U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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Storm Prediction Center ac 280727 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0227 am CDT Wed Jun 28 2017 


Valid 301200z - 011200z 


..there is a slight risk of severe thunderstorms across lower 
Michigan...including Lake Michigan... 


..there is a marginal risk of severe thunderstorms from Michigan 
southwestward to the Red River... 


... 
Isolated severe thunderstorms capable of hail or damaging wind are 
possible on Friday from lower Michigan to Oklahoma. The greatest 
severe risk will be over lower Michigan, where a few tornadoes will 
be possible. 


... 
A shortwave trough will exist over the northern plains on Fri, with 
an embedded lead wave affecting the upper Great Lakes during the 
day. A surface low is forecast to move from WI across northern mi, 
with a cold front extending southwest into OK. Ahead of this front, 
substantial moisture will exist with dewpoints generally in the 
65-70 f range. Increased southwesterly flow aloft with the upper 
trough, combined with relatively cool temperatures aloft will result 
in a broad area of thunderstorm potential from lower Michigan to OK. 


..lower Michigan and surrounding Great Lakes... 
Areas of thunderstorms are likely to be ongoing across IA, northern 
Illinois or WI early on Friday, but predictability is currently low as 
possible mcs's are involved. Still, a focused area of afternoon 
severe thunderstorm development appears likely ahead of the surface 
low, mainly over lower Michigan. Here, southerly low-level flow will 
help bring upper 60s f dewpoints northward, while also enhancing 
shear. A few supercells are possible given the forecast hodographs 
which depict effective srh around 200 m2/s2, with the greatest 
tornado threat near the surface low track. 


While lower Michigan appears to have the greatest probability of 
severe storms on Friday, greater severe probabilities could be 
expanded south or west to include parts of WI, IL, and in in later 
outlooks once predictability increases. 


..OK into MO... 
A slow-moving cold front/outflow boundary will stretch from southern 
MO across central OK Friday afternoon, with a very moist and 
unstable air mass in place. Elevated instability is likely to exist 
north of the wind shift as well as 850 mb winds remain southerly. 
Lapse rates aloft will be steep, with 500 mb temperatures around -10 
c. Further, westerly flow aloft will elongate hodographs and 
conditionally support severe storms. Storms would probably form 
close to 00z, as forecast soundings show a small capping inversion. 
Once initiation occurs, a slow southeastward movement is expected, 
with wind and hail threat. If model trends hold, a slight risk will 
be introduced in the day 2 outlook. 


.Jewell.. 06/28/2017 


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