026
ACUS01 KWNS 280453
SWODY1
SPC AC 280451

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1151 PM CDT Sun Sep 27 2026

Valid 281200Z - 291200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorm probability remains low on Monday.

... Synopsis ...

A broad mid/upper-level trough will move inland over California and
begin to close off over the lower Colorado River Valley, while a
weaker shortwave trough moves through the northern Rockies.
Large-scale flow around the Southwest US trough will draw deep
tropical moisture tied to Hurricane Polo and remnants of Odalys
northward into the Southwest. Downstream of this, a weaker mid-level
short-wave trough will move across the northern Rockies, mid-level
ridging will persist across the central US and a weakening
vertically stacked cyclone will begin to move northeast along the
southern New England coast.

At the surface, a weak trough will sharpen along the lee of the
northern Rockies ahead of a surface cold front that will move
southeast into the northern and central Dakotas overnight.


... Northern High Plains ...

Persistent southerly low-level flow will keep modest moisture over
the northern High Plains. Warm-advection showers and thunderstorms
along the low-level jet axis Monday morning, followed by thickening
mid/high-level clouds, will likely limit destabilization. Where
filtered sunshine is able to promote stronger surface heating, a
corridor of MUCAPE between 500-1500 J/kg (per mean HREF values) may
develop by late afternoon near the surface trough from northeast
Wyoming, western South Dakota, and southwest/south-central North
Dakota.

Isolated storms may form near the trough in the late afternoon or
early evening. Increasing mid-level flow ahead of the northern
Rockies short-wave trough will provide sufficient vertical shear for
a few thunderstorms capable of producing small to marginally severe
hail. Additionally, locally strong thunderstorm wind gusts will be
possible where the boundary layer becomes well mixed. However,
modest mid-level warming, weak large-scale ascent, and uncertainty
about whether intense storms form at all should keep any potential
severe window narrow in space and time.

More elevated storms are possible Monday night as the low-level jet
strengthens and the cold front moves into the northern and central
Dakotas. Buoyancy will weaken overnight and become increasingly
elevated, which should limit any severe wind threat after dark.


... Southwest ...

Numerous showers and thunderstorms are expected as an anomalously
moist airmass spreads north ahead of the western trough. Widespread
clouds and weak midlevel lapse rates should keep instability
generally weak and storm organization limited. An isolated wet
downburst is possible from heavier cores in any pockets of strong
heating, but the severe threat appears too low to warrant
unconditional probabilities.


... Northeast ...

Showers and occasional embedded thunder -- mainly near the coast --
may continue with the slowly weakening cyclone. Instability will be
weak, so severe thunderstorm potential is extremely low. However,
strong onshore gradient winds may cause isolated/sporadic damage.

..Marsh/Weinman.. 09/28/2026

$$