Marine Weather and Tide Forecast for Williams Bay, WI

SHORT TERM
Issued 339 AM CDT Mon Apr 21 2025

Today through Tuesday night:

The surface low and accompanying mid-level shortwave trough continue to lift across central WI and into northern portions of Lake Michigan through the morning. The bulk of the shower activity has already pushed through overnight and a dry slot is limiting additional widespread coverage from developing.
However, sporadic/scattered light shower chances will linger through daybreak before diminishing by mid morning hours as a cold front pushes through the area. Looking at drier conditions behind the cold front for the rest of day, but given the low deepening to sub 1000mb, the pressure gradient will remain tight across southern WI. Thus resulting in stronger westerly gusts of 20-30 mph through the afternoon with the strongest gusts possibly even approaching 35-40 mph for east-central portions of WI.

Otherwise, winds will diminish through the evening as high pressure and upper-level ridge quickly traverses just south of the area. Should see light winds and cool conditions overnight with lows dipping into the mid to upper 30s.

Then a mid-level shortwave trough from the northern Plains is progged to follow right behind the ridge and push into the Upper Midwest later tonight/early Tuesday morning. This system will the focus for our next round or two of showers/storms. The associated surface low paired with the upper-level wave is expected to break away and meander up the ND/MN border through Tuesday. Ahead of it a wing of low-level WAA will lift up the Upper Mississippi River Valley Tuesday morning. The low-level dynamics paired with a swath of MUCAPE 500-750 J/kg, steep mid- level lapse rates (7.5-8.0C/km), nose of 850mb LLJ, and increased deep layer shear looks to support elevated convection.
With the morning round of elevated storms, could see a few stronger and even an isolated severe storm or two capable of producing large hail develop across southern WI daybreak through the early afternoon.

There may be additional round of showers and convection to develop later in the afternoon and early evening if the surface warm front and nose of the higher surface moisture lifts north of the WI/IL border. There is a bit more uncertainty with this round as the environment may not have enough time to recover after the morning round of storms along with easterly flow off of the lake preventing it from lifting. However there are hints that it may have enough momentum to lift north into our CWA especially for south-central and southwestern portions. If the warm front is able to make it north of the Cheddar Curtain, then could see more surface based convection develop, which may be capable of producing hail and gusty winds. Again, uncertainty remains greater as it looks to be narrow window that favors convection development into the evening hours.

Wagner

LONG TERM
Issued 339 AM CDT Mon Apr 21 2025

Wednesday through Sunday:

Wednesday morning is expected to remain dry at this time as another surface warm front sharpens just south of the border through the daytime hours. By Wednesday evening, thunderstorm activity is expected to blossom and eventually move into southwestern WI Wednesday night into Thursday following warm advection of the LLJ northward. By Thursday morning, most of the shower activity with the front should be north of our CWA, and we stand to remain dry most of the day given most of the better forcing for ascent will be either north or west of us. Thursday night, however, a slow moving frontal boundary is expected to move toward western WI bringing chances for overnight showers and storms into Friday morning. Models depict the boundary lingering enough on Friday to allow some destabilization and some more shower and storm formation Friday afternoon over southeast Wisconsin before the front clears the state.

Beyond, high pressure looks to take hold following the frontal passage with seasonable temperatures in the upper 50s to low 60s remaining over the region.

CMiller

AVIATION
Issued 339 AM CDT Mon Apr 21 2025

Widespread MVFR and pockets of IFR ceilings sit over southern WI this morning associated with the surface low. Expecting the low to lift northeast through the day, but lower ceiling are progged to linger through the remainder of the morning and into the afternoon before clearing by this evening. Additionally will see breezy southerly winds turn westerly and increase through the morning as well. Looking at gusts of 25-30kt this afternoon.
Conditions improve and winds ease by the evening as high pressure quickly pushes through the area overnight. Then another system treks into the area from the northern Plains and will bring another period of lower flight conditions along with increased shower and thunderstorms chances Tuesday morning.

Wagner

MARINE
Issued 339 AM CDT Mon Apr 21 2025

Low pressure will continue north-northeast and track across northern Lake Michigan through today and moving to north of Lake Huron tonight. Breezy southeasterly winds will quickly become southerly, then southwesterly after daybreak, with patchy gale force gusts over most of the open waters through today. A Gale Warning remains in effect from 7AM to 7PM CDT for areas south of the center of the low pressure.

Winds then become westerly late this afternoon and evening and will gradually ease overnight into Tuesday morning. Light northwesterly will begin to turn through Tuesday afternoon as the surface high pressure passes pushes east of the Lake. Winds then increase and become southeasterly Tuesday afternoon/evening ahead of a warm front lifts and stalls across the southern third of Lake Michigan Tuesday evening. Lighter winds are expected for the middle of the week as high pressure builds in from the west.

CMiller/Wagner

MKX WATCHES/WARNINGS/ADVISORIES
WI...None.
LM
Small Craft Advisory
LMZ643-LMZ644-LMZ645-LMZ646 until 7 AM Monday.

Gale Warning...LMZ080-LMZ567-LMZ643-LMZ644-LMZ645-LMZ646- LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-LMZ870- LMZ872-LMZ874-LMZ876-LMZ878...7 AM Monday to 7 PM Monday.