126
FXUS63 KBIS 112304
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
604 PM CDT Sat Oct 11 2025

.KEY MESSAGES...

- Strong southerly winds this evening, then very strong west to
  northwest winds Sunday through Sunday night.

- Low to medium chances for rain across much of central ND
  tonight with medium to high chances for rain in the James
  River Valley and into eastern ND.

- Rain expected across much of northwest North Dakota Sunday
  morning through Sunday evening. The rain could mix with or
  change over to snow late Sunday afternoon and evening. The
  probability of accumulating snow is low.

- Cooler for the first half of next week, with highs in the 40s
  and 50s and lows in the 20s and 30s. Medium chances for rain
  return mid to late week.

&&

.UPDATE...
Issued at 546 PM CDT Sat Oct 11 2025

Only some minor changes for sky cover needed late this
afternoon. There were a couple of lightning strikes over eastern
ND a while ago. Better chances for showers will move into the
area from the south later this evening and overnight. Low to
medium chances will remain over much of central ND, with medium
to high chance in the James River Valley and into eastern ND.

&&

.DISCUSSION...
Issued at 251 PM CDT Sat Oct 11 2025

This afternoon, southwest flow aloft was present across the
Dakotas, downstream of a trough and closed low moving onshore
in the Pacific Northwest. At the surface, a north-south oriented
warm front was analyzed with a surface trough in eastern
Montana. A tight surface pressure gradient ahead of the front
was producing strong southeasterly winds, with gusts around 40
mph observed throughout the day at a few different locations.
Chances for rain the rest of the afternoon are limited mainly to
eastern North Dakota, with radar activity upstream in South
Dakota associated with low-level warm air advection.

Tonight, a leading shortwave is forecast to move into southern
North Dakota in the mid-evening, with rain chances increasing
around sunset. As this tracks north and interacts with another
surge of low- level warm air advection, CAMs produce a modest
area of rain across the central and east through the night, with
a few isolated showers possible across the west. We could see a
thunderstorm or two during this period, with the northwest the
main area of potential in forecast UH tracks, although even this
looks like a low probability outcome with limited instability
available.

The Pacific NW shortwave trough ejects over the Rockies and into
the Dakotas early Monday morning, leading to cyclogenesis in
southeast Montana with an attendant cold front developing. As
the previous shift noted, ensemble members are coming into
better agreement on this being a more progressive and open wave
compared to a couple of days ago when a more compact closed low
was favored. As the vort max aloft interacts with the nose of
an upper jet, a swath of rain will move from Montana into
western North Dakota Sunday morning. When the upper low wraps
up and pushes northeast, precipitation chances become more
limited to primarily northwest North DAkota, with dry slotting
behind the cold front across the majority of the forecast area
during the day. There could be some diurnal, isolated showers
associated with the cyclonic flow, which some high-res models
are picking up on, but the likelihood of more than a tenth of an
inch of rain is low for southwest and central North Dakota.
Even with a moderate period of rain expected through the day
across northwest North Dakota, QPF amounts have decreased in
recent guidance, with Divide County the main area with any
potential of exceeding an inch of liquid precipitation.

The chance for measurable snow in the northwest is holding
around 20 to 30 percent, with slightly higher probabilities in
Divide County, and the potential to exceed an inch of
accumulation is less than 20 percent. The sped up timing of the
front and thus the colder air does raise some questions about
available daylight and impacts to any potential accumulations. The
12Z HREF highlights a general tenth to quarter inch an hour
snowfall rates which would likely not be enough to overcome the
warm ground temperatures, especially since it switches
precipitation from rain to snow in the late afternoon with still
a couple hours before sunset.

The GEFS and ECMWF ensemble members are finally starting to reach
consensus on the center of the surface low being placed in
southeast Manitoba around 18 UTC Sunday, with the cold front
extending through eastern North Dakota by this point. Because of
this, much of western and central North Dakota will see the
daily high temperature earlier in the day, with temperatures
falling behind the front.

The most widespread impact with this system will be the strong west
to northwest winds behind the front. There is still some question
of the upper threshold of winds, with some varying levels of wind
speeds at the top of the mixed layer in forecast soundings, but
there was enough confidence to go ahead with a Wind Advisory
for virtually all of western and central North Dakota. Can`t fully
rule out some counties potentially needing an upgrade, but will
probably have to start seeing even stronger winds in upstream
observations to have confidence for that. The initial cold front
will bring a push of strong winds as it moves east, from a
combination of cold air advection, pressure rises, and steep
low-level lapse rates. Deterministic guidance is also starting
to show a secondary push of cold air advection and enhanced
pressure rises as the low deepens, which correlates with
indications of the strongest winds occurring in the late
afternoon across northern North Dakota. The general expectation
is for sustained winds of 30 to 35 mph with gusts up to 50 mph.

As the upper low progresses off to the northeast, precipitation
chances taper off relatively quickly Sunday night, with winds
staying a bit breezy with a surface pressure gradient still in
place. Colder air will continue filtering into the region, and sub-
freezing temperatures are likely across the west and north
central. Monday will be brisk in the post-frontal air mass,
with highs in the lower 40s to lower 50s, although decreasing
winds and increasing sunshine will help counteract the chilly
temperatures. Overnight lows will again be near to below
freezing across the forecast area, in the mid 20s north to mid
30s south.

By Wednesday evening, cluster analysis is in relative agreement on
the trough base extending into the southwest CONUS, with downstream
southwest flow across the Dakotas, favoring an active pattern. From
here, however, ensemble members diverge, with around a 50/50 split
between a more progressive trough vs a slower, quasi split flow
pattern for the end of the work week. Both of these would bring
precipitation chances to the area from a broad closed low moving
through the region, but would lead to some differences depending on
the speed and depth of the system. The one consistency between the
two scenarios is that temperatures stay warm enough to eliminate p-
type issues, with only rain expected. Current blended probabilities
have a low chance of exceeding an inch of rain over 48 hours during
this system, but there are a few ensemble members producing higher
amounts.

A longwave troughing pattern is strongly favored to continue into
the weekend, keeping low chances for precipitation in the forecast.
NBM temperature percentiles indicate a slight cooling trend from
Thursday through the weekend, although current spreads would keep
temperatures around average for mid October.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 546 PM CDT Sat Oct 11 2025

VFR conditions to start the TAF period, with moderate to
occasionally strong south to southeast winds this evening.
Chances for rain move into south central and eastern North
Dakota later this evening, with prevailing rain at KJMS, and
potentially MVFR ceilings for a period at KJMS and KBIS.

On Sunday, chances for rain are primarily focused in western
North Dakota, including KXWA, accompanied by more widespread
MVFR ceilings that could impact KDIK and KMOT through the end of
the TAF period. A cold front will begin moving from west to east
through the state after 12Z, with winds shifting from southerly
to westerly and becoming strong Sunday afternoon.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 7 AM CDT /6 AM MDT/ to 8 PM CDT /7 PM MDT/
Sunday for NDZ001>005-009>013-017>023-025-031>037-040>047-050.

&&

$$

UPDATE...TWH
DISCUSSION...Jones
AVIATION...TWH