Waltham, Minnesota Weather Forecast Discussion

983
FXUS63 KARX 161055
AFDARX
Area Forecast Discussion
National Weather Service La Crosse WI
555 AM CDT Tue Sep 16 2025
.KEY MESSAGES...
- Small (15-25%) chance for additional showers and
  thunderstorms through this evening across much of the region.
- Additional thunderstorms possible Wednesday and Thursday with
  increasing rain chances for Friday and Saturday.
- Warming lingers into Friday with cooler, closer to seasonable
  temps (back into the 70s) likely for the weekend into Monday.
&&
.DISCUSSION...
Issued at 321 AM CDT Tue Sep 16 2025
Small chance for thunderstorms into this evening:
08z WV satellite shows an upper trough over the Canadian Prairies
extending southwestward to the Great Basin, an upper high over the
Great Lakes, and southwesterly flow aloft over the CWA. A southerly
fetch of low level moisture is also seen over LA/AK/MO/IA into
eastern MN and western WI. At the surface, light south-southeasterly
winds are predominant with dewpoints mainly in the 60s. A small area
of showers and storms attempted to move north into NE IA but
dissipated during the 04z-05z hour.
Today into tonight, expect additional disturbances to pass northeast
of the area. As this occurs, may get additional convection as 16.00z
HREF joint probabilities suggest there is a pretty good chance (50-
90%) that sufficient CAPE will be present with low to minimal CIN.
That said, with only weak forcing, will likely need to rely on small
scale boundaries and convergence for initial updraft development.
Given this, have kept previous forecast pattern of spreading slight
chance mentions across much of the area, particularly during the 15z-
21z time frame.
Increasing rain chances through the weekend:
As the week progresses, pattern slowly begins to break down as the
ridge to our east weakens and the upper troughing trudges eastward.
For Wednesday and Thursday, additional convection may (20-40%)
develop, particularly in our west where capping will be weakest.
While confidence in exact timing is low given the recent shift
toward a slower progressing pattern in guidance, 16.00z operational
runs seem to be trying to converge on Friday into Saturday having
the best potential for rain as the main body of the upper trough
passes over the region. As for hazards, PWATs look to be in the 1-
1.5" range with values trending toward the high end of this range by
Friday. Additionally, storm motions through Thursday look to be slow
given the influence of the upper ridge. Thus, localized heavy rain
could occur but, as PWATs tick upward for Friday, so do storm
motions as the upper trough approaches. 16.00z GFS depicts around
1000 J/kg of MLCAPE would be present Saturday afternoon in the
presence of 30 knots of sfc-6km shear, suggesting a severe
thunderstorm could occur. However, ML-based outlooks do not
highlight the region and 16.00z LREF joint CAPE/CIN/shear
probabilities are minimal (6% or less), suggesting this run is an
outlier. Thus, while we cannot totally let down our guard, do not
think severe convection will occur at this time.
With quasi-zonal flow aloft favored, could see additional convection
Sunday into Monday. Have kept NBM PoPs that spread these chances
across multiple periods as timing of any upper impulses appears
highly uncertain.
Eventual temperature moderation:
Highs above normal in the 80s continue through at least Thursday as
the Great Lakes ridge lingers. As the upper trough passes and
heights aloft fall, temperatures here at the surface will moderate,
with temperatures likely remaining below 80 Friday (60-95% chance
per 16.01z NBM), Saturday (70-100%), Sunday (60-100%), and Monday
(50-95%).
&&
.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 551 AM CDT Tue Sep 16 2025
Low confidence for mostly VFR over the local forecast area in
southeast Minnesota, northeast Iowa, and southwest into central
Wisconsin through the 16.12Z TAF period due to potential
scattered storms causing isolated IFR visibilities where they
form.
WEDNESDAY THROUGH SATURDAY: Wednesday morning valley fog
possible. Increasing storm chances Wednesday persist through the
weekend. Current highest storm confidence (30-50%) seen west of
the Mississippi River Valley locally in southeast Minnesota and
northeast Iowa Wednesday through Friday.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
DISCUSSION...Ferguson
AVIATION...JAR

NWS ARX Office Area Forecast Discussion