596
FXUS63 KBIS 182257
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
557 PM CDT Fri Jul 18 2025

.KEY MESSAGES...

- Isolated severe thunderstorms are possible Saturday afternoon
  through Saturday night, and again Sunday afternoon through
  Sunday night. The main hazards will be large hail and damaging
  winds.

- Daily chances for showers and thunderstorms continue through
  next week.

- High temperatures will generally be in the mid 70s to lower
  80s through midweek next week, before warming up late in the
  week.

&&

.UPDATE...
Issued at 535 PM CDT Fri Jul 18 2025

Only some minor adjustments to sky cover with this update.
Scattered to broken, mainly low VFR clouds remain over a good
portion of western and central ND. Surface high pressure over
southern Saskatchewan and into eastern Montana and western ND
will move east tonight, settling over eastern ND Saturday
morning. This should bring a quiet night as far as showers and
thunderstorms go, although there is a small chance of overnight
or early Saturday morning convection in/near the southwest
portion of the state. We will probably see patchy, if not areas
of low stratus and fog as we get into the late evening and more
likely the overnight hours. Previous fcst has this covered.
Will see how it plays out this evening. Updated text products
will be transmitted shortly.

&&

.DISCUSSION...
Issued at 246 PM CDT Fri Jul 18 2025

This afternoon, the synoptic pattern was characterized by
longwave troughing across the northern part of the CONUS, with
a sharp trough and immediate downstream ridge in the western
Canadian Prairies. The center of a weak surface high was
analyzed in southern Saskatchewan, with a few showers exiting
our far eastern counties as an upper shortwave moves out. Cloud
cover has been a bit more widespread than expected, and is
relatively low, with a scattered deck around 2 to 4k feet. Highs
this afternoon are in the lower 70s to lower 80s.

Cloud cover is expected to diminish this evening, with the
exception of parts of the James River Valley. Forecast
soundings in parts of central North Dakota are fairly convinced
that fog will develop, so broad-brushed an area of patchy fog across
most of the central for late tonight into Saturday morning.
Lows will be in the upper 40s to mid 50s.

The aforementioned trough and attendant closed low are progged
to drop south through the day Saturday, while the ridge quickly
moves over western North Dakota while being flattened as the
closed low expands. As flow to our west begins to turn just a
bit southwesterly and embedded impulses move through,
precipitation chances begin to increase through the day
Saturday. Low chances start in the southwest, before
probabilities expand north and increase in the afternoon as a
surface low deepens in south central Montana. Breezy southeast
winds will help advect in dew points around 60 degrees F,
leading to a ribbon of increased instability along the ND/MT
state line, and bulk shear around 40 to 45 knots will be
sufficient for supercells. Storm mode and the overall
progression is still a bit fuzzy, with today`s CAMs run really
increasing the spatial coverage of convection, leading to
higher overall chances of precipitation, as well as speeding up
the timing of development. Any early afternoon thunderstorms
would likely be subsevere, but can`t rule out multiple rounds of
thunderstorms in general, especially for places south and west
of the Missouri River. Advertising isolated severe thunderstorms
with hail up to the size of golf balls and wind gusts up to 60
mph, with the most likely window of severe weather the late
afternoon through the evening.

Troughing aloft becomes more pronounced across the Pac NW on
Sunday, leading to continued southwest flow across the Dakotas.
Blended POPs are already in the 40 to 60 percent range through
the day Sunday, with some potential for holdover from the
previous night`s showers and thunderstorms. Sunday has been
highlighted in machine learning guidance as a day to watch, with
continued moisture advection leading to higher instability
across much of the forecast area, and overlapping with modest
bulk shear. There is some concern for mid-level capping with
height rises relatively neutral, but if storms do manage to
form, there is certainly potential for them to be severe.
Currently carrying mention of isolated severe thunderstorms for
the majority of the forecast area. Slow storm motion and high
PWATs could lead to locally heavy rainfall and potentially some
isolated flooding concerns as well.

The overall pattern is quite consistent Saturday through
Wednesday, with highs generally in the mid 70s to lower 80s and
overnight lows in the mid 50s to lower 60s. Troughing out west
stays persistent through midweek, with daily low to medium
chances for showers and thunderstorms. Late in the week,
ensembles favor flow to become more zonal and temperatures warm
up into the widespread 80s, with medium probabilities for highs
to return to the 90s. Above normal temperatures are favored
through the end of the month, with the active pattern continuing
through much of this time.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 535 PM CDT Fri Jul 18 2025

VFR conditions to begin the 00Z TAF period. Expect mostly VFR
conditions this evening. Late this evening or more likely after
midnight, we may see patchy to areas of fog develop over
portions of central into eastern ND. As we get into Saturday
there is also some indication of low stratus being pulled up
into southwest ND from the south. A little more confident in the
patch fog late evening and overnight, over the stratus later
Saturday. Will probably add some mention of fog at KJMS and KBIS
to begin with and see how things go this evening. Late in the
period there is the potential for thunder moving into western
ND, but at this time too much uncertainty to include at KXWA or
KDIK. Generally light easterly flow tonight, with a southeast
flow on Saturday, becoming breezy with gust to around 25kts at
western sites in the afternoon.

&&

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

&&

$$

UPDATE...TWH
DISCUSSION...Jones
AVIATION...TWH