textproduct: La Crosse

KEY MESSAGES

- Showers linger through the early morning hours (20-40%) ahead of a cold front that moves through this afternoon bringing additional showers and storms (30-50%).

- Drier conditions are expected Sunday and Monday with high temperatures in the upper 70s to low 80s.

- Shower and storm potential increases again Tuesday into Wednesday (50-80%).

DISCUSSION

Issued at 1236 AM CDT Sat Aug 15 2026

Today: Periods of Showers and Storms

Ongoing scattered showers across portions of southeast Minnesota and western Wisconsin associated with a band of 850-700hPa theta-e advection come to an end overnight as said band continues moving northward. Further south, nebulous 900-800hPa warm air advection spreads through northeast Iowa and southwest Wisconsin during the early morning hours with some scattered showers already ongoing. These showers have greater potential to continue through the early morning hours (20-40%), but little to no impacts expected.

Heading into this afternoon, a 500hPa shortwave trough lifts northeastward out of the Central Plains, forcing a cold front through the Upper Mississippi River Valley. Instability builds across the region along and ahead of the front with MLCAPE reaching 750-1250 J/Kg, greatest south of I-90 and west of the Mississippi River, supporting convective development across the region as the boundary moves through (30-50%). CAM guidance has consistently been suggesting storm coverage along the front should be more isolated to scattered in nature, likely due to some weak capping across much of the Upper Mississippi River Valley as seen in model soundings. However, given the combination of the wave aloft, forcing along the front, and evident instability, thinking the environment should be able to overcome the weak capping resulting in some greater shower/storm coverage this afternoon.

While strong/severe potential is very low (<5%) with any convective development due to 0-6km bulk shear of 15kts or less, some fairly efficient rain rates are possible given the juiced-up atmosphere that remains in place across the Midwest. As has been the case over the past several days, PWATs near 2in, warm cloud depths of 10kft+, and skinny SBCAPE profiles will support some instances of rainfall rates upwards of 1 in/hr. Since we've largely missed out on the heavy rainfall over the past few days, flooding concern is very low as the front moves through. That said, some local areas of ponding seem reasonable where the heaviest rain falls.

Sunday - Monday: Drier, Near Normal Temperatures

With the cold frontal passage tonight, a much drier airmass is ushered into the Midwest bringing relief from the persistent pattern of precipitation. High pressure will be the dominant feature across the region resulting in partly cloudy skies to end the weekend and start the new week. Some breezier northwest winds look to be on the table Sunday afternoon as cold advection steepens 0-1km lapse rates with 20-25kts of wind atop this layer. That said, not expecting gusts to be overly impressive, generally only 15-25mph. Stronger winds shift east as we head into Sunday night while high pressure and low level ridging take hold. Clearing skies and light winds are currently expected across the region during this period which could result in a night of valley fog, though low level saturation may be a limiting factor given the drier airmass. Monday looks to be a repeat of Sunday albeit with lighter winds. High temperatures top out in the upper 70s to low 80s both days, around normal for this time of year.

Tuesday - Wednesday: Increasing Shower and Storm Potential

A more zonal upper level pattern will be in place across the United States Tuesday into Wednesday. A jet streak and associated 500hPa shortwave trough over the west coast early Tuesday will be able to quickly translate eastward through the day along this zonal flow and force a cold front through the Upper Mississippi River Valley. Shower and storm potential increase along this front, sitting around 50-80% in the 15.01z NBM. There does appear to be some potential for some stronger storms during this period as 70-90kts winds associated with the aforementioned jet streak increases 0-6km bulk shear to around 40-50kts along with MUCAPE 1000-2000 J/kg present across the region. AI/ML guidance also continue to suggest there is some probability for strong/severe weather during this timeframe so it'll remain a period to monitor.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 552 AM CDT Sat Aug 15 2026

MVFR to IFR reductions this morning will persist through the afternoon as low-level moisture remains in place across the region. Cigs may improve to low-VFR by late afternoon and into the evening, however, probabilities in the NBH and deterministic guidance favor category reductions again after 06z. Showers and storms will be possible (30-50%) during the late afternoon and evening hours with MVFR to IFR reductions possible underneath any storms. Fog formation may be possible (10-30% chance in the recent HREF for IFR vsbys) as well depending on how cloud cover trends manifest Saturday night and into Sunday morning. Winds will being the TAF period from the southeast but will shift to northwesterly and generally remain around 5-10 kts.

ARX WATCHES/WARNINGS/ADVISORIES

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