Jun 12, 2017 2000 UTC Day 1 Convective Outlook
Updated: Mon Jun 12 20:00:46 UTC 2017 (20170612 2000Z Day 1 shapefile | 20170612 2000Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...Severe thunderstorms expected over parts of the north-central High Plains this afternoon and evening....   Please read the latest public statement about this event.  View What is a Watch? clip.

Categorical Graphic
20170612 2000 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MODERATE 17,207 89,587 Scottsbluff, NE...Torrington, WY...Douglas, WY...
ENHANCED 52,464 435,987 Rapid City, SD...Cheyenne, WY...Gillette, WY...Pierre, SD...Sterling, CO...
SLIGHT 256,518 9,065,260 Milwaukee, WI...Madison, WI...Sioux Falls, SD...Fort Collins, CO...Cedar Rapids, IA...
MARGINAL 291,730 24,437,440 Detroit, MI...Denver, CO...Omaha, NE...Minneapolis, MN...Aurora, CO...
Probabilistic Tornado Graphic
20170612 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
SIG SEVERE 19,392 84,484 Scottsbluff, NE...Torrington, WY...Douglas, WY...
15 % 11,840 69,346 Scottsbluff, NE...Torrington, WY...Douglas, WY...
10 % 20,297 189,751 Cheyenne, WY...Gillette, WY...
5 % 54,176 496,171 Greeley, CO...Rapid City, SD...Evans, CO...Sheridan, WY...Windsor, CO...
2 % 129,857 5,128,982 Madison, WI...Sioux Falls, SD...Fort Collins, CO...Billings, MT...Rochester, MN...
Probabilistic Damaging Wind Graphic
20170612 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 % 37,925 253,091 Rapid City, SD...Pierre, SD...Spearfish, SD...Rapid Valley, SD...Sturgis, SD...
15 % 244,034 8,919,960 Milwaukee, WI...Madison, WI...Sioux Falls, SD...Cedar Rapids, IA...Billings, MT...
5 % 316,233 23,934,704 Detroit, MI...Denver, CO...Omaha, NE...Minneapolis, MN...Aurora, CO...
Probabilistic Large Hail Graphic
20170612 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 44,396 341,103 Cheyenne, WY...Gillette, WY...Scottsbluff, NE...Sterling, CO...Torrington, WY...
45 % 16,926 85,523 Scottsbluff, NE...Torrington, WY...Douglas, WY...
30 % 52,158 436,189 Rapid City, SD...Cheyenne, WY...Gillette, WY...Pierre, SD...Sterling, CO...
15 % 258,202 9,131,169 Milwaukee, WI...Madison, WI...Sioux Falls, SD...Fort Collins, CO...Cedar Rapids, IA...
5 % 290,243 24,292,810 Detroit, MI...Denver, CO...Omaha, NE...Minneapolis, MN...Aurora, CO...
   SPC AC 122000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Mon Jun 12 2017

   Valid 122000Z - 131200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   SOUTHEAST WY...THE NE PANHANDLE...AND SOUTHEAST SD...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   WY...CO...NE...AND SD...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EXTENDING FROM
   SOUTHERN MT INTO CENTRAL/SOUTHERN WI...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   ME...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   NORTHERN ROCKIES INTO THE GREAT LAKES REGION...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   WEST TX...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   ME...

   ...SUMMARY...
   Severe thunderstorms with tornadoes, very large hail, and damaging
   winds are likely this afternoon into tonight across the
   north-central High Plains. Other severe thunderstorms are expected
   from parts of the northern Rockies to the Upper Midwest, as well as
   across Maine and west Texas this afternoon into evening.

   ...20Z Update...
   Little changes needed to the ongoing forecast. Latest observational
   trends/guidance continue to suggest that a relatively rapid increase
   of intense surface-based thunderstorms will occur over the next few
   hours across the northern CO into WY Front Range and adjacent High
   Plains, with considerable towering cu and incipient thunderstorm
   development at 20Z spanning areas from west of Boulder/Fort Collins
   CO north-northwestward to areas near/west of Laramie/Casper WY, with
   other towering cu farther east across southeast WY roughly near the
   I-80 corridor.  All indications are that supercells capable of large
   hail and tornadoes, some of which may be strong, are likely
   especially with the Moderate Risk corridor as storms spread
   northeastward through the early evening hours.

   Elsewhere, a cluster of storms are likely to continue to pose a
   damaging wind/severe hail risk from southeast MN into central WI
   this afternoon in close proximity of a roughly west/east-oriented
   front where moderate buoyancy/effective shear are collocated. These
   storms should reach eastern WI by late afternoon/early evening and
   there is some possibility a severe risk could even continue into
   lower MI.

   ..Guyer.. 06/12/2017

   .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 12 2017/

   ...Northern High Plains...
   An upper low is centered over NV this morning, with a progressive
   shortwave trough rotating through the base of the low and into UT. 
   Lift and mid-level cooling ahead of this feature is expected to
   promote thunderstorm development over parts of the northern Rockies
   and High Plains this afternoon and evening.  East-southeasterly
   low-level winds over southeast WY and northeast CO have transported
   rich boundary-layer moisture back to the foothills, where daytime
   heating and approaching trough will likely result in first
   initiation of thunderstorms.  Forecast soundings in this area show
   very steep lapse rates and large CAPE values, as well as favorable
   low-level and deep-layer vertical shear.  Discrete supercells will
   be likely as activity moves off the higher terrain and into the
   adjacent High Plains.  Parameters appear quite favorable for very
   large hail and tornadoes with these storms.  Strong tornadoes are
   possible today.  This evening, several CAM solutions suggest an
   upscale evolution to one or more bowing complexes as storms move
   into western NE/SD.

   ...NE/IA/MN/WI...
   Scattered strong/severe thunderstorms are ongoing this morning over
   parts of southeast SD and southwest MN.  This activity is in
   proximity to a surface boundary that extends eastward into southern
   WI.  Given the strong heating and destabilization occurring along
   the boundary, it appears likely that this activity will persist
   through much of the day and build eastward along the front.  Large
   hail and damaging winds will be possible in this corridor.  Models
   hint at the development of a bowing MCS this evening, affecting
   parts of IA/WI.

   ...MT/WY...
   To the northwest of the primary severe concern today (southeast WY),
   there will be a risk of severe storms capable of large hail and
   damaging winds into parts of western MT and northern WY. 
   Thunderstorms may form through the afternoon over parts of eastern
   ID and central WY, and build northward into MT during the evening. 
   Large hail and gusty/damaging winds will be possible in the
   strongest cells.

   ...Maine...
   Strong heating is occurring today over much of ME, with fast
   westerly flow aloft and dewpoints in the 60s.  A consensus of 12z
   model guidance shows considerable coverage of afternoon
   thunderstorms in this region.  Forecast soundings show moderate CAPE
   values and sufficient deep-layer shear to support a few rotating
   storms.  Hail will be the main threat in the stronger cells, but
   gusty outflow winds will also be possible.

   ..TX..
   A few high-based thunderstorms capable of gusty winds and hail will
   be possible this afternoon over parts of west TX, in a corridor of
   strong CAPE and steep low-level lapse rates.  This threat should be
   focused in the 23-03z period.

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