313
FXUS63 KBIS 101444
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
944 AM CDT Fri Oct 10 2025

.KEY MESSAGES...

- Above normal temperatures continue through Saturday night,
  with highs in the 60s and 70s and lows in the 40s and 50s.

- Windy with increasing chances for rain this weekend. Some snow
  could mix in with the rain in northwest North Dakota Sunday
  evening and night.

- Cooler next week, with highs in the 40s and 50s and lows in
  the 20s and 30s. Dry Monday and Tuesday, then low to medium
  chances for rain Wednesday through Thursday.

&&

.UPDATE...
Issued at 944 AM CDT Fri Oct 10 2025

The Freeze Warning was allowed to expire as planned, and
otherwise no significant weather concerns for today. Sunny skies
will persist through much of today, with more widespread cloud
cover seen on visible satellite imagery back in Central Montana.
Freshened up the near term grids but no big changes with this
update.

UPDATE
Issued at 640 AM CDT Fri Oct 10 2025

Highly localized patchy dense fog is impacting parts of Emmons
County, including at the Linton Airport. No other evidence of
fog reducing visibility can be found, though there could well
be some very shallow ground fog elsewhere. The 12Z BIS RAOB
shows a very strong and shallow inversion, which likely
contributed to higher terrain areas remaining above freezing.

&&

.DISCUSSION...
Issued at 442 AM CDT Fri Oct 10 2025

An upper level ridge axis is analyzed along the eastern slopes of
the Rockies early this morning, with a strong upper low spinning off
the Pacific Northwest coast. Surface high pressure is also analyzed
from southern Saskatchewan through western North Dakota. Overnight
temperatures have not cooled as much as expected, likely on account
of elevated winds just above the surface. But there are still
pockets of near to sub-freezing temperatures scattered across the
Freeze Warning.

The ridge axis is forecast to slide into the Great Plains today,
maintaining a clear sky. The surface high will also slide eastward
into the Red River Valley this afternoon, with its associated air
mass keeping afternoon temperatures slightly cooler there, while
increasing southerly return flow on the back side of the high and
underneath the ridge brings warmer temperatures into western North
Dakota. Highs this afternoon are forecast to range from the lower
60s northeast to lower 70s far west. South to southeast winds along
the Montana border could gust to around 30 to 35 mph this afternoon.

The persistent southerly return flow is forecast to remain over the
Northern Plains tonight through Saturday night, keeping overnight
temperatures very mild for the time of year with widespread forecast
lows around 50 to 55 degrees. It will remain breezy during the
overnight hours each of these 2 nights, and on Saturday afternoon
southerly winds could reach sustained speeds near 30 mph with gusts
to around 40 mph, strongest in south central North Dakota. Saturday
is expected to be warmer ahead of a deepening western CONUS trough,
especially in western North Dakota where highs could reach 80
degrees.

The aforementioned low off the Pacific Northwest coast is scheduled
to spin over land tonight and deepen into California by Saturday
morning. This should push the Great Plains ridge off to the east,
and the resulting southwest flow looks to pick up residual monsoonal
moisture tied to the remnants of Priscilla. A steady stream of
cyclonic vorticity originating from the Desert Southwest also looks
to get picked up by the southwest flow and advected toward the
Northern Plains. This could lead to some scattered showers during
the day Saturday, with higher chances over central and eastern North
Dakota than the west.

From Saturday night through Sunday, the base of the western CONUS
trough is forecast to kick out into the Northern Plains. Rapid
surface cyclogenesis is projected in southeast Montana Saturday
night, with the low tracking northeastward into southern Manitoba by
Sunday night. The 00Z cycle of ensemble guidance shows very little
spread on the path of the low, but there is a clear discrepancy
between a slower and deeper wave favored by the GEFS and a more open
and progressive wave favored by the ECMWF ensemble. Even the more
open wave solution still looks to be potent though, and there are
several ECMWF members with sub-990 mb lows. Regardless of these
differences, this system is likely to cause a period of impactful
weather across much of western and central North Dakota Sunday and
Sunday night.

