251
FXUS63 KBIS 300557
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1257 AM CDT Sun Aug 30 2026

.KEY MESSAGES...

- Showers and scattered thunderstorms expected overnight.
  Locally heavy rainfall is possible where thunderstorms
  develop.

- Patchy fog is possible across much of western and central
  North Dakota Sunday morning.

- Isolated to scattered severe storms are possible Sunday into
  Sunday night. Large hail and damaging winds are possible
  along with locally heavy rainfall. A tornado cannot be ruled
  out on Sunday as well.

- Dry and windy conditions are forecast for Monday. Locations
  south and west of the Missouri River may experience near
  critical to critical fire weather conditions through much of
  Monday.

&&

.UPDATE...
Issued at 1257 AM CDT Sun Aug 30 2026

Showers and thunderstorms are starting to push in across the
south ahead of a mid level upper wave. Modest shear and
instability could provide for an isolated stronger storm,
although a lack of mid level lapse rates, low level jet, and
favorable hodo graphs should keep hail sizes mostly sub severe.
Lower DCAPE should also limit the wind threat through tonight.
These storms will move into a rich moisture environment, with
PWATs of an inch to 1.5+ inches. Given their slow moving nature
as well, localized heavy rainfall is possible tonight. Made some
minor PoP adjustments based on the latest radar trends.
Otherwise, any clearing ahead and behind these storms could lead
to some patchy fog and low clouds. Maintained ongoing patchy
fog mention as a result.

UPDATE
Issued at 1015 PM CDT Sat Aug 29 2026

Scattered weak radar returns and isolated thunder is found over
portions of western and south central North Dakota at the time
of this mid to late evening update. Coverage of both showers and
thunderstorms is expected to increase overnight through Friday
morning as a H7 jet develops and drops out of Saskatchewan
across the forecast area. While most storms are expected to be
fairly weak and embedded within the broader are of
precpitation, CAMs still advertise a storm over portions of the
far northwest shortly after midnight CDT. While current analysis
reveals fairly robust CIN across that, if a storm manages to
develop and tap into the increasing bulk shear shear across that
area it may be able to produce marginally severe hail and wind.
The window for this development is expected to be fairly brief
and thus overall predictability is low, but we will continue to
monitor these model trends as we head into the early overnight
period. Also of note is the potential for locally heavy rainfall
overnight. Any storm that does develop is expected to be fairly
efficient rain producers, and with high PWATs around 1.5" to
2.0" across the area and the overall slow progression of these
storms, it wouldn`t be overly surprising to see rainfall rates
approach 1"/hr over portions of the northwest or the south
central. We will need to monitor for flooding potential
overnight. Regarding forecast updates, opted to blanket much of
western and central North Dakota with patchy fog overnight after
considering the ample near surface moisture behind the
precipitation and the light south easterly surface winds.

UPDATE
Issued at 645 PM CDT Sat Aug 29 2026

Showers and a few isolated thunderstorms can be found over
portions of western and central North Dakota at the time of this
early evening update. At the moment, thunder is generally
restricted to the far northwest where an H5 divergence max can
be found. These storms have been fairly pulsey so far, with
better shear found further to the south. Increasing cloud cover
and the loss of peak heating is generally anticipated to limit
thunderstorm activity across the northwest as we head into the
mid to late evening. High low level lapse rates and decent DCAPE
across this area does mean that we will have to watch this area
for gusty winds over the next few hours. In the south central,
an area of clearing in the cloud layer is helping to destabilize
as we head into the early evening. With higher dewpoints in the
upper 60s to lower 70s and temperatures well into the 80s at
this time, analysis indicates decent MUCAPE values of around
2500-3000 J/KG along and south of I-95. With moderate shear also
found across this area (around 40 to 45 knots), the potential
for a stronger to severe storm to develop is expected to be
somewhat higher here. That said, there doesn`t appear to be much
forcing across the region to get things going this late in the
day. Convection further south in SD is likely associated with H3
speed max analyzed over that area, while the convection further
west in Montana is developing an surface trough/occluded front
that isn`t expected to make into our area until late tonight.
Thus, while we will continue to monitor conditions as we head
into the evening, the overall potential for a stronger to severe
thunderstorm is expected to be limited. With this update, have
blended in the latest short-term guidance in the PoPs to
increase coverage of precipitation in the northwest and south
central this evening and tonight. Otherwise, the forecast
remains in good shape.

&&

.DISCUSSION...
Issued at 154 PM CDT Sat Aug 29 2026

Early this afternoon, a broad and strong mid/upper ridge was
centered over the southern and central plains with a vigorous deep
layer trough progressing eastward out of the PNW. Out ahead of this
trough, several perturbations were noted within southwesterly upper
flow over the northern CONUS. Despite the copious amounts of upper
level cloud cover across the region, modest destabilization is
occurring this afternoon across North Dakota out ahead of shallow
shortwave trough located over the central Rockies. As forcing for
ascent arrives later this evening into tonight, isolated to
scattered showers and storms are expected to develop across western
North Dakota and gradually work their way eastward. Continued
development and/or persistence of this activity may also be
supported by subtle mid-level WAA overnight into early Sunday
morning. The greatest coverage of showers and storms will likely be
along and south of I-94, especially given that better forcing for
ascent appears to be trending further south for tonight into early
tomorrow morning. Activity this evening into tonight will struggle
to contend with widespread convective inhibition, and chances for a
couple of isolated severe storms before 06Z appears to be waning
given the latest short term guidance. However, elevated instability
along the axis of mid-level WAA overnight into early Sunday morning
will be fairly decent (generally around 1500-2000 J/kg of MUCAPE).
Effective shear around 30 knots could support some organized
elevated convection capable of hail up to ping pong ball size.
Damaging wind gusts appears less likely, but an isolated instance of
a 50-60 mph wind gust cannot be ruled out overnight and early Sunday
morning.

