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
10 %
21,682
109,766
Scottsbluff, NE...Torrington, WY...Douglas, WY...
5 %
134,012
2,090,046
Sioux Falls, SD...Fort Collins, CO...Billings, MT...Greeley, CO...Rapid City, SD...
2 %
80,792
2,834,554
Madison, WI...Thornton, CO...Rochester, MN...Longmont, CO...Sioux City, IA...
Probabilistic Damaging Wind 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 %
40,682
274,892
Rapid City, SD...Pierre, SD...Spearfish, SD...Rapid Valley, SD...Sturgis, SD...
15 %
143,471
3,034,615
Madison, WI...Sioux Falls, SD...Billings, MT...Rochester, MN...La Crosse, WI...
SPC AC 120606
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0106 AM CDT Mon Jun 12 2017
Valid 121200Z - 131200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN WYOMING..NEBRASKA PANHANDLE...AND SOUTHWEST SOUTH DAKOTA...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTH-CENTRAL HIGH PLAINS...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
ROCKIES TO THE UPPER MIDWEST...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
NORTHERN ROCKIES TO THE GREAT LAKES...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MAINE...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS WEST
TEXAS...
...SUMMARY...
Severe thunderstorms 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,
with other strong storms possible across Maine and west Texas this
afternoon into evening.
...MT/WY/CO Front Range and North-central High Plains...
The overall setup appears very favorable for a corridor of locally
intense severe thunderstorms including supercells across the region
later this afternoon into evening, especially across eastern WY into
SD and parts of the NE panhandle. An amplifying upper trough over
the Great Basin will begin to eject more east-northeastward today,
with ample height falls and considerably strengthening
mid/high-level southwesterly winds overspreading CO/WY into the
north-central High Plains through into this evening. In concert with
this large-scale scenario, relatively rich low-level moisture will
continue to develop west-northwestward in concert with
east-southeasterly low-level upslope flow to the north of a
sharpening/northward shifting surface cyclone. Regarding this
relatively rich moisture, Sunday evening's 00Z observed soundings
from Dodge City, Amarillo, North Platte, and Denver all featured
precipitable water values in the upper 10-20th percentile for daily
climatological values.
Given the timing/degree of forcing for ascent and moisture, storms
should steadily increase initially across the northern Rockies
vicinity including parts of ID/southern MT into WY, with other
potentially more intense development expected by mid/late afternoon
near and just east of the WY/northeast CO Front Range vicinity this
afternoon. As storm increase into the High Plains, strong deep-layer
shear with ample low-level veering and very steep lapse
rates/moderate buoyancy will support supercells capable of very
large hail and some tornadoes, especially across eastern WY into NE
Panhandle/southwest SD and possibly northeast CO. It seems likely
that storms will merge and grow upscale and spread
east-northeastward toward the Black Hills vicinity/northwest NE into
other parts of SD/possible far northern NEB this evening with an
increase in severe-caliber wind potential.
...Middle MO Valley/Upper Midwest to Lake MI vicinity...
At the very least, there appears to be an appreciable conditional
severe risk across the region this afternoon into tonight. While
upper-level heights may gradually rise in most areas, a potentially
unstable air mass will exist along a roughly west-east frontal
corridor, with the possibility of at least isolated deep convective
development by late afternoon into evening owing to sufficient
near-boundary convergence/warm advection. A near-boundary maximized
corridor of moderate to strong buoyancy and 30-40 kt effective shear
would support severe storms including a few supercells capable of
large hail and damaging winds.
...Maine...
A weak mid-level disturbance/MCV, potentially related to upstream
convection over the Great Lakes early this morning, should approach
the region later today as an influx of somewhat richer low-level
moisture develops into the region. It appears that the
aforementioned forcing for ascent will be relatively well-timed with
which could be a moderately destabilized air mass this afternoon, in
the presence of relatively strong effective shear. At least some
hail/damaging wind potential appears possible.
...West TX...
Although very warm mid-level temperatures will exist across the
region, the influence of weak height falls in conjunction with ample
near-dryline mixing should be sufficient to develop a few
thunderstorms late this afternoon into early evening. While
low/mid-tropospheric winds will be weak with only 25-30 kt of
effective shear, steep lapse rates/deeply mixed boundary layers and
moderate buoyancy will conditionally support some potential for hail
and stronger downdraft winds.
..Guyer/Gleason.. 06/12/2017
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