Sep 11, 2019 0600 UTC Day 1 Convective Outlook
Updated: Wed Sep 11 05:53:51 UTC 2019 (20190911 1200Z Day 1 shapefile | 20190911 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20190911 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 21,696 137,930 North Platte, NE...Scottsbluff, NE...Torrington, WY...
SLIGHT 110,607 3,703,289 Sioux Falls, SD...Green Bay, WI...Rochester, MN...Sioux City, IA...Appleton, WI...
MARGINAL 424,208 80,428,020 New York, NY...Chicago, IL...Philadelphia, PA...Detroit, MI...Baltimore, MD...
Probabilistic Tornado Graphic
20190911 1200 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 % 21,862 97,313 Scottsbluff, NE...Torrington, WY...
2 % 86,916 5,150,600 Milwaukee, WI...Madison, WI...Rochester, MN...Sioux City, IA...Appleton, WI...
Probabilistic Damaging Wind Graphic
20190911 1200 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
15 % 132,505 3,844,530 Sioux Falls, SD...Green Bay, WI...Rochester, MN...Sioux City, IA...Appleton, WI...
5 % 381,195 79,359,841 New York, NY...Chicago, IL...Philadelphia, PA...Detroit, MI...Baltimore, MD...
Probabilistic Large Hail Graphic
20190911 1200 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 28,957 155,596 North Platte, NE...Scottsbluff, NE...Torrington, WY...
30 % 21,980 137,291 North Platte, NE...Scottsbluff, NE...Torrington, WY...
15 % 129,572 3,879,637 Sioux Falls, SD...Green Bay, WI...Rochester, MN...Sioux City, IA...Appleton, WI...
5 % 175,953 13,962,470 Milwaukee, WI...Omaha, NE...Minneapolis, MN...St. Paul, MN...Madison, WI...
   SPC AC 110553

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1253 AM CDT Wed Sep 11 2019

   Valid 111200Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
   WESTERN NEBRASKA...AND SMALL ADJACENT PARTS OF WYOMING AND
   COLORADO...

   ...SUMMARY...
   Severe thunderstorms capable of producing large hail, damaging wind
   gusts, and a tornado or two are possible mainly over parts of the
   central and northern Plains. More isolated and/or marginal severe
   storms are possible extending eastward across the southern Great
   Lakes and to the East Coast from Virginia to New Jersey.

   ...Synopsis...
   A shortwave trough will progress east across the Rockies, with a
   50-60 kt midlevel speed max moving from the central High Plains
   during the day to the central Plains by Thursday morning. Modest
   westerly winds aloft will extend across the Great Lakes, north of a
   gradually weakening upper high over the Southeast.

   At the surface, low pressure will move from northeast CO across NE,
   with a stationary front roughly from northern NE, IA and into
   southern WI. Early day storms and outflow may change the position of
   this front.  During the evening and overnight, a cold front will
   move east across the central Plains behind the low.

   Dewpoints in the 65-70 F range will be common south of the
   stationary front and ahead of the cold front, aiding the development
   of ample instability supporting strong to severe storms from eastern
   WY into southern WI.

   ...Eastern WY...far northeast CO...NE...
   An outflow boundary now over west-central NE and northeast CO is
   expected to mix during the day, and may retreat north as southerly
   winds increase ahead of the upper trough. Heating south of the
   outflow (and ahead of the developing cold front over eastern WY)
   along with ample moisture will lead to strong instability. Low-level
   winds will veer with height, but will remain relatively weak below
   700 mb resulting in long, mostly straight hodographs as the upper
   jet overspreads the High Plains. Storms are expected to form over
   eastern WY by early afternoon, and over northeast CO and western NE
   near a triple point. Supercells capable of very large hail will be
   possible, with perhaps brief tornadoes although effective SRH will
   average 100-150 m2/s2 prior to 00Z. Thereafter, storms are expected
   to merge into an MCS with damaging wind the main concern. 

   ...Upper MS Valley and Great Lakes...
   Storms may be ongoing early in the day as an MCS (now over SD/MN/IA)
   continues east along the instability gradient. Southwest winds at
   850 mb will also maintain warm/moist advection into the region,
   supporting continued development or rejuvenation of the pre-existing
   system. Damaging winds appears to be the main concern.

   ...PA and NJ southwestward into northern GA...
   Although beneath an upper ridge, the air mass will remain moist and
   the region will experience strong heating. MLCAPE of 2000-3000 J/kg
   will develop, and will conditionally favor pulse storms capable of
   marginally severe wind or hail over the Appalachians. Storm mode
   over northern areas such as PA and NJ may trend toward multicells
   with 20-30 kt mid to high-level flow. The severe threat will be tied
   to the diurnal cycle, and will dwindle by early evening.

   ..Jewell/Squitieri.. 09/11/2019

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z