textproduct: La Crosse

KEY MESSAGES

- Mostly dry and cool today with limited potential for scattered storms along southern peripheral counties dependent on exact location of overnight frontal boundary.

- Low-moderate confidence (20-60%) in subsequent precipitation overnight Wednesday into Thursday morning increases in amounts (1" - 2") and confidence (60-80%) Friday into Saturday. Location of highest rainfall rates limits confidence for areal and river flooding (<10%), potentially higher for flashier rivers in northeast Iowa (Turkey) and southwest Wisconsin (Kickapoo) should highest amounts be realized in these spots.

DISCUSSION

Issued at 227 AM CDT Tue Sep 15 2026

Overnight Storms & Heavy Rain Potential:

The low level boundary, evident in a southwest to northwest wind shift on low level VWPs between the Mississippi and Missouri River Valleys, will continue instigating storms along a parallel (southwest to northeast) orientation overnight. A slight eastern shift in the backing wind profiles resulted in the line of heaviest rainfall and strongest storms slowly shifting east of the local forecast area into central Wisconsin through the early in the overnight hours. However, a more northerly component of the trajectory to parent mid-upper level low over southern Canada overnight is gradually decreasing southerly advection of the boundary through Tuesday morning, raising slight concern for reinitiation of storms capable of heavy rain northwest of current (15.08Z) RADAR imagery where heavy rainfall totals nearing 2" have been observed. Therefore, overnight flooding concerns cannot be completely ruled out until the frontal completely exits the area through early Tuesday morning.

Drier & Cool Today, Limited Rainfall Potential:

The aforementioned upper level low eventually abandons the boundary along the southeastern periphery of the local forecast area through Tuesday. Exact southern extent will determine lingering heavy rain potential in select peripheral counties as storms potentially burble along the boundary until anticyclonic flow further shunts moisture southward into Tuesday night. Outside of the select counties in northeast Iowa into far southwest Wisconsin, a drier, cooler upstream airmass, evident in overnight surface dewpoint observations in the mid to low 50s and temperatures from the upper 50s to low 60s at 15.06Z spreads east across the forecast area through today. Daytime temperatures from the upper 60s along our northwestern peripheral counties to low 70s elsewhere expected.

Midweek Heavy Rain & Storm Potential:

Low level anticyclonic flow traverses the forecast area overnight into Wednesday, resulting in return flow returning the warm, moist airmass across the Upper Mississippi River Valley into Wednesday night. Confidence in local precipitation chances remains low- moderate (20-60%) as GEFS (15.00Z) presents a drier solution than the GEPS/EPS due differences in strength of upper level jet streak providing enhanced ageostrophic ascent within the equatorward entrance region, an accompanying lobe of mid level shear vorticity, and entrained drier air in the mid levels according to associated individual ensemble member sounding plumes. Should the stronger forcing solution in the GEPS/EPS come to fruition, another 0.5" - 1" of rainfall will be possible overnight Wednesday into Thursday morning. While overall amounts aren't overly concerning, potential subsequent flooding impacts into the weekend will be impacted by this supplementary midweek rainfall.

Heavy Rain & Flooding Concerns Through Friday:

Synoptic confluence through late week funnels the anomalous moisture in a narrow corridor, similar albeit slightly lower than current areal observations, through Friday into Saturday with LREF probabilities for 2" PWATs decreasing/increasing and shifting south/north in most recent runs of the GEFS/EPS placing temporarily maxima of 40%/70% near the southwestern half of the forecast area. While the longer forecast hour combined with aforementioned low-moderate confidence rainfall midweek limits overall confidence in flooding concerns, LREF sounding plumes suggest anomalous freezing levels and thick warm cloud depths, reraising concern for areal and river flooding potential late Thursday night through Friday into Saturday.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 604 AM CDT Tue Sep 15 2026

Rain continues for areas along and south of I-90 through mid- morning. The rain chances push farther south for the afternoon and evening, however portions of northeast Iowa and far southwest Wisconsin could see some light rain during the afternoon. IFR to MVFR conditions continue through mid-morning until a front passes through and helps to lift our CIGS above 20kft for the rest of the TAF period. Southerly winds will switch to northwest winds as the front passes through this morning. As the front passes through a location, winds may gust up to 25 mph initially then decrease by early afternoon. The northwest winds continue to decrease through the day then turn more northeasterly for the overnight.

ARX WATCHES/WARNINGS/ADVISORIES

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