Sunday appears to be quite the complicated setup for potential
severe weather across North Dakota. A strong and deep upper trough
will lumber eastward across southern Alberta during the day on
Sunday with a sharp lobe of vorticity expected to round the southern
end of the trough and kick out across eastern Montana and North
Dakota. This should provide significant forcing for ascent across
the northern CONUS for widespread showers and thunderstorms Sunday
afternoon through Sunday night. Guidance has generally backed off
the idea that shower and thunderstorm activity will be ongoing
through much of the morning hours on Sunday. This seems a little off
given the amplitude of upper level diffluence that will be
overspreading the region as early as Sunday morning, but it`s likely
other factors are at play such as subsidence behind any activity the
occurs late tonight into early Sunday morning. With short-range
models backing off on morning convection across the state, this
leaves the door open for potent destabilization across the forecast
area. Model soundings across the warm sector Sunday afternoon show
an uncapped airmass with ample instability around 2000-2500 J/kg.
Shear will also be conducive for some organized convection with 0-6
km shear around 25 to 35 knots. Given the amount of synoptic ascent,
the sharpness of the surface frontal boundary, and shear vectors
parallel to said boundary, the expectation is for thunderstorms to
rapidly grow upscale. With a linear storm mode favored, the main
concern will be damaging wind gusts around 60-70 mph. At this time,
it appears the hail threat will be limited to the first couple of
hours after convective initiation when storms still have the
opportunity to be semi-discrete. Lastly, a tornado or two cannot be
ruled out where surface winds will be slightly back along a weak
warm front draped across the state. The primary difference in the
guidance at this point is the location of the warm sector.
Solutions, like the HRRR and ARW, show a psuedo-dryline developing
in the vicinity of the US-83 keeping warm, humid air east of this
corridor. Meanwhile, other solutions, like the NAM and NSSL, show
this moisture gradient along the ND/MT state line. This may have an
impact on the intensity of convection early, perhaps modestly
suppressing thunderstorm activity in the drier solution. However,
the overall severe threats remain the same regardless of which
scenario plays out.

Monday also appears to be a somewhat busy day for much of North
Dakota, though more for wind and fire weather concerns. The surface
low and upper low are forecast to become more vertically stacked
over Saskatchewan, and a tight pressure gradient is expected across
southern Saskatchewan/Manitoba into much of North Dakota. Mostly
clear skies should allow for deep mixing across these areas, and
uniform flow in the boundary layer should allow for efficient mixing
of stout winds to the surface. Model guidance suggests 850 mb winds
could be in the neighborhood of 45 to 50 knots, mainly across
northern North Dakota. Should these winds mix down to the surface,
it`s possible some locations along and north of US-2 could
experience 45 to 55 mph wind gusts during the day on Monday. It`s
possible a wind advisory may be needed for these areas late Monday
morning into Monday afternoon. Further south, the expectation is for
wind gusts to be in the 30 to 45 mph range. RH values will generally
be around 20-30% south and west of the Missouri River. This along
with the aforementioned breezy conditions will support near critical
to critical fire weather concerns across southwest North Dakota. As
the surface low gradually weakens and lifts northeast, the pressure
gradient will begin to relax by late afternoon. Thus, breezy
conditions should generally come to an end by sunset Monday evening.

Periodic chances for showers and storms remains in the forecast from
Tuesday through the end of next week. Mid to long range guidance
continues to be on board with a series of systems traversing the
northern plains around mid/upper ridging remaining over the central
and southern plains. The best chances for showers and storms next
week will likely be Wednesday night into Thursday morning as a stout
upper trough is forecast to eject into the northern plains. Exact
details remain a bit murky this far out, so stay tuned for updates
to the forecast for this time period over the next few days.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1257 AM CDT Sun Aug 30 2026

MVFR to VFR conditions could be found tonight as an initial
round of showers and thunderstorms lifts across the forest
area. Most sites have a TEMPO or PROB30 group for thunderstorms
to account for this. Any clearing ahead or behind these storms
could lead to some IFR to MVFR ceilings and perhaps visibilities
with patchy fog. Confidence in this occurring is low, although
KMOT and KJMS are already seeing some lower clouds trying to
form. After the initial round of showers and thunderstorms moves
through Sunday morning, MVFR to VFR ceilings will prevail
across much of the area through the day. Later in the day
through the evening another round of thunderstorms looks to push
from west to east, bringing MVFR and isolated severe
conditions. Prevailing and PROB30 groups for these storm chances
were used at most sites. A south southeast wind will be found
for Sunday, changing to a westerly wind later Sunday through
Sunday night as a cold front moves through.

&&

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

&&

$$

UPDATE...Anglin
DISCUSSION...JC
AVIATION...Anglin