809
FXUS63 KBIS 181210
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
710 AM CDT Tue Aug 18 2026

.KEY MESSAGES...

- A little cooler today, with highs in the lower 70s to lower
  80s. Aside from a few morning showers, the rest of the day
  should remain dry.

- Low to medium chances (20 to 40 percent) for isolated to
  scattered showers and thunderstorms on Wednesday. A few
  storms may become strong to severe in south central North
  Dakota during the afternoon and evening.

- Near to slightly above average temperatures favored mid week
  through the weekend.

&&

.UPDATE...
Issued at 709 AM CDT Tue Aug 18 2026

A small area of showers anchored to a low level baroclinic zone
continues to propagate southeastward into central North Dakota
early this morning, and was over Lake Sakakawea at 645 AM CDT.
These showers may persist into the mid morning hours and reach
the James River Valley. Very little measurable rain is expected,
and the probability of lightning remains very low. Elsewhere,
patchy fog has developed across northern North Dakota.
Visibility observations under half a mile have recently become
more prevalent, and this is confirmed in some webcam imagery. A
Special Weather Statement for the patchy dense fog has been
issued. The fog should lift by around 9 AM CDT.


&&

.DISCUSSION...
Issued at 419 AM CDT Tue Aug 18 2026

The Northern Plains lie under a west-northwest cyclonic flow
pattern early this morning between a Hudson Bay low and Desert
Southwest ridge. Despite a surface high pressure analyzed over
southern Saskatchewan, enough low level convergence/frontogenesis
is present to have produced an area of scattered showers along
the Missouri River Valley from northeast Montana into northwest
North Dakota. CAMs that show some semblance of this activity
bring it southeastward through central North Dakota this
morning, although prognostics of the low level forcing weaken
over time. An occasional, brief thunderstorm cannot be ruled
out, but there does not appear to be enough CAPE to support
sustained lightning. Aside from these morning showers, a quiet
weather day is anticipated as surface high pressure slides
southeastward into North Dakota. Today will be a little cooler
than yesterday for most, with highs in the lower and mid 70s
north and east to lower 80s southwest.

From tonight into Wednesday, mid level shortwave energy is
forecast to approach the region from the northwest, with a
surface trough deepening over western North Dakota by Wednesday
afternoon. Several CAMs show weak, elevated convection entering
western North Dakota late tonight into Wednesday morning, but
PoPs remain lower than 20 percent over this time period due to
sparse coverage and very low RH projected in the sub-cloud
layer. But Wednesday afternoon could see an uptick in both
coverage and intensity of convection over central North Dakota
in response to diurnal heating, a pooling of low level moisture
downwind of the surface trough, and perhaps a coinciding
increase in DCVA. MLCAPE could increase above 1000 J/kg over
south central North Dakota by mid to late Wednesday afternoon
with deep layer shear initially only around 25 kts, but
increasing over time. Values of 0-3 km shear are actually quite
similar to those in the 0- 6 km layer, which is reflected in
forecast hodographs that do show a varying degree of low level
curvature depending on location. Residual CIN and dry-air
entrainment in the upper levels could work against sustained
updraft growth, but the environment is still forecast to be
supportive of a few marginally severe thunderstorms from south
central North Dakota to the James River Valley Wednesday
afternoon and evening. Shear and deep layer wind vector
orientation to the surface trough favor a mixed storm mode, but
the weak nature of the forcing may put a slight tilt towards a
more predominant discrete mode.

Despite the passage of the aforementioned shortwave(s) on
Wednesday, as well as another one that could brush northern and
eastern parts of the state on Thursday, broad mid to upper level
rising height tendencies are in the forecast mid to late week.
This brings the high temperature forecast back into the 80s
Wednesday and Thursday, closer to 90 in the southwest quadrant
of the state on Thursday. Friday may be a few degrees cooler as
another shortwave passes by to the north and east. Ensemble
guidance shows a highly-amplified wave pattern developing
heading into the weekend, with an upstream ridge being tilted
into the Northern Plains and eventually flattened by a southern
Canadian shortwave early next week. But there is notable timing
uncertainty in the latter feature, which leaves a near- average
temperature forecast in place through the weekend for now. After
Wednesday, rain/thunderstorm chances remain very low until late
Saturday into Sunday when height falls associated with the
southern Canadian shortwave could begin spreading into the
region.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 709 AM CDT Tue Aug 18 2026

Patchy fog has developed across northern North Dakota early
this morning, but is unlikely to impact KXWA or KMOT. A small
area of showers is moving through central North Dakota early
this morning, and should pass to the north and east of KBIS
between 12Z and 14Z. Aside from the early morning fog, VFR
conditions are expected to prevail through the forecast period.
Winds will remain light and variable, with 5-10 kt northwest
winds this afternoon.

&&

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

&&

$$

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