NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 202333
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
633 PM CDT Thu Aug 20 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms (30 to 60 percent chances)
  with passing cold front mainly Friday afternoon and evening.
  Gusty winds and small hail may occur.

- Small chances (20 to 30 percent) for a shower or storm
  Saturday afternoon for portions of east central and southeast
  Wisconsin.

&&

.UPDATE...
Issued 634 PM CDT Thu Aug 20 2026

Pre-frontal showers have largely dissipated to the west, so the
previous forecast update for this evening remains on track.
Storms will likely redevelop ahead of the frontal boundary
overnight, arriving across southern Wisconsin after midnight
into Friday morning. Ahead of these storms, expect southwesterly
winds to increase to gust around 15 mph. Main threat with the
morning storms will be lightning.

MH

&&

.SHORT TERM...
Issued 109 PM CDT Thu Aug 20 2026

Tonight through Saturday:

Some modest warm air and moisture advection should move into
the area tonight into Friday, which should support some showers
and a few storms northwest of Madison later tonight.

The cold front will then move southeast into the area Friday,
then exit to the southeast by later Friday night. There is not
much middle to upper level support to go with the front and
modest warm air/moisture advection. Recent CAM runs have been
producing more showers and storms along and ahead of the front
during the afternoon and early evening with peak heating,
especially in eastern portions of the area.

Thus, brought up precipitation chances in to the 50 to 60-plus
percent range in the late afternoon and early evening. Forecast
soundings are showing mean layer CAPE of 1200 to 1500-plus J/kg,
with 20 to 25 knots of deep layer bulk shear. This may support
gusty winds and small hail with any stronger storms during this
period.

There may be a shower or storm (20 to 30 percent chances) that
occurs Saturday afternoon for portions of east central and
southeast Wisconsin, with a weak surface low/convergence from
lake breeze shifting southward near the western shore of Lake
Michigan. There is some differential CVA that may move through
with a broad 500 mb trough digging through the region.
Confidence is low with the areal coverage of any precipitation
Saturday, as upward vertical motion is modest at best. Forecast
soundings do support a shower or storm if something can develop.

Temperatures look to remain near seasonal normal values into
Saturday.

Wood

&&

.LONG TERM...
Issued 109 PM CDT Thu Aug 20 2026

Saturday night through Thursday:

Shower and storm potential is expected to decrease Saturday
night. Sunday and Monday highlight a high pressure system and a
strengthening upper level ridge, which should keep the region
drier with high temperatures in the middle to upper 70s.

The next chance for showers and storms suggests to be late
Tuesday afternoon through the evening, potentially into early
Wednesday (40 to 50 percent), as a low pushes down over the
Great Lakes region from northern Minnesota and Canada. The bulk
shear of around 40 to 50 knots could bring a severe risk with
these storms, but the timing and severe risk remains uncertain.
The south central region is expected to become drier through
Wednesday, with a continued potential for precipitation near the
lake through the afternoon as the low moves east.

Wednesday night and into Thursday show generally drier and fair
conditions to return, as high pressure and a shortwave ridge
build in.

Zawlocki

&&

.AVIATION...
Issued 634 PM CDT Thu Aug 20 2026

VFR conditions expected throughout tonight and through Friday,
with local reductions in visibilities under thunderstorms Friday
morning into midday, and again Friday afternoon. Expect
increasing cloud cover around 11,000 ft tonight, with clouds
lowering to ~3500 ft into Friday morning. Thunderstorm chances
are highest (60%) in the afternoon to evening hours. Storms exit
into Lake Michigan Friday night.

Light winds this evening will become steady and southwesterly
around 10 kt overnight, remaining southwesterly throughout
Friday before shifting to northwesterly behind a cold front
overnight.

MH

&&

.MARINE...
Issued 109 PM CDT Thu Aug 20 2026

Light to modest winds are expected into this evening, as high
pressure around 30.0 inches tracks through the western Great
Lakes region. As the high pressure exits to the southeast later
tonight, south to southwest winds will develop. Theses winds
will increase for Friday, along with shower and thunderstorm
chances, as low pressure around 29.8 inches moves across the
region and drags a cold front through Lake Michigan.

Gusty winds will then shift to the northwest later Friday night
into Saturday after the front exits. Another high pressure
system around 30.2 inches is expected to build into the region
later this weekend, which may maintain gusty northerly winds as
it moves in.

Winds may get close to Small Craft Advisory levels Friday
afternoon north of Port Washington, though it may only be for a
short period of time.

Wood

&&

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

$$

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