099
FXUS63 KMPX 282100
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
400 PM CDT Mon Sep 28 2026

.KEY MESSAGES...

- Wet weather for Tuesday.

- Heavy rain threat for Tuesday night into Thursday has shifted
  south into Iowa.

- Seasonable temperatures remain in place over the next 7 days.

&&

.DISCUSSION...
Issued at 400 PM CDT Mon Sep 28 2026

The morning fog (a rare pure radiational fog to impact the core of
the Twin Cities urban heat island) has burned off, but as seen with
the 12z MPX sounding, the low level moisture that led to the fog is
trapped beneath a stout inversion around h85, which means that fog
simply lifted into the stratocu field we have. This low level
moisture trapped beneath an inversion setup will continue through
tonight, which means a mostly cloud night, though with enough wind
to keep us from getting fog. Rain tonight will be confined to the
north of the wavy frontal boundary that this afternoon sits from
roughly Fargo to Duluth and then back west in the Dakotas along an
eastward advancing cold front.

For Tuesday and Wednesday, there are two features to watch, a short
wave currently over western Montana and the combination of the upper
low near Las Vegas and Hurricane Polo approaching the Baja Peninsula
of Mexico. Overall, we`ve seen a significant downward trend in
precipitation potential across the MPX area and it is because of the
expected track of the upper low/Polo remnants.

Starting with the Montana shortwave, this is the one that
will drive a cold front across the Dakotas tonight that will
continue east across MN on Tuesday. We`ll see rain showers spread
into western early Tuesday morning, that will spread east with the
front through the rest of the day. This boundary will push southeast
of the MPX area Tuesday evening, taking the bulk of the rain with.
The one thing to watch Tuesday night night is both the HRRR and RRFS
are showing another widespread dense fog event unfolding across most
of the MPX area behind this rain. In general, this is expected to
bring a widespread 0.25" to 1" of rain to the area, with the highest
amounts in south central and southeast MN. It`s looking increasingly
likely that this will be the extent of the precipitation we see in
the Tuesday through Wednesday night time frame.

Now to the upper low and Hurricane Polo. These two features will
merge Tuesday night over AZ/NM, with the remnant low ejecting out
across the Plains toward the lower MO Valley by Thursday. This
system will be filling in as it moves across the central CONUS, but
the presence of remnant tropical moisture will push PWAT anomalies
up toward the 300% of normal territory, but that moisture looks to
only get as far north the cold front that pushes southeast of our
area Tuesday night. After a drastic shift north yesterday with the
GFS/GEFS in its QPF, we have seen the GFS settle back close to the
QPF footprint the ECMWF-AIFS has basically had the last several
days. This means confidence is now moderate to high that the heavy
rain event for Wednesday/Wednesday night will remain south of the
MPX area, with that heavy rain axis likely to line up from roughly
the southwest corner of Iowa over to the IL/WI border. The northern
edge of this rain shield may come up and clip the Albert Lea area on
Wednesday, but it is looking increasingly likely that the threat for
an excessive rainfall event in the MPX area this week has all but
disappeared into Iowa.

Although the rain may miss us on Wednesday, it`s not until Wednesday
night that we see a legit cold frontal passage that will clear out
the dewpoints in the 50s/60s and drop temperatures back. There is
potential for a mild day, with highs into the low 70s on Wednesday,
assuming we don`t waste too much of the day trying to burn off
another round of dense fog. Behind the cold front Wednesday night,
we`ll see lows fall back into the 30s with highs in the 60s. We`ll
see a clipper type system work across the international border on
Saturday, but it will be moisture starved with the best forcing
north of the MPX area. Still, you can`t rule out a few showers
moving through Saturday night before cool/dry Canadian high pressure
moves in for Sunday to give us a dry end to the weekend. This will
put in place perfect conditions on Sunday for those weirdos that
think running 26.2 miles is a good idea (note, this is one of those
weirdos).

Early next week, the high from Sunday moves into the Great Lakes,
with southerly flow quickly developing. This will bring in what is
looking to be a milder (with respect to the ever falling normals)
and drier stretch of weather. The drier part is good news for
farmers looking to get a jump on the 2026 harvest.

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 101 PM CDT Mon Sep 28 2026

12Z MPX sounding showed a strong inversion at h85 sitting atop
our low level moisture layer. This setup limits the mixing,
which is why we`ve seen the fog lift into a stratus/stratocu
deck with limited clearing. This statocu deck will remain in
place through the night, though will lift to high MVFR/VFR
levels. We will remain dry much of tonight, but as we get toward
6am Tuesday morning, rain showers will be moving into western
MN. Instability is limited, so TS threat is there, but not high
enough to include any TS in the TAFs for now. Timing of showers
in MN was based on a consensus of short term models from the
NBM, which is a bit slower than the 12z HRRR, but dealt with the
onset uncertainty with prob30s before prevailing precip. Also
coming with the precip will be a return to MVFR or lower cigs
for anyone that happens to go VFR tonight.

KMSP...CIGS continue on a rising trend and we expect MSP to be
VFR by sunset. We will go back to MVFR on Tuesday, but right
now, that looks to be timed with the arrival of the rainfall. As
for rainfall arrival, we`re seeing the HRRR on the early side,
bringing in showers at 15z, with most of the other CAMs starting
showers more in the 17z/18z timeframe.

/OUTLOOK FOR KMSP/
WED...IFR, chc LIFR/FG in mrng then VFR. Wind SW 5-10 kts.
THU...VFR. Wind NW 10-15G25 kts.
FRI...VFR. Wind SE 5-10 kts.

&&

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

&&

$$

DISCUSSION...MPG
AVIATION...MPG