030
FXUS63 KBIS 081932
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
132 PM CST Wed Jan 8 2025

.KEY MESSAGES...

- Light precipitation is expected across western and central
  North Dakota late this afternoon through early Thursday
  morning. A mix of snow, rain, and freezing rain is possible
  along the leading edge of the system, with a transition to all
  snow.

- Windy conditions are also expected late this afternoon through
  Thursday afternoon, which could create patchy blowing snow.

- Much warmer today, with highs in the mid 20s to mid 30s.

- There is a 60 to 80 percent chance of accumulating snow across
  western and central North Dakota Friday night into Sunday,
  with low to medium chances of at least 3 inches.

- Temperatures are favored to fluctuate between below and above
  normal through next week, with Monday likely to be the coldest
  day.

&&

.UPDATE...
Issued at 128 PM CST Wed Jan 8 2025

No updates early this afternoon. New forecast shortly.

UPDATE
Issued at 935 AM CST Wed Jan 8 2025

No significant updated this morning. It looks like the system
has slowed a bit with most precipitation holding off until after
00Z. It also still looks like a wintry mix along the leading
edge with a transition to snow. The initial wintry mix should be
short lived (1-3 hrs???) with light qpf accumulations. Thus at
this time the probabilities for light ice accumulations remain
low. Will continue to monitor.

UPDATE
Issued at 604 AM CST Wed Jan 8 2025

An area of fog and flurries has developed near the Turtle Mountains.
Conditions should improve once surface winds turn southwesterly
later this morning.

More recently initialized CAMs are shifting toward a later time of
arrival for precipitation with more of an early evening entrance and
early to mid Thursday morning exit. Still expecting a mix with
nearly equal conditional probabilities of frozen and melted
hydrometeors through mid to late evening.

&&

.DISCUSSION...
Issued at 416 AM CST Wed Jan 8 2025

A mid to upper level shortwave will eject off the Canadian Rockies
and dig into the Northern Plains today through tonight. Chinook
winds are already warming the lower to mid atmosphere, and the
attendant surface warm front is forecast to enter western North
Dakota this afternoon. This will bring us out of the prolonged
Arctic air, with forecast highs ranging from the mid 20s east to mid
30s southwest. Ensembles are in strong agreement that the synoptic
scale forcing will bring widespread light QPF across all of western
and central North Dakota late this afternoon through early Thursday
morning, with very high probabilities for at least a hundredth of an
inch and mostly low probabilities for exceeding a tenth of an inch.

There are two aspects of this system that carry a higher level of
uncertainty given the shorter forecast time range. The first issue
is timing of precipitation moving from west to east across the
state, with CAM outcomes ranging from as early as the early
afternoon through late tonight to as late as the early evening
through late Thursday morning. Global ensembles appear to generally
fall within this envelope, with a slight skew toward the later
solution. But a difference of several hours does show up in GEFS vs.
ECMWF ensemble mean QPF. The other challenging aspect of this system
is precipitation types. There is a notable difference between high
and coarse resolution guidance during the late afternoon and early
evening, with much higher probabilities for 850 mb temperatures
above freezing in the HREF than in the global ensembles. These
differences wash away by midnight as colder air aloft moves in
behind the upper trough axis. Deterministic soundings also suggest a
low level isothermal layer around zero degrees Celsius at
precipitation onset. Both CAMs and NBM precpitation type
probabilities have trended toward freezing rain (or rain where
surface temperatures are above freezing) as either a dominant type
or equally as probable as snow through around mid to late evening.
The risk of icing will likely be dependent on precipitation onset
time, with an earlier start timing favoring higher chances of
freezing rain as a type, and a later start time favoring lower
chances. HREF mean ice accumulations highlight northwest and central
North Dakota for the highest risk of a glaze of ice.

The onset of windy conditions in southwest North Dakota has sped up
in the forecast, with mixing potential in the warm sector as high as
35 kts this afternoon. Still anticipating the more widespread
increase in winds to be tonight into Thursday morning with the
arrival of the cold front and trailing pressure rises. The initial
frontal passage will likely bring a shorter duration of 30-40 mph
gusts, followed by an early to mid morning lull before gusts of
similar strength return with diurnal mixing Thursday afternoon. The
strong winds could create patchy blowing snow, especially where and
when snow is falling. But blowable snow on the ground is expected to
be minimal for most areas. The timing of the cold front could result
in high temperatures for Thursday being observed in the very early
morning hours, with upper 20s to lower 30s for most areas. There
will not be a significant drop in temperatures behind the front
though, with afternoon highs forecast around 25 to 30.

A much colder air mass is forecast to be shoved into the eastern
half of the region by the departing upper trough on Friday. NBM
spread is large given the forecast time range, with 25th-75th
percentile highs ranging from the mid single digits to upper teens
in the greater Turtle Mountains area, to the mid 20s to mid 30s in
the southwest. The daytime hours on Friday should remain dry with
deep layer ridging in place. But another shortwave landing on the
Pacific Northwest coast Friday afternoon will initiate a clipper
system crossing the region Friday night through Saturday. Ensembles
are in fair agreement on a surface low track from around Williston
to Bismarck. The highest probabilities for at least one inch of snow
(around a 70 to 90 percent chance) generally lie just north of the
favored low track, with a smaller maximum extending south along and
west of Highway 85 likely due to a vort max/cold front combo. 3-inch
probabilities are low to medium, but there are some hints of banding
potential in deterministic guidance that will need to monitored as
the time approaches.

Low to medium chances for lighter snow remain in the forecast
through Sunday night as flow aloft remains cyclonic. The bigger
story after Saturday though will be another plunge in temperatures
Sunday through Monday. NBM spread remains large for highs on Sunday,
but the 75th percentile is barely above the single digits in the
Turtle Mountains area, and the 25th percentile brings that same
isotherm as far south and west as the Missouri River. While the NBM
temperature distribution remains quite large next week, there is a
clear signal for the coldest temperatures to occur Sunday night
through Monday night when its deterministic forecast projects
overnight lows in the single digits and teens below zero and highs
on Monday from a few degrees below zero north and east to the lower
teens above southwest. A transition back to milder Pacific air with
above normal temperatures is favored by the middle of next week, but
uncertainty of the timing of this transition is exemplified by a
25th-75th percentile spread of 15 to 30 degrees Fahrenheit for highs
on Tuesday. Looking further ahead, both the GEFS and ECMWF ensemble
show a return of very cold 850 mb temperature anomalies leading up
to Martin Luther King Day.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 128 PM CST Wed Jan 8 2025

VFR conditions to begin the 18Z TAF period with some gusty winds
developing in the southwest this afternoon. Chances for
precipitation increase from west to east late this afternoon
through this evening and diminish in a similar fashion late
tonight into Thursday morning. Snow could be mixed with freezing
rain (or rain in the southwest where temperatures could be
above freezing) through mid to late evening before a transition
to all snow late tonight. The precipitation will be accompanied
by MVFR to IFR visibility and ceilings. Later tonight, a cold
front sweeping across the state will shift winds to the
northwest around 20 kts with gusts to 30 kts.

&&

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

&&

$$

UPDATE...TWH
DISCUSSION...Hollan
AVIATION...TWH