textproduct: La Crosse

KEY MESSAGES

- A few rounds of showers and storms today, but severe weather unlikely.

- Periodic shower and storm chances Thursday through Friday night, then likely drier and slightly cooler than normal.

DISCUSSION

Issued at 1236 AM CDT Tue Aug 18 2026

A few rounds of showers and storms today

Potentially a few rounds of showers and storms today as some weak shortwaves and MCSs embedded in northwest flow aloft ripple through the region. Scattered upstream evening convection over portions of Minnesota and the Dakotas was tied to a plume of modest instability approaching 2000 J/kg, with a sharp instability gradient eastward into our forecast area. Through daybreak, that diminishing plume of instability will spill eastward with MUCAPE around 1000 J/kg or less, supporting gradually weakening clusters of storms diving east/southeast through the forecast area. Because of the rather weak forcing, CAMs aren't in the best agreement, but they lend support for most of our area to be impacted by at least one such cluster through the morning hours, with the greatest chances (50-60%) generally near and west of the Mississippi River. No severe weather expected with this round of elevated morning convection.

Lingering clouds after morning showers and storms will likely temper our daytime warming, and the forecast has been trending a smidge cooler for today's highs. The main forecast question revolves around how much we manage to destabilize ahead of potentially another round of scattered storms this afternoon. This activity would seem to be focused mainly south of I-90 as drier air will be encroaching from the north, but CAMs are not in much agreement as it hinges on how morning convection plays out. Better theta-e convergence will be found south of I-90, and that is where the 00Z HRRR initiates late- afternoon scattered storms. While deep layer near-unidirectional shear magnitude will be respectable (50+ knots), weak forcing and limited instability thanks to weak mid-level lapse rates should inhibit severe potential locally. Forecast soundings show the deeper (albeit skinny) CAPE profiles in our far south, suggesting that would be where any healthier updrafts could conceivably manage to develop, but it looks marginal at best. So, thinking a marginal SPC risk is adequate for potentially an isolated wind threat late this afternoon-evening.

Today does not have the look of a widespread soaking rainfall event, given weak to modest moisture transport, limited warm cloud depths, and progressive storm cluster motion. Looking like 0.25 to 0.5" on average, with some higher pockets perhaps exceeding 1 inch.

Periodic rain chances Thursday and Friday, then generally drier

Under broad upper troughing, a drier airmass briefly takes hold for Wednesday with embedded shortwave activity just clipping our far southern forecast area. Weak moisture return gradually takes hold Thursday into Friday, ushering in PWATs around 1.25". This will allow for the return of periodic shower and storm chances as an active northwest flow pattern takes hold aloft. Thursday night into Friday brings the highest chances (50-70%).

This weekend and beyond becomes a little murkier of a forecast for rain chances given diverging upper level flow patterns between various guidance, but overall it looks fairly dry and slightly cooler than normal.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 604 AM CDT Tue Aug 18 2026

VFR conditions are expected throughout much of the TAF period with showers and storms being the primary TAF concern. Recent CAMs highlight areas near I-94 for convective development so have opted to maintain a prob30 for -tsra at KLSE through 00z. Strong wind gusts may accompany any more robust storms. Otherwise, winds will shift from southwesterly to westerly today with winds around 5-10 kts before diminishing overnight.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...None. IA...None.