May 20, 2018 1300 UTC Day 1 Convective Outlook
Updated: Sun May 20 12:53:45 UTC 2018 (20180520 1300Z Day 1 shapefile | 20180520 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180520 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 246,560 27,638,694 San Antonio, TX...Dallas, TX...Indianapolis, IN...Austin, TX...St. Louis, MO...
Probabilistic Tornado Graphic
20180520 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 % 20,450 68,684 Carlsbad, NM...Pecos, TX...
Probabilistic Damaging Wind Graphic
20180520 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
5 % 230,339 27,556,985 San Antonio, TX...Dallas, TX...Indianapolis, IN...Austin, TX...St. Louis, MO...
Probabilistic Large Hail Graphic
20180520 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
5 % 143,461 10,951,185 San Antonio, TX...Austin, TX...St. Louis, MO...Springfield, MO...Waco, TX...
   SPC AC 201253

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0753 AM CDT Sun May 20 2018

   Valid 201300Z - 211200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
   MISSOURI VALLEY AND OHIO VALLEY AS WELL AS PARTS OF TEXAS...

   ...SUMMARY...
   Strong to severe storms are possible across portions of the lower
   Missouri and Ohio Valley today.  Additional strong storms are
   possible across portions of central and southwest Texas.

   ...Lower Missouri Valley to Lower Ohio Valley...
   Multiple eastward-moving clusters of strong thunderstorms are
   ongoing early this morning across Missouri into southern Illinois.
   Storm-scale cold pools aside, this activity appears to be aided by a
   weak impulse/MCV across Oklahoma into southeast Kansas and low-level
   jet-enhanced isentropic ascent. These storms are generally moving
   into an air mass that has been overturned or at least muddled and
   influenced by convection yesterday afternoon and evening. Thus, any
   early-day severe risk should remain very localized, with convective
   outflows and cloud debris otherwise complicating forecast details
   later today amidst a late spring-like flow pattern.

   Although subtle/weak surface wave development may occur into
   Missouri through the day along the remnant synoptic frontal zone,
   prevalent outflow (across much of southwest Missouri early this
   morning) should effectively limit the northward extent of the severe
   risk while likely muting the magnitude of the region's overall
   severe potential. While forecast-detail confidence is not
   particularly high, and various model forecasts are likely overly
   aggressive with air mass recovery/destabilization, the best
   potential for strong to severe thunderstorm development this
   afternoon into evening should be across southern/south-central
   Missouri into southern Illinois as outflow presumably modifies and
   some northward-return of moist/unstable air across Arkansas occurs.
   As a belt of modestly enhanced mid-level winds (30-40 kt at 500 mb)
   overspreads the region today, some potential for damaging winds and
   sporadic severe hail may exist especially later this afternoon into
   evening pending sufficient destabilization. 

   ...Texas...
   An outflow-augmented cold front continues to surge southward across
   southwest Texas and at a somewhat slower southeastward pace across
   central Texas. While deep-layer shear will be very weak across
   central/east-central Texas, convective outflows could focus some
   stronger pulse-type updrafts later today, but any severe potential
   is current expected to remain very marginal/localized across
   south-central/east-central Texas.

   Farther west, moist upslope low-level flow will increase across far
   west Texas into southeast New Mexico today. The influence of upslope
   trajectories and heating over the high terrain will aid storm
   development this afternoon particularly over the Transpecos.
   Increasing moisture, moderate buoyancy, and upwards of 35-40 kt
   effective shear should support a few isolated supercells capable of
   large hail.

   ..Guyer/Goss.. 05/20/2018

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z