448
FXUS63 KBIS 300935
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
435 AM CDT Mon Sep 30 2024

.KEY MESSAGES...

- Strong northwest winds will gust up to 50 mph across all of
  western and central North Dakota today.

- Much cooler today, with high temperatures in the mid 50s
  northwest to lower 70s southeast.

- Critical fire weather conditions are expected across much of
  western and south central North Dakota through this afternoon.

- Areas of frost are possible across the western half of the
  state tonight into Tuesday morning, and there are medium to
  high chances for sub-freezing temperatures in southwest and
  central parts of the state.

- Very little to no measurable precipitation is expected this
  week.

&&

.DISCUSSION...
Issued at 432 AM CDT Mon Sep 30 2024

A potent shortwave trough is ejecting off the Northern Rockies early
this morning. The attendant cold front has driven through western
and into central North Dakota as of 4 AM CDT, and should clear our
forecast area shortly after sunrise. So far, gusts with the frontal
passage have been slightly weaker than expected, especially more
recently and with eastward progression of the front. Once diurnal
mixing commences, we should start to see gusts more routinely in the
40 to 50 mph range as the post frontal air mass maintains moderately
strong cold air advection and surface pressure rises. Temperatures
will continue to fall behind the front through the morning and only
recover a few degrees this afternoon. Forecast highs for today range
from the mid 50s northwest to lower 70s southeast. The base of the
shortwave trough will pass through the state this afternoon, but the
atmosphere is expected to remain too dry to support any measurable
precipitation on a widespread basis. Some high-resolution models do
show potential for isolated showers along and north of Highway 2
this afternoon, but the probability of this occurring is not high
enough to mention in other forecast products at this time.

Short-range, high-resolution model guidance has trended around 5 to
10 degrees higher with dewpoints behind the front. This results in
lower confidence that Red Flag Warning criteria will be reached this
afternoon, especially north of I-94. See the Fire discussion below
for more detailed information.

Surface high pressure is forecast to slide from central Montana into
western South Dakota tonight into Tuesday morning. This should set
the stage for strong radiational cooling for all of southwest North
Dakota and other sheltered, low-lying areas along and southwest of
Highway 52. The NBM now shows medium to high chances of overnight
temperatures falling below freezing from southwest into central
North Dakota, where a Freeze Watch has been issued. The rest of the
western half of the state is expected to see lows in the lower to
mid 30s, where a Frost Advisory will likely be needed.

Flow aloft will become anticyclonic on Tuesday before transitioning
to zonal on Wednesday. This should allow a return of warmer low
level temperatures. The NBM shows low spread in high temperatures in
the lower 60s to mid 70s these two days. It is also expected to
remain breezy on Tuesday (southwest around 20 mph) and Wednesday
(northwest around 20 mph), and low afternoon RH on Tuesday could
create near, if not critical fire weather conditions in western
parts of the state. From Wednesday night through Thursday night, a
large Canadian upper level cyclone will push lowering heights with
quasi-zonal cyclonic flow into the Northern Plains, resulting in
seasonably cool temperatures. There will be a potential for sub-
freezing low temperatures both of these nights, and highs on
Thursday are only expected to reach the mid 50s to mid 60s.

Ensemble guidance provides a variety of solutions on details of the
synoptic pattern from Friday into early next week, which is being
reflected in increasing NBM temperature spread. The general trend
though is a slight favoring of western CONUS ridging and eastern
CONUS troughing, with 850 mb temperature anomalies over the Northern
Plains tilted warmer than normal. There is still no sign of any
appreciable precipitation in any ensemble guidance any time soon. In
fact, NBM probabilities for a tenth of an inch of liquid through the
first 10 days of October are less than 10 percent, and there is an
80 to 90 percent chance of no measurable precipitation at all over
that entire time period.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 432 AM CDT Mon Sep 30 2024

VFR conditions are expected through the forecast period.
However, there is a low chance for a period of MVFR ceilings in
northwest North Dakota late this morning into the afternoon. A
cold front moving across the state early this morning will
bring strong northwest winds gusting to around 40 kts through
this afternoon. Ahead of the front, significant low level wind
shear will impact south central and eastern North Dakota
early this morning, including at KBIS and KJMS.

&&

.FIRE WEATHER...
Issued at 432 AM CDT Mon Sep 30 2024

A strong cold front moving across the state from west to east early
this morning will cause a wind shift to the northwest and increase
gusts to around 40 to 50 mph along and behind the front.
Relative humidity ahead of and immediately trailing the cold frontal
passage will remain in the 25 to 35 percent range, with some
recovery expected after sunrise. Northwest winds will remain strong
through this afternoon, with sustained speeds up to 35 mph and gusts
up to 50 mph. Relative humidity is also expected to fall back into
25 to 35 percent range this afternoon, especially near the South
Dakota border. However, the latest forecast update has trended
afternoon minimum humidity higher than what was previously forecast.
This is especially true farther to north, where the Fire Danger
Index for today is now projected to be in the Low category. These
factors have prompted the removal of Williams County from the Red
Flag Warning. Other counties along and north of Interstate 94 may be
allowed to have their Red Flag Warning expire ahead of time
depending on how conditions progress throughout the day. Areas
closer to the South Dakota border maintain the highest probabilities
of critical fire weather conditions through this afternoon. LaMoure
and Dickey Counties were added to the warning on account of minimum
humidity less than 25 percent and a projected Fire Danger Index in
the High category. The threat for critical fire weather conditions
for all areas will quickly end after sunset early this evening.

Near-critical fire weather conditions are likely to return to
western parts of the state on Tuesday, with southwest winds around
20 mph and minimum humidity around 15 to 20 percent. At this time,
there is not enough confidence in the duration of critical fire
weather conditions for the issuance of a Fire Weather Watch.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM CDT /6 PM MDT/ this evening for
NDZ001>005-009>013-017>023-025-031>037-040>048-050-051.
Red Flag Warning until 7 PM CDT /6 PM MDT/ this evening for
NDZ017>020-031>034-040>048-050-051.
Freeze Watch from late tonight through Tuesday morning for
NDZ018-019-033-040-041-043-044.

&&

$$

DISCUSSION...Hollan
AVIATION...Hollan
FIRE WEATHER...Hollan