173
FXUS63 KBIS 292345
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
645 PM CDT Sat Aug 29 2026

.KEY MESSAGES...

- Isolated strong to severe storms are possible this evening
  into tonight. Best chances remain south of I-94. Main hazards
  will be up to ping pong ball size hail and up to 60 mph wind
  gusts.

- 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 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 /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 645 PM CDT Sat Aug 29 2026

VFR ceilings and visibility is found at most terminals to begin
the 00Z TAF period. Low VFR to high MVFR ceilings found over
KJMS are expected to generally persist through the evening.
Chances for showers and a few storms will increase across the
forecast area this evening through tonight, though persistant
mid to high level cloud cover will generally help limit the
convective potential to mainly the far northwest and the
southwest into south central North Dakota. For this update, have
included PROB30 for light TSRA at KBIS later this evening into
early tonight, mainly where better destabilization is expected
to occur under a gap in the clouds. Where thunderstorms do
occur, MVFR visibility due to moderate to heavy rainfall and
gusty winds should be anticipated. Elsewhere, rainy light rain
is expected overnight. In the north central into the James River
Valley, lower ceilings are expected to accompany this rain,
with low MVFR to IFR ceilings expected to develop at KMOT and be
sustained at KJMS through Sunday morning. Light easterly winds
this evening are expected to gradually turn southeast Sunday
morning, then southerly Sunday afternoon. Winds across portions
of the west may become gusty Sunday afternoon, becoming
sustained around 15 to 20 MPH and gusting as high as 30 MPH.

&&

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

&&

$$

UPDATE...Adam
DISCUSSION...JC
AVIATION...TWH