798
FXUS63 KBIS 061537
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
937 AM CST Sat Dec 6 2025

.KEY MESSAGES...

- Accumulating snow will fall across most of western and central
  North Dakota through this evening. There is high confidence in
  new snow amounts around 1 to 3 inches, and a low potential
  for pockets of up to 5 inches.

- Another area of light snow is expected to cross the state from
  west to east on Sunday, with new snow accumulations from a few
  tenths of an inch to near 2 inches.

- A more impactful system is anticipated late Monday night
  through Tuesday night, which may bring a period of freezing
  rain, accumulating snow (high chances north and east), and
  very strong winds to parts of western and central North
  Dakota.

- Below average temperatures this weekend, above average for
  most on Monday and Tuesday, then below average favored for
  the rest of next week.

&&

.UPDATE...
Issued at 930 AM CST Sat Dec 6 2025

A frontogenesis heavy band of snow has setup across western and
southern North Dakota. Given the 1/2 mile visibilities and the
3 to 4 hour forecast of the fgen band staying in ND, we issued a
Winter Weather Advisory for snow up to 4 inches. Currently the
heaviest band of snow is in Mercer county and down through the
Bismarck/Mandan area. Blowing and drifting snow will also be
possible statewide today.


UPDATE
Issued at 629 AM CST Sat Dec 6 2025

Quick update to PoPs to account for observations and trends.
Snow has reached Jamestown much sooner than expected, but is
struggling to commence at Bismarck despite the 12Z RAOB showing
a deep layer of near-saturation with respect to ice. CAMs are
not handling the coverage and placement of snow very well, and
the latest HRRR and RAP are incorrectly eliminating much of the
snow they are assimilating in their current conditions by
forecast hour two.

&&

.DISCUSSION...
Issued at 514 AM CST Sat Dec 6 2025

Synopsis: Confidence remains high that an active northwest flow
pattern will persist through late next week. Near daily
shortwaves/clipper systems will bring repeated chances for
accumulating snow across parts of the region. There is moderate
to strong ensemble agreement on the general placement and timing
of systems through Tuesday night, and that another wave is
likely to follow late Wednesday/Thursday but with greater
uncertainty in timing and placement. There is also high
confidence that Tuesday will feature the most impactful clipper,
which could produce a period of freezing rain, accumulating
snow, and very strong winds (but not necessarily overlapping
with the snow). Wild fluctuations in day-to-day temperatures
also remain in the forecast through late next week as we
alternate between periods of Arctic cold and mild Pacific air.
This weekend will feature below normal temperatures with highs
mostly in the single digits and teens above zero, and lows
tonight around zero to 10 below. Sunday will begin to warm up in
the west (especially southwest) as a warm front moves through.
Above normal temperatures are then expected for Monday and
especially Tuesday when areas along and to the south and west of
the Missouri River could reach the 40s. The maximum and minimum
NBM temperature distributions take a distinct shift colder on
Wednesday, but there is very large spread (in some cases as much
as 20 to 30 degrees in the 25th-75th percentile range). The
following paragraphs will summarize the important forecast
details for each shortwave/clipper.

Today: Snow has been falling across much of northwest and north
central North Dakota (except the Turtle Mountains area) since
late last evening. There has also been some freezing drizzle
along the I- 94 corridor from around Dickinson to Bismarck, but
this threat should be waning as deeper moisture in DGZ migrates
southward. The snow that has fallen thus far has been farther
north than expected, but there has been a more recent trend in a
southward shift. Overnight radar reflectivity across northern
North Dakota has presented banding and convective signatures at
times, suggesting there could be some periods of enhanced
snowfall rates. This thinking is supported by RAP analysis
showing 850 mb frontogenesis, steep mid to upper level lapse
rates, and strong vertical lift through the DGZ. The latest RAP
maintains moderate to strong low level frontogenesis through at
least mid morning. Snow accumulation threshold probabilities
have risen with the latest model cycle, particularly for 2
inches and above. Areas bounded by the Missouri River, Montana
border, and Highway 12 have a 50 to 80 percent chance for
exceeding 1 inch, a 30 to 60 percent chance for exceeding 2
inches, and a 5 to 20 percent chance for exceeding 4 inches per
the experimental NBM version 5.0. These probabilities can likely
be extrapolated farther north, as most 00z guidance did not
pick up on the northward shift that has already been observed.
Also keep in mind these probabilities are point-specific,
meaning there is higher confidence in this system producing
amounts this high somewhere. This leads us to advertise a broad
area of 1 to 3 inches of snow through this evening, with local
amounts as high as 5 inches. This also lines up well with HREF
snow output.

