623 FXUS63 KMKX 172013 AFDMKXArea Forecast Discussion National Weather Service Milwaukee/Sullivan WI 313 PM CDT Wed Sep 17 2025
.KEY MESSAGES...
- Low chances (15% or less) for a stray shower of thunderstorm west of a Monroe / Madison / Fond du Lac line thru Thursday.
- Shower and thunderstorm chances edge eastward into Friday, with more widespread 20-50% chances arriving this weekend.
&&
.SHORT TERM... Issued 300 PM CDT Wed Sep 17 2025
Tonight through Thursday night:
The upper level ridge maintains its foothold in the region through thursday, hanging on to much of it`s amplitude as well. With weak surface pressure developing over South Dakota through Thursday, the majority of the associated showers and thunderstorms are expected to remain well west of our region, with very low (generally < 15%) chances for these to push in west of Monroe / Madison / Fond du Lac.
Expecting dry weather and occasional scattered mid to high altitude cloud cover through the short term period. A weak (dry) backdoor cold front sliding down Lake Michigan Thursday may briefly amplify the lake breeze circulation, producing a 10 to 15 MPH northeast breeze along the shoreline and bordering counties. Other than that, winds are nearly calm.
Temperatures on Thursday similar to today, with mid 80s inland and cooler temps by the shoreline thanks to the aforementioned lake breeze.
Sheppard
&&
.LONG TERM... Issued 300 PM CDT Wed Sep 17 2025
Friday through Wednesday:
The ridge finally begins to break down into Friday, allowing shower and storm chances (15-30%) to push into the western half of the CWA Friday (along and west of a Janesville to Fond du Lac line). The surface low pressure to our west decays, yet the upper level low and remnant surface pressure trough / confluence axis will drift eastward through our region into this weekend, leading to higher and higher (20-50%) chances for showers and thunderstorms. The lack of dynamics with this setup would suggest sub-severe storms, though lightning is certainly still on the table. Synoptic easterly winds off the lake Friday help keep temperatures in check (70s east to around 80 inland), and though winds veer south into the weekend, the cloud cover helps to hold temperatures around 80 (all areas).
Low predictability in the forecast for the early half of next week (Mon thru Wed). Some models / ensemble members hint at the potential for a cutoff low pressure system to extend the shower / thunderstorm chances through this period, while others allow for a more progressive pattern, with subsidence and dry wx.
Sheppard
&&
.AVIATION... Issued 300 PM CDT Wed Sep 17 2025
Dry weather and VFR through tonight, with nearly calm wind. A stray shower or weak thunderstorm cannot be completely ruled out for far southwestern / western Wisconsin. Patchy ground fog may occur in central / east-central Wisconsin tonight, as well as the Wisconsin River Valley, though some scattered high- altitude clouds are expected to prevent it from becoming prevalent / widespread.
Winds remain light into Thursday, with continued VFR. A very weak (dry) backdoor cold front is expected to join forces with the lake breeze circulation Thursday afternoon, which may create a 10-15kt northeast breeze for lakeshore terminals Thursday afternoon.
Sheppard
&&
.MARINE... Issued 300 PM CDT Wed Sep 17 2025
Low pressure around 29.4 inches will continue eastward across northern Quebec Canada today, with high pressure around 30.3 inches moving into Ontario through Friday.
Winds remain nearly calm through tonight, with a light northeast wind developing over the northern half of the lake in response to a weak backdoor cold front. This front sags southward across the rest of the lake Thursday, bringing roughly 15 kt north to northeast winds behind it. Light northeast winds continue into Friday, becoming breezy and veering southeast Friday night through Saturday morning as the aforementioned high pressure system strengthens to around 30.4 inches and approaches southern Ontario/Quebec and low pressure around 29.9 inches moves into the Dakotas / Minnesota. There will be chances for thunderstorms at times this weekend.
Sheppard
&&
.MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. &&
$$
Visit us at weather.gov/milwaukee
Follow us on Facebook, X, and YouTube at: www.facebook.com/NWSMilwaukee www.x.com/NWSMilwaukee www.youtube.com/NWSMilwaukee
NWS MKX Office Area Forecast Discussion