307
FXUS63 KBIS 041801
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
101 PM CDT Fri Sep 4 2026

.KEY MESSAGES...

- Critical fire weather conditions in far southwest North
  Dakota this afternoon and early evening.

- Chances for showers and thunderstorms increase through the
  holiday weekend. A few strong to severe thunderstorms could
  develop Saturday through Sunday.

- Well above normal temperatures today and Saturday, followed
  by a gradual cooling trend through the middle of next week.

&&

.UPDATE...
Issued at 100 PM CDT Fri Sep 4 2026

Limited updates needed early this afternoon. Dense fog has
dissipated thus the Dense Fog Advisory has been allowed to
expire. A weak complex of rain and thunderstorms is currently
moving across south central ND. These should move into an area
of less instability as they push east, thus confidence in how
they last is low. There is some steep mid level lapse rates and
just enough elevated shear and instability though to keep PoPs
in for at least the early afternoon hours. Later this evening
through tonight a weak warm front will lift across the area
returning another round of showers and thunderstorms.

UPDATE
Issued at 1015 AM CDT Fri Sep 4 2026

Fog is overall starting to improved across the state, however,
observations and webcams still showing dense fog in western and
northern portions. Decided to extend the Dense Fog Advisory for
areas with lingering dense fog through the morning. Meanwhile,
some showers and isolated thunderstorms are slowly moving
northward out of South Dakota. If these hold together then some
light rain is possible across the south later this morning into
the afternoon. Added some slight pops to account for this shower
activity.

UPDATE
Issued at 643 AM CDT Fri Sep 4 2026

The early morning forecast remains on track. Widespread dense
fog continues to impact all but far southwest North Dakota.

&&

.DISCUSSION...
Issued at 528 AM CDT Fri Sep 4 2026

A low-amplitude ridge is building over the Northern Plains
early this morning ahead of a deep longwave trough digging into
the western CONUS. Broad surface high pressure over Manitoba/
Ontario is providing a weak easterly upslope surface flow into
an antecedently moisture-rich air mass, which has resulted in
widespread dense fog across much of western and central North
Dakota. A Dense Fog Advisory is in effect for all but far
southwest portions of our forecast area. The fog should lift
during the mid to late morning hours as a deepening lee cyclone
over central Montana strengthens southeasterly return flow over
the western Dakotas. Surface winds are forecast to increase to
around 25 mph in western North Dakota this afternoon, with gusts
up to 35 mph. Meanwhile, the thermal ridge will also expand
into western North Dakota this afternoon, bringing unseasonably
warm temperatures as high as the mid 90s to southwest parts of
the state, decreasing to more pleasant temperatures in the mid
to upper 70s in the northeast. The combination of stronger winds
and hot temperatures yielding RH as low as 15 percent is
expected to result in critical fire weather conditions in far
southwest North Dakota this afternoon and early evening. A Red
Flag Warning is in effect for Golden Valley, Slope, and Bowman
Counties.

The latest suite of CAMs shows low probabilities for convection
initiating over parts of central North Dakota late tonight into
Saturday morning in response to strong warm air and moisture
advection induced by the nocturnal low level jet. Despite MUCAPE
possibly increasing above 2000 J/kg, weak effective bulk shear
and the elevated nature of the convection keeps severe
probabilities very low. The upper level height ridge axis and
underlying thermal ridge axis will become more focused over the
Northern Plains on Saturday, keeping high temperatures well
above normal in the mid 80s to mid 90s. Shortwave energy will
begin ejecting from the base of the deep western CONUS trough
on Saturday. There may be a narrow window for surface-based
convection in southern North Dakota during the late afternoon
and early evening hours on Saturday. Otherwise, elevated
showers and storms could become more prominent Saturday night.
In the event of surface-based convection, strong buoyancy and
modest deep layer shear could support a few strong to severe
thunderstorms across southern North Dakota during the late
afternoon and evening. Severe probabilities should diminish
late Saturday night, but lingering strong buoyancy could still
support a pulse strong to severe storm.

Broad mid level height falls in response to a potent shortwave
ejecting from the base of the western CONUS longwave trough
keeps medium chances for showers and thunderstorms in the
forecast for much of western and central North Dakota during
the day Sunday, increasing to high chances (60 to 90 percent)
Sunday night into Labor Day as the potent shortwave lifts
northeast off the mountains of Montana and Wyoming. CAPE on the
order of 2000 J/kg and effective bulk shear around 30-40 kts
keeps a low risk for strong to severe thunderstorms in the
forecast for nearly all of North Dakota on Sunday. As mentioned,
the highest rain chances are focused from Sunday night through
Labor Day as the upstream longwave trough begins to kick
northeast. NBM probabilities for at least an inch of rain over
the Sunday through Labor Day time period range from only around
10 percent in far southwest North Dakota to as high as 80 to 90
percent along the Canadian border. This disparity appears to be
at least partially influenced by a dry slot attendant to a
surface cyclone lifting northeastward through the region on
Labor Day. The frontal boundary ushering in the dry slot could
initiate a conditional severe risk in a lower CAPE/higher shear
environment, but forecast confidence in convective details at
this time range remains quite low. From Tuesday to Wednesday,
an occlusion of the low is projected over the southern Canadian
prairie provinces on Tuesday before it quickly jets toward the
northern Great Lakes and New England. This favors drier,
slightly cooler, and windier conditions for western and central
North Dakota Tuesday and Wednesday. Flow aloft may then
transition to quasi-zonal by the end of next week, which could
moderate temperatures to near normal values and return periodic
lower chances for rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 100 PM CDT Fri Sep 4 2026

Mainly VFR conditions are expected through the forecast period.
Some MVFR clouds may return later tonight into Saturday morning.
Placed in some FEW layers to account for this. Isolated to
scattered showers thunderstorms are possible through the
forecast period, although confidence is overall low and only
placed a PROB30 group at KJMS for now. Gusty southeast winds
will be found today diminishing tonight. Low level wind shear
is forecast to impact parts of western and central North Dakota
late tonight, especially from KMOT to KBIS.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for NDZ031-040-
043.

&&

$$

UPDATE...Anglin
DISCUSSION...Hollan
AVIATION...Anglin