Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0230 AM CDT Thu Aug 20 2026

Valid 221200Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
OHIO VALLEY TO THE LOWER GREAT LAKES...AND OVER PARTS OF THE
NORTHWEST...

...SUMMARY...
Afternoon storms may produce marginal hail or wind gusts from the
Upper Ohio Valley to the Lower Great Lakes, and over parts of the
Northwest on Saturday.

...Upper OH Valley to Lower Great Lakes...
An upper trough will dig across the Great Lakes/OH Valley on
Saturday with a 50 kt backside speed max in the midlevels from MN
into IL. While winds aloft will be weaker farther east, cooling
aloft will overspread the entire region. Meanwhile, a cold front
will push across Lower MI, IN and OH during the day, with a plume of
1500 J/kg MLCAPE developing. This will support clusters of storms
with strong to severe gust potential. The cool temperatures aloft
and effective shear to 30 kt may also support marginal hail.

...Parts of eastern WA...ID...western MT...
A shortwave trough will move across the Northwest on Saturday, with
a 50-60 kt midlevel speed max moving across the region along with
cooling aloft. This trough will steepen midlevel lapse rates,
resulting in an unstable air mass as daytime heating occurs. Storms
are likely to form near the surface trough, and spread across
northern ID and into western MT through the evening and overnight.
The strengthening wind fields combined with favorable lapse rates
will support cells with marginal hail, as well as corridors of
strong wind gusts.

..Jewell.. 08/20/2026

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0329 AM CDT Thu Aug 20 2026

Valid 231200Z - 281200Z

...DISCUSSION...
An upper trough will move slowly across the Northeast Sun/D4 into
Mon/D5, with thunderstorms likely ahead of a cold front. This front
will likely push offshore on Mon/D5 as a surface low ejects
northward across Quebec. A moist air mass will remain ahead of the
front across the Mid Atlantic and into New England, though ongoing
rain and thunderstorms reduce predictability as far as how unstable
it will become on Sun/D4. Also mitigating overall severe risk
appears to be relatively modest low-level wind speeds, with 10-20 kt
at 850 mb. These areas will be monitored for possible low severe
probabilities in the coming days.

To the west, low severe probabilities are possible over parts of the
northern High Plains, as a small but progressive shortwave trough
moves out of the Northwest and across the northern Rockies atop the
upper ridge. West to northwest winds across the northern High Plains
combined with a lee trough and ribbon of 2000 J/kg MUCAPE should
support at least isolated hail/wind activity, perhaps from eastern
MT into the Dakotas.

Additional storm potential, generally low-end, will be possible
Tue/D6 into Wed/D7 over much of the Midwest to Great Lakes, though
predictability is quite low in forecasting the track of the northern
wave, which may begin phasing with a developing upper low over
Ontario.