575
FXUS63 KBIS 140250
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
950 PM CDT Fri Jun 13 2025

.KEY MESSAGES...

- Cloudy and cool conditions for most areas through tonight and
  into Saturday, with fog and mist possible across the south.

- Near daily chances for showers and thunderstorms beginning
  tonight and lasting through next week. A few periods of strong
  to severe thunderstorms are possible over this time period,
  with the first coming on Sunday across southwest and south
  central North Dakota.

- Temperatures return closer to average Sunday through next
  week, with daily highs in the 70s to lower 80s.

&&

.UPDATE...
Issued at 950 PM CDT Fri Jun 13 2025

No major updates are needed at this time. Storms continue to
develop across portions of southeastern Montana, and are
expected to approach the MT/ND over the next few hours. A robust
cap has already developed across much of eastern Montana, so
whether any of these storms survive that long remains to be
seen. We will continue to monitor radar and model trends.

UPDATE
Issued at 700 PM CDT Fri Jun 13 2025

Low stratus can be found across western and central North Dakota
at the time of this early evening update. A few areas of weak
reflectivity can be found in north central North Dakota at this
time, but little to no precipitation from this is expected to
reach the ground. Otherwise, a line of thunderstorms, a few of
which have become strong to severe, has developed in central
Montana and is expected to make its way eastward through the
evening. With significant capping starting to develop along the
MT/ND border, it is questionable if they will persist long
enough to reach into our western counties. CAMs continue to back
off on storms in our CWA, though with the status deck beginning
to erode in the far southwest we would not be surprised if an
elevated storm manages to survive long enough to make it that
far east. Overall the chance for severe weather is very low, but
we will continue to monitor these storms in case a stronger
storm, with gusty winds, persists. No major adjustments to the
forecast were performed with this update, as it remains broadly
on track.

&&

.DISCUSSION...
Issued at 341 PM CDT Fri Jun 13 2025

Broad longwave ridging is analyzed over the Northern Plains this
afternoon, with remnants of a mid level shortwave trough meandering
underneath. Surface high pressure over Ontario maintains a broad
easterly upslope flow across the state. A large expanse of low
stratus has been trapped along the surface pressure gradient at the
southwestern edge of the influence of the Ontario high, blanketing
most of western and central North Dakota. Most guidance does not
dissolve these clouds through tonight, and actually has the stratus
expanding north and east through the evening with little to no
expected change in the low level wind fields. The nearly saturated
boundary layer could result in fog formation across southern North
Dakota tonight into Saturday morning. As was the case last night
into earlier this morning, it may be more of a case of ceilings
lowering to the surface along higher terrain areas. But visibility
could also be reduced by mist or light drizzle. Lows tonight will
mainly be in the 50s.

Organized convection developing off the Montana mountains this
afternoon is forecast to approach western North Dakota later this
evening into tonight. The environment becomes increasingly
unsupportive of severe convection from eastern Montana into western
North Dakota, and several CAMs suggest most of the convection could
fall apart completely before crossing the stateline. The highest
chances for showers and storms overnight are in southwest into far
south central North Dakota, but it is still only around a 20 to 40
percent chance.

The low level wind field is forecast to weaken on Saturday, and low
clouds should eventually diminish from west to east through the day.
Boundary layer mixing could remain poor though, especially if clouds
stick around longer than expected. The high temperature forecast for
Saturday ranges from the mid and upper 60s east to mid and upper 70s
west. Rising heights aloft countered by embedded pieces of shortwave
energy result in a low confidence precipitation forecast for
Saturday. Nearly every CAM produces a cluster or two of showers and
weak thunderstorms, but there is great variance in timing and
location. Saturday night sees an increase in shower and storm
chances across western and south central North Dakota as another
potential round of organized convection approaches from Montana.
Should these storms materialize, they carry a slightly higher risk
of being strong on account of increased elevated buoyancy. Any
stronger storms would mainly be confined to southwest North Dakota.
The probability of severe storms Saturday night remains very low.

Sunday marks the beginning of a more established period of quasi-
zonal flow aloft with intermittent periods of transient low-
amplitude ridging and shortwave passages. This favored pattern
promotes a slight warmup in temperatures and increased chances for
showers and thunderstorms. The NBM maximum temperature distribution
is markedly warmer next week, but its deterministic output is
heavily skewed towards the cooler side of the distribution. In other
words, high temperatures next week are more likely to end up warmer
than the current forecast than they are to shift cooler. The
deterministic NBM forecast keeps highs mainly in the 70s, but the
50th percentile is more in the mid 70s to mid 80s. However,
temperatures each day could be greatly influenced by mesoscale
phenomena (clouds, rain, outflow, etc.) that will be unresolvable
until much shorter forecast time ranges.

This expected pattern also yields higher chances for showers and
thunderstorms. Furthermore, a longer-term establishment of 50s to
60s surface dewpoints yielding daily maximum SBCAPE around 1000-2000
J/kg per the NBM combined with the more active flow leads to an
increased risk for strong to severe thunderstorms. This begins in
earnest on Sunday when the Storm Prediction Center has
introduced a Slight Risk for southwest parts of the state, and a
Marginal Risk for most of the rest of the forecast area.
Timing, mode, and threat ceilings for the severe risk on Sunday
remain highly uncertain as there is no discernible surface
feature presenting itself in model guidance. But mean ensemble
CAPE around 1000-2000 J/kg and deep layer shear around 30-40 kts
are sufficient for severe convection. For the rest of next
week, machine learning guidance carries low probabilities for
severe storms each day, but the days with the highest and lowest
probabilities keep changing from run to run. Today`s iterations
are now less supportive of a severe storm risk on Tuesday and
Wednesday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 950 PM CDT Fri Jun 13 2025

Low stratus can be found across the forecast area, promoting
mainly MVFR to IFR ceilings to begin the 00Z TAF period. VFR
ceilings linger over KMOT at this time, though is expected to
also drop into MVFR to IFR conditions later this evening and
overnight. Lowering stratus is expected over portions of
south western and south central North Dakota tonight, which
could promote LIFR ceilings are the terminals of KDIK and KJMS.
With these lowering ceilings, the development of patchy
fog/mist/drizzle is also possible at these same terminals.
Isolated to scattered showers and a few rumbles of thunder are
also possible overnight, mainly across western and south central
North Dakota. Have opted to include a PROB30 group for light
rain at KDIK with this update, with confidence too low to
include elsewhere at this time. Otherwise, winds are expected to
remain out of the east southeast throughout the 00Z period,
starting a little gusty with speeds up to 15 MPH and gusts up to
around 20 MPH early this evening, before generally diminishing
overnight through tomorrow afternoon.

&&

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

&&

$$

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