531
FXUS63 KMPX 011139
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
639 AM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Isolated to scattered showers this afternoon west of the I-35
corridor.

- A few severe storms (risk level 1 of 5) possible Tuesday
  afternoon/evening with the arrival of a strong cold front.

- Temperatures cool down significantly midweek in next weekend,
  rebounding next week.

&&

.DISCUSSION...
Issued at 308 AM CDT Mon Sep 1 2025

Surface analysis this morning kind of looks like it has this entire
weekend, with high pressure over the Great Lakes and a ridge axis
extending back to the west across WI and MN. Water vapor imagery
shows the primary plume of deep moisture still across southern Iowa,
extending northwest into the Dakotas. However, the nighttime
microphysics satellite imagery and cloud observations shows
scattered to broken cloud cover developing in the 4k-5k foot range,
which is associated with a pool of higher moisture air centered
around the h85 level. By this afternoon, HREF shows mlCAPE values
just sneaking over 1000 j/kg and this instability combined with the
moisture around the h85 level will be enough to spark isolated to
scattered showers this afternoon and evening along and west of the I-
35 corridor, so perhaps a dry run of the State Fair during
operational hours could be done in by some rain on its last day.

Tonight, the plume of deeper moisture and associated shortwave
energy currently over the Dakotas will start nudging east into MN,
with the threat for at least isolated showers continuing through
tonight and into Tuesday morning. Also happening tonight is the
potential to see the Northern Lights as the solar flare that left
the sun Saturday afternoon reaches the Earth. However, we are going
to have cloud cover to contend with, just how much cloud cover will
determine whether or not we can give you a good reason to keep the
long holiday weekend going a bit longer on Monday night!

Tuesday afternoon, a cold front will be moving into central MN by
the afternoon. Surface dewpoints will nudge back up into the low to
mid 60s ahead of the cold front, which will allow of mlCAPE to build
to around 1500 j/kg. This will support a broken line of storms to
develop along the front Tuesday afternoon that will head southeast
through the night with the front. The one limiting factor for severe
weather is that the main upper forcing trails the cold front a bit
and doesn`t really start moving into the MPX area until Tuesday
evening, which limits our shear until later in the period. Still,
given the strength of the wind fields coming in behind the cold
front, there will at least be a threat for some stronger wind gusts
with any line segments that can mix some of these winds down. The
SPC added a Marginal Risk (1 of 5) for much of the MPX area, which
seems reasonable given the instability and potential for multiple
clusters of storms to develop.

Wednesday through Saturday, the big story here is the taste of fall
we`ll have as an h5 low deepens between Lake Superior and Hudson
Bay. We`ll be within cyclonic flow Wednesday through Friday, which
means potential for shortwaves and showers. With the 01.00 run of
the models, we`re starting to see guidance hone in on a stronger
shortwave late in the day Thursday into Thursday night. This looks
like a pretty classic clipper we see in the winter when it comes to
forcing. This results in a slight bump up in PoPs we saw from the
NBM Thursday evening, but they could certainly go higher in the
coming days as models start to come into better agreement on this
wave. This clipper will also bring a reinforcing shot of cold air
for Friday that will continue into Saturday. The NBM shows breezy
northwest winds for us Wednesday through Saturday, where highs each
day will only be in the mid 50s to lower 60s. The NBM has been
coming down on its highs, but it still looks to be running about 2
to 5 degrees too warm Wednesday through Saturday thanks to its bias
correction. We see southerly winds return on Sunday, with airmass
modification beginning to end next weekend, with highs returning to
the 70s to start the next work week.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 610 AM CDT Mon Sep 1 2025

Nighttime satellite shows bubbling Cu early this morning, and
overnight hi-res models are starting to latch onto this idea of
isolated to scattered showers developing today. As of typing
this, we already had a brief shower move over our office in
Chanhassen. Most likely timing for more showers is later this
afternoon and evening after instability is able to increase a
bit, and the highest confidence is for east-central MN near the
Twin Cities metro. Impacts should remain low, unless any of the
showers develop a stronger updraft and produce lightning.

VFR cigs expected for the rest of the period once fog starts to
dissipate this morning. The next period to watch will be with
the approaching cold front from the north Tuesday PM. There
could potentially be multiple rounds of TSRA ahead of the front,
but confidence is too low to include in any of the TAFs outside
of AXN for now.

KMSP...Introduced a prob30 for -SHRA during the late afternoon. We
are already seeing a few small showers pop up around the SW
metro this morning, so there could be some isolated stuff before
more scattered showers develop around 22-02z.

/OUTLOOK FOR KMSP/
TUE PM...VFR. -SHRA likely, chc -TSRA/MVFR. Wind SW 5-15kts.
WED...Chc -SHRA/MVFR early. Wind NW 10-15G25kts.
THU...VFR. Wind NW 10-20kts.

&&

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

&&

$$

DISCUSSION...MPG
AVIATION...BED