577
FXUS63 KBIS 211409
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
909 AM CDT Fri Aug 21 2026

.KEY MESSAGES...

- Near average temperatures are favored to continue through
  next week, with Monday being a slightly warmer day.

- There is a 20 to 40 percent chance of light rain showers
  moving from northwest North Dakota this morning to south
  central North Dakota this afternoon.

- Medium chances (30 to 60 percent) for showers and
  thunderstorms late Saturday night through Monday.

&&

.UPDATE...
Issued at 905 AM CDT Fri Aug 21 2026

Patchy fog over eastern parts of the area continues to
gradually dissipated as we warm up this morning. Otherwise, a
few showers continue to move through northwest/north central
North Dakota. Latest guidance has some of these continuing to
push towards the southeast as the day goes on, with possibly a
weak thunderstorm. For morning update have adjusted
timing/position of the higher chances in line with latest
guidance.

UPDATE
Issued at 653 AM CDT Fri Aug 21 2026

Patchy fog persists in the Turtle Mountains, Devils Lake Basin,
and northern James River Valley areas early this morning. Most
of the fog appears to be causing little to no impacts, but a
more concentrated area of dense fog has settled over northern
Pierce County. Conditions should improve from 8 to 9 AM CDT.

Scattered light showers are moving into northwest North Dakota
early this morning. The near-term forecast was refined to better
align with observed trends. The showers should hold together
into central North Dakota around midday, but recent model
guidance now tends to favor showers diminishing before they
reach the southern James River Valley by late afternoon.

&&

.DISCUSSION...
Issued at 429 AM CDT Fri Aug 21 2026

Northwest flow aloft continues over the Northern Plains early
this morning while the upstream western CONUS ridge is beginning
to become more amplified. A shortwave embedded in the northwest
flow is depicted on water vapor imagery over southern
Saskatchewan and is forecast to move from northwest to southeast
North Dakota through this afternoon. Scattered showers have
been ongoing with this wave since late last evening, and most
guidance suggests these will hold together at least until
reaching central North Dakota around midday. A couple of CAMs
have hinted at a strong thunderstorm between the Missouri and
James River Valleys this afternoon, but it is difficult to find
model support for CAPE higher than 100-200 J/kg. An occasional
brief thunderstorm cannot be ruled out at any point with this
activity, but the probability of lightning is not high enough
to carry a mention in the forecast.

The surface pattern this morning is very benign, with broad
ridging extending from Alberta/Saskatchewan through the
Missouri River Valley. Shallow fog has developed from near the
Turtle Mountains to the northern James River Valley and back
west towards Lake Sakakawea. The fog could reduce visibility in
low lying areas before clearing by mid morning. The high
temperature forecast for today is similar to what was observed
yesterday, generally ranging from the upper 70s far north to
upper 80s far southwest. The center of the surface high pressure
will become more focused over Saskatchewan, Manitoba, and into
North Dakota tonight. NBM spread for low temperatures tonight
is small, but would not be surprised to see colder percentiles
in the 40s verify. On Saturday, the surface high/ridge slides
into the Red River Valley as the highly-amplified upper level
ridge begins to shift off the Northern Rockies. Highs on
Saturday are projected to remain similar or be just a touch
cooler at most locations, with mid 70s to mid 80s.

Shortwave energy preceding a potent Pacific Northwest upper low
will begin ejecting off the Northern Rockies Saturday night.
The Pacific Northwest low will push the upper ridge axis into
the High Plains, but with embedded shortwave energy and
underlying moisture return. Recent consensus guidance has
trended to a slower progression of the synoptic scale wave
pattern, but the NBM has actually refined PoPs to higher
percentages and a more focused corridor moving from southwest
North Dakota early Sunday morning to northwest-south central
North Dakota Sunday afternoon. Model soundings show strong
capping, and deterministic guidance would suggest QPF outpacing
a ribbon of higher CAPE. Therefore, any convection during the
day Sunday is favored to remain elevated, with a very low risk
for severe weather. Medium shower and thunderstorm chances
(around 30 to 60 percent) expand across all of western and
central North Dakota Sunday evening. But despite increasing
buoyancy, even for elevated parcels, confidence in any severe
threat through Sunday remains low. Monday could be a different
story though if the slower progression of the potent upper low
comes to fruition. Ensembles now favor an occlusion of the low
over Saskatchewan on Monday, with the primary surface frontal
boundary attendant to the low moving through western and
central North Dakota during the day. The environment downstream
of the surface front could become supportive of severe
thunderstorms, with CAPE as high as 2000 J/kg and deep layer
shear around 35 to 45 kts. But there is still too much
uncertainty in forecast details to begin messaging a severe
threat at this time. The post-frontal air mass could become
hot, dry, and breezy, which may lead to near-critical fire
weather conditions in western North Dakota Monday afternoon.

The occluded low is forecast to track southeastward, reaching
the Great Lakes late Wednesday. In its wake, the upper ridge is
forecast to rebound from the Southern Rockies through the
Northern High Plains ahead of another potent trough digging
into the Pacific Northwest. Ensemble spread grows by the end of
next week, but there are hints that the Pacific Northwest
trough could break down the ridge and transition flow aloft to
quasi-zonal. A slight warmup continues to be advertised for
Sunday and Monday, with highs reaching the lower 80s to lower
90s, followed by a return to near or slightly below
temperatures that could last through the rest of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 653 AM CDT Fri Aug 21 2026

Patchy fog has developed across central and eastern North
Dakota early this morning. The fog is unlikely to impact any
TAF sites, but terminals to the east of KMOT and north of KJMS
could see reduced visibility until around 14Z. VFR conditions
are otherwise expected through the forecast period. Light rain
showers will move from northwest North Dakota this morning into
central North Dakota around midday, likely diminishing in the
mid to late afternoon. The rain is unlikely to cause categorical
flight restrictions, and may only fall over KXWA this morning
and possibly KBIS in the late morning and early afternoon.
Light and variable winds early this morning will increase to
around 10 kts this afternoon, with a north to northwest
direction in central North Dakota and a northeast to east
direction in western North Dakota.

&&

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

&&

$$

UPDATE...JJS
DISCUSSION...Hollan
AVIATION...Hollan