textproduct: La Crosse

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 /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1201 AM CDT Tue Sep 16 2025

Low confidence in mostly VFR over the local forecast area in southeast Minnesota, northeast Iowa, and southwest into central Wisconsin through the 16.06Z TAF period. Increased VFR cloud cover seen on satellite imagery at 16.06Z TAF issuance associated with weakening radar returns.

Ongoing low level moisture transport persists low (<25%) storm chances through most of the 16.06Z TAF period. IFR-LIFR visibilities possible where storms do 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.