241
FXUS63 KBIS 132025
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
325 PM CDT Sun Jul 13 2025

.KEY MESSAGES...

- Very warm south through Monday, but becoming cooler north
  with increasing chances for scattered showers.

- Isolated strong to severe storms possible statewide late
  Monday afternoon through Monday night. Expected hazards are
  hail as large as quarters and wind gusts up to 60 mph.

- Well below normal temperatures Tuesday through Thursday, with
  near-record cold highs in the lower to mid 60s on Wednesday.

- Medium to high chances for rain Monday night through
  Wednesday. The highest rain amounts are broadly expected over
  southwest North Dakota.

&&

.DISCUSSION...
Issued at 325 PM CDT Sun Jul 13 2025

An unperturbed northwest flow aloft lies over the Northern Plains
this afternoon. An eastward progressing surface trough with a
positively tilted axis from southwest Ontario to central South
Dakota leaves behind surface high pressure that is now centered
along the ND/MT border. Some mid level clouds have moved into
northern portions of the state, while the south remains sunny.
Meanwhile, a blob of smoke, both near the surface and aloft, is
caught up in the downstream surface trough/cyclonic flow. However,
the smoke has not been as impactful nor has advanced southeast as
quickly as earlier modeling had suggested. Areas from the Turtle
Mountains to the northern James River Valley could still see some
visibility reduction from smoke and/or a hazy, milky sky through the
afternoon. But the most impactful smoke should remain east of our
forecast area. Late afternoon high temperatures are expected to
range from the lower 80s far north to lower 90s far west central.

An upper level jet will begin to strengthen over southern Canada
tonight, inducing a low level jet response and subsequent mid level
cyclonic vorticity generation. Global and high-resolution models are
consistent in bringing waves of scattered light showers across
northern parts of the state late this evening through Monday
morning. A few rumbles of thunder cannot be ruled out with this
activity, but instability/buoyancy look to be very limited. Lows
tonight are forecast to range from the mid 50s north to mid 60s
south.

Broad surface cyclogenesis is forecast over the front ranges of the
Wyoming and Colorado Rockies on Monday as flow aloft over the
Northern Plains turns zonal. A low level baroclinic zone is forecast
to sharpen across northern North Dakota throughout the day, where
persistent low to medium chances for scattered light showers remain
in the forecast. The latitudinal placement of the baroclinic zone
along with an underlying surface trough extending northeast from the
surface low has been inconsistent from model cycle-to-cycle. The 12Z
suite of models/ensembles shifted these features slightly to the
south, but still keeps them well within the northern half of the
state. Areas along and north of the temperature gradient can likely
expect high temperatures only in the 70s on Monday. Areas to the
south are more likely to see mid 80s to mid 90s, hottest along and
south of I-94 and along and west of the Missouri River. Higher
dewpoints over south central North Dakota (around 60 F) could push
maximum afternoon heat indices near 100, and the forecast maximum
wet-bulb globe temperature is well into the high category.

Initiation and evolution of convection Monday afternoon through
Monday night is uncertain. Most guidance seems to project capping
will be too strong to allow convective initiation to occur until at
least 5 PM CDT, and other than a pooling of low level moisture near
the SW-NE surface trough cutting through south central North Dakota,
there aren`t any notable forcing mechanisms. This changes heading
into the evening and overnight hours as mid level height falls
associated with increasing cyclonic vorticity over southern
Saskatchewan begin to drive a cold front into northwest North
Dakota. The cold front is likely to intercept a plume of poleward
850-700 mb moisture transport, resulting in a band of strong low
level frontogenesis across the state. CAM guidance remains very
mixed on all aspects of the convective forecast, and there is
clearly uncertainty in the timing and placement of forcing
mechanisms. A couple CAMs initiate convection along the SW-NE
surface trough early Monday evening, while others are more focused
on the clashing of the cold front, low level frontogenesis, and low
to mid level moisture transport during the mid to late evening.
Separately, a few CAMs are generating UH tracks across southern
Canada and northeast Montana late Monday afternoon and evening, with
some encroachment into North Dakota. Two separate regimes for CAPE
and shear are being projected: modest CAPE (1000-2000 J/kg) and deep
layer shear (30-40 kts) across the south, and low CAPE (less than
1000 J/kg) with high shear (at least 50 kts) across the north. Aside
from the surface trough potential in south central North Dakota
during the late afternoon and early evening, all other convection
seems likely to remain elevated. Given what has been discussed along
with an uncertain storm mode, we will message base severe hazards of
quarter size hail and 60 mph wind gusts. The SPC has expanded the
Marginal Risk across all of western and central North Dakota, which
aligns with our forecast thinking and accounts for the variety of
outcomes being projected by model guidance. Lastly, there is a low
probability that training convection could introduce a localized
excessive rainfall threat in central parts of the state late Monday
evening.

By Tuesday afternoon, the surface cold front is forecast to have
cleared all but southeast North Dakota. A continuous stream of mid
level shortwave energy ejecting from the base of a Northern Rockies
trough keeps medium to high chances for rain in the forecast through
Wednesday, decreasing from north to south Wednesday night. There is
decreasing confidence in the chances of showers as the forecast time
range increases, with some guidance suggesting dry air advection
from the northeast could push the rain farther south sooner than
what is currently projected. Total rain amounts could be highly
variable, especially depending on how convection plays out Monday
night. But a majority of western and central North Dakota could see
a beneficial rain. The NBM shows probabilities for at least half an
inch of QPF as high as 70 percent in the southwest, decreasing to
around 20 percent north central. If the cold front is slower to
clear the southern James River Valley Tuesday afternoon, a narrow
window for strong to severe storms could emerge. Otherwise, the post-
frontal air mass is expected to be stable, limiting thunderstorm
chances to very low at best. Also anticipated is a 3-day stretch of
below normal temperatures. While overnight lows are merely forecast
to be around 5 to 10 degrees below normal, daytime highs will be
exceptionally cold for mid July, closer to around 15 to 25 degree
below normal. Wednesday is expected to be the coldest day, with near-
record cold high temperatures only in the lower to mid 60s. Ensemble
tools such as the ECMWF EFI lend forecast confidence to this period
of anomalous cold.

Ensembles favor temperatures warming back to near normal through the
end of the week, but show nearly equal probabilities of either a
zonal flow pattern or upstream ridging over the Rockies. This
uncertainty keeps shower and thunderstorm chances mostly around 10
to 20 percent through the weekend, with no severe probabilities
being noted by machine learning guidance at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 325 PM CDT Sun Jul 13 2025

VFR conditions are expected through the forecast period. Near-
surface smoke is likely to remain east of the local area. Scattered
rain showers are possible across northern North Dakota beginning
late this evening. Northwest winds will be gusty early this
afternoon before becoming lighter and variable this evening. Varying
wind direction at around 5-10 kts is expected across the state
tonight into Monday, with northeasterly across the north and
southerly to southwesterly across the south. Low level wind shear
could impact KBIS and KDIK late tonight into Monday morning.

&&

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

&&

$$

DISCUSSION...Hollan
AVIATION...Hollan