440
FXUS63 KBIS 131431
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
931 AM CDT Thu Aug 13 2026

.KEY MESSAGES...

- Dense fog advisory southwest and portions of south central
  North Dakota west of the Missouri River through 9 AM CDT.

- Isolated showers and a few thunderstorms early this morning
  over central North Dakota. Scattered showers and isolated
  thunderstorms today west and north central, mainly dry
  elsewhere.

- Widespread showers and isolated thunderstorms later this
  evening through Friday morning west central through north
  central with locally heavy rain possible.

- Scattered showers and isolated thunderstorms southwest and
  central Friday and Friday evening then mainly dry late Friday
  and through the weekend.

- Temperatures near to slightly below normal through the weekend
  with highs generally in the 70s. The exception being some 60s
  northwest and some lower 80s southeast.

&&

.UPDATE...
Issued at 926 AM CDT Thu Aug 13 2026

Fog continues to burn off across the region, therefore the
Dense Fog Advisory will expire at 10AM. Rain will slowly push
into the northwest this morning and afternoon with decent
probability of an inch of rain. The forecast remains on track
through the period no updates are needed at this time.

UPDATE
Issued at 603 AM CDT Thu Aug 13 2026

Fog has developed over much of southwest North Dakota this
morning. We have issued a Dense Fog Advisory through 10 AM for
most areas south and west of the Missouri River. Otherwise,
made some minor adjustments to pops based on latest radar
analysis.

&&

.DISCUSSION...
Issued at 304 AM CDT Thu Aug 13 2026

A very broad and shallow upper level ridge extends from an upper
trough over the Pacific Northwest to another trough over the
northeast U.S. The apex of the ridge is currently situated
around eastern Montana. Latest satellite imagery shows an upper
level jet laying over the northern Great Lakes region with
current isolated convection over central ND associated with the
entrance region of this jet. Additional isolated convection over
central and into northeast Montana is associated with another
impulse lifting northeast through central MT, approaching the
apex of the ridge. With this broad upper flow over the area
today scattered showers and isolated thunderstorms will be
possible. However, the general thinking is that the current
convection in central ND will wane with the diurnal temperature
minimum and as the Great Lakes wave continues exiting to the
east. Scattered showers and isolated thunderstorms may linger
this morning in the northwest to north central ahead of the next
approaching wave, but with upper level ridging expected over
the state today, the confidence in shower/thunderstorm activity
beyond this morning is low. Will maintain some low to medium
pops today mainly in the west through north central as CAMS do
indicate some shower activity with mainly light qpf amounts.
The main show will be late tonight through Friday.

Upper level flow around the northwest U.S upper low will direct
moisture from the central Pacific, across the Desert Southwest
and eventually into the northern High Plains. In addition, a
subtropical mid level high over the Gulf of America will allow
gulf moisture to work its way northward into the Northern
Plains. By 12Z Friday NAEFS PW anomalies in excess of the 99th
percentile are situated over the Montana and North Dakota border
and track northeast across northwest North Dakota during the
day Friday. In addition, ECMWF EFI values in excess of 80
percent are situated over northeast Montana into northwest North
Dakota for the period centered on 12Z Friday, with a shift of
tails in excess of 2 in the far west, north of the Missouri
River (indicating an elevated probability of an extreme event).
Thursday night a mid-level impulse lifts into eastern Montana,
then across western and into north central ND during the day
Friday as a surface low over southeast Montana with an inverted
trough into northeast Montana, lifts into north central ND by
00Z Saturday. Although the overall instability is not great
during this timeframe, there should be enough forcing from the
approaching shortwave, combined with the resulting surface
cyclogenesis and FG forcing to produce some rather significant
precipitation amounts. The NBM 24 hour probability (06Z Friday
to 06Z Saturday) of an inch of QPF is greater than 70 percent
over far northwest ND, and greater than 50 percent from northern
McKenzie county into western Bottineau county. The probability
of 2 inches of QPF during that same timeframe ranges from
around 30 to 60 percent in far northwest ND. Looking at some
heavy rain parameters for Crosby around 12Z Friday, we see a
PWAT in excess of 1.50", mean RH around 90 percent and warm
cloud depth in excess of 11,000 ft, all very favorable
parameters for heavy rain. A couple of negative factors are the
lack of instability giving us that tall skinny CAPE, and a
rather progressive MBE movement. One thing to note was that
early in the period (late Thursday into early Friday) when you
may have better potential for stronger convection with heavy
rain, is when MBE movement is greatest. You may have
thunderstorms with very high rainfall rates, but they may be
moving rather quick. Later in the period, say during the day
Friday, as the surface low tracks slowly northeast through
western ND, the MBE movements slow down. Thus you may not have
the excessive rainfall rates from stronger convection, but the
movement of the system as a whole slows. From a winter
perspective there is a quite impressive signature of very strong
Omega, 2D FG forcing and deformation to the north of the
surface low on Friday. Looking at the HREF PMM and LPMM 24 hour
qpf, you can make out a couple bands of high qpf. One over
northeast MT and far northwest ND, possibly associated with the
stronger convection, and another tracking more from west central
into north central ND, possibly associated with the slower MBE
movement. Both produce some locally heavy rain amounts in excess
of 3 inches.

Of course there`s plenty of time for this scenario to shift
east or west or break down or intensify. We will definitely need
to monitor. Given our dry summer so far, an areal flood watch
is not in the forefront of our minds, but if this scenario
holds, it`s a possibility that we may need some headlines for
excessive rainfall. WPC has the northwest in a slight risk for
excessive rain. Stay tuned.

After Friday we dry out over the weekend. Temperatures Today and
through the weekend will be mainly in the 70s. The exception
being perhaps some lower 80s in the James River Valley, and some
60 degree readings today and especially Friday in the northwest
where we could see a cool and rainy day.

Early next week a quasi-zonal flow will bring near daily chances
of showers and thunderstorms. Temperatures early next week
remain generally in the mid 70s to mid 80s, pretty typical for
this time of year.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 603 AM CDT Thu Aug 13 2026

Areas of fog, dense at times, through 10 AM CDT for most of
southwest ND, including KDIK. Otherwise, partly to mostly
cloudy skies this morning across western and central ND. An MVFR
ceiling can not be ruled out, outside of the fog, but ceilings
at all TAF sites except KDIK have been VFR. Isolated to
scattered showers and a few thunderstorms today with an
increasing easterly wind. Showers and scattered thunderstorms
become more widespread across western ND tonight and may spread
into portions of the north central towards 12Z Friday. Look for
low VFR to areas of MVFR ceilings in shower and thunderstorm
activity late tonight.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CDT /9 AM MDT/ this morning for
NDZ018>020-031>033-040>044-059>062.

&&

$$

UPDATE...Johnson/TWH
DISCUSSION...TWH
AVIATION...TWH