Aug 11, 2019 1300 UTC Day 1 Convective Outlook
Updated: Sun Aug 11 12:48:06 UTC 2019 (20190811 1300Z Day 1 shapefile | 20190811 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20190811 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 19,166 85,295 No Major Population Center in Risk Area
SLIGHT 174,906 1,500,472 Billings, MT...Greeley, CO...Rapid City, SD...Cheyenne, WY...Grand Island, NE...
MARGINAL 239,049 14,664,961 Denver, CO...Kansas City, MO...Omaha, NE...Colorado Springs, CO...St. Louis, MO...
Probabilistic Tornado Graphic
20190811 1300 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 % 36,455 306,443 Billings, MT...Gillette, WY...Sterling, CO...Fort Morgan, CO...Laurel, MT...
2 % 120,066 914,805 Greeley, CO...Rapid City, SD...Cheyenne, WY...Bozeman, MT...Hays, KS...
Probabilistic Damaging Wind Graphic
20190811 1300 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 % 19,239 85,025 No Major Population Center in Risk Area
15 % 174,357 1,446,319 Billings, MT...Greeley, CO...Rapid City, SD...Cheyenne, WY...Grand Island, NE...
5 % 240,935 14,936,896 Denver, CO...Kansas City, MO...Omaha, NE...Colorado Springs, CO...St. Louis, MO...
Probabilistic Large Hail Graphic
20190811 1300 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 35,454 252,557 Billings, MT...Gillette, WY...Livingston, MT...Laurel, MT...
15 % 164,818 1,224,823 Billings, MT...Greeley, CO...Rapid City, SD...Cheyenne, WY...Bozeman, MT...
5 % 160,255 5,342,121 Denver, CO...Colorado Springs, CO...Aurora, CO...Lincoln, NE...Lakewood, CO...
   SPC AC 111248

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0748 AM CDT Sun Aug 11 2019

   Valid 111300Z - 121200Z


   Areas of strong to severe storms are expected over portions of the
   northern through central High Plains this afternoon into tonight. 
   Large hail and severe gusts are the primary threats.

   ...Central High Plains to the middle MS Valley through tonight...
   A belt of somewhat enhanced midlevel flow extends from the southern
   Rockies to the central Plains, around the northwest periphery of the
   midlevel ridge over the southern Plains.  Within this belt, an MCS
   and associated MCV are moving eastward over northeast KS.  The
   convection has been maintained overnight by warm advection on the
   nose of a 30-40 kt low-level jet, within a corridor of PW near 2
   inches and moderate buoyancy.  The low-level jet will veer to more
   westerly through late morning and weaken, and the MCS will likewise
   weaken.  Some additional storm development is expected during the
   day along the leading edge of the residual cold pool and zone of
   ascent preceding the MCV, but the storm environment will be less
   favorable for organized severe storms with damaging winds/hail with
   eastward extent across MO/IL.

   In the wake of the morning convection, an upslope regime will
   establish from northwest KS into northeast CO/southwest NE, north of
   a lee cyclone in southeast CO.  Recovery of low-level moisture and
   surface heating will again boost MLCAPE to 2000-3000 J/kg by
   mid-late afternoon.  Thunderstorm development is expected first near
   and immediately east of the Front Range in CO, while the boundary
   layer should remain capped through much of the afternoon in far
   northeast CO and vicinity.  Buoyancy and deep-layer vertical shear
   will be sufficient for both supercells and multicell clusters with
   large hail/damaging winds with the initial deep convection east of
   the Front Range.  Wind profiles will be more favorable for
   supercells farther east on the High Plains where low-level easterly
   flow and hodograph curvature will be greater, though there will be a
   tendency for cell interactions and upscale growth later into the
   evening and farther east.  Any semi-discrete supercells will pose a
   threat for a couple of tornadoes and large hail, while the damaging
   wind threat will increase with storm clustering into the evening. 
   Storms will likely evolve into an MCS tonight while spreading
   eastward on the immediate cool/moist side of a quasi-stationary
   front expected to reside a little south of I-70.

   ...MT/northern High Plains this afternoon/evening...
   A midlevel trough near the OR/ID border will eject
   east-northeastward over MT this afternoon and reach the northern
   High Plains overnight.  Easterly low-level flow will be maintained
   through the day across southern MT, to the north of a surface
   cyclone in central WY.  This will help draw 58-62 F dewpoints
   westward across southern MT, beneath steep midlevel lapse rates,
   which will contribute to MLCAPE of 1500-2000 J/kg.  Convective
   initiation is expected by early afternoon over the high terrain of
   southwest MT, with storms subsequently moving northeastward and
   developing eastward across southern MT to northeast WY by mid-late
   afternoon.  Effective bulk shear of 35-50 kt will favor supercells
   initially with large hail and possibly a couple of tornadoes, and
   convection is expected to grow upscale into a couple of
   clusters/line segments across MT/western SD by this evening, with an
   accompanying threat for damaging winds.

   ..Thompson/Kerr.. 08/11/2019