The highest confidence aspect of the forecast is that it will be
windy, but there is still uncertainty on the magnitude of strongest
winds. The cold front is forecast to quickly move across the state
from west to east during the day Sunday, with ensemble timing spread
of around 3 hours give or take. The frontal passage and post frontal
air mass should be highly favorable for strong momentum transfer
given deterministic model output of cold air advection, surface
pressure rises, steep low level lapse rates, and a strong surface
pressure gradient. The low level wind field is then forecast to
increase Sunday evening into Sunday night as the low lifts into
Canada, with the aforementioned ingredients remaining favorable for
downward momentum transfer. We have moderate to high confidence that
the timing of the strongest winds will be Sunday evening, and that
gusts will be stronger across northern parts of the state than the
south. However, there is still large ensemble spread on the
magnitude of mean BL winds, ranging from around 25 to 35 kts during
the afternoon, and from as low as 35 kts to as high as near 55 kts
in the evening and overnight. These outcomes would be the difference
between perhaps not even needing a Wind Advisory to northern parts
of the state needing a High Wind Warning. We will continue to
advertise windy conditions regardless, as ECMWF EFI output and
conceptual dynamics of this type of system lean the most likely
outcome toward the windier solution.

The other potential impact from this system is precipitation, more
specifically a) whether there will be any thunderstorms and b) if,
or more likely when, rain changes over to snow in northwest North
Dakota Sunday evening. On Saturday night, warm air advection and
isentropic ascent downstream of the approaching trough could
initiate showers across western North Dakota, and CAMs that extend
out this far simulate a few thunderstorms in a highly sheared
environment. MUCAPE could reach into the 500-1000 J/kg range, but
any convection would be highly elevated. Additional thunderstorms
cannot be ruled out in the warm sector and along the advancing cold
front Sunday morning and afternoon, but this signal is not as
prevalent in model guidance, and a quicker frontal passage would
shove this potential off to the east. Rain showers will become
likely in northwest North Dakota by Sunday afternoon as the wrap-
around deformation zone intensifies, but the rest of the area could
be impacted by dry slotting for much of the day. The concern then
becomes the timing and southern extent of the deformation band
Sunday evening through Sunday night. There are several potential
reasonable low-impact outcomes that could involve 1) temperatures
only cooling enough for a rain/snow mix that produces no
accumulation of snow; 2) wrap-around precipitation lifting into
Canada before temperatures sufficiently cool for snow; 3) the
deformation band tracking farther north and only giving the
northwest corner of the state a glancing blow; or 4) some
combination thereof. In contrast, a reasonable highest-impact
outcome would be for a period of moderate to heavy snow for at least
Divide County, but possibly as far south as Highway 2 and as far
east as Highway 83, combining with strong winds to produce near-
blizzard conditions. That remains far from the most likely outcome,
as the NBM is only showing a 15 to 25 percent chance of at least 2
inches of snow. However, the mean of the NBM distribution is heavily
skewed to the higher percentiles, implying that a majority of NBM
inputs produce little to no snow accumulation while a handful of
outliers produce several inches. At this time, we think that the
most likely outcome is for a few hours of snow falling across the
northwest corner of the state, with the combination of winds causing
minor to moderate travel impacts.

Much cooler and drier weather is expected for Monday and Tuesday as
a Canadian high pressure slides across the region. There is medium
confidence that most of North Dakota will see at least one night of
sub-freezing temperatures, with western and north central parts of
the state more likely to see 2 consecutive nights of lows in the
20s, if not colder. Highs on Monday could be limited to the lower 40s
to lower 50s, followed by a few degrees warmer on Tuesday. A general
western CONUS troughing regime appears favored to resume mid to late
next week that could result in a slight warming trend as well as a
return of precipitation chances. This lends to the NBM showing a 20
to 40 percent chance of rain only Wednesday through Thursday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 640 AM CDT Fri Oct 10 2025

VFR conditions are expected through the forecast period. A few
showers could enter southern North Dakota late tonight, but no
impacts to aviation are anticipated. Winds will become
southeasterly today, ranging from around 5-10 kts across
central North Dakota to as high as 15-20 kts in western North
Dakota. Then this evening through tonight, south-southeast winds
around 10-15 kts are expected across all of western and central
North Dakota. Low level wind shear is also expected to impact
most of the western half of the state tonight.

&&

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

&&

$$

UPDATE...Jones
DISCUSSION...Hollan
AVIATION...Hollan