060
FXUS63 KBIS 220201
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
901 PM CDT Thu Aug 21 2025

.KEY MESSAGES...

- Isolated showers, perhaps with an occasional rumble of
  thunder, may linger through tonight.

- Well below average temperatures Saturday through Monday, with
  highs mostly in the mid 60s to mid 70s and lows in the 40s.

- Dry weather is expected Friday through the middle of next
  week.

&&

.UPDATE...
Issued at 901 PM CDT Thu Aug 21 2025

Isolated showers continue to linger mainly over the south
central. Thunder hasn`t been observed in a while, although a
rogue rumble here and there remains possible. Updated PoPs over
the next few hours to align better with the latest radar trends.
Otherwise, the ongoing forecast remains on track.

UPDATE
Issued at 639 PM CDT Thu Aug 21 2025

A narrow broken line of showers, along with a very occasional
rumble of thunder, remain present over parts of southern ND,
although although have been showing signs of dissipating over
the past hour or so. Additional showers, along with a few
thunderstorms, are possible this evening and overnight mainly
near the ND/SD border. However, the highest probabilities for
further development remain on the South Dakota side.

&&

.DISCUSSION...
Issued at 259 PM CDT Thu Aug 21 2025

The Northern Plains lie under a quasi-zonal flow pattern this
afternoon, with embedded shortwave energy downstream of an upper
level jet streak from southwest Montana into western North Dakota. A
surface cold front has cleared all but the Red River Valley and far
southeast parts of the state. Scattered showers and occasional
isolated thunderstorms have been traversing the southern half
of the state for much of the day. Measurable rain is being
limited by a stout layer of dry air that was sampled by the 12Z
BIS RAOB. The mid to upper layers are modestly unstable and
buoyant, but even a strong forcing mechanism would not be
sufficient to overcome the high surface and mixed layer CIN that
is in place. A stronger wind gust from a rouge storm cannot be
ruled out through the afternoon, but severe weather is no longer
expected.

A strong upper level low spinning into the Canadian prairie
provinces will begin to tilt flow aloft to the northwest tonight,
pushing the active part of the flow farther south and lining up over
the stalling cold front. This could lead to another round of
scattered light showers and perhaps a few thunderstorms across
southern North Dakota overnight, but probabilities for this are much
higher into South Dakota. Any lingering activity into early Friday
morning should be quickly extinguished by strong low level
subsidence building down from Canada. Lows tonight are forecast
to range from the lower 50s north to lower 60s far south
central and southeast.

A more potent cold front tied to a stacked and occluded low spinning
over Manitoba is set to plunge through the state on Friday. A dry
west-northwest wind around 20 to 25 mph will follow the cold front
into the state and persist through the day, with forecast afternoon
gusts around 35 mph. This will mark the beginning of a period of
unseasonably cool weather. The timing of the frontal passage does
keep mid to upper 70s across southern parts of the state for highs
on Friday, with lower 70s more likely across much of the north.

For Saturday through Monday, the deep low pressure system is
forecast to spin into Ontario and stall, setting up northwest flow
over the Northern Plains. A weaker mid level shortwave is also
forecast to bring a reinforcing shot of cooler and drier air into
the region late Saturday into Sunday. All the while, a prolonged
surface ridge extending south from high pressure over Saskatchewan
is forecast to remain established over the region. This sets the
stage for a multi-day stretch of unusually cool temperatures for
late August. The ECMWF EFI lends support to the anomalously cool
temperatures being projected by the NBM, which itself contains very
low spread. High temperatures are only expected to reach the mid 60s
to mid 70s Saturday and Monday, and only lower 60s to lower 70s in
between on Sunday. Several nights with temperatures in the 40s are
expected, with Saturday and Sunday nights favored to be the coldest
as the center of high pressure drifts southeastward into the
Dakotas. These 2 nights could easily see low temperatures closer to
the lowest quartile of the NBM distribution, especially in low lying
areas and the typical corridor for strong radiational cooling from
around Beulah to Hettinger. The 10th percentile for Sunday
night/Monday morning, which is a more realistic outcome than normal
given the expected pattern, would bring mid 30s to lower 40s across
the state and could even allow patchy frost to develop. Given the
forecast time range, will maintain the straight NBM forecast of
lower to mid 40s for now, but this may need adjusting if confidence
continues to increase.

Heading towards the middle of next week, ensembles favor a continued
northwest flow over the region, but with a gradual trend of rising
heights as an upstream ridge begins to exert a greater influence.
The NBM shows a modest warmup back to near or just slightly below
average temperatures Tuesday through Thursday. The passage of a
subtle wave or two cannot be ruled out next week, but there is no
consensus on the timing or placement of any such feature, which
keeps the forecast dry through the extended period.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 639 PM CDT Thu Aug 21 2025

VFR ceilings and visibility will generally prevail through the
period. However, a narrow line of broken showers is present
from west to east over southern ND. An occasional rumble of
thunder has also been observed. While these showers have shown
signs of dissipating over the past hour or so, a few of them
are heading directly towards KBIS. Due to uncertainty in whether
or not they will dissipate before reaching the terminal, used a
PROB30 at KBIS for a couple hours. Otherwise, windy conditions
out of the northwest are expected Friday afternoon.

&&

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

&&

$$

UPDATE...Telken
DISCUSSION...Hollan
AVIATION...Telken