Jun 8, 2018 2000 UTC Day 1 Convective Outlook
Updated: Fri Jun 8 19:49:44 UTC 2018 (20180608 2000Z Day 1 shapefile | 20180608 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180608 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 23,739 67,328 No Major Population Center in Risk Area
SLIGHT 92,315 820,533 Rapid City, SD...North Platte, NE...Norfolk, NE...Gillette, WY...Columbus, NE...
MARGINAL 396,612 28,190,236 Indianapolis, IN...Columbus, OH...Omaha, NE...Miami, FL...Cincinnati, OH...
Probabilistic Tornado Graphic
20180608 2000 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
5 % 3,909 97,266 Rapid City, SD...Rapid Valley, SD...
2 % 72,050 1,645,555 Des Moines, IA...Fargo, ND...Ames, IA...West Des Moines, IA...Grand Forks, ND...
Probabilistic Damaging Wind Graphic
20180608 2000 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
30 % 23,739 67,328 No Major Population Center in Risk Area
15 % 92,626 821,321 Rapid City, SD...North Platte, NE...Norfolk, NE...Gillette, WY...Columbus, NE...
5 % 391,887 27,885,764 Indianapolis, IN...Columbus, OH...Omaha, NE...Miami, FL...Cincinnati, OH...
Probabilistic Large Hail Graphic
20180608 2000 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
SIG SEVERE 16,815 196,344 Rapid City, SD...Spearfish, SD...Rapid Valley, SD...Sturgis, SD...Belle Fourche, SD...
15 % 86,333 452,078 Rapid City, SD...Gillette, WY...Scottsbluff, NE...Pierre, SD...Spearfish, SD...
5 % 377,937 25,923,090 Indianapolis, IN...Columbus, OH...Omaha, NE...Miami, FL...Cincinnati, OH...
   SPC AC 081949

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0249 PM CDT Fri Jun 08 2018

   Valid 082000Z - 091200Z


   A cluster of storms producing severe wind and hail is likely across
   parts of South Dakota and Nebraska this evening, including the Black
   Hills region of Wyoming.


   Have increased severe probabilities across portions of eastern WY
   and extreme southeast MT. Otherwise, only minor changes have been
   made to 1630z outlook.

   Isolated thunderstorms are now forming over the southern Big Horn
   Mountains of north-central WY and the Black Hills of SD. This
   activity is expected to expand in areal coverage/intensity as it
   spreads slowly east-southeast this evening. Given the degree of
   moisture/instability holding across the plains of WY have expanded
   severe probs a bit to account for this threat.

   For more information regarding this evolving severe threat, ref MCD

   ..Darrow.. 06/08/2018

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Fri Jun 08 2018/

   16Z surface analysis placed a weak lee cyclone near the WY/NE border
   with a composite front/outflow extending east across NE to southern
   IA. Robust diabatic heating is underway in the wake of a small MCV
   exiting the Mid-MO Valley which will support the boundary advancing
   north into parts of SD by this afternoon. Large buoyancy is expected
   along and south of the boundary with MLCAPE reaching 2000-3000 J/kg
   with boundary-layer dewpoints in the mid 60s beneath steep mid-level
   lapse rates. Initial storm development is expected in the weak
   upslope flow regime across the Black Hills by early afternoon and
   off the Laramie Range by mid afternoon. 30-kt effective shear will
   be adequate for a few supercells initially, with a threat for
   isolated very large hail and a tornado. Storms should grow upscale
   into an MCS during the evening through mergers and outflow
   interactions and spread east then southeast across southern SD and
   NE tonight, north of a strengthening low-level jet over the central
   High Plains. The steep lapse rate environment will favor a
   predominant risk of severe wind gusts this evening, in addition to a
   continued large hail threat. These hazards should wane overnight as
   the MCS approaches the Lower MO Valley.

   ...Southern High Plains...
   Low-level moisture has spread westward into eastern NM, on the west
   side of outflow from decayed early-morning storm clusters in west
   TX.  Strong surface heating will contribute to scattered high-based
   storm development this afternoon along the lee trough from the CO/KS
   border southward along the NM/TX border. Given weak shear, multicell
   clusters will be the primary convective mode, with inverted-V
   profiles favoring isolated severe outflow gusts and marginally
   severe hail from about 22-03Z.

   ...IA to OH...
   Elevated storms are ongoing in a zone of weak low-level warm
   advection from the Upper MS Valley to northern IN, to the north of a
   wavy west-east oriented surface front. This convection will help
   reinforce the front through differential heating,  and isolated to
   scattered surface-based storms are expected along the boundary this
   afternoon. Vertical shear will be weak, but moderate instability
   should support a marginal wind/hail threat until just after sunset.

   ...Central/south FL...
   A weak mid-level low will persist near the north FL Gulf coast, with
   slight enhancement of 500-mb winds over south FL, along with
   relatively cool mid-level temperatures. Surface heating in cloud
   breaks and sea breeze circulations will focus storm development this
   afternoon across much of the Peninsula this afternoon. Where
   deep-layer shear is modest, isolated marginally severe hail and
   strong downburst winds are anticipated.