Area Forecast Discussion

KEY MESSAGES

- Several rounds of moderate to locally heavy rainfall from midday today through early Tuesday morning. Widespread total rainfall amounts around 1" with localized pockets of 2-3" could result in some river rises and flooding of poor drainage locations.

- Additional rounds of heavy rainfall are possible Thursday through the weekend. If these storms track over the same areas, the risk for flooding could increase.

- Seasonal temperatures for the upcoming work week with highs in the upper 60s to mid-70s.

DISCUSSION

Issued at 1120 AM CDT Mon Sep 14 2026

This Afternoon - Tuesday Morning: Periods of Heavy Rain

Multiple waves of moderate to heavy rainfall affect the local area over the next 24 hours. This first broad but not necessarily intense wave of rain currently upstream over southwestern MN and western Iowa lifts into the region through the day as the associated zone of theta-e advection likewise lifts northeast. While the mid-level tropical Pacific moisture river will be in place by midday, the lower tropospheric Gulf airmass lags behind by 4-6 hours, resulting in deep tropical rainfall processes not being fully realized until late this afternoon and tonight.

This late afternoon to overnight timeframe--with PWATs near 2" and deep warm cloud depths of 10-12 kft (climatological highs for this time of year)--is the period worth watching for higher rainfall rates and potential flooding impacts. The good news is that soils are dry heading into this event and the rainfall looks to be on the progressive side with enough breaks between each round to reduce the overall risk of any flooding. By Tuesday morning, there is a solid signal in the CAMs that most areas should see total rainfall amounts around 1" with localized pockets of 2-3", with these corridors driven by the tracks of the individual small convective cells containing the higher rain rates (a 20-30% shot that a given location will fall under one of these higher rainfall swaths). A cold front pushing southeastward overnight will also aid in keeping the heavy rain corridors fluid in space and gradually shifting off to the southeast of the area by mid- morning Tuesday.

Later in the Week: The Rain Returns, Could be Heavy

Broad subtropical upper tropospheric ridging builds across the southern and southeastern U.S. in the wake of our passing shortwave tonight into Tuesday, lingering well into the weekend. This feature and the attendant surface ridge act to keep the lower tropospheric baroclinic zone from sliding too far south of the forecast area for Tuesday into Wednesday, with the surface to 700-mb front likely pivoting over northern Missouri and southern Iowa Tuesday night as a northern stream wave approaches along the U.S./Canadian border and lee cyclogenesis takes place along the Front Range. The mid-tropospheric front returns to the region by Wednesday afternoon, which could serve to generate elevated showers. Similar to this afternoon, the deeper moisture lags to the south and doesn't arrive until Wednesday night into early Thursday. Therefore, any rain on Wednesday does not look to be of much impact.

The zonal flow and subtleties of any upper level forcing make the timing and amounts of any rainfall for Thursday difficult to nail down. Nevertheless, the thermodynamic environment will be primed and ready to produce efficient rainfall rates should the forcing come to fruition. At this point, the threat for heavier rainfall is progged to be south of I-90.

There is an increasing signal for Friday and the weekend that the upstream pattern amplifies as a cutoff low begins to advance eastward out of California. This facilitates a greater risk for heavy rainfall, which will be dictated by the placement of near surface baroclinic zone--lifting northward during this time towards central Minnesota/Wisconsin. The recent EPS/GEFS runs are honing in on this Friday into Saturday period for the next widespread heavy rain potential with 40-50 percent of the EPS members exceeding 2 inches for total rainfall amounts and upper end ensemble members exceeding 3-4 inches. Given the strength of this signal and the stronger synoptic forcing at play, it is more of a question of where, rather than if, this heavy rain occurs. Such details will be refined over the next few days given that this event is still 5-6 days out. One cannot also fully rule out the risk for stronger storms on Friday afternoon and evening depending, again, on how far north the surface front tracks.

What we can say with higher certainty is that temperatures should remain solidly in the 60s and 70s for highs through the week, a solid taste of late summer/early fall weather.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1243 AM CDT Tue Sep 15 2026

Showers and storms continue for portions of southwest Wisconsin and northeast Iowa through the early morning hours before exiting by mid-morning. Some lingering showers are possible in portions of northeast Iowa and far southwest Wisconsin through the early afternoon, however those chances will continue to dip further south as the morning and afternoon progress. MVFR to IFR CIGS and visibilities will move into most locations during the early morning hours and then exit southwest Wisconsin by mid- morning. Southerly winds will gradually shift more westerly and then northwesterly as a front moves through between 12 and 16Z. Expect wind gusts between 25 and 30 mph when the front moves through then for the remainder of the day the northwest winds will be sustained at 5 to 15 mph. Wind shear is also possible before the frontal passage as strong westerly winds at 2000ft will be around 35 to 45kts over the next few hours.

ARX WATCHES / WARNINGS / ADVISORIES

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