May 22, 2021 1730 UTC Day 2 Convective Outlook
Updated: Sat May 22 17:27:49 UTC 2021 (20210522 1730Z Day 2 shapefile | 20210522 1730Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20210522 1730 UTC Day 2 Outlook Graphic
Day 2 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 151,113 893,997 Rapid City, SD...Bismarck, ND...Garden City, KS...North Platte, NE...Aberdeen, SD...
MARGINAL 453,241 26,744,146 Boston, MA...Minneapolis, MN...Aurora, CO...St. Paul, MN...Lubbock, TX...
Probabilistic Tornado Graphic
20210522 1730 UTC Day 2 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 2 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 19,964 68,681 Rapid City, SD...Rapid Valley, SD...
2 % 83,701 460,257 Garden City, KS...North Platte, NE...Pierre, SD...Spearfish, SD...Sturgis, SD...
Probabilistic Damaging Wind Graphic
20210522 1730 UTC Day 2 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 2 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 149,705 886,004 Rapid City, SD...Bismarck, ND...Garden City, KS...North Platte, NE...Aberdeen, SD...
5 % 443,064 25,590,336 Boston, MA...Minneapolis, MN...St. Paul, MN...Lubbock, TX...Amarillo, TX...
Probabilistic Large Hail Graphic
20210522 1730 UTC Day 2 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 2 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 145,204 758,345 Rapid City, SD...North Platte, NE...Aberdeen, SD...Mitchell, SD...Pierre, SD...
5 % 309,398 9,800,147 Minneapolis, MN...Aurora, CO...St. Paul, MN...Lubbock, TX...Amarillo, TX...
   SPC AC 221727

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 PM CDT Sat May 22 2021

   Valid 231200Z - 241200Z


   Severe thunderstorms capable of severe gusts and large hail are
   possible across portions of the northern Great Plains tomorrow
   afternoon and evening.

   A mid-level trough will eject into the northern High Plains, with
   surface lee troughing encouraging the northward advection of a warm,
   relatively moist airmass across the northern and central CONUS
   tomorrow. Deep-layer ascent associated with the approaching trough,
   and strong surface heating with upslope flow will support scattered
   strong to severe thunderstorm development along the lee of the
   Rockies, from the U.S./Canada to Mexico borders. Upper ridging and
   surface high pressure will dominate much of the Ohio Valley into the
   Southeast, with deep-layer northwesterly flow prevailing across the
   Northeast, where scattered storms (some strong to locally severe)
   are likely tomorrow afternoon ahead of a cold front.

   ...Northern High Plains into the Dakotas...
   Weak surface low development is expected along a warm front across
   the northern High Plains during the morning hours, with the low
   expected to be positioned across western SD by afternoon peak
   heating. Ahead of the low, low 60s F dewpoints will reach northern
   SD during the afternoon, overspread by 7+ C/km mid-level lapse
   rates, supporting widespread 1500 J/kg MLCAPE. 30-50 kts of
   effective bulk shear is expected ahead of an eastward moving cold
   front given ample speed shear. However, troposheric flow will be
   meridional, with unidirectional wind shear above 700 mb expected
   across the central/northern Plain states tomorrow. As such, storms
   should rapidly grow upscale into linear segments, with damaging
   winds and large hail expected as the primary severe hazards. Ahead
   of the surface low and along the warm front across portions of
   western SD, relatively greater backing of the surface winds will
   contribute to locally better low-level veering vertical wind
   profiles. Modestly enlarged hodographs/200+ m2/s2 effective SRH will
   promote some tornado threat with circulations embedded in line
   segments, along with any storms that can manage to stay discrete
   ahead of the line.

   ...Central into the southern High Plains...
   Low-level convergence due to upslope flow and afternoon peak heating
   will encourage scattered thunderstorm development along the lee of
   the higher terrain. Ahead of the storms, a moist low-level airmass
   (characterized by low 60s F dewpoints) will contribute to 1000-1500
   J/kg MLCAPE. Relatively weak deep-layer and low-level shear will
   foster cold pool mergers with multicellular clusters/transient
   supercells upscale-growing into line segments an hour or so after
   maturity. Large hail may occur with the initial, more discrete storm
   modes, with damaging gusts becoming more prevalent after upscale

   Mid 60s F dewpoints beneath 5.5-6 C/km mid-level lapse rates will
   foster 500-1000 J/kg MLCAPE ahead of the cold front, where at least
   isolated thunderstorm development is expected tomorrow afternoon.
   While tropospheric flow will be unidirectional (northwesterly),
   40-50 kts of effective bulk shear suggests that some of the storms
   may become organized/strong. As temperatures warm into the 80s F,
   modest boundary-layer mixing may encourage downward momentum
   transport of the stronger flow aloft, with a couple of damaging
   gusts possible with the stronger storms.

   ..Squitieri/Gleason.. 05/22/2021