430
FXUS63 KBIS 121925
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
225 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.

&&

.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 /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1242 PM CDT Sat Sep 12 2026

VFR conditions expected through the 18Z TAF period. A few
isolated rain showers continue in far southwest North Dakota,
but any precipitation coming out of them will be very light.
Breezy northwest winds will continue to diminish through the day
today, with light and variable winds overnight before southeast
winds start to increase at the end of the TAF period. Another
round of light rain showers is possible overnight, although low
confidence in any timing and location, although would be low
impact overall.

&&

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

&&

$$

DISCUSSION...Jones
AVIATION...Jones