Sun Prairie, WI Weather

Key Messages

- Lingering fog along the immediate Lake Michigan shoreline through mid-afternoon (~3 PM).

- Above normal temperatures & rain-free conditions continue into the weekend.

- Temperatures closer to normal next week, with chances for rain northwest Monday night/Tuesday & areawide at some point Wednesday through Friday.

Short Term

Issued 200 PM CDT Fri Oct 23 2026

This Afternoon through Saturday Night:

Synopsis/Mesoanalysis: Low pressure is centered over northeastern Montana this afternoon. Water vapor imagery places an upper trough over the north-central Rocky Mountains. The trough will eject northeast into the Canadian Prairies tonight, allowing the surface low to concurrently deepen and build northeast. Both the low and the upper trough will continue on toward the Hudson Bay Saturday night, pulling a cold front into the western Great Lakes in the process. The front will remain north of the region through Saturday night/the conclusion of the short term period, with prefrontal southwesterly winds maintaining above normal high temperatures.

This Afternoon: Areas of fog will continue to linger along the immediate Lake Michigan shoreline through ~3 PM. Persistent southeasterly surface flow has helped maintain marine fog longer than modeled by forecast guidance, with the western edge of the fog bank leaking into portions of the immediate lakeshore areas in Ozaukee, Milwaukee, Racine and Kenosha Counties. Abrupt drops in visibility have been noted in these areas, with drastic improvements to full visibility occurring just a few miles inland. Given the impactful but limited areal scope of the inland fog, have handled pockets of lakeshore fog with a Special Weather Statement through 3 PM. With satellite trends showing steady erosion of the responsible marine fog bank, not expecting the need to extend this statement beyond 3 PM or upgrade to any Dense Fog Advisories at this time. Slow down, use low beam headlights, and allow for extra following distance if traveling lakeside through early afternoon.

Tonight: Will need to watch for some patchy fog across far northeastern parts of the CWA. More widespread fog potential should be curbed by increasing southerly winds as the surface pressure gradient tightens ahead of the developing Canadian Prairies surface low. Will be monitoring visibility trends. Increasing warm advection in the 925-700 mb layer will support increasing mid-upper level clouds, with any appreciable rain chances expected to remain over northern Wisconsin. Will be monitoring for any possible changes into this evening.

Quigley

Long Term

Issued 200 PM CDT Fri Oct 23 2026

Sunday through Friday:

Synopsis: The cold front lingering to the north of the region will progress through the area on Sunday, slowly washing out in the process. North-northeast winds will become established in the wake of the boundary, and will be reinforced into Monday as high pressure moves into Ontario from the Canadian Prairies. Affiliated with upper troughing currently moving into southern California, an upper wave will slowly eject from the Rockies into the Northern Plains on Monday. The wave will deamplify as it tries to work toward northern Wisconsin on Tuesday, decaying over the general vicinity Tuesday night. Rain is possible in the vicinity of the upper wave Monday night into Tuesday, particularly over the northwest half of the area. Uncertainty increases---both in deterministic and ensemble guidance---moving into the mid-late portions of next week, with an upper trough & affiliated surface front expected to move through the western Great Lakes at some point during the Wednesday-Friday time frame. Amplitude, strength, and precise passage timing of the features remain uncertain, making it difficult to offer exact details regarding precipitation chances and any post-frontal temperature drops at this time. Will continue to provide updates as trends clarify over coming forecasts.

Monday night into Tuesday: Will be monitoring for possible rain chances ahead of an approaching upper shortwave. General consensus depicted in guidance is for the wave to induce weak surface cyclogenesis from the Dakotas into Iowa, with rain blossoming along the northeast periphery of the surface low where 1) mid-level DPVA and 2) frontogenesis will be maximized in the 1000-700 mb layer. Some uncertainty remains regarding where exactly these forcing mechanisms will overlap, with the strength of high pressure in the Ohio Valley being the primary northwest-southeast modulator of precip placement. As of this forecast, appears that the northwest half of the area will be most favored for precip, as this is where separation from the Ohio Valley high pressure will be greatest. Blended precip probability solution from the NBM thus appears reasonable at this time, and has been largely maintained in the afternoon update. Will continue to provide updates in coming forecasts.

Wednesday through Friday: Expecting that rain chances & cooler temperatures will return areawide at some point as an upper trough and cold front move through the region. Primary question is that of timing, with a number of different solutions evident in current global forecast guidance. As such, blended precip probabilities from the current NBM depict a wide range of chance (~20-40%) rain potential during this portion of the period, when in reality a narrower window of widespread rain potential will emerge as the forecast picture clarifies into next week. With a multitude of potential solutions in place & none more favored than the other, have maintained the wider window of precip potential in the afternoon update. Will continue to monitor trends into next week.

Quigley

Aviation

Issued 200 PM CDT Fri Oct 23 2026

Predominantly VFR flight categories prevail through the period at all terminals. Earlier day fog has largely dissipated region-wide, though VIS reductions continue to linger along the immediate Lake Michigan shoreline. While said reductions have remained east of MKE and ENW, they have resulted in reports of FEW clouds based near FL010 at MKE. Have accounted for these trends near-term at MKE, with the expectation for VIS reductions to remain largely in place/without any inland expansion prior to their dissipation later this afternoon. SCT to BKN mid-upper level clouds will gradually build in tonight into Saturday as a disturbance moves from the Northern Plains toward Lake Superior. Not anticipating any precipitation with this disturbance at this time.

Quigley