523
FXUS63 KBIS 120546
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1246 AM CDT Wed Aug 12 2026

.KEY MESSAGES...

- Low to medium chances (30 to 50 percent) for thunderstorms
  through tonight. Isolated to scattered severe storms are
  possible, mainly in the south.

- Showers and thunderstorms return through the week. Isolated
  severe storms are possible in the south again Wednesday.

- A cooling trend is expected through Friday, followed by a
  warming trend through the weekend and into early next week.

&&

.UPDATE...
Issued at 1235 AM CDT Wed Aug 12 2026

Severe thunderstorm watch remains in effect until 1 AM CDT.
Convection currently over Stutsman county has shown a downward
trend over the past hour or so, although there are still some
localized intensification. Activity should be pushing out of
Stutsman county in the next 30 minutes or so. Do not intend to
extend the watch. Sub-severe convection also indicated over
Adams/Hettinger counties and into western Grant county. This
activity is pushing east southeast and should be out of the
forecast area in the next hour or so. Current thinking is that
this activity may be strong at time but should remain below
severe levels. Made some updates to pops and sky cover based on
latest radar and satellite data.

UPDATE
Issued at 958 PM CDT Tue Aug 11 2026

Scattered supercells persist in south central ND as of 0245Z,
but coverage is gradually diminishing concurrent with gradual
increases in MLCIN. Radar trends and CAMs -- especially time-
lagged HRRR cycles -- suggest the severe-storm risk will
continue until around 05Z, while continuing to slowly decrease.
In the interim, sufficient CAPE and deep-layer shear remain in
place to support large hail (mainly 1 to 2 inches in diameter
with the most-intense supercells), and perhaps damaging wind
gusts up to 60 mph. Recent CAMs suggest the risk of storms is
rapidly ending in southwestern ND as of late evening, and that
the odds of redevelopment after 05Z in south central ND are
lower than previously anticipated. Nonetheless, a low chance
of storms is prudent late tonight with broad, albeit modest
midlevel warm air advection expected.

UPDATE
Issued at 706 PM CDT Tue Aug 11 2026

Scattered supercells have evolved over southwestern ND after
initiating on a weak confluence zone. They are occurring in an
environment characterized by 2000-3000 J/kg of MLCAPE and
effective-layer shear on the order of 50 kt. Hodographs have
sufficient length to support supercells, and have favored
splitting storms, with a slight preference toward the right-
moving supercells being dominant once they are well-established.
This scenario is expected to continue the next 1-2 hours with
scattered supercells capable of producing large hail mainly up
to around 2 inches in diameter. There`s some uncertainty in how
far eastward these storms will sustain given warmer midlevel
capping both with eastward extent and with time, but several
CAMs suggest they will persist into south central ND through
late evening, e.g., beyond 02Z. Otherwise, the earlier storms
in the southern James River Valley have weakened, likely as a
result of increasing MLCIN in an environment that already had
more residual midlevel capping than elsewhere per the 18z KABR
RAOB. Nonetheless, a low chance of isolated development
remains, as evidenced by visible satellite imagery showing
attempts at updraft development in Emmons County recently.

&&

.DISCUSSION...
Issued at 240 PM CDT Tue Aug 11 2026


Currently quasi-zonal flow is over the Northern Plains, with a
broad ridge over the Southern Plains. The severe storms in the
James River Valley this morning have mostly moved into South
Dakota. At the surface weak high pressure is in the region.

The severe storm risk today looks very conditional. There is
plenty of CAPE with dew points in the 60s and 70s across the
south, however the Bismarck 18z sounding shows a strong cap. So
the majority of the CAPE (2727 J/kg) is elevated. What might
start the event before sunset is the convective temperature is
84, however there is plenty wildfire smoke aloft that might
prohibit that. Shear across the area is around 50kts so
organized. Most of the CAMS keep convection happening until
close to sunset when maybe the jet stream speed max connects
with them. There is some storms starting to fire on the Black
Hills, but that is near the stationary front. Whatever boundary
kicked off storms in our east is still there and has some
cumulus trying but currently hitting the cap. If or when storms
go the hazards are 2 inch hail and 70mph winds. Thunderstorms
are possible through tonight and into the morning, especially in
the south central.

The rest of this week will be much cooler, below average in
fact, in the 70s. The upper pattern will turn northwest
Wednesday, before turning to the southwest Thursday. Daily
chances of showers and thunderstorms are possible, including
overnight through Saturday morning in the active southwest flow.
There is currently a level 1 risk of severe storms again
Wednesday in the south, with current hazards being golf balls
and 70mph winds. It is possible that over an inch of rain could
fall between today and Saturday morning across our forecast
area. Thursday and Friday look very breezy from a pressure
gradient. This weekend looks warmer in the lower 80s, then
maybe back to average early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1235 AM CDT Wed Aug 12 2026

Convection currently over Stutsman county is expected to impact
KJMS TAF at 06Z-07Z, with MVFR-IFR visibilities and MVFR
ceilings, along with gusty and erratic winds. Elsewhere, VFR
conditions are expected to begin the 06Z TAF period. Low
stratus/fog is possible early Wednesday morning. For the time
being only included a TEMPO at KBIS for low stratus, but
certainly can`t rule out low stratus/fog at any TAF site, but
mainly the southern Taf sites. Another round of thunderstorms is
possible again Wednesday afternoon and evening.


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...TWH
DISCUSSION...Smith
AVIATION...TWH