textproduct: Milwaukee/Sullivan

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.

UPDATE

Issued 946 PM CDT Wed Sep 17 2025

No major updates to the going forecast. A few areas of patchy fog are possible in central Wisconsin and the Wisconsin River Valley areas, but confidence remains low as cloud cover increases and prevents temperatures from falling to the dewpoints in those areas. Main concern will be low-lying regions.

MH

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 946 PM CDT Wed Sep 17 2025

Expecting calm winds and VFR cloud cover tonight. A few pockets of patchy fog reducing visibility to 4-5 SM are possible late tonight into early Thursday morning, primarily from MSN westward and in central Wisconsin. Any fog will dissipate shortly after sunrise. VFR conditions then continue through the remainder of Thursday, although a very isolated shower or thunderstorm cannot be ruled out. Expect light southeasterly winds becoming easterly into Thursday evening.

MH

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.