Sunday: A shortwave dragging a warm front across the state from
west to east during the early morning to late afternoon is
expected to bring a few hours of light to moderate snow to most
locations across most of western and central North Dakota on
Sunday, with the lowest probabilities again in the Turtle
Mountains area. Ensemble systems project high probabilities for
measurable precipitation, but only low probabilities for
exceeding a tenth of an inch of liquid. Deterministic model
soundings show a deep saturated layer within or just slightly
warmer than the DGZ up to 700 mb, with another 100 mb layer of
steep lapse rates through the DGZ placed above it. This could
drive snow ratios closer to 20:1 (but elevated winds through the
saturated column should discourage extremely high snow ratios).
It follows that our updated snowfall forecast for Sunday is
around a few tenths of an inch to near 2 inches, which is also
in line with HREF output.

Monday: A weak clipper is forecast to move from southern
Saskatchewan through the Red River Valley during the day
Monday. The Turtle Mountains area has a 30 percent chance of
accumulating snow, but less than a 10 percent chance of
exceeding 1 inch. The rest of western and central North Dakota
is expected to remain dry through Monday evening, with milder
temperatures but breezier winds.

Monday night through Tuesday night: A strong Alberta clipper is
forecast to cross the region over this time period. From late
Monday night into Tuesday morning, the greatest concern is the
potential for a period of freezing rain across western and
central North Dakota. This will be dependent on whether above
freezing temperatures aloft outpace those at the surface, for
which there are medium probabilities. Those probabilities joined
with the probability for measurable precipitation are no
greater than 30 percent, but this setup seems to have the
potential making of a low predictability/high impact event. The
surface low is forecast to cross the state from northwest to
southeast during the day Tuesday, and there is little spread in
its timing and track among the 3 highest membership clusters out
of 4 (composing around 85 percent of all global ensemble
members). This results in high probabilities for accumulating
snow along and northeast of a line from around Crosby to
Jamestown, and exceedance probabilities for as high as 4 inches
remain greater than 50 percent in the Turtle Mountains. The
greatest overall concern with this system though is the
potential for a very strong wind event, for which there is
increasing ensemble confidence. Every ensemble cluster has an
area of medium to high probabilities for 850 mb winds exceeding
50 kts crossing western and southern North Dakota, and recent
EFI output is shifting towards higher probabilities for a high-
impact event. One of the big questions is how much, if any,
overlap there could be with fresh snow accumulations and the
strong winds (snow that has fallen before Tuesday should not be
blowable by that time). Even a slight overlap could pose
significant blowing snow issues.

Wednesday and beyond: There is broader ensemble agreement in
yet another clipper crossing the region late Wednesday into
Thursday, but with much greater uncertainty in details. The
latest experimental NBM output shows a 50 to 60 percent chance
for measurable snow across most of a western and central North
Dakota Wednesday evening through Thursday afternoon, with a 30
to 40 percent chance of exceeding 1 inch and a 15 to 25 percent
chance for exceeding 2 inches.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 629 AM CST Sat Dec 6 2025

Snow is expected across most of western and central North
Dakota this morning (except areas to the north and east of
KMOT), ending from northwest to southeast this afternoon and
evening. Visibility under falling snow should mostly be in the
IFR range, with brief periods of LIFR possible. Early morning
ceilings range from LIFR in southwest North Dakota to VFR in the
far north. Expect ceilings to gradually lift throughout the
day, likely reaching VFR levels around the same time snow
diminishes. By the end of the forecast period, another round of
snow with MVFR ceilings and IFR visibility could be entering
western North Dakota. Winds through this afternoon will mainly
be east to northeast around 10 kts, becoming lighter and
variable this evening.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 8 PM CST /7 PM MST/ this evening
for NDZ017>020-031>036-040>047-050.

&&

$$

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