May 17, 2018 0600 UTC Day 1 Convective Outlook
Updated: Thu May 17 05:53:42 UTC 2018 (20180517 1200Z Day 1 shapefile | 20180517 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180517 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 116,154 1,076,937 Amarillo, TX...Rapid City, SD...Bismarck, ND...Plainview, TX...Mandan, ND...
MARGINAL 224,932 1,930,975 Lubbock, TX...Abilene, TX...Midland, TX...Odessa, TX...Minot, ND...
Probabilistic Tornado Graphic
20180517 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 % 32,576 260,993 Bismarck, ND...Mandan, ND...Dickinson, ND...Sterling, CO...Fort Morgan, CO...
Probabilistic Damaging Wind Graphic
20180517 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 % 112,893 1,057,729 Amarillo, TX...Rapid City, SD...Bismarck, ND...Plainview, TX...Mandan, ND...
5 % 143,880 1,534,731 Lubbock, TX...Abilene, TX...Midland, TX...Odessa, TX...Garden City, KS...
Probabilistic Large Hail Graphic
20180517 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 % 115,719 1,063,251 Amarillo, TX...Rapid City, SD...Bismarck, ND...Plainview, TX...Mandan, ND...
5 % 224,038 1,951,098 Lubbock, TX...Abilene, TX...Midland, TX...Odessa, TX...Minot, ND...
   SPC AC 170553

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1253 AM CDT Thu May 17 2018

   Valid 171200Z - 181200Z


   Severe storms are possible this afternoon and evening across
   portions of the High Plains.

   Convectively induced vorticity maximum currently over northwest MO
   will slowly drift southeastward toward the middle MS valley amidst
   the generally weak mid/upper level flow across the majority of the
   CONUS. The progression of this vorticity maximum will encourage
   persistence, and perhaps a slight deepening, of the mid/upper level
   trough extending from the Southeast states into the lower MO Valley.
   Farther west, an upper low initially over the western Great Basin
   will move northeastward into northern UT with southwesterly flow
   aloft ahead of it extending into the Plains. 

   This southwesterly flow aloft coupled with a pair of subtle
   shortwave troughs will encourage a deepening lee trough and two
   instances of lee cyclogenesis. The northernmost instance is
   anticipated over southeast MT with general southeastward progression
   of the resulting low after 00Z Friday. Southernmost instance is
   expected over southeast CO with little motion anticipated through
   12Z Friday. Resultant strengthening of the surface pressure gradient
   will support increasing southerly/southeasterly return flow,
   although boundary-layer mixing will temper afternoon surface
   dewpoints. Favorable moisture and steep lapse rates will result in
   thunderstorm development along the length of the lee trough across
   the High Plains during the afternoon.

   ...Northern/central High Plains into the northern/central Plains...
   Instability will build throughout the day as low-level moisture
   advects into the region, temperatures warm into the upper 70s/low
   80s, and lapse rates (both mid and low-level) steepen. These same
   processes will lead to airmass destabilization by the mid to late
   afternoon. Surface convergence as well as large-scale forcing for
   ascent amidst this unstable airmass will result in the development
   of strong to severe thunderstorms. Hodographs throughout the region
   show good low-level curvature but weak mid to upper level flow,
   resulting in weak bulk shear and generally unfavorable vertical wind
   profiles. As a result, the expectation is for most of the storms to
   quickly develop strong updrafts but to then struggle with updraft
   maintenance and become outflow dominant. Even so, instability is
   high enough across the region to support severe hail and damaging
   downburst winds. 

   Two areas, one across southwest/south-central ND and the other over
   northeast CO and vicinity, do have some low tornado potential. For
   the ND area, an outflow boundary and cloudiness from overnight
   convection will impede the northward progress of the better
   low-level moisture, resulting in an effective warm front extending
   from the developing lee low into central ND. This front could act to
   locally enhance the low-level shear as well as provide vertical
   vorticity, resulting in a marginal tornado threat. For the northeast
   CO area, slightly better low-level moisture as well as
   orographically enhanced vorticity generation and stronger mid-level
   flow contribute to local tornado potential.

   ...Southern High Plains...
   Another day of dryline convection is anticipated, with higher
   coverage than Wednesday. Mid-level flow will be weak but stronger
   upper level flow and lift under the left exit region of the upper
   jet will likely contribute to an area of relatively higher severe
   threat across the eastern TX and OK Panhandles.

   ..Mosier/Cook/Wendt.. 05/17/2018