be large hail across IA, but the threat for damaging wind may
   increase as storms grow upscale from eastern IA into northern IL and

   ...Southern and central Plains...

   Influx of richer low-level moisture beneath steep lapse rates
   associated with a warm elevated mixed layer should result in strong
   instability (2500-3000 J/kg MLCAPE) in the southern and central
   Plains warm sector. Strong diabatic warming and dryline mixing
   should eventually erode the cap, and storms are expected to initiate
   from northwest TX into the TX Panhandle and eventually move east
   into western OK during the evening. Despite weak vertical shear
   (25-30 kt, 0-6km) The thermodynamic environment appears very
   favorable for wet downbursts and large hail before activity weakens
   later in the evening. 

   ...Central Rockies region...

   Storms should once again initiate in upslope flow regime where winds
   aloft and vertical shear along southeast periphery of upper low will
   be sufficient for a few rotating updrafts.  MUCAPE from 500-800 J/kg
   and 50+ kt effective shear will support a threat for supercells
   capable of large hail. In addition, steep lapse rates and large
   temperature-dewpoint spreads will promote a threat for downburst
   winds. At this time, marginal instability could be a limiting factor
   for a more robust severe threat, but an upgrade to slight risk might
   be warranted in later updates. 

   ...Central Appalachians to Middle Atlantic region...

   Backdoor front has shunted warm sector south of the stronger winds
   aloft. Most storms (modulated by vorticity maxima embedded within
   the west-northwest flow regime) will remain confined to north of the
   quasi-stationary front. However any storms developing near this
   boundary may become capable of producing a few strong to damaging
   wind gusts as the boundary layer destabilizes during the afternoon
   and early evening.

   ..Dial/Karstens.. 05/13/2018