textproduct: La Crosse

KEY MESSAGES

- Low potential for heavy rainfall across northeast Iowa and southwest Wisconsin this morning with only a 10-20% chance for amounts of 1 inch or more.

- Showers and storms are possible this afternoon (20-40%) before additional heavy rainfall potential moves into northeast Iowa and southwest Wisconsin this evening into Saturday. Probabilities for 1 inch or more sit around 30-60%.

- Briefly drier conditions to close out the weekend and start the new week before showers and storms return by the middle of next week.

DISCUSSION

Issued at 1237 AM CDT Fri Aug 14 2026

This Morning: Heavy Rainfall Potential

A surface boundary remains situated across central Iowa into northern Illinois early this morning as 850hPa warm advection and moisture transport nose into it, providing a source of lift for convective development through the morning hours. The environment along this boundary remains favorable for heavy rainfall as PWATs above the 90th percentile of climatology exist across the region, warm cloud depths exceed 10kft, and storm motion vectors parallel the boundary, favorable for training storms. While the heaviest rain is expected across central Iowa and northern Illinois within the vicinity of the boundary and in the region of higher instability, CAM solutions to suggest precipitation makes its way northward into our portions of northeast Iowa and southwest Wisconsin through this morning. Probabilities of precipitation across these regions sit around 40-60% though probabilities for 1 inch or greater are far lower and have trended southward as compared to 12 hours ago, generally 10-20% at most per the 14.00z HREF. That said, there's also remains some uncertainty in how far north rainfall is actually able to make it given the current position of the surface boundary and little in the way of synoptic forcing to shift it northward.

This Afternoon - Saturday: Additional Heavy Rainfall Potential

Through this afternoon, there is some suggestion of scattered shower activity across the area, primarily for those along and south of I- 90, as some areas of maximized 850hPa moisture transport nudge into the Upper Mississippi River Valley. Many CAM solutions do highlight this potential with the 14.00z HREF suggesting probabilities sit around 10-30%. Amounts with any showers would be light, generally on the order of 0.1 inches.

Heading into this evening and tonight, the upper level ridge axis located over much of the United States builds northward slightly while another 500hPa shortwave moves eastward across the Midwest. The boundary associated with this morning's rainfall also remains somewhere across Iowa and Illinois throughout the day, though where exactly it situates itself is somewhat uncertain. Regardless, another round of heavy rainfall looks likely along the boundary as the wave moves through given a very similar set-up to this morning. With the northward trend of the upper ridge and 850hPa moisture transport/warm advection by association, there is some potential for this round of heavy rain to make its way into those areas mainly along and south of Highway 18 (60-80%) and perhaps towards I-90 (30- 60%). That said, the 14.00z HRRR solution suggests that any activity will largely remain south of our area, primarily along and south of I-80. Curious if the majority of the model suites are somewhat too far north with precipitation potential given the several rounds of rain across the region over the last few days and a more HRRR-like solution would be more likely, though given the consensus regarding the northward trend, there is currently higher confidence in this more northern solution regarding rainfall potential tonight. Fortunately, amounts look to be far less impressive than they have been for those across central Iowa into Illinois. Probabilities for amounts of 1 inch or more sit around 30-60% in the 14.00z HREF with some members suggesting a few pockets around 2 inches could occur per the LPMM.

Rainfall largely shifts eastward through Saturday morning resulting in primarily dry conditions through the afternoon. However, there is some low potential for some scattered showers through the afternoon hours as another shortwave moves through the region.

Sunday - Mid Week: Briefly Drier, Additional Shower/Storm Chances

The upper level ridge begins to break down and retrograde on Sunday as a jet streak and associated trough along the US/Canada border translate eastward. A weak surface front moves through the Upper Midwest along with these upper level features while high pressure sinks southward behind the front. Can't completely rule out some scattered showers south of I-90 Sunday afternoon as this boundary moves through the region, though there's quite a bit of discrepancy within the ensemble suites as far as timing and location of precipitation is concerned. Because of this, the 14.01z NBM suggests probabilities for precipitation during this period are 20-30%. Heading into Sunday night and Monday, a drier period looks to be in store for the region as the high pressure takes a stronger hold over the region, though this will be short-lived as deterministic models suggest another shortwave trough and associated surface front move through the region by the middle of next week bringing additional showers and storms (50-70%).

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1237 AM CDT Fri Aug 14 2026

Mostly VFR conditions present across the region with some patchy fog already building in. Some valley fog will be possible for the KLSE terminal this morning but uncertainty in the depth of the light wind layer north of the Minnesota state line has lead to varying guidance on the intensity of valley fog. Have included some IFR visibilities for now but will continue to monitor observations (upstream as well) through the night to see if amendments may be needed. VFR conditions should prevail from mid morning through the afternoon with east/southeast winds gusting to between 15-20 kts for a few hours. Areas of rain look to build north into the evening, bringing low MVFR/IFR stratus with it. Actual rain chances look better across Northeast Iowa and portions of Southeast Minnesota so have gone prevailing at KRST with PROB30s for KLSE. Widespread IFR to LIFR CIGs will be expected overnight tomorrow night just beyond the end of the forecast period.

ARX WATCHES/WARNINGS/ADVISORIES

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