170
FXUS63 KBIS 291718
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1218 PM CDT Sun Jun 29 2025

.KEY MESSAGES...

- Breezy today and Monday, with slightly cooler temperatures and
  lower humidity.

- Other than a 20 percent chance of showers and perhaps a
  thunderstorm in northern parts of the state this evening, dry
  weather is expected through Tuesday afternoon.

- Above normal temperatures favored Wednesday and Thursday, with
  highs possibly reaching 90 degrees.

- Low chances for showers and thunderstorms during the evening
  and overnight hours Tuesday and Wednesday, then medium
  chances late Thursday. Widespread severe storms are not
  expected at this time.

&&

.UPDATE...
Issued at 1214 PM CDT Sun Jun 29 2025

Forecast remains on track with only minor adjustments to sky
cover this afternoon. Will probably see some thicker cloud cover
drop south from Canada later this afternoon and tonight.

UPDATE
Issued at 913 AM CDT Sun Jun 29 2025

No changes needed for the mid-morning update.

UPDATE
Issued at 644 AM CDT Sun Jun 29 2025

The forecast for today remains on track. Current observations
and trends were blended in for this update. Except for southern
Dickey County for the next hour or so, the chance of rain across
far southwest and far south central North Dakota this morning
has ended.

&&

.DISCUSSION...
Issued at 358 AM CDT Sun Jun 29 2025

Southwest flow aloft prevails over the Northern Plains early this
morning. As of 330 AM CDT, only light stratiform rain extending
north from a South Dakota MCC was potentially falling across far
south central North Dakota, but it may just be virga. Otherwise,
quiet weather prevails this morning, with the southern half of the
state under a mostly cloudy sky from the anvil of the MCC.

A mid to upper level shortwave over southeast Saskatchewan early
this morning will deepen and dig into the Northern Plains/Upper
Midwest through tonight, with the trough axis reaching western
Ontario by Monday morning. This may bring some scattered showers and
perhaps a few thunderstorms to northern parts of the state this
evening into the overnight hours. At the surface, low pressure over
Manitoba/Ontario and high pressure along the eastern slopes of the
Canadian and Montana Rockies will tighten the surface pressure
gradient today, especially over the northern half of the region.
Northwest and north central North Dakota are forecast to see west-
northwest winds increase to around 25 mph this afternoon, with gusts
as high as around 35 mph. Slightly weaker winds are expected to the
south, but it could still be a breezy day there. The westerly
surface/low-level flow will push the more humid air mass off to the
southeast, and lowering heights will result in slightly cooler
temperatures for most areas this afternoon, with forecast highs in
the mid 70s to lower 80s.

The departing shortwave on Monday will leave behind a transition
from cyclonic to anticyclonic northwest flow aloft over the region.
Deterministic models are in general agreement that a trailing
longitudinal streak of vorticity will mark this transition from
western North Dakota in the morning to central North Dakota around
midday, and reaching eastern North Dakota by late afternoon. Areas
that remain downstream of the vorticity streak during the afternoon
could see diurnally driven showers and possibly a few thunderstorms,
although mid level lapse rates look exceptionally poor for this time
of year (between 5 and 6 C/km). By the time anything develops
though, the vorticity streak may have already shifted completely
east of our forecast area. Therefore, the most likely outcome is a
dry Monday for all of western and central North Dakota. High
temperatures and dewpoints on Monday will be similar to today. It is
expected to be less windy on Monday than today, but the eastern half
of the state will likely continue to see breezy northwesterly winds
ahead of surface high pressure sliding into eastern Montana and
western South Dakota.

Dry weather is expected to continue through Tuesday afternoon under
anticyclonic flow aloft and broad surface high pressure over the
central CONUS. A deamplification of the upstream western CONUS ridge
will allow warmer temperatures to return, with forecast highs
solidly in the 80s on Tuesday. A weak disturbance embedded in the
northwest flow aloft could spark a few showers and thunderstorms as
it passes through the region Tuesday evening into the night.
Moisture and buoyancy appear lacking, with ensemble mean MUCAPE
forecast to be lower than 1000 J/kg. However, deep layer shear could
be as high as 35 to 45 kts, which could be sufficient for a stronger
storm with just a few hundred J/kg CAPE. CSU machine learning
guidance paints a low probability (5 percent) of severe hail over
southwest North Dakota for this time period. But the probability of
any shower or storm at any given location is only around 10 to 20
percent.

For Wednesday and Thursday, the synoptic scale upper ridge axis is
forecast to shift from the High Plains to the Mississippi River. In
response, the NBM has increased both its deterministic maximum
temperature forecast and ensemble distribution thereof each of these
days. Lower 90s have now entered the forecast in some parts of the
western half of the state. The deterministic NBM output is actually
heavily skewed to the cooler side of the distribution, with the 75th
percentile showing 90s everywhere on Wednesday and mid 90s to lower
100s on Thursday. However, the advertised southeasterly surface flow
and dewpoints rising back into the 60s would favor a slightly
"cooler" outcome. There is a small chance that convection forming
across central Montana Wednesday afternoon could make it into
western North Dakota Wednesday night, with maintenance being
supplied by a strengthening low level jet. Should this happen,
severe weather appears unlikely on this side of the state border. By
Thursday night, ensembles transition flow aloft back to
southwesterly as the upper ridge axis approaches the Mississippi
River. In turn, NBM PoPs increase to around 30 to 50 percent
Thursday evening into Friday morning. Ensemble mean MUCAPE is
considerable over this time period, at around 2000-3000 J/kg. But
mean deep layer shear is only currently forecast around 25 to 30 kts.

Ensemble solutions begin to diverge more noticeably on the Fourth of
July through the holiday weekend, with 3 or 4 distinct regional
synoptic patterns showing up in cluster analysis with varying
probability, including southwest flow, northwest flow, zonal flow,
and top of a ridge. Temperatures are favored to remain near to above
average over this time period, and the NBM maintains daily low to
medium chances for showers and storms.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1214 PM CDT Sun Jun 29 2025

VFR conditions are expected to prevail through the forecast
period. There is a low chance of showers and perhaps a
thunderstorm in northwest and north central North Dakota late
this afternoon through the evening. The probability of a shower
or storm moving over a terminal is not high enough to mention in
the TAFs at this time. West-northwest winds will increase to
around 15-20 kts this afternoon, with gusts as high as 30 kts
across the north. Winds diminish this evening, but remain breezy
at times. There is a low probability of a period of MVFR
ceilings from around KMOT to KJMS Monday morning, but too far
out to include in either TAF at this time.

&&

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

&&

$$

UPDATE...TWH
DISCUSSION...Hollan
AVIATION...TWH