Marine Weather and Tide Forecast for Spring Green, WI

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 313 PM CST Mon Dec 15 2025

VFR ceilings are expected to continue across the area through tonight. However, areas of fog may develop across southwestern to south-central Wisconsin overnight as winds diminish and moisture increases across the region. Currently remain uncertain in potential for dense fog, but confidence has increased in at least MVFR conditions from MSN to JVL south and westward. Adjustments will be made as necessary for TAF purposes tonight. Winds will become southwesterly and begin to increase early Tuesday morning, with gusts of 20 to 25 kt expected starting midday Tuesday. This will help to reduce fog density across the region, but will also bring in a more moist airmass over snowpack. Therefore, may see additional drops in visibility lingering into Tuesday and even Tuesday night. Gusty winds will continue through Tuesday night, with a cold front shifting winds to northwesterly and bringing an end to any lingering fog concerns.

MH

MARINE
Issued 313 PM CST Mon Dec 15 2025

Southwest wind will continue to diminish this evening into tonight as a weak low over Lake Superior moves northeast. Light south to southwest winds are expected through Tuesday morning before increasing ahead of approaching strong low pressure. This low will move east across Canada 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 as the low passes to the north. A Gale Warning is in effect for the northern third during this time. In nearshore regions, a Small Craft Advisory is in effect.

A cold front will cross the lake Tuesday night with winds veering to westerly behind the front. Gusty 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 southerly and remain light Wednesday morning before increasing. Strong southerly wind will develop ahead of the low Wednesday night. Strong winds will veer Thursday morning as another cold front crosses the lake and becomes west- northwesterly. Southerly gales Wednesday night and west- northwest gales Thursday afternoon through Thursday night are likely. Brief periods of gales are possible in nearshore regions as well.

Patterson/MH

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.