109
FXUS63 KBIS 231519
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
919 AM CST Sun Feb 23 2025

.KEY MESSAGES...

- Well above normal temperatures expected this week, with daily
  highs generally in the mid and upper 30s north to around 50
  south.

- Very windy in southwest North Dakota on Monday, with gusts as
  high as 55 mph.

- There is a 40 to 60 percent chance of light rain across
  northwest, central, and southeast North Dakota on Monday. Some
  light freezing rain or snow could mix in, but little to no
  accumulation of snow or ice is expected.

&&

.UPDATE...
Issued at 914 AM CST Sun Feb 23 2025

Fog has cleared out across the north. Temperatures continue to
warm above freezing across the western half of the state, while
the central and eastern half of the state climb to near
freezing. Temperatures are forecast to climb above freezing
every where in the state this afternoon. Winds are expected to
increase as mixing occurs which will also aid warmer
temperatures aloft to mix down to the surface.

UPDATE
Issued at 603 AM CST Sun Feb 23 2025

Infrared satellite imagery shows thick high clouds streaming over
the region early this morning. At the surface, fog is beginning to
lift from west to east as expected. The dense fog is now mainly
confined to areas south and east of the Turtle Mountains, and
visibility should greatly improve within the next hour or two. The
forecast for today remains on track.

&&

.DISCUSSION...
Issued at 357 AM CST Sun Feb 23 2025

The Northern Plains sit under northwest flow aloft early this
morning, with upstream ridging over the Northern Rockies. A surface
trough that is effectively a warm front extends from eastern Alberta
through north central and eastern North Dakota. To the east of this
boundary, patchy dense fog has developed across far northern and
central parts of the state. The most concentrated and persistent
areas of fog have been in Bottineau and Rolette Counties, but brief
quarter mile visibility has been reported as far south as Harvey.
There has already been a notable west-to-east improvement through
the night, and expect this trend to continue as the surface trough/
warm front progresses eastward.

Flow aloft will remain northwesterly/quasi-zonal today as the upper
level shortwave responsible for the Alberta surface low tracks
eastward across the Canadian prairie provinces. A secondary surface
trough extending south of the Canadian surface low is forecast to
cross the state later this morning, followed by weaker mid level
impulses ejecting off the Northern Rockies. This sets the stage for
a very mild but windy day, with more clouds than sun. The lack of
full sunshine and lingering snowpack will limit full heating
potential, but downslope westerly winds remain favorable for strong
boundary layer mixing and adiabatic heating. High temperatures this
afternoon are forecast to range from around 40 degrees north and
east to around 50 degrees south of Lake Sakakawea between Highways
85 and 83. Most of western and central North Dakota will see
westerly winds increase to around 20 to 25 mph this afternoon, with
gusts locally as high as 40 mph. The broad, weak atmospheric lift
could generate a few very light rain showers throughout the day, but
only trace amounts are expected. It will remain breezy through
tonight as a tight surface pressure and mid to upper height gradient
persists over the region. This, along with at least partial cloud
cover, will keep overnight temperatures near record-warm values
around freezing to a few degrees above.

A strong upper jet is forecast to cross the Northern Rockies over
Montana and South Dakota on Monday, clipping southwest North Dakota.
Atmospheric lift from left exit region jet dynamics, differential
advection of cyclonic shear vorticity, and mid level frontogenesis
should contribute enough forcing to generate light precipitation
across parts of northwest, central, and southeast North Dakota
during the day Monday. Ensembles appear to have consolidated on a
distinct axis of maximum QPF threshold probabilities, located from
near Williston to Garrison to Oakes. But the footprint of measurable
ensemble mean QPF covers nearly the entire state. Point-specific
probabilities for at least a tenth of an inch of liquid are
maximized at around 40 to 50 percent, but think this threshold
probability applied to the system as a whole is higher. That is to
say, we think there is at least a 60 percent chance that
frontogenetical forcing will produce a narrow corridor of at least a
tenth of an inch of liquid somewhere. Most traditional thermal
profile prognostics, both deterministic and ensemble-based, point
toward rain as a dominant precipitation type. However, forecast wet-
bulb temperatures above the near surface layer are forecast to
remain below freezing. This could allow rain to mix with or change
over to snow where precipitation rates are highest. Even if this
lower-probability outcome is realized, it is not anticipated that it
will snow hard enough and long enough at any given location for
there to be anything beyond minor impacts. Another lower-probability
outcome being advertised by some models is the potential for
precipitation to fall as light freezing rain in the morning. Given
our expectation that early morning temperatures are more likely to
fall on the warmer side of guidance, think that any impacts from
freezing rain would be limited to northwest parts of the state,
where precipitation will first begin falling, and be short in
duration.

A bigger concern on Monday is the potential for very strong winds as
a 40-50 kt low level westerly jet cross southwest North Dakota. This
feature has been very consistent over several forecast cycles. Some
forecast parameters that typically drive higher-end wind events are
not impressive, such as cold air advection and surface pressure
rises. However, BUFKIT soundings show a well-mixed boundary layer
with strong downward vertical motion, resulting in nearly-full
momentum transfer of the low level jet. We will continue to
advertise very windy conditions in southwest North Dakota on Monday,
with surface gusts as high as 55 mph. The maximum strength of winds
and gusts is forecast to be consistently lower moving towards the
north and east.

A persistent downslope component off the Northern Rockies will keep
mild temperatures in the forecast for the upcoming week. The NBM is
nearly consistent in its daily high temperature projection Monday
through Saturday, with around 35 to 40 north to around 50 south. A
notable exception jumps out on Thursday when the deterministic NBM
forecast shows lower to mid 50s for all areas along and south and
west of the Missouri River, and these values fall between the 10th
and 25th percentiles of the total NBM distribution. By that time,
snow should have a negligible impact on diurnal heating, which could
allow the 75th percentile of lower to mid 60s to have a higher
chance of verifying!

Beyond Monday, the only notable precipitation chances through the
upcoming week are associated with an open wave crossing the region
on Tuesday. QPF threshold probabilities at all values are lower
compared to the system on Monday, but there is a higher potential
the precipitation could be mixed phase. The NBM places its highest
PoPs of 30 to 40 percent across the southern half of the state on
Tuesday. On Friday, all deterministic models and ensemble clusters
show a strong clipper moving from southern Canada towards the Great
Lakes. The coldest air is favored to remain east of our area, as is
any measurable snowfall. But there are already signs in ensemble
datasets that it could be quite windy on Friday, and the NBM does
begin to show a slight cooling trend on that day, albeit with
increasing spread and the colder side of the distributions remaining
near to above normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 603 AM CST Sun Feb 23 2025

Dense fog will continue to impact terminals north and east of KMOT
early this morning, with conditions improving by mid morning.
Otherwise, VFR conditions are expected through the forecast period.
Westerly winds will become strong today, with sustained speeds
around 15-25 kts and gusts to 25-35 kts. The elevated winds will
persist into the evening and overnight. Strong low level wind shear
is expected at all terminals at various times throughout the next 24
hours.

&&

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

&&

$$

UPDATE...Johnson
DISCUSSION...Hollan
AVIATION...Hollan