266
FXUS63 KBIS 031751
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1251 PM CDT Thu Apr 3 2025

.KEY MESSAGES...

- A band of snow is forecast to move across parts of the state
  this evening through Friday afternoon. The highest chances for
  at least 2 inches of snow (around 60 to 70 percent) are
  focused over central North Dakota where there is also a low
  chance of at least 4 inches.

- Temperatures will remain below normal through early next week.

- A transition to above normal temperatures is still expected
  next week, but it could be delayed until the second half of
  the week.

&&

.UPDATE...
Issued at 1242 PM CDT Thu Apr 3 2025

Again, no significant updates other than sky cover. Will be
diving into the tonight-Friday system shortly. Latest guidance
suggests there will be a good area of FGEN forcing, combined
with -EPV and steep lapse rates, suggesting some banded snow.
Unfortunately there is quite a bit of spread in where any band
do eventually end up.

UPDATE
Issued at 941 AM CDT Thu Apr 3 2025

Only some minor updates this morning for sky cover. Otherwise
no significant changes to the going forecast.

UPDATE
Issued at 651 AM CDT Thu Apr 3 2025

Low stratus is the primary forecast challenge early this morning.
Erosion of the stratus deck from the north is occurring, but a bit
slower than expected. Becoming a little more pessimistic in the sun
coming out across western and south central North Dakota later
today, but hope to still see at least a few peeks of sun. Otherwise,
the forecast remains on track.

&&

.DISCUSSION...
Issued at 439 AM CDT Thu Apr 3 2025

The Northern Plains are surrounded by three synoptic scale waves
early this morning: a closed low over northern Saskatchewan/
Manitoba, another closed low over northeast Minnesota/southwest
Ontario, and an open wave over Utah. A surface low over western Lake
Superior is nearly stacked underneath the Minnesota/Ontario upper
low. As of this writing, the downstream low was still bringing some
wrap-around light snow as far west as the Red River Valley. But
western and central North Dakota are now precipitation free and will
remain so for much of the day. A large area of low stratus remains
blanketed over the region early this morning, but there is medium to
high confidence that a drier air mass pushing down from the north
will erode the low clouds from the north through mid afternoon. Most
areas should see at least a few hours of sunshine today. Afternoon
high temperatures are forecast in the mid 30s to mid 40s, warmest
along and south of I-94 and along and west of the Missouri River.

Two separate pieces of energy will move into the region this evening
through Friday: a sharpening trough attendant to the Canadian upper
low and a shortwave ejecting poleward from the deeper western CONUS
trough. These two waves bring medium to high chances for
precipitation across western and central North Dakota early this
evening through Friday afternoon. The northern stream wave will be
the primary source for precipitation in the western half of the
state. Ensemble guidance favors snow northwest and rain southwest
for types this evening, transitioning to all snow from north to
south as the precipitation shifts eastward across the state through
the night. Deterministic models are showing several mesoscale
features that could contribute to enhanced precipitation rates,
including strong low to mid level frontogenesis with above layer
negative EPV, steep mid level lapse rates, and strong omega through
the dendritic growth zone. Snow-to-liquid ratios are unlikely to
greatly exceed 10:1 on an event average as soundings suggest heavy
riming should occur, but the mesoscale instability is translating to
CAMs` maximum QPF output in the 0.25 to 0.5 inch range. Every CAM
places its maximum QPF in a slightly different location though, and
some of the maximum QPF could fall as rain. All ensemble systems
place the highest QPF threshold probabilities within an area from
around Dickinson to Minot to Bismarck, but not including Williston.
The highest snow probabilities are shifted slightly to the north on
account of precipitation type uncertainty. Forecast confidence is
high that this system will produce at least a small area of 2 to 4
inches of snow in the span of a few hours, but exact timing and
location details will likely remain uncertain until closer to
forecast-hour zero.

The shortwave ejecting north from the western CONUS trough is
forecast to interact with the northern stream wave over the eastern
Dakotas Friday morning. This could result in a period of heavier
precipitation over the southern James River Valley during the
daytime hours on Friday, with both rain and snow possible. Despite
the heavier rate potential, the time of day, solar angle, and low
snow-to-liquid ratios result in lower threshold probabilities for
snow amounts in this part of the state. There are also a few
deterministic models projecting a brief period of freezing drizzle
in our southeast early Friday morning prior to the wave interaction.
The probability of icing impacts is currently not high enough to
message this threat, but is something that will bear monitoring as
the time approaches.

Precipitation chances diminish from west to east throughout the day
Friday, although a few CAMs hint at diurnally driven rain/snow
showers over parts of the western half of the state Friday afternoon
under cyclonic flow aloft. Highs on Friday are forecast to be
limited to the 30s, although some clearing of clouds could occur in
the west by the end of the day. For the weekend, the Northern Plains
look to be under the influence of broad surface ridging under
northwest flow aloft between a trough extending south of Hudson Bay
and a highly amplified upper ridge between the Pacific coast and the
Rockies. We maintain a dry forecast for the weekend, although Sunday
afternoon looks like a favorable setup for diurnally-driven showers
with potential for a weak disturbance embedded in the northwest flow
aloft. Additionally, ensembles show increasing confidence in a
backdoor cold front plunging down from the northeast by Sunday
evening, with the trailing air mass being of Arctic origins. The
Arctic air mass will quickly become modified during its residence
time in the Upper Midwest, but the eastern half of the state could
experience quite a chilly 24 hours by early April standards as the
NBM is advertising highs on Monday in the lower to mid 30s and early
morning lows possibly falling into the single digits above zero. The
influence of this colder air mass quickly diminishes to the west,
with forecast highs on Monday along the Montana border near average
in the lower to mid 50s.

For the rest of next week, ensembles tend to favor a more
progressive northwest or quasi-zonal flow pattern with strong
upstream ridging shifting into the central CONUS by the end of the
week. It follows that a distinct warming trend to above normal
temperatures is presented by all ensemble systems from the beginning
to end of the work week. The mid week pattern could bring periods of
showers across the region, and the NBM has introduced a 10 to 20
percent chance of rain late Tuesday through Wednesday. The overall
dry and warm pattern could prompt closer attention to fire weather
next week, though there is not a particularly strong signal for
critical conditions at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1242 PM CDT Thu Apr 3 2025

MVFR to low VFR ceilings to begin the 18Z TAF period, but there
are a couple of breaks, including KMOT and KJMS. Think later
this afternoon we should trend to more low VFR ceilings north
and MVFR ceilings south. Still could be some breaks as well.

Tonight and through Friday morning, we are expecting another
area of snow to spread across western and central North Dakota.
Expecting MVFR to IFR ceilings and visibilities in areas of
snow. Precip may be a mix of rain and snow early in the period
as it moves into the west. Winds mainly variable at 10 knots or
less today, turning north to northeast tonight through Friday
morning. At this time the better chances for low visibilities in
snow will be over the southern TAF sites tonight through Friday
morning.


&&

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

&&

$$

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