247
FXUS63 KBIS 181955
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
255 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- Strong winds are forecast from this afternoon through
  Thursday evening, with sustained winds up to 30 mph at times.

- Showers and thunderstorms are possible (40-60% chance) across
  western and northern North Dakota this evening through
  tonight.

- A cooling trend is forecast for the end of the week, with
  highs in the 60s by the weekend.

&&

.DISCUSSION...
Issued at 255 PM CDT Wed Sep 18 2024

The expansive, stacked low pressure system that brought us our
thunderstorms earlier this morning sits across eastern Montana
today, with a large band of precipitation wrapping around it. Across
western and central North Dakota, skies have cleared out, allowing
for some heating and drying to occur. Highs today range from the mid
70s to lower 80s.

Southerly winds continue to increase as the low slides eastward,
tightening the surface pressure gradient and allowing for sustained
wind speeds around 20-25 mph, gusting up to 30-35 mph, especially
across the southern tiers of counties. At the moment, winds are not
necessarily exceeding advisory criteria, but there is the potential
for some areas to see isolated speeds right around the lower
threshold of advisory criteria. Wrap-around precipitation may begin
to nose into the southwest in the afternoon hours, which may
potentially help limit the mixing at the surface, so there is no
Wind Advisory out at this time. We will continue to monitor winds
throughout the day, in case the mixing begins to overperform.
This precipitation should then continue to expand to the
northeast as the surface low tracks to the northeast into
southern Saskatchewan, bringing about 40-70% chances for showers
and an occasional thunderstorm to much of the west and north
through the evening and through the overnight hours. Portions of
the south central also see some near critical fire weather
conditions, given the increased wind speeds and minimum relative
humidity values around 20-23%, but our live herbaceous fuel
moisture values in that area exceed 130%, helping limit much of
the concern for critical fire weather.

As the aforementioned low continues moving northeast, wind speeds
will remain breezy overnight, with the wind direction becoming more
southwesterly, before becoming entirely westerly by Thursday
morning. Along the nose of the precipitation band moving into our
far southeast, winds are expected to increase in speed, with
portions of Bowman, Adams, and Slope counties potentially seeing
sustained wind speeds above 30 mph for a time. There is the
potential for these winds to remain elevated long enough for a Wind
Advisory, so we will have to keep a close eye on how the forecast
evolves in that area. Some forecast soundings indicate stronger
winds aloft (30-35 kts) mixing down to around 500-700 ft for a few
hours in that area, which could certainly support some stronger
winds there. The EFI for wind speeds does indicate parts of the
southwest as potential areas for strong winds, but the shift of
tails remains further west and out of our area. Some models,
including the HREF, also suggest wind speeds dying out overnight
before they really establish themselves in our area. All in all, it
is a somewhat strange setup that will need to be closely monitored
through the rest of the evening. Otherwise, overnight lows will
mostly remain within the 50s.

Through the day Thursday, the low pressure system will transit to
our north, resulting in continued breezy winds from the west.
Chances for showers and thunderstorms (mostly 25-50%) will slowly
cross the northern counties, before eventually lifting north into
Canada by Thursday evening. Wind speeds will once again remain close
to advisory criteria but staying just below, mostly across the far
south and far northwest. Given the strong influence from the low,
high temperatures will be a bit cooler tomorrow than they are today,
with highs mostly in the upper 60s to mid 70s.

Very brief upper level ridging will help bring highs back into the
upper 70s to lower 80s Friday. With the low finally moving entirely
out of our region, winds should decrease across the area. Friday
should remain mostly dry under the influence of the ridge, with very
low chances (roughly 15-20%) for showers in the evening.

Through the weekend, models suggest a large trough digging down
across the Canadian Prairies, with the trough axis positioned just
to the north of the International Border. As a result, upper level
flow becomes more westerly, bringing about cooler temperatures to
the state. High temperatures on Saturday and Sunday mostly remain in
the 60s, with overnight lows in the low 40s. Some areas in the west
may see lows in the upper 30s as well. Long range guidance has
shifted flow to be more westerly as opposed to southwesterly over
the past few runs, so chances for precipitation through the weekend
has decreased quite a bit, with only portions of the southeast
seeing 15% chances for rain. These dry conditions are forecast to
continue into next week, where cluster analysis suggests the
beginning of a warming and drying trend, with upper level ridging
building into the western CONUS.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1234 PM CDT Wed Sep 18 2024

VFR conditions are present across all terminals this afternoon.
A low pressure system sits across eastern Montana, forecast to
move northeast through the rest of the day. Wrap-around
precipitation is forecast to arrive in the southwest, which will
increase cloud coverage and lower ceilings to around MVFR
criteria. These ceilings, along with increased chances for
showers, will arrive at KDIK and KXWA around 21z, expanding
northeast and impacting KMOT around 00z. Breezy
southerly winds are present, with sustained wind speeds from 15
to 20 kts persisting through the TAF period. These winds will
shift southwesterly late tonight, becoming more westerly
Thursday morning.

&&

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

&&

$$

DISCUSSION...Besson
AVIATION...Besson