NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 291117
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
617 AM CDT Wed Apr 29 2026

.KEY MESSAGES...

- Chances (20 to 50 percent) for showers this afternoon. There
  could be a few rumbles of thunder with the showers this
  afternoon as well. This setup may occur again Thursday and
  Friday afternoon.

- Cooler temperatures are expected through the end of the week,
  with lows in the lower to middle 30s each night tonight into
  Friday night. A Frost Advisory may eventually be needed each
  night for most of the area.

&&

.UPDATE...
Issued 617 AM CDT Wed Apr 29 2026

Showers have developed into a broken like of light rain across
southeastern Wisconsin, with patchy drizzle to the west.
Expecting rain to end within the next few hours, with a brief
break before a shortwave propagates southeastward through
Wisconsin midday into this evening. With this wave and slight
instability (~100 J/kg SBCAPE), an isolated thunderstorm is
possible. However, more likely will be isolated to scattered
showers (20-50% coverage). Highs in the upper 50s inland and in
the lower 50s to upper 40s near Lake Michigan.

MH

&&

.SHORT TERM...
Issued 1146 PM CDT Tue Apr 28 2026

Overnight through Friday night:

Middle to high clouds will continue to push northeast through
the area overnight into Wednesday. Winds will shift northeast
overnight as a backdoor cold front shifts southwestward. Winds
will increase from the northwest to north on Wednesday, with a
northeast turn in the afternoon near Lake Michigan.

There will be small chances (around 20 to 30 percent) for
showers to occur overnight, as some frontogenesis response in
the 850 mb to 700 mb layer moves through southern parts of the
area, with some differential CVA aloft from a passing shortwave
trough. There is a fair amount of dry air to overcome initially,
though forecast soundings do saturate toward sunrise and may
allow for a few showers to reach the ground.

The shower chances (20 to 50 percent) linger into Wednesday, as
another vorticity maximum rotates through with a more elongated
500 mb trough in the region. This will bring more differential
CVA, along with some weak instability with daytime heating and
steep low level lapse rates. Left small (around 20 percent)
chances for thunder in the afternoon, as there may be enough low
level CAPE reaching the -10 degree Celsius level to bring some
rumbles of thunder.

Lows overnight should drop into the lower to middle 40s, with
highs Wednesday in the middle to upper 50s inland, with 40s to
lower 50s closer to the lakeshore.

Cyclonic flow around a deep 500 mb low to the northeast of the
region should remain into Thursday and Friday. Various 500 mb
vorticity maxima should rotate through the area at times, with
forecast soundings showing a similar look to this afternoon
with weak instability during peak heating. Thus, kept small
chances (20 to 30 percent) for showers Thursday afternoon in
parts of the area, and may need to add some for Friday afternoon
eventually. A rumble of thunder is possible again Thursday
afternoon, and perhaps Friday afternoon as well.

Ensembles suggest temperatures will remain a little below
seasonal normal values through Friday night. Lows Wednesday
night, Thursday night and Friday night should drop into the
lower to middle 30s for most areas away from the lakeshore, so
frost is expected to develop each night. A Frost Advisory may
eventually be needed each night for a good portion of the
forecast area.

Wood

&&

.LONG TERM...
Issued 1146 PM CDT Tue Apr 28 2026

Saturday through Tuesday:

500 mb cluster analysis shows the deep and anomalously below
normal low slowly shifting east across Quebec Saturday. This
feature then gets enveloped with another 500 mb low to the west
and maintains a deep and broad 500 mb trough over the region
into early next week.

This would suggest northwesterly cyclonic flow at 500 mb during
this period, with high pressure at the surface Saturday
shifting east and perhaps allowing for additional shortwave
troughs and surface lows to move southeast through the region.

Ensembles support 20 to 30 percent chances for showers at times
during this period, so left them in the forecast for now.
Ensembles suggest that temperatures may moderate slowly this
weekend into early next week in this setup, as winds try to turn
more south to southwest by later in the weekend and early next
week.

Wood

&&

.AVIATION...
Issued 617 AM CDT Wed Apr 29 2026

VFR conditions are expected to prevail, with a brief period of
MVFR ceilings possible mid-morning into midday as a weak low
pressure system progresses through the area. Isolated to
scattered showers (20-50% coverage, with the most widespread
activity in central to southeastern Wisconsin) will develop
midday and continue on and off through the afternoon and early
evening before dissipating. An isolated thunderstorm is possible
within these showers (~20% chance). Dry conditions are expected
overnight.

Expect predominately northwesterly winds today, with gusts up to
20 kt in southwestern to south-central Wisconsin. A lake breeze
will keep winds northerly near Lake Michigan, and will progress
inland this afternoon to turn winds northeasterly. Winds will
diminish this evening and shift to be light and northwesterly
through Thursday morning.

MH

&&

.MARINE...
Issued 1146 PM CDT Tue Apr 28 2026

High pressure around 30.3 inches over the Canadian Prairies
will gradually shift southeastward into the western Great Lakes
by the end of the week. Winds will shift to the north northeast
overnight, as a backdoor cold front moves southward across the
lake. These winds should linger into Wednesday morning, before
weakening in the afternoon.

As the high pressure system approaches and moves into the region
by the end of the week, winds will generally remain light. Light
showers will be possible at times through the rest of the week, as
weak low pressure areas move through.

Wood

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

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