Donnybrook, North Dakota Weather Forecast Discussion

394
FXUS63 KBIS 251132
AFDBIS
Area Forecast Discussion
National Weather Service Bismarck ND
632 AM CDT Thu Sep 25 2025
.KEY MESSAGES...
- Above average temperatures and dry weather expected through
  the weekend.
- Breezy conditions on Friday.
- Well above average temperatures continue into next week, with
  low chances for rain returning by mid week.
&&
.UPDATE...
Issued at 631 AM CDT Thu Sep 25 2025
No major forecast changes are needed with this update. At 6 AM
CDT, the cold front was analyzed roughly from Grafton to
Hettinger. Wind speeds and gusts have been highly variable with
and trailing the front, with some areas gusting to 20 mph and
others remaining under 5 mph. The wind speed and gust forecast
for the rest of the morning has been decreased slightly overall,
and more closely aligned to observed trends.
&&
.DISCUSSION...
Issued at 358 AM CDT Thu Sep 25 2025
An omega-shaped height pattern is analyzed across the the western
and central CONUS early this morning, with a tangential ridge axis
extending northeastward from the top of the omega ridge through the
Northern Plains and into Ontario. A cold front attendant to a
shortwave trough crossing central Canada has entered northwest and
north central North Dakota. There is not enough moisture in the
atmosphere to even support any clouds with the front, but a brief
period of gusty northerly winds to around 25 mph has been observed
at some locations with the frontal passage. Expect the sporadic
gusty winds to translate with the front as it moves southeastward
through the state this morning. Trailing the front is an area of
surface high pressure that will steadily move eastward across
southern Saskatchewan and Manitoba throughout the day. The
positioning of the high and its associated cooler air mass will
bring noticeably cooler afternoon temperatures to northern parts of
the state today, with forecast highs mostly in the upper 60s and
lower 70s. Mid to upper 70s are broadly expected elsewhere, though
the southern James River Valley and southwest corner of the state
could reach the lower 80s.
Another shortwave trough that is approaching British Columbia this
morning will quickly cross the Canadian Rockies tonight and eject
into the prairie provinces on Friday. This feature will briefly
amplify an upper ridge over the Northern Plains tonight and setup
southerly return flow across the western Dakotas as its surface
cyclone deepens over southern Saskatchewan. The attendant cold front
is set to move across North Dakota during the late morning through
the afternoon on Friday. Deterministic models continue to show
appreciable cold air advection and pressure rises with the front,
signaling a strong mixing potential of mean BL winds around 25-30
kts to the surface. A few CAMs have introduced some light showers in
their simulated reflectivity fields across northern parts of the
state with the cold front, but model soundings suggest this would
amount to nothing more than sprinkles given the very high cloud
bases and underlying dry air. So no mention of this will be made in
the forecast at this time. If anything, the sprinkles or virga could
further enhance wind gusts should it materialize. Most areas are
actually forecast to see warmer temperatures on Friday, although an
earlier than expected timing of the frontal passage could change
this thinking. Nevertheless, there is medium to high confidence in
highs on Friday in the lower to mid 80s across central North Dakota,
and the coolest forecast highs in the northwest are still in the mid
70s.
Another transient surface high pressure follows the cold front into
the region Friday night, and is forecast to be centered over South
Dakota by sunrise Saturday morning. Most areas will see their
coldest temperatures for the rest of the month Friday night into
Saturday morning when forecast lows are in the 40s. The timing of
the surface high could allow for strong enough radiational cooling
to bring temperatures into the lower quartile of the NBM
distribution, which would introduce upper 30s into low-lying and
sheltered areas across the west and north central. Widespread frost
is not expected, but patchy frost cannot be ruled out. Will leave
this mention out of the forecast for now though. The relatively
cooler air mass will linger in south central and eastern North
Dakota on Saturday, leaving highs in the lower to mid 70s. But
western and north central parts of the state are expected to rebound
into the upper 70s and lower 80s in response to rising heights and
low level southwesterly winds.
From Sunday through Tuesday, there is high ensemble confidence in an
upper level ridge becoming highly amplified throughout the entire
stretch of the Mississippi River Valley and surrounding regional
areas, this in response to a longer-wave trough digging into the
western CONUS. This is expected to bring temperatures even further
above average over this time period, resulting in a multi-day
stretch of weather more typical for summer with highs mostly in the
upper 70s and 80s, lows in the mid 50s to mid 60s (near record warm
values for late September), and seasonably high dewpoints in the 50s
and even lower 60s. The main aspect of forecast uncertainty over
this time period is whether there will be any shortwaves embedded in
the southwesterly to southerly flow aloft that could bring scattered
showers and perhaps a few thunderstorms to the region, beginning on
Monday. 00Z ensemble clusters are heavily weighted by systems, with
the GEFS strongly favoring chances for rain, the Canadian ensemble
strongly favoring a dry solution, and the ECMWF ensemble favoring a
drier Monday but wetter Tuesday. Needless to say, we anticipate that
at some point more widespread low to medium chances for rain will be
introduced to the forecast early next week once ensemble spread in
timing and location details is reduced.
Cluster-based solutions begin to notably diverge by the middle of
next weak, with the main source of uncertainty being the progression
and evolution of the western CONUS trough. 3 out of 4 clusters with
around 75 percent total ensemble membership swing a potent shortwave
from the Pacific Northwest to the southern Canadian prairie
provinces, and one of these clusters that is composed of around half
of the GEFS and Canadian ensemble members digs this trough further
east into the Northern Plains. Interestingly, the outlying cluster,
which maintains a southwest flow with near-neutral height
tendencies, is composed of nearly half of the ECMWF membership and
exactly zero members from the other two ensembles. By the end of
next week, most ensembles and clusters devolve their mean upper
height fields into a progressive and wavy mess with very low
predictability. One common theme though that can be gleaned from the
NBM temperature distributions is that a cooling trend is favored for
the first few days of October. But this could merely bring
temperatures closer to averages, which themselves begin to cool
quite rapidly this time of year.
&&
.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 631 AM CDT Thu Sep 25 2025
VFR conditions are expected through the forecast period. A cold
front moving southeast through the state this morning will turn
winds northerly and could have some 15-20 kt gusts. For this
afternoon and evening, expect wind direction turning clockwise
from northeast to southeast, with speeds around 5-10 kts. Later
tonight, southeast winds could increase closer to 10-15 kts.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Hollan
DISCUSSION...Hollan
AVIATION...Hollan

NWS BIS Office Area Forecast Discussion