922
FXUS63 KBIS 190559
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1259 AM CDT Tue Aug 19 2025

.KEY MESSAGES...

- Patchy to areas of fog across northern, central and the James
  River Valley tonight through Monday morning.

- Expect drier and warmer weather Tuesday and Wednesday with
  some moderate to high heat impacts possible each afternoon.

- Low chances (20 to 30 percent) for thunderstorms return
  Wednesday night through Thursday.

- A significant cooldown starts Thursday and continues through
  the weekend.

&&

.UPDATE...
Issued at 1254 AM CDT Tue Aug 19 2025

Saturation is already occurring across the north and portions
on central North Dakota. So we updated the fog forecast to start
now. Otherwise the current forecast was adjusted with the new
NBM data.

UPDATE
Issued at 950 PM CDT Mon Aug 18 2025

Showers and thunderstorms have ended over the southern James
River Valley this evening, leaving generally calm and clear
weather across western and central North Dakota at the time of
this update. With winds dying off, and with ample near surface
moisture lingering across central North Dakota, fog development
tonight is anticipated. With this update, went ahead and blended
in the latest models into the fog grids from early tonight
through the mid morning hours Friday. Otherwise, have made some
minor tweaks to the PoP grids. Overall, the forecast remains on
track.

UPDATE
Issued at 623 PM CDT Mon Aug 18 2025

Scattered strong thunderstorms have developed over the southern
James River Valley along a trailing surface boundary at the
time of this early evening update. While moderate MLCAPE values
of around 2000 to 2500 J/KG can be found in this area, 0-6 KM
bulk shear values remain around 15 knots or less, and thus these
showers have been fairly pulsey in nature. Of note is the high
PWATs lingering over the James River Valley of around 1.5 to 1.6
inches. With this in mind, these storms are likely producing
heavy rainfall and lots of small hail. Considering how slowly
these storms are moving, we will continue to monitor flooding
potential at this time. As we move away from peak diurnal
heating, as as this surface boundary moves slowly eastward out
of our forecast area, we should see storms diminish through the
early to mid-evening. Update wise, have slightly modified PoPs
and cloud cover to account for the latest satellite, radar, and
model trends through the mid evening. Overall, the forecast
remains broadly on track.

&&

.DISCUSSION...
Issued at 333 PM CDT Mon Aug 18 2025

Broad upper-level ridging is currently draped over the central
part of the country with generally weak flow aloft. A shortwave
is located over central North Dakota and is visible on water
vapor satellite imagery propagating through the ridge. This
shortwave was the culprit of showers and thunderstorms across
the south earlier this morning. As this wave continues to move
east we could see some reinvigoration of convection later this
afternoon or early evening in the vicinity of the far south
central or James River Valley. SPC mesoanalysis trends suggest
that if storms form, they will develop in an environment
characterized by 2000 to 3000 J/kg MLCAPE and weak deep layer
shear on the order of 20 to 30 knots at most. Thus a few pulse
or multi-cell storms could become strong to marginally severe,
but storm coverage remains uncertain. Recent CAM iterations have
been in fairly good agreement that a few storms may form over
James River Valley this afternoon but may not fully mature until
they move into the Grand Forks office forecast area.
Development further west is more uncertain as the main forcing
will be moving into eastern North Dakota and model consensus
suggests rising heights through the rest of the day. Still, if a
storm can mature, there is a conditional threat for hail to the
size of ping pong balls and wind gusts to 60 mph. Slow storm
motions and high precipitable water could also lead to locally
heavy rainfall.

Any storms that do form will either diminish or move out of the
area during the evening, giving way to dry conditions overnight.
Lows tonight are forecast to be in the low to mid 60s. We will
then warm through mid-week as dry conditions prevail on Tuesday
and Wednesday. On Tuesday, highs will range from the low to mid
80s east to the low to mid 90s west and then by Wednesday we
will see widespread highs in the 90s. Some lower triple digit
readings are even likely across the far west on Wednesday. At
this time, apparent temperatures are not quite high enough for
heat headlines, but the wet bulb globe temperature forecast is
suggesting the potential for moderate to high impacts on
Tuesday and high impacts on Wednesday for almost all of western
and central North Dakota. This means that anyone partaking in
physical activity outdoors in direct sunlight should use
caution and take plenty of breaks.

Thunderstorm chances return Wednesday night as the ridge axis
moves east and we transition back into low amplitude southwest
flow aloft. A shortwave will approach the state from northeast
Montana with most of the energy staying north of the
International border. That being said, there should be enough
of a glancing blow for some low to medium thunderstorm chances
(20 to 30 percent) northwest by the evening hours, especially
along a cold front and weak surface low moving into the state
from eastern Montana. As this front continues to move east
southeast overnight, thunderstorm chances translate into the
central with the best chances remaining north closer to the
synoptic forcing. If storms can mature across the north, shear
and instability would be sufficient for a few strong to severe
storms. SPC has placed most of the northwest and north central
in a Day 3 Marginal Risk (level 1 of 5) for this potential which
seems reasonable. Chances for showers and storms continue on
Thursday and CSU Machine Learning guidance suggests low chances
for severe thunderstorms across much of the area again. Given
some of the CAPE/shear scenarios that guidance is illustrating,
it will be the next period to watch.

We start to cool in the west on Thursday behind the front and
then across the entire area on Friday. Expect widespread highs
in the 60s and 70s and dewpoints in the 40s and 50s by the
weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1254 AM CDT Tue Aug 19 2025

VFR across most of the west and south tonight. Portions of the
north, central, and east will experience fog again overnight.
Expect VIS around 1sm and CIGs around 500ft or less through 14z
Monday. The TAF sites affected are KMOT and KJMS. Otherwise
light winds and mostly clear skies.

&&

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

&&

$$

UPDATE...Smith
DISCUSSION...ZH
AVIATION...Smith