Mc Henry, North Dakota Weather Forecast Discussion

183
FXUS63 KBIS 101139
AFDBIS
Area Forecast Discussion
National Weather Service Bismarck ND
639 AM CDT Wed Sep 10 2025
.KEY MESSAGES...
- Areas of dense fog across southern North Dakota this morning.
- Above average temperatures continue through the end of the
  work week, with highs mostly in the upper 70s to mid 80s.
- Isolated severe thunderstorms are possible across western and
  central North Dakota Thursday afternoon and evening.
- High chances for rain across the western half of the state
  this weekend, with medium chances for one half to one inch of
  accumulation.
&&
.UPDATE...
Issued at 615 AM CDT Wed Sep 10 2025
Fog continues to expand across southern North Dakota early this
morning. Satellite trends imply the fog formation is more of a
radiational process west of the river and more of an advective
process east of the river. Nevertheless, visibility below one
half mile is becoming much more prevalent just over the past
half hour. A Dense Fog Advisory has been issued until 10 AM CDT.
&&
.DISCUSSION...
Issued at 429 AM CDT Wed Sep 10 2025
An upper level ridge axis extends from eastern Colorado to along the
Saskatchewan/Manitoba border early this morning. At the surface,
broad high pressure from western Ontario through the Upper
Mississippi River Valley promotes a weak easterly to southeasterly
flow that is advecting moisture into the Northern Plains. Fog is
rapidly expanding northwestward across eastern South Dakota and
southwest Minnesota, and has reached into parts of southeast and
south central North Dakota as of 4 AM CDT. A Dense Fog Advisory may
eventually be needed.
An upper level jet streak ejecting from the base of a longwave
trough off the Pacific Coast could bring some very light rain to
northwest parts of the state later this morning and afternoon as its
left exit region passes through the area. Model soundings show cloud
bases around 10,000 ft with low RH underneath, so handled this
potential with a 20 percent chance of sprinkles. Ahead of the jet, a
500 mb shortwave is lifting north through Montana early this morning
and is responsible for scattered showers and, earlier in the night,
a few isolated thunderstorms lifting off the Bighorn Mountains.
Current trajectories would bring this activity into far west central
North Dakota by mid morning, and it is possible this wave could
supplement forcing for the sprinkle/light rain potential later on.
Overall though, dry weather is expected today with afternoon highs
in the upper 70s east to mid 80s west. Smoke will remain aloft
through the morning, with clearing expected from southwest to
northeast this afternoon and evening. The HRRR and RAP are still
showing concentrations of near-surface smoke that would typically
result in reduced visibility and poor air quality across western
North Dakota through this afternoon, but the model simulations do
not match observed conditions. Therefore, will not mention smoke in
the forecast at this time. A tightening isobaric gradient between
the downstream high pressure and lower pressure over the Northern
Rockies will increase southeasterly surface winds to around 20 to 25
mph across western and south central North Dakota this afternoon,
with some gusts to around 30 to 35 mph.
The upper ridge axis is forecast to drift eastward overnight.
Despite rising mid level height tendencies, a strengthening low
level jet with strong moisture transport and wind vectors turning
perpendicular to the isothermal gradient could provide enough lift
to generate widely scattered showers and thunderstorms across
western and central North Dakota late tonight into Thursday morning.
CAMs have been very inconsistent in coverage and location of
convection. Even though MUCAPE is forecast to rise above 1000 J/kg,
model soundings show the base of the EML to be highly capped, so
think that the overall potential for thunderstorms during this time
period is low.
A continuous supply of mid level shortwave energy ejecting from a
closed low over the western CONUS keeps shower and thunderstorm
chances (around 20 percent south to 60 percent north) in the
forecast through Thursday night. While our PoP forecast does not
advertise a break, the showers and storms are more likely to be
periodic and scattered in nature. By late Thursday afternoon, a lee
surface trough is forecast to form near the MT/ND border. An
anomalously warm and moist air mass given the time of year will be
reinforced by the persistent southeasterly flow to the east of the
lee trough. Forecast highs on Thursday are mostly in the 80s outside
of the Turtle Mountains/Devils Lake Basin areas, and a few locations
in the far southwest could breach 90. Dewpoints are also forecast to
reach the mid 60s, except in the far southwest. This could yield a
highly unstable atmosphere with CAPE around 2000-3000 J/kg, but one
that is also capped by an inversion. There is no shortage of forcing
though, so the capping inversion would seem more likely to be a
regulator of convective intensity rather than initiation. While it
remains highly uncertain whether any storms will become surface-
based or rooted in the mixed layer, shear profiles from any inflow
layer appear supportive of severe convection Thursday afternoon and
evening. Storm mode is somewhat uncertain, but there would appear to
be a slight favoring of a discrete mode given the perpendicular
orientation of deep layer shear and anvil level winds to the lee
trough. This would imply the potential for supercells capable of
large hail. However, given the chaotic nature of the projected
forcing, some multicell clusters and bowing segments from cold pool
conglomerations seem near-equally as reasonable. There is also a low
probability scenario that could allow a tornado risk to emerge. This
would require a supercell with surface based inflow near the triple
point feature at the top of the lee trough in northwest North Dakota
during the early evening hours, where long looping hodographs are
forecast. All these requisite conditions are unlikely to come
together in a spatiotemporal sense though, so will not message a
tornado threat at this time.
The daytime hours on Friday appear to be the most likely period of
drier weather between Thursday and early next week due to weaker
deep layer flow, but there is still a 20 percent chance of showers
and thunderstorms throughout the day. A similar high temperature
forecast of around 80 to 85 degrees is featured on Friday, which
could be even more humid than Thursday. From late Friday through the
weekend, there is strong ensemble consensus that the upstream upper
low will lift into Alberta with the longwave trough axis pivoting
counter-clockwise into the Northern and Central Plains. This could
set the stage for a rainy weekend, albeit one that is relatively
warm and quite humid for mid September. Forecast highs remain in the
70s over the weekend, with dewpoints mostly in the 60s. NBM QPF
threshold probabilities for the weekend have risen slightly, now
with a 50 to 70 percent chance of exceeding half an inch across the
western half of the state and a 30 to 50 percent chance for
exceeding one inch along and west of Highway 83. It remains
uncertain whether there will be enough CAPE and/or shear to support
strong to severe convection over the weekend.
It may take until Monday for the trough axis to lift northeast into
Canada and extinguish the higher chances for rain. The evolution of
the subsequent synoptic pattern remains unclear, with cluster
analysis showing a near 50/50 split between southwest and quasi-
zonal flow aloft. Either outcome lends to low chances for rain
remaining in the forecast through the middle of next week.
Temperatures are favored to remain above normal to start next week,
but the NBM shows a distinct cool down by the end of next week.
&&
.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 638 AM CDT Wed Sep 10 2025
LIFR conditions from fog and low stratus will impact parts of
southern North Dakota through mid morning. Confidence is low on
whether these impacts will reach KDIK, KBIS, and KJMS. VFR
conditions are otherwise expected through the forecast period. A
few isolated showers and thunderstorms could develop across
parts of western and central North Dakota late tonight, but
confidence on location and timing is very low. Southeasterly
winds will increase to around 15 kts with gusts to around 20-25
kts this afternoon, strongest in southwest North Dakota.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CDT /9 AM MDT/ this morning for
NDZ033-034-041-042-044>048-050-051.
&&
$$
UPDATE...Hollan
DISCUSSION...Hollan
AVIATION...Hollan

NWS BIS Office Area Forecast Discussion