Lewiston, Minnesota Weather Forecast Discussion

540
FXUS63 KARX 141834
AFDARX
Area Forecast Discussion
National Weather Service La Crosse WI
130 PM CDT Sun Sep 14 2025
.KEY MESSAGES...
- The summer heat and humidity sticks around for the start of the
new week with low end rain chances (20-30%). Highs in the 80s.
- The 2nd half of the week promises higher, more widespread rain
chances (40-50%) along with cooler, more seasonable temperatures.
Highs in upper 60s/low 70s.
&&
.DISCUSSION...
Issued at 130 PM CDT Sun Sep 14 2025
* START OF THE WEEK: summery airmass, low end (20-30%) rain chances
Upper level ridge makes slow progress eastward as we move through
the front end of the new week, flattening-bending over as its axis
eases over the eastern great lakes. An upper level trough over the
plains will continue to rotate shortwaves through it, but the brunt
of each still slatted to hold west/north of the local area.
In between the ridge and trough a fetch of warm/moist air will push
northward. While the models continue to hold most of the upper level
forcing west/north, most due hint that weak ripples (likely
convectively produced/enhanced) could shift from the plains to
across the region later tonight/Monday. Add in weak convergence and
MUCAPES north of 1kft j/kg and there would likely be enough forcing
for at least isold/scattered showers/storms. Most CAMS show this.
Without a more distinct forcing mechanism, how widespread and/or
vigorous any shower-storm could get is questionable. For now, 20-30%
chances look reasonable.
Of note, PWs push 1.5" with NAEFS and EC PW anomalies around +1.5.
Warm cloud depths around 3 kft - not much in the summer, but not bad
for mid Sep. If storms train or are relatively slow, localized
rainfall in excess of an inch is possible.
Similar rain chances could persist into Tue before more widespread
rain chances move in for the middle part of the week.
Unseasonably warm, humid air will continue to pool under the ridge,
keeping the region under this summery regime. While the GEFS have
trended as the warmer model on the whole, approx 75% of the EPS and
GEFS members have highs climb to/above 80 into Wed. Summer lovers
enjoy it while you can - the latter half of the week promises a
return to the seasonable norms.
* SECOND HALF TO WEEK: cooler temps, widespread shower chances (40-
  50%)
Moving into the middle part of the new week, the EPS and GEFS trend
toward taking the upper level trough and developing a cutoff low.
With shortwaves dropping southward out of Canada, and not much for
west-east push in the upper level flow, this low could reinforce,
hang around for awhile. The WPC clusters show the same scenario,
with varying degrees of depth/strength to the low/trough. All keep
its influence across the region into the weekend, not edging east
until closer to Sunday.
Sensible weather outcomes will be the return of a cooler, less humid
airmass along with periodic bouts with showers and a few storms. 850
mb temps in the GFS/EC deterministic runs drop from around +20 C
during this warm span of days to around +10 C by next weekend. The
grand ensemble drops the potential to reach the mid 70s for highs
down to 5 to 30% starting Friday. The GEFS remains the warmer model
and drives most/all of those higher chances. If you like the EPS,
its suite is closer to around 70 and cooler. Eitherway, a lot of
support for a return to temps more reminiscent of mid Sep.
With the slow movement of the upper level low, spiraling shortwave
bands and the cyclonic flow will have a longish residence time
across the upper mississippi river valley. Clouds and periodic
showers (30-60%) will be the result. Some low end thunder chances.
Differences in timing of the small features/locations within/between
the ensemble suites working to hold chances a bit lower than they
might be. Expect some adjustments to expectations as we move through
the new week.
&&
.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1223 PM CDT Sun Sep 14 2025
As the 850 mb moisture increases late tonight, showers and storms
will develop near Interstate 35. Some of these may impact KRST.
Otherwise, VFR conditions are expected.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Rieck
AVIATION.....Boyne

NWS ARX Office Area Forecast Discussion