Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
444 FXUS63 KMKX 260957 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 457 AM CDT Sat Sep 26 2026 .KEY MESSAGES... - Patchy fog continues through dawn before dissipating. Some pockets may become dense. - Temperatures within a couple degrees of normal over the next several days. - Chances for rain and a few storms return Tuesday into Tuesday night. && .UPDATE... Issued 455 AM CDT Sat Sep 26 2026 Patchy fog has formed over parts of southern Wisconsin this morning. Some pockets have become locally dense. This fog should continue through dawn before daytime mixing causes it to dissipate. Otherwise expect a mix of sunshine and high clouds today as some WAA moves overhead. Temps will be pleasant in the mid to upper 60s with light winds. CMiller && .SHORT TERM... Issued 1000 PM CDT Fri Sep 25 2026 Saturday through Monday: With some gaps forming in the cloud cover, and radiational cooling already sending a few METAR sites to saturation, some patchy ground fog is possible overnight into early Saturday morning. Nothing particularly widespread is expected given the occasional upper-altitude cloud cover and very dry boundary layer, mainly just the most susceptible low-lying marshy areas and river valleys expected to see this fog. High pressure remains dominant over southern Ontario Canada and the Great Lakes through the rest of the weekend and into early next week, slowly weakening with time. Near normal temperatures and predominantly dry weather is expected through the period, with highs in the mid to upper 60s this weekend and roughly 70 degrees on Monday. Lows will be around 50 degrees, locally cooler in some areas (mid 40s). A light northeast or southeast breeze across the region at times (generally 10 MPH or less), otherwise practically calm. Our best shot at a stray rain shower this weekend would be Saturday night into Sunday morning (10-15% chance), mainly west of a Janesville to Green Lake line as an additional round of mid-level WAA and cyclonic flow aloft attempts to push east into southern WI. Low-level dry air should evaporate most of it. Sheppard && .LONG TERM... Issued 1000 PM CDT Fri Sep 25 2026 Monday night through Friday: The aforementioned high pressure shifts into the Ohio Valley into Tuesday. Meanwhile, a positively-tilted upper trough digs east from Nevada into Utah, allowing diffluent upper-level flow to overspread the Great Plains and form broad low pressure at the surface. Southerly WAA will develop between the two pressure systems Tuesday, driving rain chances that build west to east into southern WI through the day. Widespread 50-65% rain chances are then forecast into Tuesday night (due to potential for a LLJ to form overhead and reinforce the rain showers). Instability is looking very limited for now, but a few rumbles of thunder can`t be ruled out Tuesday night. Some of this rain could then linger into Wednesday morning. From midday Wednesday onwards, predictability remains very low at this time; ensembles members continue to disagree on whether the aforementioned upper trough will remain an open wave (and track faster) or close off into a pseudo "upper low" (and track slower). Even amongst ensemble members that agree on the phase of the trough, there is considerable variability on the track of any attendant surface low pressure. 500mb cluster analysis reveal even greater ensemble dispersion regarding the longwave trough/ridge pattern of the polar jet along the US / Canada border. In other words, the central CONUS as a whole is in for active weather (rain and thunder) mid to late next week, but whether or not that specifically includes southern WI (or sets up further south) is to be determined. On the bright side, thunder potential can generally be limited to "slight chance" in the forecast for now, given that GEFS instability plumes are predominantly centered well south of our region. Sheppard && .AVIATION... Issued 456 AM CDT Sat Sep 26 2026 Patchy dense fog continues until after dawn with vis down to 1/4SM in isolated spots. After the fog dissipates, expect VFR conditions through today and light east to southeasterly winds. CMiller && .MARINE... Issued 1000 PM CDT Fri Sep 25 2026 Open Waters / Synopsis: High pressure around 30.3 inches will linger over southern Ontario Canada and the Great Lakes through the weekend and into Monday, gradually weakening to 30.1 inches. Quiet weather expected through said period, with light northeast to southeast winds (light and variable at times). High pressure will progress into the Ohio Valley early Tuesday, allowing winds to turn south and increase as low pressure approaches from the west. Nearshore Zones: Breezy south winds and building waves are forecast Tuesday night through Wednesday. Conditions could potentially become hazardous to small craft. 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