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Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1300Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion


000
ACUS01 KWNS 201239
SWODY1
SPC AC 201238

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0738 AM CDT Wed Sep 20 2017

Valid 201300Z - 211200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS UPPER MI TO
NORTHERN MO...

...SUMMARY...
Isolated severe hail and damaging winds are possible from the Upper
Peninsula of Michigan to northern Missouri between about 4 to 11 pm
CDT.

...Upper MI to northern MO...
A potent shortwave trough over the southern Canadian Prairies to Red
River Valley will move northeast towards Hudson Bay. Attendant cold
front will push east into central WI with trailing portion about to
stall over the Lower MO Valley. Middle 60s to lower 70s surface dew
points will be maintained ahead of this boundary with mean mixing
ratios of 12-16 g/kg common in area 12Z observed soundings. The 06Z
NAM appears overdone with depictions of mean mixing ratios reaching
17-19 g/kg and extreme MLCAPE of 3500-5000 J/kg. A plume of
2000-3500 J/kg appears more probable from central WI southwestward
at peak heating.

Capping will inhibit surface-based storm development until after 21Z
amid weak mid-level height rises. Convergence near the front, aided
by modest low-level warm advection, may eventually yield widely
scattered storms during the evening. Hodographs will remain small
west of the MS River. The WI vicinity will lie on the fringe of
moderate mid-level southwesterlies, marginally favorable for a
couple transient supercell structures. The predominant mode should
be multicells offering a risk of isolated severe hail and damaging
winds. Storms should weaken by late evening owing to the modest
shear and forcing for ascent.

..Grams/Kerr.. 09/20/2017

$$