NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 201839
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
139 PM CDT Mon Apr 20 2026

.KEY MESSAGES...

- Temps rise well above normal Tuesday through Thursday.

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

&&

.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 137 PM CDT Mon Apr 20 2026

We have a lake breeze (defined by a line of VFR cumulus clouds)
this afternoon that is fighting against increasing south-
southwest winds. This is creating uncertainty in when winds will
shift from southeast to southwest at KUES and KENW. With
southwest winds and 40 to 45kt winds just above the surface over
all of southern WI overnight, kept a period of LLWS in TAFs.
Morning mixing will allow for some gusty southwest winds
initially, but then they will diminish in the afternoon as the
LLJ exits and high pressure settles over the state.

Tuesday afternoon, 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 by mid afternoon. 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 virga could help accelerate the
winds in localized areas and small aircraft should remain
cautious.

Expect northeast winds to spread into southern WI off Lake
Michigan during the overnight and into Wednesday morning.

Cronce

&&

.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...2 PM Monday to 7 AM
Tuesday.

&&

$$

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