Jun 9, 2018 0600 UTC Day 1 Convective Outlook
Updated: Sat Jun 9 04:41:57 UTC 2018 (20180609 1200Z Day 1 shapefile | 20180609 1200Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180609 1200 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SLIGHT 29,276 210,693 Great Falls, MT...Helena, MT...
MARGINAL 341,935 47,315,406 Chicago, IL...Indianapolis, IN...Columbus, OH...Washington, DC...St. Louis, MO...
Probabilistic Tornado Graphic
20180609 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
2 % 36,933 2,313,153 Des Moines, IA...Rochester, MN...Waterloo, IA...Ames, IA...West Des Moines, IA...
Probabilistic Damaging Wind Graphic
20180609 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 % 29,867 211,061 Great Falls, MT...Helena, MT...
5 % 343,663 47,590,205 Chicago, IL...Indianapolis, IN...Columbus, OH...Washington, DC...St. Louis, MO...
Probabilistic Large Hail Graphic
20180609 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
5 % 248,331 19,344,770 St. Louis, MO...Madison, WI...Des Moines, IA...Aurora, IL...Rockford, IL...
   SPC AC 090441

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1141 PM CDT Fri Jun 08 2018

   Valid 091200Z - 101200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   WEST-CENTRAL MONTANA...WITH AN UPGRADE FROM MARGINAL TO SLIGHT
   POSSIBLE ACROSS IOWA INTO SOUTHERN MINNESOTA...

   ...SUMMARY...
   A few severe storms are expected across parts of west-central
   Montana, and from southern Minnesota and Iowa. Scattered strong
   storms are also possible from Illinois eastward into northern
   Virginia.

   ...Synopsis...
   A large upper trough will move east across the Pacific Northwest and
   Great basin, with strong meridional flow aloft spreading into the
   northern Rockies. At the surface, a cold front will move into
   western MT during the afternoon, with southeasterly surface winds
   helping to bring moisture westward to the front and supporting a few
   severe storms.

   To the east, a large-scale upper ridge will remain across the
   Plains, but will weaken with time. In addition, areas of convection
   will likely be ongoing across eastern NE and SD into IA and MN, with
   a possible MCV helping to focus latter-day convection.

   Elsewhere, a moist and unstable air mass will extend from IL to VA,
   with sporadic daytime storms capable of marginal wind. Last,
   isolated storms capable of hail are again possible around the Black
   Hills as southeast winds maintain 50s F dewpoints into that area.

   ...Southern MN and IA into southern WI and northern IL...
   A complex forecast scenario exists for today, with a conditional
   risk of severe storms. Models generally agree that an MCS or MCV
   will be present across southern MN into IA early in the day, but
   this also brings a chance of air mass contamination from outflow and
   also the possibility of extensive clouds. If contamination is
   minimized, then strong instability would likely develop, with
   enhanced convergence near the MCV helping to focus diurnal
   development. Forecast soundings show that although winds aloft are
   not strong, there may be substantial low-level hodograph curvature,
   which could support a brief tornado or two along with hail. Wind
   would become a concern if enough of a cold pool could be produced
   and storms accelerate, perhaps into northern MO and IL. Given these
   uncertainties, will maintain a Marginal Risk, with the possibility
   of an upgrade across parts of IA into southern MN in later outlooks.


   ...Western Montana...
   Strong heating will result in deep mixed layers across MT just ahead
   of a cold front. Lift along the front as well as the steep lapse
   rate environment will utilize 40s F dewpoints and support a few
   severe storms capable of wind or hail, as wind profiles will
   strengthen and become favorable for a few long-lived cells or small
   bows. While moisture will be more robust farther east, it is unclear
   how many storms will form away from the cold front, but any isolated
   activity could also become severe.

   ..Jewell/Wendt.. 06/09/2018

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