480
FXUS63 KBIS 130230
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
930 PM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Below normal temperatures continue this weekend, with highs
  about 5 to 10 degrees below average.

- High chances for rain showers (~70-100%) Sunday night into
  Monday. The greatest chances are over central and eastern
  North Dakota.

- Becoming windy late Sunday, with the strongest winds expected
  on Monday before diminishing Monday night. Gusts to 50 mph
  are possible over western North Dakota.

&&

.UPDATE...
Issued at 930 PM CDT Sat Sep 12 2026

Quiet weather is found across western and central North Dakota
at the time of this mid to late evening update. A few blips of
weak radar returns linger over the southwest and south central
this evening, but have greatly diminishing over the last few
hours. Short term CAMs continue to advertise the potential for
some showers across portions of the south central into the
southern James River Valley tonight through early Sunday morning
as a upper level jet cuts across the area. Will maintain low (10
to 30 percent) chances for now. No major adjustments to the
forecast were performed with this update, as it remains on track
at this time.


UPDATE
Issued at 615 PM CDT Sat Sep 12 2026

Weak radar returns persist across portions of southwestern and south
central North Dakota at the time of this early evening update.
Induced by the weak divergence found along the right exit region of
an upper level jet, very dry conditions up to around 7kft above the
surface has so far limited the amount of precpitation reaching the
ground, if any indeed has. Low chances (10 to 30 percent) for
precpitation is expected later this evening into early tonight as
saturation of the column increases, though most locations are
expected to remain dry. For this update, have blended the latest
short term model trends into the PoPs to slightly increase coverage
of showers in the south central overnight, but this change is
relatively minor. Otherwise, the forecast remains in good shape.

&&

.DISCUSSION...
Issued at 225 PM CDT Sat Sep 12 2026

This afternoon, broadly zonal flow was present over the Northern
Plains, with a Hudson Bay low to the northeast and a secondary
closed low just offshore of the Pacific Northwest. A shortwave
aloft associated with the Hudson Bay low was over the central
Canadian Prairies. At the surface, broad high pressure extended
from east central Alberta into northwest North Dakota.

An embedded vort max in the mean flow has been producing light
radar returns across southwest North Dakota throughout the day
so far today, although we have to see any confirmation of any
rain making it to the surface, which is not too surprising given
the high ceilings. Northwest winds are a bit breezy with the
surface pressure gradient, but will be diminishing through the
rest of the day as the surface high continues to push across the
state. Highs this afternoon will be in the upper 50s to upper
60s. Lows tonight will be seasonably chilly, mainly in the upper
30s to mid 40s, although we could see some mid 30s across the
International Border.

We did contemplate whether or not a Frost Advisory would be needed
tonight. Although the surface high moving in would typically
favor temperatures dropping well below guidance, latest
deterministic guidance is advertising a shortwave diving south
from the Canadian Prairies overnight tonight. Recent CAMs runs
are all in agreement on scattered precipitation across at least
central North Dakota tonight, with forecast RH and BUFKIT
soundings showing midlevel clouds extending across the forecast
area. This, plus current satellite imagery showing widespread
cloud cover upstream across southern Alberta and Saskatchewan,
has us wondering how much clouds will clear out even as the
surface high moves through and subsequently how much
temperatures will drop below the deterministic NBM which is
already skewed close to the 25th percentile. Some isolated
frost is still possible mainly across our four northwest
counties and into Renville and Bottineau Counties, but at this
point we are not confident enough in widespread impacts to go
ahead with an advisory. Forecasters this evening will re-
evaluate.

On Sunday, the aforementioned deep closed low will continue to
move onshore into the Pacific Northwest, with downstream
shortwave ridging across the Northern Plains that will warm
temperatures some for Sunday and Monday. Highs rebound back
into the lower 60s to lower 70s on Sunday, and then the mid 60s
to mid 70s on Monday. As the low approaches the region, expect
widespread showers and occasional thunderstorms to start late
Sunday evening across western North Dakota, expanding east
through the night and Monday. NBM PoPs continue to be quite high
especially for areas along and east of Highway 83, with a rainy
Monday morning commute expected. This is the dividing line of a
50/50 chance for more than 0.50 inches of rain (east) and less
than that (west). Showers and thunderstorms will end rather
quickly from west to east through the day Monday as the upper
low lifts northeast.

The main threat will be for localized heavy rain, with PWATs
forecast around 1.5 inches which is towards the upper end of
climatology for mid September. We are also expecting strong
winds with this system, starting southeasterly on Sunday and
switching to westerly on Monday behind the front that moves
through. ECMWF EFI highlights southwest North Dakota as the area
of most concern with a shift of tails across much of the
forecast area, so current thought is wind gusts of 50 to 55 mph
across western North Dakota on Monday.

We quickly return to zonal flow on Tuesday, with highs in the
60s but lighter winds after the early week system. Moderate
chances for rain return on Wednesday as a progressive embedded
wave moves in as synoptic flow turns more southwesterly across
the region. NBM temperature percentiles signal a return to near
normal temperatures by the end of the work week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 930 PM CDT Sat Sep 12 2026

VFR ceilings and visibility is expected at most terminals
throughout the 00Z TAF period. Scattered showers will be
possible across south central North Dakota late this evening
into the early overnight period, which may briefly promote low
VFR to high MVFR ceilings as precpitation is falling. With this
update, opted to include a PROB30 for light rain at KBIS.
Winds will continue to diminish this evening, becoming light and
variable across the west and then across central North Dakota
overnight. Winds will then reorganize out of the southeast late
sunday morning, becoming gusty with sustained speeds up to 25
knots and gusts up to 35 knots over western North Dakota. Light
and variable winds will generally persist over the James River
Valley through the end of the TAF Period.

&&

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

&&

$$

UPDATE...Adam
DISCUSSION...Jones
AVIATION...Adam