ACUS01 KWNS 062002
SWODY1
SPC AC 062000

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0300 PM CDT Sun Sep 06 2026

Valid 062000Z - 071200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHEAST...MONTANA...AND THE MISSOURI VALLEY...

...SUMMARY...
Scattered damaging winds should occur across parts of the Southeast
this afternoon/early evening. Scattered large hail is forecast
across portions of Montana this afternoon and evening. A focused
corridor for damaging winds and severe hail is forecast across parts
of the Middle and Lower Missouri Valley. Isolated strong to severe
thunderstorms may also occur today across parts of the northern
Great Basin, northern/central Plains, and the Ozarks.

...20Z Update...
A Slight Risk was added across parts of the Middle and Lower
Missouri Valley -- driven by 15-percent wind and hail probabilities.
Here, ample diurnal heating amid a very moist air mass is yielding a
corridor of strong surface-based buoyancy (around 4000 J/kg MLCAPE
per the latest HRRR SFCOA data). Large-scale ascent preceding a
convectively augmented midlevel impulse should promote an increase
in storm coverage in this north/south corridor through the
afternoon. The strong buoyancy and around 30 kt of effective shear
should promote a mix of organized clusters and possibly some
supercell structures -- capable of producing damaging wind gusts and
severe hail. See MCD #2253 for more details. 

Farther north, the Slight Risk in ND was removed. The latest mode
evolution suggests a reduced hail threat compared to this morning.
However, a locally favorable corridor for damaging wind gusts may
develop into parts of eastern ND this afternoon/early evening. 

Elsewhere, the previous forecast remains on track.

..Weinman.. 09/06/2026

.PREV DISCUSSION... /ISSUED 1130 AM CDT Sun Sep 06 2026/

...Southeast/Lower Mississippi Valley...
Recent visible satellite imagery shows mostly clear skies across
GA/SC late this morning, with surface temperatures already in the
mid/upper 80s to low 90s. A weak front is draped from northwest to
southeast from the southern Appalachians to the Atlantic Coast, with
generally low to mid 70s surface dewpoints present to its south.
Continued diurnal heating of this moist airmass will support the
development of moderate to strong instability (greater with
southward/westward extent into GA/AL and north FL). Compared to the
past couple of days, this region will be displaced from the stronger
mid-level west-northwesterly flow present across the
Mid-Atlantic/Northeast. Corresponding deep-layer shear is expected
to remain rather modest (less than 25 kt), with only loosely
organized updrafts forecast. Even with these kinematic limitations,
steepening low-level lapse rates through the afternoon may still
promote isolated to scattered damaging winds with clusters that
develop and spread south-southeastward through the early evening.
Isolated hail may also occur with the more robust cells that can
develop initially. The damaging wind threat should be more isolated
with westward extent into the lower MS Valley compared to GA and the
Carolinas, where the Slight Risk has been maintained with some expansion.

...Northern Great Basin into the Northern Rockies/High Plains...
A closed mid/upper-level low over the Pacific Northwest and British
Columbia will pivot towards the northern Rockies through the period,
with a belt of enhanced mid-level flow overspreading the northern
Great Basin into the northern Rockies and adjacent High Plains in
MT. At the surface, mostly cloudy conditions are present over much
of western/central MT this morning. Even so, recent NAM/RAP forecast
soundings across this region show supercell profiles later this
afternoon and evening as mid/upper-level winds foster strong
deep-layer shear. Current expectations are for multiple supercells
to develop initially over the higher terrain and spread quickly
northeastward. While there is still some uncertainty regarding
boundary-layer destabilization, sufficient MUCAPE is forecast to
support supercell maintenance into the adjacent High Plains through
the evening. Large hail should be the main threat with this activity
(with some 2+ inches possible given the very favorable deep-layer
shear), but isolated severe gusts may also occur. The Slight Risk
has been adjusted/expanded a little eastward in MT based on latest
short-term guidance trends. High-based thunderstorms may also pose
an isolated threat for severe gusts across parts of the northern
Great Basin this afternoon.

...Northern/Central Plains into the Upper Midwest/Missouri Valley and Ozarks...
Ongoing and likely elevated supercells with a threat for large hail
across parts of western ND are being aided by a subtle mid-level
shortwave trough cresting the upper ridge that is anchored over the
central CONUS. Favorable lapse rates aloft and modestly enhanced
mid/upper-level southwesterly flow is likely supporting updraft
organization/intensity with this ongoing activity. The airmass
downstream across central/eastern ND should gradually destabilize
through the afternoon, with a moist low-level airmass present to the
east of a weak surface low over eastern MT/southwest ND/northwest
SD. It remains unclear whether these ongoing supercells will be
maintained farther east across ND, but given the favorable airmass
and sufficient deep-layer shear present, have opted to add a
targeted Slight Risk for the large hail potential.

Additional convection is occurring farther south in SD, southwest
MN/northwest IA, and northeast NE in association with a mid-level
vorticity maximum evident on water vapor satellite imagery moving
eastward across SD/NE. There is a narrow corridor of greater
instability present across this region southward to the Ozarks,
generally along/near a weak surface front. Isolated hail may occur
with the stronger cores in the short term, but it remains unclear if
convection will be able to form into a southward-moving cluster
across eastern NE/western IA later this afternoon and evening. If
this does occur, then a greater threat for severe/damaging winds
would exist. Have deferred a possible upgrade to Slight Risk given
the uncertainty with how ongoing convection will evolve/impact the
developing warm sector, and due to the presence of the large-scale
mid/upper-level ridge and generally modest flow aloft. A separate
area of high-based thunderstorms that should develop this afternoon
along/east of a surface lee trough across the central High Plains
could produce occasional hail and severe gusts, even as deep-layer
shear remains modest.

$$
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