textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Patchy fog and low stratus may form overnight into Tuesday morning, though uncertain if they will occur and how widespread they may be. - Above average temperatures develop Tuesday afternoon through Thursday, with highs in the middle to upper 30s.

- The next chances for precipitation (60 to 80 percent) develop late Wednesday night into Thursday morning. Initial stages may be a mix of snow and rain, becoming all rain by midday Thursday. A transition to light snow is expected Thursday evening (~20% chance).

- Significantly colder temperatures in the single digits expected to develop Thursday evening, freezing any surfaces that remain wet from Thursday's rain and snow.

UPDATE

Issued 930 PM CST Mon Dec 15 2025

Skies have cleared over most of the area this evening, with winds decoupling. There is an area of low clouds that may sag southward into Sheboygan County and nearby areas late this evening into early Tuesday morning. The calm winds and clear skies should allow for small temperature and dew point depressions over the snowpack, which may lead to patchy fog and possibly low stratus development overnight over south central Wisconsin.

Confidence is low in how widespread this may be, and if any dense fog may form, as some weak warm air advection should develop overnight into Tuesday morning with light south winds. This may help with fog formation, but still have uncertainty in this happening without a good push of moisture from the south.

For now, left the forecast for patchy fog for the most part in south central Wisconsin overnight into early Tuesday morning. Lows will depend on if the low stratus develops overnight or not. If these low clouds and fog develops, the lows should hold steady near current values. Otherwise, may need to adjust lows down a bit.

Wood

SHORT TERM

Issued 313 PM CST Mon Dec 15 2025

Tonight through Tuesday night:

High clouds and southwesterly breezes will continue throughout tonight. Expecting highs in the low 20s this afternoon, with lows in the upper single digits to low teens overnight.

Light and variable winds are expected overnight, which may lead to areas of fog in southwestern to south-central Wisconsin overnight as temperatures fall toward the dew points. With WAA occurring in the mid levels of the atmosphere during the overnight hours as well, any mixing from aloft will actually serve to increase dew points at the surface, allowing any fog that does develop to linger through the overnight hours. Inversion is expected to be very shallow, with snowpack expected to be the main influence on how low temperatures can fall tonight. Still some uncertainty with fog density, especially going into the early morning hours as mixing increases. Will monitor through tonight for areas of potentially dense fog, but currently most concern is in far southwestern Wisconsin.

As mixing increases into Tuesday, expecting fog to generally rise to become low clouds. However, with WAA over frozen ground, may see reduced visibilities continue through at least the morning hours and potentially even later. Highs on Tuesday are expected to be in the mid-30s, leading to snow melt and therefore inclusion of additional water vapor into the air. Will continue to update the forecast as confidence in the evolution of this setup increases.

Overnight Tuesday, temperatures fall back toward dew points again, with lows in the mid-20s. Southwesterly winds will shift northwesterly overnight, so any fog development overall is less likely than tonight.

MH

LONG TERM

Issued 313 PM CST Mon Dec 15 2025

Wednesday through Monday:

Northwesterly breezes as low pressure exits to the northeast, then a ridge of high pressure will nudge northward again during the afternoon hours, allowing for light and variable winds, decreasing sky cover and bringing high temperatures in the mid-30s. Meanwhile, expecting an atmospheric river pointed into the Pacific Northwest to trigger low pressure development in the lee of the Alberta and Montana Rockies. This low is expected to be steered north of the high pressure in the Southeast U.S. Wednesday night into Thursday, keeping southern Wisconsin within the warm sector. A mix of rain and snow is expected (~60% chances) early Thursday morning along a prefrontal precipitation region, likely transitioning to all rain (60-80% chance of precipitation) by midday as gusty southwesterly winds bring strong WAA to the region. Expecting highs around 40 degrees.

As low pressure exits into eastern Quebec into Thursday night, expect winds to shift to northwesterly, with intense CAA bringing a return to all snow (~25% chance of precipitation) and potential for a rapid refreezing of any remaining wet roads. Lows Thursday night are expected to be in the single digits. Only light snow accumulations are expected, as the low and forcing exit eastward. Remaining snow showers exit by Friday morning.

An up-and-down pattern continues Friday through Monday as the atmospheric river continues to impact southern British Columbia and the Pacific Northwest, allowing for multiple clipper systems to propagate across southern Canada and the northern Great Lakes regions through the weekend. With high pressure remaining dominant over the Eastern Seaboard, expecting the majority of precipitation with these systems to remain across northern to central Wisconsin. However, multiple shifts between southerly and northerly winds will keep temperatures variable through the weekend into early next week.

MH

AVIATION

Issued 930 PM CST Mon Dec 15 2025

Skies have cleared over most of the area this evening, with winds decoupling. There is an area of low clouds around 2500 feet AGL that may sag southward into the Sheboygan terminal late this evening and overnight. Otherwise, the calm winds and clear skies may allow for patchy fog and possibly low stratus below 1000 feet AGL overnight over or just southwest of the Madison and Janesville terminals.

Confidence is low in how widespread any fog and low clouds may be overnight into Tuesday morning, and if any dense fog may form. Would need a good push of moisture from the south, which is quite uncertain. For now, may mention 3 to 5 mile fog in Madison and Janesville terminals overnight into early Tuesday morning. The low ceilings may remain to the southwest of those areas.

Gusty southwest winds are expected by late Tuesday morning through the afternoon and evening. Middle to high clouds should push through at times. A cold front will push through the area later Tuesday night, with winds shifting northwest behind it.

Wood

MARINE

Issued 930 PM CST Mon Dec 15 2025

West to southwest winds will continue to diminish overnight, as weak low pressure around 29.9 inches over Lake Superior moves northeast. Light south to southwest winds are expected Tuesday morning, before increasing ahead of an approaching strong low pressure around 29.0 inches.

This low will move east from central Saskatchewan into northern Ontario Tuesday afternoon through Tuesday night. Southwest winds will increase across the lake, with gales likely across the northern third of the lake, as the low passes to the north. A Gale Warning is in effect for the northern third of the lake during this time. A Small Craft Advisory is in effect for the nearshore waters of Lake Michigan as well.

A cold front will cross the lake Tuesday night, with winds veering to west behind the front. West to northwest winds will be short lived, and will diminish behind the front Tuesday night. Another strong low pressure system is expected to track eastward along the Canadian border Wednesday into Thursday. Winds will turn south and remain light Wednesday morning before increasing.

Strong south winds will develop ahead of the low Wednesday night. Strong winds will veer Thursday morning, as another cold front crosses the lake and becomes west northwest. South gales Wednesday night and west northwest gales Thursday afternoon through Thursday night are likely over the open waters. Small Craft Advisory level winds and waves are also anticipated over the nearshore waters.

Patterson/MH/Wood

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Gale Warning...LMZ261-LMZ362-LMZ364-LMZ563...10 AM Tuesday to 3 AM Wednesday.

Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...9 AM Tuesday to 6 AM Wednesday.