418
FXUS63 KMPX 011813
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
113 PM CDT Tue Sep 1 2026

.KEY MESSAGES...

- Multiple clusters of storms are expected across southern MN
  tonight to the north of a warm front. There is a level 2 of 5
  risk of severe weather, with damaging winds being the highest
  risk.

- A low confidence precipitation forecast through Labor Day
  weekend, with multiple low chances for rain.

- Summer-like temperatures and humidity continue through Labor
  Day weekend.

&&

.DISCUSSION...
Issued at 112 PM CDT Tue Sep 1 2026

Water vapor imagery this afternoon shows a subtropical ridge
centered over the bootheel of MO, with a monsoon shortwave coming
out of Wyoming that will run around the north side of the ridge
through the night. At the surface, there`s a stationary front a
little north of the I-80 corridor in Iowa, with dewpoints pooling up
into the upper 70s along it. As we go through the night, the WY
shortwave and IA warm front will work together to support an
overrunning convective event over southern MN. Current expectations
are that storms will develop this afternoon in the Dakotas
associated with the shortwave, with elevated storms developing north
of the warm front near the MN/IA border shortly after sunset as the
LLJ over IA starts to ramp up (eventually getting up into the 35-40
kt range). We`re seeing the idea from the HRRR and other CAMS that
we could see multiple clusters of storms develop on the nose of the
LLJ, with the convection in the Dakotas that develops this afternoon
eventually sweeping up any clusters ahead of it late tonight. The
favored zone for heavy rain and severe potential will be on the nose
of the LLJ and along the MUCAPE gradient. The HREF/REFS continue to
show these two features lining up along the MN/IA, with the southern
two or three tiers of counties in MN being most at risk for storms,
heavy rain, and severe weather tonight, which matches up well with
the Day 1 Slight Risk from the SPC. From the severe weather
perspective, instability (muCAPE > 3000 j/kg) and deep shear (over
40 kts) are certainly favorable for severe weather, but weak mid-
level lapse rates and overnight timing/nocturnal stabilization will
be limiting factors that will put a ceiling on this being a
significant severe weather setup.

For the rest of Wednesday, we`re expected to be dry as the
atmosphere recovers from the early morning convection. We`ll have
height rises through the day, with easterly low level winds, so we
may have to battle some morning stratus as the low level moisture
gets trapped beneath a building inversion. Those easterly winds and
potential for morning clouds will result in Wednesday being the
"coolest" day of the work week, with highs generally in the low to
mid 80s, with ever increasing dewpoints, as tropical dewpoints in
the 70s begin spreading back north across southern and southwest MN.

Going into Wednesday night, we`ll begin to see the stationary/warm
front lifting back north across the area. The LLJ will not be as
strong as what we see Tuesday night, but WAA will still be present.
HREF shows over 2000 j/kg of muCAPE coming up with that warm front
and the presence of the weak WAA will give us a chance of storms,
but it`s highly uncertain if we`ll get storms to fire with our
subsidence and building cap. This uncertainty is why we ended up
with pretty broad 20-40 PoPs across the area Wednesday night as we
await some hopefully better clarity on where mesoscale features will
be.

Answering the question of where mesoscale features will be will
continue to be a headache as we go through Labor Day weekend. We`ll
see a ridge axis centered over us by Saturday, that shifts to our
west Sunday into early next week. That ridge will come with strong
capping, along with a rather uncomfortable airmass, as we see highs
near 90 Friday and Saturday, with dewpoints in the low to mid 70s
sending heat index values both days up into the mid to upper 90s,
welcome to Augtember! That ridging will also result in capping.
However, given how unstable the atmosphere is, it`s not taking much
for convective parameterization schemes in the deterministic models
to start firing off convection. There is lots of spread with QPF in
the ensembles, so the on/off, mostly low chances for PoPs makes
sense. Again, where any weak shortwaves happen to meetup with a
surface boundary, chaos could ensue, but where that may happen is
still uncertain given the capping and weak forcing.

For Sunday into early next week, the ridge axis shifts to our west,
with MN/WI transitioning into northwest flow. This is why you`ll
notice temperatures in the forecast taking a step back after
Saturday. We`ll still be placed within the northern stream and
susceptible to mesoscale shenanigans though. At the moment, it looks
like Sunday night through Monday night would be a period with
increased storm potential, but there`s still time for this to change
in the coming days.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1258 PM CDT Tue Sep 1 2026

VFR conditions today and this evening with light winds. Later
tonight, storms will approach from the west, and should impact
KRWF and KMKT. Did continue with a Prob30 mention of thunder at
KMSP, KRNH, and KEAU.

Precipitation should occur within a 4-hour window, and then
storms will exit to the east. There is a small chance for MVFR
ceilings in the wake of the precipitation, but otherwise expect
VFR for Wednesday.

KMSP...
Confidence continues to increase in precipitation overnight, so
did add a prevailing SHRA group. There is still a chance for
thunderstorms, especially after 06Z, but better chances are to
the south, so did continue with the Prob30 group.

For Wednesday, expect southeast winds and VFR conditions.

/OUTLOOK FOR KMSP/
THU...VFR with MVFR and -SHRA/TSRA possible early.
FRI...VFR. Small chance TSRA. Wind S 5-10 kts.
SAT...VFR. Wind SE 5-10 kts.

&&

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

&&

$$

DISCUSSION...MPG
AVIATION...JRB