NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 201259 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
759 AM 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.

&&

.UPDATE...
Issued 758 AM CDT Mon Apr 20 2026

Thin high clouds overhead will not prevent plenty of sunshine
today. Breezy southwest winds up to 20 mph are expected this
afternoon. Low relative humidity values dropping to 20 to 30
percent with lowest values well inland will help dry us out a
bit. After a cold start with frost, temperatures are heading
into the lower to mid 50s, except cooler by the lakeshore.

Cronce

&&

.SHORT TERM...
Issued 1130 PM CDT Sun Apr 19 2026

Today through Tuesday night:

Lows this morning in the mid 20s to low 30s combined with calm
winds and clear skies will allow for widespread frost
development this morning, burning off shortly after sunrise.
High clouds are expected to move in by the afternoon hours, with
south- southwesterly winds increasing through the day as high
pressure exits to the southeast and low pressure propagates
through northern Manitoba. Gusts around 20 mph are expected,
with highs in the low 50s. Temperatures overnight are only
expected to dip into the low 40s, as southwesterly winds
continue.

A weak frontal boundary from the northern low will propagate
through southern Wisconsin Tuesday morning. A few showers are
possible across far southern Wisconsin as the front stalls, but
confidence is low with plenty of dry air in the 700 mb to
surface layer. Majority of this precipitation would evaporate
before reaching the ground. Expecting highs in the 70s as
southerly winds continue. A lake breeze may contribute to highs
in the mid 60s near Lake Michigan. Tuesday evening, the cold
front from the northern low will sweep through southern
Wisconsin from northeast to southwest. Expect lows in the mid
40s to upper 30s, with the lowest temperatures in the
Sheboygan/Fond du Lac areas.

MH

&&

.LONG TERM...
Issued 1130 PM CDT Sun Apr 19 2026

Wednesday through Sunday:

Second half of the week will be a warm one. Temps quickly
recover on Wednesday as the the upper-level ridge axis works its
way across the region. Given the high probabilities (+80%) from
the GEFS, ENS, and GEPS, expect daytime temps to warm back into
the 70s for Wednesday and even a potential for upper 70s and
maybe even crack 80F on Thursday. However, any easterly wind off
of Lake Michigan will keep things several degrees cooler along
the lakeshore to the Kettle Moraine, while further inland will
likely see the warmest temps. Overnight temps are also looking
milder for this time of year ranging from upper 40s to lower 60s
through the end of the week.

Accompanying this warm stretch will be another potential for
showers and thunderstorms as an upper-level trough swings across
the the Northern Plains and Upper Mississippi River Valley for
Thursday into Friday. The long range models continue a trend
pivoting the mid- level trough back northward as another trough
tries to phase with it. Given this trend, expect to see the
surface low follow suit and likely track across the Dakotas and
lift into Manitoba/northwestern Ontario later Thursday. While
southern WI will be on the warm side of this system with
instability building toward 1000J/kg, the better upper-level
forcing along with more favorable shear looks to remain to the
west-northwest close to the center of the low itself. Thus, the
more favorable setup for severe thunderstorm activity looks to
remain along and west of the Upper Mississippi River Valley at
this time. May see the decaying remnants of this activity work
its way into the western half of the area later Thursday. While
there is fairly consistent agreement on the long-range ensembles
as well as the ML severe probs for things to remain just
outside our area, we are still several days out and will be
monitoring for any eastward shift in the trends.

Friday is trending warmer, but the cold front associated with
the Thursday system is progged to gradually work its way across
southern WI through the day. This will bring cooler airmass to
the region for the weekend under mainly zonal upper-level flow.
However, not expecting as cold of temps as we saw with this past
weekend system, but generally looking at temps closer to
normal.

Wagner

&&

.AVIATION...
Issued 758 AM CDT Mon Apr 20 2026

VFR conditions through the period. Breezy southerly winds will
persist through the night, but expect low level wind shear as SW 40
to 50 kt winds will persist just above the surface.

Cronce

&&

.MARINE...
Issued 758 AM CDT Sun Apr 19 2026

High pressure of 30.4 inches shifting over Lower Michigan today
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...4 PM Monday to 7 AM Tuesday.

&&

$$

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