textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Temps rise well above normal Tuesday through Thursday.

- Next chances (50-80%) for showers and thunderstorms Thursday night.

UPDATE

Issued 703 PM CDT Mon Apr 20 2026

Forecast remains on track. Lake breeze continues for the next few hours, with winds generally diminishing to around 10 mph late this evening throughout tonight. Expecting temperatures to fall into the low 40s, with some areas near Lake Michigan seeing lows in the upper 30s.

MH

SHORT TERM

Issued 137 PM CDT Mon Apr 20 2026

Rest of Today through Tuesday:

We have a lake breeze (defined by a line of VFR cumulus clouds) this afternoon that is fighting against increasing south- southwest winds. Very dry air with dewpoints in the teens (except around 30 near Lake Michigan) is in place with highs getting into the lower 50s inland this afternoon. Southwest winds will remain steady overnight (a few rogue gusts to 20mph possible) as a south-southwest low level jet pivots overhead, and lows will only dip down to the lower 40s (upper 30s toward Sheboygan). We will be in a new air mass on Tuesday, with high temperatures reaching the lower to mid 70s for most areas and dewpoints in the 40s to around 50.

Tuesday, a subtle feature will bring increasing clouds and virga to far southern WI. A very weak shortwave trough dropping southeast across WI will drop a very weak surface trough into far southern WI around midday. That exiting low level jet and warm air advection will be over far southeast WI or northern IL at this time, which will help produce some thicker mid level clouds over the area. Any precip associated with these clouds is expected to evaporate by the time it hits the ground, so we continue to leave precip chances out of the forecast. There is a small chance of thunderstorms with this feature just over the IL border late in the afternoon.

A back door cold front will slowly drop down Lake Michigan Tuesday night, so lows will range from the upper 30s in Sheboygan to upper 40s in Monroe.

Cronce

LONG TERM

Issued 137 PM CDT Mon Apr 20 2026

Wednesday through Monday:

Temperatures will be much cooler by Lake Michigan on Wednesday with a steady onshore breeze, while inland temps will get into the mid 70s. Overall, expect plenty of sunshine, but cannot rule out some diurnal cumulus clouds as well.

Low pressure developing in the Northern Plains Wednesday will undergo cyclogenesis and strengthen as it reaches Manitoba Thursday morning. A steady stream of moisture and humidity from the Gulf will make its way into Iowa on Thursday ahead of this system, and southern WI high temps will be pushing 80 on breezy southerly winds. At this time, thunderstorms developing along this pre-frontal trough/warm front will be well west of our area (IA and MN and western WI). If an organized line of storms develop, then they could race through the east half of Wisconsin during the late evening and overnight hours. If ingredients come together, damaging winds are possible.

Precip chances will linger through at least midday Friday until the surface front clears southeast WI. Meanwhile, that parent closed upper low over the Canadian Plains is expected to sit there over the weekend and little ripples in the flow to the south of it could bring precip back into southern WI by Monday.

Cronce

AVIATION

Issued 703 PM CDT Mon Apr 20 2026

VFR conditions are expected to continue throughout tonight and Tuesday. High clouds around 15,000 to 25,000 ft will continue on and off for the next several hours. Expecting a scattered deck of 5000-7000 ft clouds from MKE to JVL southward Tuesday afternoon, with a few of these clouds producing virga or even an isolated rain shower (10-20% chances). Showers will end around sunset.

Expect southerly winds gusting between 15 and 20 kt through late this evening, becoming steady around 10 kt overnight. This will also allow for low level wind shear around 40 kt to develop. As winds shift to southwesterly, increase and begin gusting again Tuesday morning, wind shear will end. Winds will gradually veer to northwesterly Tuesday afternoon through Tuesday evening.

MH

MARINE

Issued 137 PM CDT Mon Apr 20 2026

High pressure of 30.4 inches over Lower Michigan and low pressure around 29.7 inches developing in the Plains will bring increasing southerly winds to Lake Michigan through Tuesday morning. A few gales are possible tonight into early Tuesday morning, especially over the northern third of the lake as low pressure around 29.5 inches also progresses across the Hudson Bay. A cold front from this low will progress southward through the lake Tuesday afternoon and evening, shifting winds to northeasterly. High pressure around 30.4 inches builds into Ontario on Wednesday, bringing light and variable winds. Winds will then become southeast and increase Thursday into Friday as strong low pressure around 29.2 inches develops in the northern Plains.

Increasing southerly winds with gusts up to 25 kt will build high waves in the nearshore areas north of Port Washington this afternoon. A Small Craft Advisory is in effect.

Cronce

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643 until 7 AM Tuesday.