251
FXUS63 KBIS 261749
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1249 PM CDT Sat Sep 26 2026

.KEY MESSAGES...

- Temperatures favored to remain near to slightly above average
  until late next week.

- High chances for showers and thunderstorms late Sunday evening
  through Monday night for all but northwest North Dakota. There
  are medium to high chances for exceeding 1 inch of rain from
  south central to northeast North Dakota. A few storms could be
  strong to severe.

&&

.UPDATE...
Issued at 1245 PM CDT Sat Sep 26 2026

Added more fog to the forecast as the low stratus continues to
reduce visibilities at times. The cold front is now nearing
Highway 83, turning winds to the west and clearing skies. We
also added sprinkles to the central and east with very light
rain falling out of the stratus.


UPDATE
Issued at 1011 AM CDT Sat Sep 26 2026

Little updates needed this morning. The cold front mentioned
below is in western North Dakota, clearing skies as it moves
east. The latest NBM was loaded into the forecast.

UPDATE
Issued at 651 AM CDT Sat Sep 26 2026

Light rain that had been falling over parts of central North
Dakota overnight has shifted off to the east. Meanwhile, widely
scattered showers with an occasional thunderstorm have
developed along the leading edge of a shortwave over northwest
North Dakota. With only around 500 J/kg MUCAPE and effective
bulk shear 20 kts or less, strong to severe convection is not
anticipated. This activity may persist northeastward through
north central North Dakota through the morning, though the
chance for a thunderstorm should diminish with eastward extent.
Meanwhile, a cold front is approaching the MT/ND border, and
satellite confirms this should begin scouring out the low
stratus. The forecast has been updated to better reflect
current conditions and trends.

&&

.DISCUSSION...
Issued at 516 AM CDT Sat Sep 26 2026

A broad, negatively-tilted upper level trough axis extends from
the Canadian Rockies to the Central Plains early this morning.
Shortwave energy moving poleward has produced a broken area of
light rain from north central North Dakota through eastern South
Dakota. This rain will continue to lift north/northeastward
this morning and should shift east of the forecast area by noon.
Another shortwave embedded in the main trough can be seen on
water vapor imagery ejecting off the Rockies of Montana early
this morning, and a lee surface trough has already sharpened
through eastern Montana in response. As had been advertised by
some high-resolution models, scattered showers and isolated
thunderstorms are beginning to develop along the ND/MT
stateline, north of the Missouri River. Model consensus has this
activity gradually dissipating while moving into north central
North Dakota later this morning. The NAMnest has been an outlier
in simulating strong, if not marginally severe thunderstorms,
but effective bulk shear around 25 kts and MUCAPE no greater
than around 1000 J/kg is not really supportive of a severe
threat.

The surface lee trough is attendant to a deepening cyclone over
northern Alberta/Saskatchewan and will gain forward momentum
into western North Dakota as a cold front/dryline as the
Canadian low becomes stacked and begins occluding this morning
and afternoon. Gusty west-northwest winds (maximum gusts around
25-30 mph) are expected behind the front in western North
Dakota from mid morning to early afternoon, with winds along
and behind the front trending weaker as it reaches central
North Dakota. The front is expected to clear persistent low
clouds, but may not reach the Turtle Mountains through James
River Valley before peak diurnal heating ceases. The high
temperature forecast in the mid to upper 60s in these parts of
the state may be too optimistic if an overcast sky prevails
through the day. The western half of the state will likely see
high temperatures around 70 to near 75 this afternoon, warmest
just ahead of the front during the mid to late afternoon due to
compressional heating. The dry air mass trailing the front is
expected to bring RH as low as 25 percent in far southwest
North Dakota during the mid to late afternoon. But because the
strongest winds are expected to subside by mid afternoon, near-
critical fire weather conditions are not anticipated.

