milan il

- A cold front will bring low chances (10-20%) for showers and storms early this morning with isolated storms possible (20-30%) this afternoon along and south of Highway 34.

- An active pattern is in store next week with multiple rounds of showers and storms likely through Friday. Currently, the greatest severe potential is Monday afternoon and evening where there is a Marginal Risk, Level 1 out of 5, for eastern IA and northwest IL.

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Issued at 1222 AM CDT Sat Sep 12 2026

Storm chances return today as a cold front moves into the area from the northwest. During the morning hours, isolated showers and storms (10-20% coverage) will form along the front across eastern Iowa before fizzling out once they reach the Mississippi River as low-level WAA weakens during the afternoon and the wind shifts from southwesterly to northwesterly. There is some disagreement among CAMs on a possible second round of convection forming over southwestern Iowa and moving eastward with a subtle shortwave in the zonal flow, but current HREF guidance only has a 10-20% chance of this occurring. If any storms do redevelop, frontal placement will also be key in determining the severe potential along and south of Highway 34 as there is going to be a short window where the 250-500 J/kg of SBCAPE and 25-30 knot 0-6-km bulk shear overlap.

Heading into tonight, the cold front pushes into northern Missouri and central Illinois before stalling out, and a weak high pressure positions itself over the Dakotas and Minnesota. Winds will shift to northeasterly as lows drop into mid-50s to low 60s. By Sunday, a longwave ridge builds across the Northern Rockies as another shortwave trough swings into the Great Lakes region. A Front Range low is expected to develop in Colorado in response, enabling a mid-level F-gen band to develop over Iowa on the north side of the stationary front as a stratiform rain shield forms with isolated lightning. There will be a break in the rain heading into Sunday night before storms redevelop Monday morning as the upper level flow becomes southwesterly, converting the stationary front into a warm front.

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Issued at 1222 AM CDT Sat Sep 12 2026

Monday-Tuesday...The longwave ridge over the Northern Rockies shifts eastward over the Mid-to-Upper Mississippi Valley as a closed heights center replaces it over the Northern Rockies. Diffluent flow aloft and strong low-level WAA should support storms (50-80% coverage) along the warm front in eastern Iowa, but limited moisture, especially near the surface, will put a hamper on the coverage (20-40%) across west-central and northwest Illinois. Regardless, the southerly return flow behind the warm front is forecasted to allow dew points to climb back into the upper 60s and low 70s along the cold front diving southeastward as the trough over the Northern Rockies lifts into south-central Canada. After another dry period Monday afternoon, storms will once again redevelop Monday evening along the approaching cold front where a 40-knot LLJ is expected to enhance the low-level shear. Current LREF guidance has the sfc-to-500 mb wind shear vector oriented at a 45-degree angle and close to 35 knots which would suggest a mixed convective mode. However, by the time any convection reaches our CWA, it will likely be in the form of linear clusters, promoting a more damaging wind threat. This is why the SPC has a Marginal Risk, Level 1 out of 5, for severe storms Monday night in our northwestern counties.

By Tuesday, the storms are expected to decrease in intensity along the front as upper-level dynamical support is lost. A weak high pressure is forecasted to slide into Minnesota Tuesday night, reinforcing the northeasterly flow over the CWA and pinning the stationary front in our south. This stationary front will act as the focal point for showers and storms through the middle of next week.

Wednesday-Friday...The entire area will be sandwiched between a ridge over the Southeast and a positively tilted trough over Hudson Bay that extends back towards the Pacific Northwest. This pattern should support diffluent flow aloft over the residual stationary front as rounds of stratiform rain and storms develop along it on Wednesday and Thursday. As the Southeast ridge retrogrades westward, the flow is forecasted to return to a more stable zonal flow as the boundary begins to wash out Friday without any major air mass changes. By the end of the next week though, there is a good chance (50-80%) that areas across eastern Iowa and northwest Illinois will see over 2 inches of rainfall with swaths of 4+ inches possible (20-30%).

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Issued at 621 AM CDT Sat Sep 12 2026

Brief MVFR/IFR vsbys to impact BRL through sunrise. A weak cool front to drop south through the terminals this morning turning winds northwesterly. Some post-frontal MVFR stratus across southeast MN to move south southeast and may clip CID/DBQ this morning. Confidence is highest at DBQ and have included a prevailing group for this occurrence. Current expectations is for this deck to gradually lift to VFR prior to reaching MLI. An occasional gust may occur this afternoon, with VFR conditions.

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IA...None. IL...None. MO...None.

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