La Salle, Minnesota Weather Forecast Discussion

701
FXUS63 KMPX 071056
AFDMPX
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
556 AM CDT Sun Sep 7 2025
.KEY MESSAGES...
- Instances of patchy dense fog and patchy frost are possible
  through daybreak.
- Active weather returns Monday & Tuesday, with a couple rounds of
  showers and thunderstorms possible.
- Temperatures warm back into the 70s for the upcoming work week.
&&
.DISCUSSION...
Issued at 258 AM CDT Sun Sep 7 2025
It`s a cool and calm start to Sunday across the forecast area.
Expansive surface high pressure has become the dominant weather
feature over the Upper Midwest, as forcing associated with upper-
low over Hudson Bay departs to the east. GOES GeoColor imagery
reveals mostly clear skies and surface observations display 2 AM
temperatures in the mid 40s across much of the region. We`re
looking at a few evolving pieces to the forecast through daybreak.
The first revolves around isolated pockets of patchy dense fog
that have developed over the past few hours. Surface dew points
have remained in the low to mid 40s (likely due to Saturday`s rain
showers), so there are spots where temperatures have quickly
cooled to the dew point. The other piece to the forecast is the
potential for patchy frost. As mentioned, slightly warmer dew
points have perhaps promoted the potential for fog, but at the
same time will likely play a role in limiting widespread frost
potential. The best chance for patchy frost will be across central
MN (north of I-94), where temperatures are forecast to dip into
the mid 30s. Large scale subsidence will support a quiet forecast
to close the weekend. Soundings feature the development of diurnal
Cu mid to late morning, so we`ll call it a mostly sunny Sunday
with light winds and highs in the mid 60s.
Surface high pressure shifts southeast over the Ohio Valley heading
into Monday. Winds take on a southerly direction tonight into
Monday, owing to return flow on the western extent of the surface
high. Moisture advection will increase in response to the southerly
wind shift and will be further supported by an incoming shortwave
over the central Plains. We may see a batch of showers early Monday
within the wing of warm advection, however the better potential for
rain and storms comes later in the day. The large scale evolution of
rain/storm chances will be tied to a 30+ kt low-level jet, which is
forecast to extend across the eastern Plains into west central WI.
Previous forecast cycles had favored convection across southeastern
MN, however, the latest NBM has shifted the axis of 60+ PoPs a bit
farther to the north (TC Metro to Duluth). New hi-res solutions from
the RRFS-A and the HRRR develop showers/storms on the nose of the
jet axis/along a surface warm front, which matches the trends in the
NBM PoPs. Forecast guidance shows an axis of strong instability
across the Dakotas into far western MN, however that axis is
displaced from the low-level jet forcing to the east. Still,
guidance suggests 500-1000 J/kg of CAPE near the zone favored
for convection, which will combine with steepening lapse rates
and favorable shear to support thunderstorms. Speaking of shear,
a look at forecast hodographs reveals curvature indicative of
deep layer shear supportive of a few stronger storms. Given the
meager instability, would tend to lean in the direction of an
elevated hail threat as the ceiling for this event. CSU`s MLP
advertises low probs for hail and wind across the forecast area.
The overall severe weather threat is low, but remains something
to watch. Coverage of showers/storms will further increase as
the low-level jet intensifies into Monday night (still, the best
chances for precipitation are across eastern MN/western WI).
Scattered showers/storms may still be ongoing Tuesday morning. A cold
front will move from northwest to southeast through the region
Tuesday afternoon and evening. As previously discussed, guidance has
had a tendency to run drier with this frontal passage and as such
we only have slight chance PoPs from the NBM (15-20%) in the grids
Tuesday afternoon. However, suspect that the frontal interaction
with a pool of lingering moisture/higher theta-e air across southern
MN may eventually result in higher PoPs for the second half of
Tuesday. Will wait for more of the hi-res guidance to arrive for a
deeper dive, but the initial feeling is that the severe weather
threat would be low and likely along the lines of an elevated
hailer setup.
The forecast will dry out for the remainder of the work week. Upper-
level ridging will support the continuation of warmer temperatures,
in the upper 70s to lower 80s through the end of the week. Attention
will turn back to the west heading into the upcoming weekend, as
western troughing will bring the return of wet weather across the
northern CONUS. Solutions diverge when it comes to how soon rain
chances will return to our portion of the Upper Midwest, so at
this time I like the NBM`s isolated (~20-30%) PoPs for the
upcoming weekend.
&&
.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 555 AM CDT Sun Sep 7 2025
Dense fog is the main aviation concern to open the 12z period.
Have included TEMPOs through 13/14z at terminals that have
already observed visibility reductions from isolated pockets of
dense fog. It`s possible that we may need a quick AMD early in
the 12z TAF period should additional fog develop. Otherwise,
expect a Cu field around ~5k feet from mid-morning through the
afternoon. Westerly winds sustain 5-10 kts through the day.
Winds shift out of the south heading into tonight.
KMSP...No additional concerns.
/OUTLOOK FOR KMSP/
MON...VFR. Chc -TSRA/MVFR late. Wind S 10-15G20 kts.
TUE...VFR. Chc -TSRA/MVFR early. Wind SW 5-10 kts.
WED...VFR. Wind E 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
DISCUSSION...Strus
AVIATION...Strus

NWS MPX Office Area Forecast Discussion