697
FXUS63 KFGF 190455
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
1155 PM CDT Mon Aug 18 2025

.KEY MESSAGES...

- Scattered thunderstorms this afternoon evening in southeast
  North Dakota and then patchy fog tonight for all areas.

- Strong to severe thunderstorms are possible Thursday with
  strong winds and large hail as the primary threats.

&&

.UPDATE...
Issued at 1148 PM CDT Mon Aug 18 2025

Storms have since dissipated in west-central Minnesota.

With moist air mass still in place and calming winds, fog is
forecast to develop overnight tonight before diminishing mid
morning Tuesday. There are areas of very low stratus in
Minnesota and Manitoba. On the flanks of this stratus, clouds
may lower enough to "scrape" the ground, turning into fog.

There is a high chance for fog to become dense, although
location and duration of dense fog remains in question.
Relatively highest chances for this to occur resides in lakes
country of west-central Minnesota as well as west of the Red
River Valley in eastern ND.

UPDATE
Issued at 648 PM CDT Mon Aug 18 2025

Cluster of thunderstorms have recently developed near the upper
James and Sheyenne River Valleys. While there is strong
instability to feed storms, wind shear is greatly lacking. This
will promote outflow boundary to propagate away from storms.
With instability gradient to the southeast as well as upper flow
to the east, expecting storms to migrate generally east through
the remainder afternoon into early evening.

Storms have exhibited gusty winds as high as 60 mph, and will
be capable of doing so given wet microburst-type potential
reinforcing the outflow boundary. The chance for other hazards
like large hail and tornado is very low, although cannot be
ruled out should outflow and/or storm interactions occur from
newly developed storms not undercut by outflow boundaries.

&&

.DISCUSSION...
Issued at 229 PM CDT Mon Aug 18 2025

...Synopsis...

As can be seen in current regional satellite imagery lead shortwave
activity across the upper great lakes continues to bring heavy rain
to areas of IA/MN/WI this morning with the SW monsoon ongoing in
areas of AZ/NM beneath building western ridging. In between closer
to home we have present southwest flow aloft with a transition to
more zonal flow today. Hurricane Erin can also be noted to the east
of the Bahamas. As this is influenced by the subtropical Bermuda high
the current midwest shortwave activity will aid digging eastern
troughing in pulling the storm north while upper diffluence stalls
mid level flow leading to slowing in the CONUS wide flow with riding
in the central and western US dominating Tuesday and Wednesday
before giving way to progressive troughing in the northern plains
Thursday and Friday with northwest flow across the upper Great Lakes
then prevailing through the weekend leading to overall cooler
temperatures in the 60s and 70s for highs Friday and beyond.

Today/tonight...

Lingering drizzle from this morning has subsided with the stratus
making a good effort to clear once it hit 11am. Overnight
thunderstorms to the east of Bismarck have dissipated but and
evident circulation in visible imagery with 2000 MUCAPE and maybe 20-
25kts of eff shear could serve as the focus point for afternoon
initiation. As the low tracks east though the afternoon along the
leading edge of an evident shortwave some strong but likely still
sub severe storms are possible in far southeast North Dakota between
5 and 8pm. MLCAPE around 2000-2500j/kg and up to 25kts of eff shear
will support a primary convective threat of lightning in addition to
some small hail and wind gusts up to 45 mph. Beyond possible storms
tonight fog once again appears likely though coverage will depend on
just how much low level saturation can be achieved though based on
water vapor across western and central North Dakota there appears to
be no lack of moisture to work with. Capped coverage at patchy
wording but would be entirely unsurprised to see a dense fog
advisory issued both tonight and Tuesday night given a once again
similar setup.

Aside from fog chances each relatively  weather Now through the
mid week. With ridging dominating through this time we will see
seasonable temperatures of highs in the low to mid 80s through
Thursday though dewpoints in the upper 60s to low 70s likely
aided by late August evapotranspiration will make for a humid
few days.

Severe Weather Thursday?...

By Thursday afternoon progressive troughing will swing through the
Canadian Prairies with an attendant cold front draped south
across the Dakotas and Minnesota by the evening/overnight. Will
the true degree of any severe threat would be contingent upon
the timing of the this front for the primary source of forcing
as it moves through an untapped warm sector already in place
with ensembles and even longer range CAMS such as the NAM
showing 2000-3000j/kg of MLCAPE ahead of the cold front with
enough shear to support organized convection. Would currently
anticipate a more linear mode given the forcing but would still
think to maintain at least some hail risk initially should
there be a window for more discrete convection. Beyond this main
window for potentially severe storms on Thursday General
thunderstorm activity remains possible both Tuesday and
Wednesday with more quiet northwest flow behind Thursday front
through the weekend as temps drop into the 60s for highs (almost
fall like).

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1148 PM CDT Mon Aug 18 2025

Main impact to aviation will be low ceilings and fog tonight
into Tuesday morning.

Areas of very low stratus and fog are already being noticed
within portions of north-central and northeast Minnesota, as
well as into Manitoba. This is forecast to spread into portions
of eastern ND into northwest and west-central MN. Confidence
remains high enough to include BR/FG in TAFs, however, it still
remains unclear how thick fog will be at each site. KBJI and
KDVL hold relatively highest chances for seeing dense fog/LIFR
conditions between 09-15Z.

During the day Tuesday, VFR conditions return with light winds
under 10 kt.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.

&&

$$

UPDATE...CJ
DISCUSSION...TT
AVIATION...CJ