717
FXUS63 KBIS 030902
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
402 AM CDT Sun Aug 3 2025

.KEY MESSAGES...

- Periods of smoke will continue to linger over the next few
  days. Patchy fog will also be possible this morning over much
  of western and central North Dakota.

- Periodic chances for showers and thunderstorms (20 to 70
  percent) remain in the forecast through today and into early
  next week. Isolated severe thunderstorms are possible on
  Tuesday.

- Expect highs today in the mid 70s to the mid 80s with a
  gradual warmup likely through the new workweek. Some highs in the
  lower 90s return to the forecast by Wednesday and Thursday.

&&

.DISCUSSION...
Issued at 402 AM CDT Sun Aug 3 2025

Western and central North Dakota continues to be under the
influence of stagnant/weak flow in the mid to upper levels. A
weak shortwave will continue to interact with a nearly
stationary surface boundary across the far west, leading to a
couple of clusters of showers and thunderstorms. One cluster is
located in the vicinity of Williston and another is located
across the southwest. Additionally, the low level jet has kicked
in and has led to some shower development over the James River
Valley, north of a remnant MCV moving through northeast South
Dakota. CAMs suggest that the convection across the James River
Valley could become a bit more widespread but the activity
across the west should start to slowly diminish as the weak
shortwave/upper low moves further away from the surface
boundary. Shear is weak over the entire area so severe weather
is not much of a concern, but high PWATs and slow storm motions
could lead to some locally heavy downpours.

Patchy fog has developed as expected across portions of the
west and central with some transient dense fog across the
southwest as Dickinson and Hettinger have been down to a quarter
mile visibility at times. It remains to be seen how long the
patches of dense fog will last or how widespread it may become,
so for now we just decided to go ahead and issue an SPS for
areas south and west of the Missouri River through 15z. Outflow
from storms near the Montana border may disrupt the fog briefly
but satellite imagery suggests that it has been building back in
after outflow passes through. Periodic visibility reductions
from near surface smoke will also continue through the day and
potentially even longer considering the weak flow aloft.

After the showers and storms across the James River Valley move
out to the east by mid to late morning, most of western and
central North Dakota should see dry conditions through the rest
of the day. Highs will generally remain below normal today with
values ranging from the low to mid 70s east, to the low to mid
80s west.

For tonight, the story will be similar to previous nights. The
stagnant flow and another weak shortwave will lead to more
low/medium chances (20 to 40 percent) of pulsey showers and
storms, mainly west and south. Lows will range from the upper
50s to the lower 60s.

Monday will see ridging trying to build back in across western
North Dakota through most of the day. Highs will be a little
bit warmer Monday afternoon, with values ranging from the mid
to upper 70s east to the mid to upper 80s west. Precipitation
chances should remain fairly low during the day, but they will
start to increase (20 to 30 percent) across the west at night
as the ridge axis starts to move east and we transition back
into modest southwest flow aloft. Showers and storms will be
ongoing Tuesday morning as a compact shortwave trough moves
into the northern Plains. While this morning convection should
diminish to some extent, we should see some additional
development in the afternoon and evening (30 to 60 percent). It
remains to be seen how much the early day convection will
impact the atmosphere later in the day, but models are
suggesting the potential for some MLCAPE values in the 1500 to
2500 J/kg range and some higher deep layer shear than in recent
days, possibly in the 30 to 40 knot range. Thus, if the morning
convection doesn`t work over the atmosphere too much, there does
appear to be a conditional severe weather threat Tuesday
afternoon and evening across much of western and central North
Dakota. SPC has placed most of the area in a Marginal Risk
(level 1 of 5), so this lines up well with what we are thinking.

After the Tuesday wave moves through, we transition into zonal
flow aloft for Wednesday, promoting warmer temperatures and
mainly dry conditions. We could see some lower 90s return to the
southwest and south central Wednesday afternoon. The next wave
then starts to approach the west on Thursday, putting us back
into southwest flow aloft and potentially leading to our next
severe weather threat. Deterministic models currently suggest
strong to extreme instability collocated with some decent deep
layer shear. CSU Machine Learning guidance and CIPS analogs also
continue to highlight this period over our area. While it is
still a ways out, this will be a day to watch closely as we move
closer in time.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1242 AM CDT Sun Aug 3 2025

MVFR to low VFR visibilities continue late tonight across all of
western and central North Dakota from near surface smoke. Some
fog is also forecast to develop overnight and may have already
started with KHEI seeing the visibility drop to a quarter mile.
KDIK has dropped to three miles.

Along with the fog, IFR to MVFR stratus may develop overnight
and into Sunday morning across much of the area, before starting
to lift in the afternoon.

There will be some chances of showers and thunderstorms across
the far west over the next couple of hours, mainly impacting
KXWA. Another area of showers will continue to develop across
the James River Valley, possibly bringing a shower or isolated
rumble of thunder to KJMS in the next few hours. More showers
and storms will be possible across the west Sunday afternoon and
evening and we have decided to utilize PROB30 groups to account
for this potential.

&&

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

&&

$$

DISCUSSION...ZH
AVIATION...ZH