667
FXUS63 KBIS 101420
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
920 AM CDT Sun Aug 10 2025

.KEY MESSAGES...

- Areas of smoke will reduce surface visibility today.

- Daily high temperatures through the upcoming week will mainly
  be in the mid 70s to upper 80s.

- Isolated to scattered showers and thunderstorms on Monday,
  otherwise dry through Tuesday.

&&

.UPDATE...
Issued at 916 AM CDT Sun Aug 10 2025

Wildfire smoke continues to stream in from Canada, and spread
east. The latest surface observations were blended into the near
term forecast.

UPDATE
Issued at 649 AM CDT Sun Aug 10 2025

Observations at daybreak suggest the smoke moving in may actually be
thicker than anticipated both at the surface and aloft. Visibility
across the western third of the state is now mostly in the 1.5 to 3
mile range, and many sites are reporting broken to overcast ceilings
where satellite shows no clouds. These deteriorating conditions
will spread eastward across central North Dakota this morning.
Western portions of the state could see a slight improvement
later this afternoon through tonight, but in central North
Dakota the smoke is not expected to move out until Monday
morning.

&&

.DISCUSSION...
Issued at 338 AM CDT Sun Aug 10 2025

A stacked low pressure system is spinning from eastern Manitoba into
northwest Ontario early this morning. The broad circulation of the
upper low is taking on a negative tilt, but a positively-tilted
longer-wave trough extends back into northeast Utah. The west-
northwest deep layer flow has returned higher concentrations of
smoke to the region overnight, both aloft and at the surface. Early
morning observations in western North Dakota have shown visibility
as low as 3 miles, but parts of northeast Montana have seen as low
as a mile and a half. The large blob of smoke is forecast to migrate
eastward across the state this morning and afternoon, with HRRR/RAP
modeling simulating a slow dispersal of smoke in western parts of
the state this evening through tonight followed by a quicker erosion
from west to east Monday morning. Smoke is the only forecast concern
for what would otherwise be a very pleasant day, with a mostly sunny
sky, much lighter winds than yesterday, and high temperatures around
75 to 80. If the smoke aloft is thicker than anticipated, highs
could end up a few degrees cooler. Quiet weather continues through
tonight, with forecast lows around 55 to 60.

A broad but deepening mid level shortwave is forecast to dig into
the region from the northwest on Monday, with an attendant surface
cold front pushing through the state during the day. All ensemble
guidance has shown an increase and southward expansion with shower
and thunderstorm chances on Monday, but CAMs in particular are now
quite bullish on scattered convection as far south as northern South
Dakota. SBCAPE approaching 1000 J/kg and effective bulk shear
approaching 30 kts could yield a few stronger storms Monday
afternoon, but the highest CAPE and shear may not overlap, and the
timing of the cold frontal passage, for which there is still
forecast uncertainty, will likely be a determining factor in
convective coverage and intensity. The NBM high temperature spread
on Monday is surprisingly small given the frontal passage timing
differences that are being displayed across deterministic guidance,
with values ranging from the mid and upper 70s north to mid 80s
south. Breezy conditions are likely behind the cold front. While
rates of cold air advection and surface pressure rises are not
overly high, mean boundary layer winds around 30 kts could easily be
transfered to the surface, especially by showers or storms.

The post-frontal air mass is now expected to result in a very slight
cool down for Tuesday, with highs in the lower 70s to lower 80s. Dry
weather is expected during the day Tuesday under deep layer ridging.
The NBM maintains a 10 to 15 percent chance of rain with the passage
of an elevated warm front Tuesday night into Wednesday morning, but
deterministic model soundings look too dry to support any
precipitation reaching the ground. From Wednesday onward, ensembles
favor the synoptic pattern becoming much more active over the
region, with a possible transition from quasi-zonal to southwest
flow aloft by the weekend. The NBM maintains a nearly continuous 20
to 30 percent chance of showers and storms beginning Thursday
evening as there is a lack of ensemble consensus for any distinct
forcing mechanism, though there will likely be periods of
atmospheric ascent over this time frame. Deterministic models show
requisite ingredients for severe convection at times, and machine
learning guidance continues to show low severe probabilities
Wednesday through Friday. The NBM temperature distribution trend
suggests a quick warmup Wednesday and Thursday followed by a slight
cool down Friday through the weekend. The general expectation at
this time is for near or slightly below average temperatures north
to near or slightly above average temperatures south for the second
half of the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 649 AM CDT Sun Aug 10 2025

Smoke will reduce visibility to MVFR/IFR levels throughout the
forecast period. A low stratus deck with MVFR ceilings will
pivot southeastward from north central into eastern North Dakota
this morning. Aside from this, little cloud cover is expected
today. However, surface observations will likely continue to
report BKN to OVC at 2,000 to 4,000 ft because of the smoke.
Since it is not being caused by clouds, will be handling with a
SCT mention. West-northwest winds around 10-15 kts are expected
through this afternoon, becoming light and turning to the
south-southwest tonight.

&&

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

&&

$$

UPDATE...Smith
DISCUSSION...Hollan
AVIATION...Hollan