Marine Weather and Tide Forecast for Sheboygan, WI

UPDATE
Issued 1030 PM CDT Thu Apr 17 2025

Currently observing a lull in activity as showers / weak thunderstorms push northeast of Sheboygan. Things are looking relatively quiet for the next 2 hours or so as the low-level jet continues to intensify.

Referring to 925-850mb mesoanalysis charts, the LLJ will advect a plume of higher temps / dewpoints into the region later tonight, increasing the HRRR mean MUCAPE to over 1000 joules (with the HRRR producing 1200-1500 joules). After midnight we expect thunderstorms to approach from the west, and between then and the Friday AM commute, the threat for strong thunderstorms with hail as the primary threat (possibly gusty winds) will be present. As is often the case with elevated convection, CAMs are unlikely to help us narrow down this wide time window, until patterns on radar become evident.

Surface WAA ahead of Friday afternoon's cold front then creates a surface-based unstable environment over southeastern WI, creating the Friday afternoon/evening strong storm threat, with wind gusts and hail as equal threats. Front-parallel shear would suggest the environment favors rapid upscale growth of any convection into a line Friday afternoon along the front, yet weak synoptic forcing for ascent (besides the cold front itself)
yields plenty of uncertainty on the exact timing and placement of Convective Initiation (CI), though there is consensus that any storms in southeastern WI would likely grow stronger than elsewhere.

Most models favor late Friday afternoon / early evening CI along the cold front (which could be along a Janesville to Port Washington line, or one county east/west of there depending on which model you choose), with the convection sweeping east with the front thereafter. Models largely depict a cellular convective mode, but as discussed above, the environment, rather, would suggest rapid conglomeration into a line (bolstering the wind threat). Either way, hail and damaging wind gusts would be the main concern, and southeastern WI would be the hazard area. Generally a level 2 out of 5 severe risk.
Scattered showers and weaker storms could also be present west of the boundary throughout the day, but ultimately less impactful.

A less likely scenario (generally not depicted in 00z models), but one we must discuss, would involve a discrete cell or two firing off in the warm sector (east of the cold front, in southeastern WI) a bit earlier, perhaps mid Friday afternoon. In the unlikely event this were to occur, said storm (or two)
would be capable of hail, wind gusts, or a brief tornado. This scenario is less favored in guidance, due to the lack of forcing for ascent.

Sheppard

SHORT TERM
Issued 323 PM CDT Thu Apr 17 2025

Tonight and Friday:

Warm air advection may continue to bring scattered showers and a few storms northeastward through parts of the area into this evening. Mostly cloudy skies are expected to continue, with gusty south to south southeast winds.

Still expecting scattered showers and thunderstorms to move through the area later this evening and overnight, generally entering between 10 PM and 12 AM CDT in the far west and exiting between 3 AM and 5 AM CDT in the far east. The low level jet increases and taps into increasing elevated CAPE and deep layer bulk shear during this period across the area. Mostly sub- severe hail is possible with the storms during this period, with perhaps some gusty winds.

Thunderstorm potential on Friday afternoon and early evening still is very conditional, as the cold front moves east through the area. Mean layer CAPE and deep layer shear increases enough for a risk for large hail and strong winds, if any storms can develop. Despite clouds possibly lingering most of the day, warm air and moisture advection will bring in highs into the 60s and 70s, warmest southeast, with dew points to around 60 degrees F.

The question will be if and where the storms form, as there is little upper level support. CAMs seem to be trending more towards developing convection along the front in northern Illinois by middle to late afternoon, as the cap weakens. Some develop more storms into southeast Wisconsin or initiate storms in southeast Wisconsin, while others keep it south or southeast of the area. Will continue to monitor this potential into early Friday evening.

Wood

LONG TERM
Issued 323 PM CDT Thu Apr 17 2025

Friday night through Thursday:

There may be some post-frontal showers and a few storms that linger Friday evening, before drier air with cold air advection arrives by later Friday night. High pressure should bring a dry period to the area on Saturday and Saturday night, with cooler but more seasonable temperatures.

Deterministic models and ensembles continue to bring a fairly strong low pressure system and negatively tilted 500 mb shortwave trough through the region mainly Sunday night into Monday. Probabilities for 0.50 inches or more of precipitation are over 50 percent for most of the area, with almost all ensemble members showing a good wetting rainfall. Kept higher end PoPs (around 80 percent) for Sunday night, with a ramp up of PoPs Sunday afternoon and ramp down Monday afternoon.

Ensembles suggest mild temperatures gradually moving into the region for the rest of next week, with periodic chances for showers, as the 500 mb flow remains relatively zonal.

Wood

AVIATION
Issued 1030 PM CDT Thu Apr 17 2025

A lull in shower / storm activity over the next two hours or so, followed by gradual approach of stronger showers and thunderstorms from the west overnight through the Friday AM commute. Breezy south winds overnight. A low level wind shear threat is already present, with a low level jet producing south to southwest winds at 2,000 ft of 50 kts or more. This will persist through the night into early Friday morning before dissipating. Main concern with the overnight / Friday AM commute storms will be small hail, a few storms may become strong to severe with hail and gusty winds. Mostly VFR cloud ceilings until storms arrive, then a gradual drop. MVFR and brief windows of IFR looking likely at some point Friday AM.

From late Friday morning through early Friday afternoon, expecting a general lull in shower / storm activity, followed by additional showers / storms later Friday afternoon into the evening along a cold front, with the strongest storms in southeastern WI capable of wind gusts and hail. Winds veer northwest behind the front.

Sheppard

MARINE
Issued 323 PM CDT Thu Apr 17 2025

Breezy south to southeast winds will continue into tonight, as high pressure slides east of the lake, and low pressure around 29.4 inches moves across the central Great Plains into Iowa. A few gale force gusts are possible during this period over the open waters of Lake Michigan.

A Small Craft Advisory continues tonight for the nearshore waters for gusty winds and high waves, and continues into Friday north of Port Washington. It may need to be extended south of there into Friday, if gusty winds remain. There are chances for thunderstorms mainly later tonight across the nearshore and open waters of the lake.

Modest southerly winds on Friday will then shift northwesterly late Friday afternoon or evening, with the passage of a cold front. There are chances for thunderstorms later Friday into Friday night with the cold front, with large hail and strong winds possible over southern portions of the lake.

Modest northwest winds continue behind the cold front Friday night, followed by lighter north winds Saturday, as high pressure around 30.4 inches builds into the Great lakes region.

Wood

MKX WATCHES/WARNINGS/ADVISORIES
WI...None.
LM
Small Craft Advisory
LMZ644-LMZ645-LMZ646 until 7 PM Friday.

Small Craft Advisory...LMZ643 until 4 PM Friday.