Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0222 AM CDT Sat Aug 29 2026

Valid 311200Z - 011200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Isolated severe thunderstorms, accompanied by wind and hail, are
possible Monday afternoon across parts of the Upper Mississippi
Valley.

...Synopsis...
A 500 mb anticyclone will become established over the central Plains
to the Mid-MS Valley on Monday, with a low-amplitude mid-level
shortwave trough poised to crest the ridge and impinge on the Upper
MS Valley. A surface trough will become established across the Upper
MS Valley/Midwest during the afternoon, promoting enough deep-layer
ascent for isolated thunderstorm development when also considering
the approach of the upper trough. Additionally, stronger mid-level
flow, accompanied by cooler temperatures aloft, will overspread a
moist boundary layer, supporting scattered strong to isolated severe
thunderstorms over portions of the Upper MS Valley. 

...Portions of the Upper MS Valley...
The aforementioned low-amplitude mid-level trough will impinge on
the Upper MS Valley and support surface lee troughing by afternoon.
A diffuse warm front may also materialize roughly along the MN/IA
border into central WI. An appreciable EML will extend from the
central Rockies to the western Great Lakes, with up to 8 C/km
mid-level lapse rates possible. These lapse rates will overspread
mid 70s F dewpoints, yielding over 3000 J/kg MLCAPE on a widespread
basis, especially near the warm front. Given the possibility of an
increasing low-level jet beneath 30-50 kt 500 mb flow, elongated
hodographs with 40+ kts of effective bulk shear are possible. Such
conditions would favor supercellular development, with at least
severe wind and hail possible. However, storm coverage remains in
question since the strongest deep-layer ascent accompanying the
low-amplitude upper trough will only graze the warm frontal zone to
the north. Higher severe probabilities may be needed pending greater
confidence in higher storm coverage.

..Squitieri.. 08/29/2026

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0355 AM CDT Sat Aug 29 2026

Valid 011200Z - 061200Z

...DISCUSSION...
Medium range guidance consensus depicts a persistent ridge fortified
across the central CONUS through the Days 4-8 (Tuesday-Saturday)
period. Multiple mid-level shortwave troughs and smaller scale
impulses will pivot around the broader upper ridge and traverse the
Pacific Northwest to northern Plains, Great Lakes, and Northeast
through the week. The best chance for rounds of organized strong to
severe thunderstorms will be with impulses overspreading a moist
boundary layer from the Upper MS Valley to the southern New
England/Mid-Atlantic regions. Details regarding the timing and
placement of some of these impulses varies among medium-range
guidance, rendering predictability too low for several potential
severe scenarios. 

...Days 4-7 (Tuesday-Friday) - Northeast/Mid-Atlantic...
The Northeast to Mid-Atlantic will experience the east-northeast
periphery of the aforementioned upper ridge, with multiple impulses
expected to overspread the region through the middle of the week. At
least isolated to scattered severe thunderstorms are expected each
day Tuesday-Friday. At the moment, medium range guidance consensus
shows the strongest signal in a mid-level impulse impinging on
southern New England and the Mid-Atlantic on Day 5/Wednesday, where
severe probabilities have been maintained. 

Guidance also depicts these same regions to have adequate vertical
wind shear and instability Tuesday and Thursday, perhaps even
extending into Day 7/Friday. Like Wednesday, several members of
medium range ML/AI generated guidance also has severe probabilities
over these regions Days 4-7. Unlike Wednesday though, deterministic
medium range guidance varies in place and time of the more subtle
impulses expected to support severe weather over the Northeast. It
is acknowledged that severe probabilities will likely be needed in
the future. However, probabilities have been withheld outside of
Wednesday out of prudence given the degree of changes in forecast
details expected in the coming days.