Area Forecast Discussion

KEY MESSAGES

- Light to moderate rain will exit by mid to late morning, followed by breezy west winds gusting 20 to 30 mph this afternoon.

- Hazardous marine conditions with gale-force gusts on Green Bay and Lake Michigan will transition to Small Craft Advisories later this morning. A dangerous rip current risk along Lake Michigan beaches will continue through this afternoon.

- A stronger system brings widespread rain late Friday into Saturday, with a 40 to 50 percent chance of rainfall exceeding 1 inch across much of north-central and northeast Wisconsin.

DISCUSSION

Issued at 133 AM CDT Tue Sep 15 2026

A potent surface low pressure system centered over southern Manitoba early this morning is tracking northeast toward Hudson Bay, pulling a cold front eastward across Minnesota while a warm front lifts northward into Iowa. Aloft, a strong 50 to 60 knot low-level jet directed into northeast Wisconsin has generated widespread showers and scattered embedded thunderstorms early this morning. Latest radar imagery and surface observations confirm a swath of 1 to 3 inches of rain, with localized reports exceeding 3 inches, extending from Portage and Waushara counties northeastward into Outagamie and Brown counties. Although local county dispatch reported no widespread flooding overnight, radar estimates and private weather stations indicated rainfall rates exceeding 6-hour flash flood guidance, maintaining a localized urban and small stream flooding risk early this morning. Will maintain the Flood Advisory for east-central WI until expiration. As the low- level jet veers eastward, the heaviest precipitation is shifting south and east of the area.

Light to moderate rain today through Wednesday Night... Light to moderate showers along with isolate storms will linger through mid to late morning until the cold front sweeps across the area. Additional rainfall amounts up to 0.50 inches will be possible across east- central and northeast WI. Strong boundary layer mixing behind the front will yield clearing skies and breezy west winds this afternoon, with frequent gusts of 20 to 30 mph expected before winds diminish rapidly near sunset.

Surface high pressure building across the northern Great Lakes will bring dry and tranquil weather for tonight and Wednesday. Radiational cooling beneath clear to partly cloudy skies and light winds will promote the formation of patchy ground fog late tonight into early Wednesday morning, particularly across far northern Wisconsin. High temperatures Wednesday will be seasonable, reaching the upper 60s to low 70s. As the frontal zone slowly returns north Wednesday night, elevated warm advection will bring a 30 to 50 percent chance of light showers to central and east- central Wisconsin. However, moisture availability is modest and elevated instability reaches only 100 to 200 J/kg, keeping the probability of rainfall exceeding 0.50 inches under 10 to 20 percent in the southern Fox Valley, with no heavy rain impacts anticipated.

Widespread rain late Friday into Saturday... A more dynamic weather system is forecast to impact north-central and northeast Wisconsin late Friday into Saturday as a shortwave ejects from the western United States trough. Supported by a 40 to 50 knot low-level jet and precipitable water values rising to around 1.70 inches (roughly 95 percent of seasonal normal), widespread showers and embedded thunderstorms will spread across the region. Model guidance indicates a 40 to 50 percent probability for 24-hour rainfall amounts to exceed 1 inch across much of the area from Friday night through Saturday morning. Elevated instability remains limited with Most Unstable CAPE generally under 500 J/kg, keeping the severe thunderstorm risk low. Forecast predictability decreases markedly Sunday into Monday depending on how quickly the main western trough moves eastward, but lingering mid-level energy will maintain a 20 to 30 percent chance of showers through Sunday.

AVIATION

for 06Z TAF Issuance Issued at 133 AM CDT Tue Sep 15 2026

Rain and scattered thunderstorms, some with heavy rain, will gradually end from northwest to southeast overnight into early Tuesday morning. VFR CIGS will steadily fall into the IFR/MVFR category from west to east through the overnight. Some fog may form late north-central, including at RHI. Conditions will gradually improve to VFR by Tuesday afternoon.

Concerning winds, south to southeast winds with gusts 20-30 kts are expected at times through the night as winds veer southwest. Low-level jet up to 50 kts will be present most of the night, leading to LLWS at all TAF sites. The cold front will push across the area late tonight into Tuesday morning, with gusty west winds lingering behind it into Tuesday afternoon. Winds will become light on Tuesday evening.

MARINE

Issued at 133 AM CDT Tue Sep 15 2026

Hazardous marine conditions remain present early this morning with gale force gusts measured at Sheboygan Light to the northern Lake Michigan buoy. These gale force gusts look mainly confined to Lake Michigan. Southerly wind gusts up to 35 knots will subside through early morning as the cold front approaches and the pressure gradient relaxes somewhat. Gales will expire by 7 AM CDT, giving way to Small Craft Advisories across all nearshore waters through the afternoon as winds shift west at 15 to 25 knots. Additionally, residual high wave action along Lake Michigan beaches will create a high risk of dangerous rip currents through this afternoon, supporting an active Beach Hazards Statement for the shoreline of Door, Kewaunee, and Manitowoc counties.

GRB WATCHES / WARNINGS / ADVISORIES

Beach Hazards Statement through this evening for WIZ022.

Beach Hazards Statement through this afternoon for WIZ040-050.

MARINE...Gale Warning until 7 AM CDT this morning for LMZ521-522- 541>543. Small Craft Advisory from 7 AM this morning to 4 PM CDT this afternoon for LMZ521-522. Small Craft Advisory from 7 AM this morning to 7 PM CDT this evening for LMZ541>543.