A few CAMs want to develop some light showers ahead of the cold
front this evening in the southern James River Valley, but the
chance for measurable rain is very low. The southern flank of
the cold front is forecast to stall between Lake Oahe and the
southern Red River Valley overnight while the northern flank
surges eastward through the northern Red River Valley. The
cooler and drier air mass behind the front associated with
surface high pressure expanding southeastward off the Canadian
Rockies will allow temperatures to drop into the 40s tonight,
possibly falling into the upper 30s in low-lying areas across
the west. There may be just enough of a low level breeze to
prevent strong radiational cooling from tanking temperatures
below the 10th percentile of the NBM minimum temperature
distribution, which is as cold as the mid to upper 30s.

Surface high pressure will slide eastward through the region on
Sunday, keeping winds light for most areas with afternoon highs
in the 60s. By Sunday evening, shortwave energy will begin
racing from the Great Basin to the Northern Plains ahead of a
potent trough digging into California. The downstream response
of increasing low level warm air advection and moisture
transport lends to increasing chances for showers and
thunderstorms through Sunday night, with widespread showers and
scattered thunderstorms likely across all but northwest North
Dakota by Monday morning. That is not to say that there will
not be any showers or storms in the northwest, but odds are
lower there (10 to 40 percent chance of rain) than elsewhere
(70 to 100 percent chance of rain). The initial round of
showers and storms is forecast to propagate into eastern North
Dakota Monday afternoon, but the arrival of a northern stream
wave under a coupled upper level jet could force another batch
of showers and storms Monday afternoon before the first round
fully departs. A weak cold front attendant to the northern
stream wave should push showers and storms off to the southeast
through Monday night. Ensemble guidance continues to hone in on
a corridor from south central North Dakota to northwest
Minnesota for the highest rain amounts, where the latest NBM
shows high chances (80 to 95 percent) for exceeding half an
inch of rain, medium to high chances (60 to 85 percent) for
exceeding one inch of rain, and low to medium chances (20 to 45
percent) for exceeding 2 inches of rain. These calibrated,
point-specific QPF threshold probabilities taper off greatly to
the north and west, and there is now less than a 20 percent
chance for exceeding just a tenth of an inch of rain from
Williston northward.

We are still monitoring a potential risk for strong to severe
storms from late Sunday evening through Monday afternoon that
has had consistent support from CSU machine learning severe
probabilities. The low level warm air advection and moisture
transport underneath steep mid level lapse rates could yield as
much as 1000 J/kg MUCAPE across southern North Dakota by early
Monday morning. Deep layer shear will be strong, but perhaps
insufficient for severe storms when taken from the base of the
EML. The main hazard from any storm through Monday morning
would be large hail. The more intriguing severe potential
appears to be along and ahead of the aforementioned cold front
from south central to northeast North Dakota Monday afternoon.
There is still uncertainty whether afternoon storms would be
fully rooted in the near-surface layer, and whether rising
parcels would be uninhibited. But in the event convection does
become surface or mixed-layer based with parcels forced above
the LFC, there is strong enough shear at all layers for all
severe hazards, including a conditional tornado risk. There is
also a concern for locally excessive rainfall caused by
training convection in an anomalously high precipitable water
environment from late Sunday through Monday.

For the rest of the upcoming work week, ensembles are trending
towards a quasi-zonal flow pattern with very few embedded
disturbances, although two ensemble clusters with 60 percent of
the total membership do bring a shortwave along the Canadian
border around Wednesday. This keeps the forecast mostly dry for
now, with near to slightly above average temperatures of highs
in the 60s to lower 70s and lows in the 40s. There is still a
signal for cooler weather over the first weekend of October
that could feature highs in the 50s and lows in the 30s, but
prospects for precipitation remain highly uncertain.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1245 PM CDT Sat Sep 26 2026

Patchy IFR east to VFR west. A cold front is currently moving
east through the state, clearing out the MVFR CIGs and turning
winds to the west. This trend will continue west to east through
the period, becoming mostly SKC overnight. The breezy west winds
will mostly calm overnight as well.

&&

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

&&

$$

UPDATE...Smith
DISCUSSION...Hollan
AVIATION...Smith