630
FXUS63 KBIS 010545
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1245 AM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Chance for showers and thunderstorms returns on Labor Day. An
  isolated strong to severe storm is possible.

- Showers and thunderstorms may accompany passage of a cold
  front on Tuesday. The probability for severe weather is low.

- Cooler weather with highs in the 60s and 70s then anticipated
  mid to late week. Overnight lows in the 30s and 40s also
  forecast.

&&

.UPDATE...
Issued at 1245 AM CDT Mon Sep 1 2025

Other than a few isolated sprinkles, mainly dry conditions are
expected tonight. Some low clouds are starting to enter into
southwestern portions of the state. This and perhaps patchy fog
could begin to spread across much of the south tonight into
Labor Day morning. Humidity values could again be high tonight,
although a steady southerly wind may limit fog formation. Made
some minor adjustments to patchy fog given these low clouds
already moving in. Otherwise the forecast remains on track.

UPDATE
Issued at 926 PM CDT Sun Aug 31 2025

Other than a few very isolated returns, showers have ended in
the state. A few showers and thunderstorms persist in far
northeastern Montana. However, as expected, they have been
dissipating as they slowly head towards the state. Still, an
isolated shower or thunderstorm may reach the northwest
sometime over the next couple hours.

UPDATE
Issued at 649 PM CDT Sun Aug 31 2025

A few showers persist in the southwest and south central, with
an occasional rumble of thunder being observed as well. These
showers and thundershowers will likely end within the next few
hours. There is a broken line of scattered showers and
thundershowers over far northeastern Montana and far
southeastern Saskatchewan that is heading towards northwestern
ND. Indications are that this broken line may reach the state
within the next couple hours before mostly dissipating as well,
though a few sprinkles may pass through the north overnight.

&&

.DISCUSSION...
Issued at 250 PM CDT Sun Aug 31 2025

Western and central North Dakota lies under a split-flow regime
this afternoon as a center of high pressure moves over northern
Minnesota, an upper level low sinks south through South Dakota,
and a weak upper level wave moves in behind them both. With
this, showers and a few thunderstorms are possible across much
of western and portions of central North Dakota this afternoon
as a weak surface boundary is lifted eastward. At least
sufficient forcing and moderate instability, with model MUCAPE
values around 1000 J/KG this afternoon, could allow for an
isolated storm to become stronger over the far southwest or
south central. That being said, very limited environmental shear
is expected to keep the severe weather potential very low
today. All showers and storms are expected to diminish through
the evening. High temperatures this afternoon are forecast
broadly from the lower 70s southwest to the lower 80s north.
Lingering near surface moisture and clear skies may allow for
another round of fog development across the southwest and
central North Dakota, including the James River Valley and the
Turtle Mountains region, early tonight through the morning hours
of Labor Day. Low temperatures tonight are forecast broadly in
the 50s to lower 60s.

The aforementioned weak shortwave is anticipated to lift a low
pressure center across western and central North Dakota through
much of the day Labor Day, again promoting low to medium
chances for showers and a few thunderstorms tomorrow afternoon
and evening. With slightly warmer temperatures, forecast in the
mid 70s to mid 80s, and with dewpoints starting to tickle the
mid to lower 60s across portions of the south, the convective
environment on Monday is slightly more robust than what we`ve
seen this weekend. Model MUCAPE values during the late
afternoon, early evening being peaking into the 1500+
J/KG across the south. Environment shear also ticks up during
this period, peaking into the 25 to 35 knot range over portions
of southwestern and south central North Dakota. With this in
mind, there is a very conditional threat for a stronger to
severe storm or two to develop in the late afternoon, early
evening Monday. An interrogation of BUFKIT model soundings
during this period reveals that these storms would be fairly
elevated, with robust near surface capping present, and thus the
main hazard associated with any severe storm would be damaging
wind gusts up to 60 MPH, though small hail is also possible. At
this time, SPC has North Dakota in a general thunder outlook for
Monday while the CSU machine learning algorithm has not
highlighting the forecast area at all, emphasizing the
conditional nature and limited scope of the severe weather
threat. The 18Z run of the NCAR HRRR Neural Network does paint
portions of central North Dakota with a low probability (10
percent or less) for damaging wind gusts for Labor Day.

A cold front is still anticipated to dive through the forecast
area Monday evening through Tuesday. Cooler high temperatures in
the 60s and 70s are thus expected Tuesday afternoon, though the
far south may linger in the mid 70s to mid 80s ahead of the
front. Another round of low to medium chances for showers and
thunderstorms are expected along and behind this cold front
Tuesday afternoon through early Wednesday. Notably, wildfire
smoke starts to move in aloft over the northern Plains during
this same period, possibly mixing down to the surface behind the
front on Tuesday. The post frontal environment is anticipated
to be cool and breezy on Wednesday, with low temperatures in the
morning broadly in the 40s and high temperatures in the
afternoon mainly in the 60s. Moderate north winds are also
anticipated in the southern James River Valley, where the
pressure gradient remains tight through the afternoon, with
speeds up to 20 MPH and gusts around 25 to 30 MPH. With high
pressure continuing to sink through North Dakota and into
eastern South Dakota, we again are expected to fall into our
cool pattern. With this, low temperatures Thursday could drop as
low as the mid to upper 30s across portions of the north and
southwest. We will need to monitor the potential for frost for
this period over the next few forecast cycles. Generally dry
conditions are anticipated through the later half of the week,
as the northern Plains remains under northwesterly flow as a
broad ridging develops over the Rockies. A large spread in
daytime high temperatures is present in the ensemble as attempts
to resolve the rate at which this ridge expands eastward, with
a majority of members (65 percent) favoring it moving into the
Great Plains more quickly, keeping highs mainly in the lower 60
to lower 70s. Notably, a much cooler scenario also exists (25
percent membership), which champions a robust Hudson Bay Low
limiting the eastward expansion of the ridge until much later in
the workweek, in which case high temperatures in the mid 50s to
mid 60s is not out of the question, though this cluster is
somewhat underdispersed due to high GEFS and very low GEPS buy-
in.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1245 AM CDT Mon Sep 1 2025

Another round of fog and low clouds could move into the area
tonight into Monday morning. Confidence in fog formation is
modest tonight, although was high enough to include BR mention
from KDIK to KBIS to KJMS. Any low clouds or fog that forms
could bring IFR to LIFR conditions. Otherwise look for mainly
dry conditions tonight into Labor Day morning, with a light
southerly wind. The rest of Labor Day then looks to see mainly
VFR conditions with a light south wind, perhaps becoming
westerly later in the day, then light and variable in the
evening. Chances for showers and thunderstorms could return in
the afternoon and evening. Some sites with higher confidence
have a PROB30 group for these chances of precipitation.

&&

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

&&

$$

UPDATE...Anglin
DISCUSSION...Adam
AVIATION...Anglin