Sentinel Butte, North Dakota Weather Forecast Discussion

685
FXUS63 KBIS 112345
AFDBIS
Area Forecast Discussion
National Weather Service Bismarck ND
645 PM CDT Thu Sep 11 2025
.KEY MESSAGES...
- Several rounds of scattered showers and thunderstorms through
  the middle of next week.
- Isolated severe thunderstorms are possible today, Friday, and
  Saturday.
- Through tonight, the highest chances for severe storms are during
  the late evening and overnight hours.
- Temperatures favored to remain near to above average through
  the middle of next week.
&&
.UPDATE...
Issued at 645 PM CDT Thu Sep 11 2025
Surface analysis places a low pressure center crossing out of
Montana into northwestern North Dakota at the time of this early
evening update. Scattered showers and thunderstorms developed
across portions of eastern Montana and are expected to move into
our western counties over the next few hours. Modest amounts of
elevated shear has kept these storms fairly pulsey, though this
has started to trend up over the past few hours. So far, storms
have be actively diminish as they approach our shared border as
ongoing low to mid level warm air advection has kept a lid on
things. The development of a low level jet late this evening
through the overnight period may be enough to shake things
loose. Update wise, have blended the latest model and radar
trends into the PoPs and Sky grids, but otherwise have left
things alone due to the high amount of uncertainty that remains.
&&
.DISCUSSION...
Issued at 338 PM CDT Thu Sep 11 2025
This afternoon, a surface low was analyzed in western South Dakota,
while a high was placed over the Great Lakes region. A modest
surface pressure gradient over the forecast area was producing
breezy south to southeast winds, advecting in substantial moisture
with widespread dew points in the 60s. Afternoon temperatures range
across the area, from the mid 70s in the Turtle Mountains area to
around 90 in the southwest. Showers and thunderstorms have been
more persistent this afternoon than expected, with some current
development in the far north central. Mesoanalysis advertises
sufficient shear for supercell development but marginal
instability and lapse rates. Expectation is for this activity to
move off to the northeast and for quiet weather to dominate for
the rest of the afternoon and into the evening.
The question then turns to potential for strong to severe
thunderstorms tonight, with isolated to scattered severe storms
possible across most of the forecast area, with the exception of the
southeast. Confidence in storm development at any one spot is low. Forcing
aloft is a bit nebulous and not very well defined, and combined with
capping, there is uncertainty in where exactly storms will
develop and at what time. This is likely why CAMs have been
advertising a variety of solutions all day and are not in good
agreement, both between runs and between different models. Our
current best guess is for initial development somewhere in the
southwest and central between 8 to 11 PM central time, with
storms then moving northeast.
We are still advertising hail up to the size of ping pong balls and
wind gusts up to 70 mph. Some soundings showing the inverted v
profile which could help mix down stronger winds, and the 0-3 km
shear is favorable for some higher end wind gusts as well. The 0-6
km shear could be more lacking, with a cluster storm mode favored.
If storms can overcome the capping inversion, 2000-3000 J/kg of
MLCAPE will be available, and high PWATS could lead to some moderate
to high rainfall rates. We almost more confident in the potential
for strong to severe thunderstorms on Friday, with more consistency
in some of the extended high-res guidance. Friday will bring
another day with highs in the 80s and dew points in the 60s,
with slightly less forecast instability but stronger shear. HREF
has more defined max UH tracks late Friday afternoon through
the evening, which would fit with the stronger shear, so will be
keeping an eye on how this trends through tonight and into
Friday morning, with precipitation chances low until the
afternoon.
We did add in a mention of patchy fog late today into Friday morning
across the northwest and north central. Forecast soundings are
somewhat split between either a very low stratus deck or actual fog
development.
As the trough slowly drifts east over the Rockies, multiple waves
will eject around the trough base, bringing widespread precipitation
chances to the state. Latest blended guidance produces medium
to high chances for showers and thunderstorms, focused on
Saturday and Saturday night. Medium chances continue through
Sunday as the trough base becomes negatively tilted, with
overall cyclonic flow aloft across the western and central CONUS
with an additional trough digging over the Pacific Northwest.
Current NBM probabilities for at least an inch of rain in 48
hours is broadly around 40 percent across western North Dakota
for this weekend. This could differ significantly if
thunderstorms end up a bit more isolated, and we cannot rule
out some heavy rain and potentially localized flooding concerns,
with forecast PWAT values starting to approach daily maximums.
NSSL and CSU machine learning probabilities carry some low
chances for severe thunderstorms from previous days, although
deterministic guidance is showing instability decreasing from
Saturday to Sunday and beyond. The current Day 3 outlook does
have isolated severe thunderstorms possible (level 1 out of 5)
across most of North Dakota.
The active pattern continues into next work week. Although there is
relatively low confidence on the overall progression of the synoptic
pattern, cluster analysis shows the majority of solutions favor a
broad troughing pattern through at least midweek. This conclusion is
also advertised in CIPs extended analogs and in the ECMWF EFI, which
has forecast QPF amounts highlighted as abnormal compared to
climatology, especially in the north central. NBM temperature
percentiles are confident in above normal temperatures Monday and
Tuesday before a modest cool down through the remainder of the week
and into the weekend, bringing temperatures to near to below
normal.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 645 PM CDT Thu Sep 11 2025
VFR ceilings and visibility is found at all terminals to begin
the 00Z TAF period. Later this evening, chances for showers and
thunderstorms will increase across western and central North
Dakota as a low pressure system crosses through the forecast
area. Confidence in the evolution of this system is low
especially regarding timing and coverage of showers and storms.
Have included a PROB30 group for -SHRA at KXWA this evening with
this update, but confidence remains too low to include mentions
at any other terminal at this time. Later tonight through Friday
morning, fog is possible across portions of northwestern and
north central North Dakota. Have included BR at KXWA and KMOT
with this update, with the highest confidence in MVFR visibility
and MVFR to IFR ceilings at KMOT. South to southeast winds this
evening are expected to diminish overnight, turning
cyclonically around the low pressure system before reorganizing
out of the east to northeast late Friday morning and afternoon.
While remains are expected to remain somewhat light, gusty and
erratic winds should be anticipated where thunderstorms develop.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Adam
DISCUSSION...Jones
AVIATION...Adam

NWS BIS Office Area Forecast Discussion