654
FXUS63 KBIS 271933
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
233 PM CDT Sun Sep 27 2026

.KEY MESSAGES...

- Widespread showers and scattered thunderstorms late tonight
  through Monday.

- A few strong thunderstorms are possible Monday morning through
  Monday afternoon, with a conditional threat for a severe
  thunderstorm or two in the afternoon.

- High chance (60 to 90 percent) for at least 1 inch of rain
  over much of central North Dakota tonight through Monday
  night. Thunderstorms may also produce locally heavy rainfall.

- Near to slightly above normal high temperatures then expected
  through the mid to late workweek.

&&

.DISCUSSION...
Issued at 230 PM CDT Sun Sep 27 2026

Cyclonic flow is found over the northern Plains this afternoon
as a deep upper level low exits to the northeast out of the
Canadian Prairies. A weak cold front slowly exiting to the
southeast of the forecast area continues to promote some
isolated showers across portions of our south central. Overall
rain accumulations are expected to be very limited to non
existent. Elsewhere clear skies are generally expected through
the early to mid afternoon as a surface center of high pressure
moves across the far northwest, before beginning to cloud back
over as a second cold front associated with the Canadian Low
beings to move in.

Late tonight into early Monday, a broad shortwave trough
ejecting off a closed low over the western Canadian coast is
expected to begin moving in the northern Plains. At the surface,
a low pressure center developing on the lee side of the rockies
is progged to be lifted up and across Wyoming into the Dakotas
through the day, pushing an attendant warm front across
southwestern through eastern North Dakota. At the same time, a
moderately strong (50 to 60 knot) H7 jetstreak is expected to
develop across south central into eastern North Dakota early
Monday morning through Monday afternoon. With such ample sources
of lift across the area, and with moisture returns increasing
up ahead of the developing low center, widespread medium to high
chances (60 to 90 percent). A fairly modest convective
environment is also expected to develop by early Monday morning,
with model MUCAPE values peaking up to around 1000 J/KG and
bulk shear values around 35 to 40 knots. An interrogation of
BUFKIT model soundings through early Monday afternoon indicates
that much of the predicted instability should be fairly elevated
about a robust cap, and above the better shear found below 1 KM
AGL. The questions remains what will occur as we head into the
later portions of Monday afternoon as the H7 jet begins to kick
in. While the majority of short term CAMs advertise the robust
capping over North Dakota persisting through the day, one of two
of them do capture a storm or two becoming surface based by the
mid to late afternoon. In such a circumstance, an isolated
stronger to marginally severe thunderstorm or two cannot be
ruled out, with the area to watch being southwestern and south
central North Dakota into the northern James River Valley. The
primary hazards associated with any severe thunderstorm that
does develop would be large hail up to the size of a quarter,
and damaging wind up to 60 MPH. Of note is a potential window
during which an isolated tornado would become possible, mainly
in late afternoon into the early evening as the surface low
lifts into central and eastern North Dakota. While predicated on
a surface based storm developing, the strong near surface shear
near the triple point of the low could promote near surface
(0-1km) SRH values around 150-200 KM and decently curved
hodographs across the southern James River Valley. While the
overall potential of a tornado remains low as this time, we will
need to monitor forecast trends over the next 24 hours,
especially if surface based storms become more likely.

Otherwise, moderate to heavy rainfall can be expected across
portions of western and much of western North Dakota starting
late tonight through Monday night. With high PWAT values
exceeding 1.5" by the late afternoon, the NBM probability of
exceeding 1.0" of rain accumulation is high (70 to 90 percent)
across much of central North Dakota, with a low chance (20 to 40
percent) to exceed 3.0" over portions of the James River
Valley. With such high PWATs, moderate to heavy rainfall
approaching at least 0.5" to 1.0" per hour can also be expected
where and when thunderstorms occur. As of this forecast cycle,
the EFI highlights portions of central North Dakota for high
values approaching 0.9-0.95 and a shift of tail values of 2,
which indicates high confidence on an anomalously high
precpitation event compared to our climatology. Of note is that
a handful of CAMs capture training thunderstorm development
along the warm front as it occludes over south central into
northeastern North Dakota late Monday afternoon through Monday
evening. If this scenario were to play out, localized flood can
be anticipated despite the fairly dry, thirsty ground present
over much of central North Dakota.

Looking ahead to the remainder of the workweek, near zonal to
southwesterly flow is anticipated over the northern Plains
through at least Wednesday promoting relatively dry somewhat
warmer weather with highs broadly in the mid 60s to mid 70s. By
Thursday, ensemble members advertise cooler weather with highs
mainly in the 60s as a robust upper level passes far to the
north through the Canadian Prairies, turning flow more
northwesterly. By late Friday into the weekend, there`s decent
agreement that a clipper system passing through toward the Great
Lakes Region will reinforce this cooling trend, promoting
cooler highs mainly in the mid 50s to mid 60s, as well as some
low chances (20 to 40 percent) for light rainfall over portions
of north central into eastern North Dakota. Overall, the signal
for widespread and accumulating precpitation during this period
remains low at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 230 PM CDT Sun Sep 27 2026

VFR ceilings and visibility are found at all terminals to begin
the 18Z TAF period. Lowering ceilings and chances for
precpitation are expected to increase beginning early tonight
through Monday morning, with widespread MVFR and some IFR
ceilings as well as widespread showers expected by the end of
the TAF period. Some isolated thunderstorms will also be
possible over portions of central North Dakota by early to mid
Monday morning, though confidence remains too low to include
mentions of such at any given terminal at this time. Light
northwesterly winds this afternoon will becoming light and
variable through the early evening as a center of high pressure
moves to the north of the forecast area, then turn southeasterly
overnight through the end the TAF period.

&&

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

&&

$$

DISCUSSION...Adam
AVIATION...Adam