639
FXUS63 KMPX 210805
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
305 AM CDT Thu Aug 21 2025

.KEY MESSAGES...

- Patchy fog this morning with mostly sunny skies for most of the
day. Clouds increase by the evening ahead of an incoming cold front.

- A chance for showers has been added to western WI and eastern
  MN Sunday afternoon/evening. Showers will be isolated as
  available moisture remains low.

&&

.DISCUSSION...
Issued at 304 AM CDT Thu Aug 21 2025

Much like yesterday morning there is patchy fog across portions of
the area, with the dense fog over the eastern half of Wisconsin as
of around 3am and the lowest visibility within our area around 3-4
miles. A bit of lingering cloud cover has kept the fog development a
bit lower despite the lack of wind, and the falling dew points have
aided in this endeavor as well. Plenty of sun is in store once any
morning fog burns off once again, as an incoming cold front late
tonight into Friday will bring a chance to isolated to scattered
showers and storms to the area from northwest to southeast, with the
front moving through around sunrise tomorrow as isolated showers
continue for a good portion of Friday per the latest CAM guidance.
The storm potential is a pretty big question along the front, with
CAMs not entirely enthusiastic due to a decent cap in place due to
the timing of the front moving through. NAMNest forecast soundings
show abundant capping despite also having dew points that are at
least 3-4 degrees too warm resulting in higher than expected
instability. Lapse rates above the inversion will be decent around 6-
7 C/km alongside decent shear aloft, which would allow for elevated
storms and an isolated hail threat, alongside a wind threat if a
gust ends up strong enough to bust through the cap. PWATs will be
much lower than our last few systems, on the order of around 1 to
1.25 inches compared to near 2 inches from this past weekend,
limiting the flooding threat to only those areas which saw abundant
rainfall and have yet to fully recover.

After the frontal boundary passes on Friday, temperatures and dew
points will both be falling as northwesterly flow stacks throughout
the troposphere with dry and cool air flowing into the region. Dew
points will drop to near 50 degrees over the weekend which alongside
expected high temperatures in the mid 60s to near 70 should make for
a beautiful weekend for outdoor activities. Recent rainfall over
portions of Canada should limit our smoke potential, as well as
steering flow taking what has been the origin for our smokey skies
and pushing it farther east instead of south. The only chance for
smoke we will have is upstream fires in the western US, with the
chance for this kind of smoke to reach the surface much lower due to
having to pass over the mountains alongside a much lower
concentration. While we cannot completely rule out some haze in the
skies due to smoke, it is not expected to be a concern compared to
our previous nicer stretches of weather this summer.

One change to the forecast within the last 24 hours has been a bump
up in the chance for isolated showers on Sunday as the upper level
occluded trough over Hudson Bay has begun to move farther south
within deterministic guidance, with the big 3 global models all
showing a bit of deformation on the southwest side of the occlusion
as it approaches the Great Lakes resulting in a wave of vorticity
advection across the area Sunday afternoon and evening. This would
give us enough forcing to produce showers, however the spread and
intensity of showers looks to be limited by access to moisture as
the aforementioned dew points near 50 result in PWATs under an inch
which may keep most of it as virga. The best chance for the isolated
showers within the region looks to stretch from Duluth to Eau Claire
with the Twin Cities on the western fringe of where the showers seem
possible for now. If your plans include the State Fair this weekend,
be sure to keep checking the forecast as these shower chances could
potentially impact the area on Sunday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1222 AM CDT Thu Aug 21 2025

The immediate concern within the first 6 hours of the TAF will
be patchy dense fog, which we will handle with AMDs except for
RNH/EAU due to a similar setup to yesterday at this time, which
ended up missing most of the sites. Winds remain light before
favoring a 180 direction ahead of an incoming front which will
bring -TSRA after the end of the period.

KMSP...Expect -TSRA to be added for the 12/18z TAF periods along
the cold front.

/OUTLOOK FOR KMSP/
FRI...VFR, chc MVFR/-TSRA early. Wind W 5-10kts.
SAT...VFR. Wind NW 10-15kts.
SUN...VFR. Wind NW 5-10kts.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.

&&

$$

DISCUSSION...TDH
AVIATION...TDH