138
FXUS63 KMKX 180403
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1003 PM CST Wed Dec 17 2025

.KEY MESSAGES...

- Mild temperatures continue through early Thursday, with highs
  in the upper 30s to low 40s in the early afternoon.

- Widespread light rainfall is expected late tonight through
  Thursday morning.

- A front with potential for snow squalls will progress west to
  east late Thursday afternoon into the evening, with increasing
  concern for at least snow showers during this time frame.

- Significantly colder temperatures (overnight lows in the
  single digits to low teens) expected Thursday night,
  potentially flash freezing any surfaces that remain wet from
  Thursday`s rain and snow.

&&

.UPDATE...
Issued 1003 PM CST Wed Dec 17 2025

Forecast remains on track. Main wave of rainfall has developed
over western Minnesota and will track eastward into southern
Wisconsin early Thursday morning (80-100% chance of rainfall
across southern Wisconsin between 4 AM and noon Thursday).
Ahead of this band of steady rain, a few showers are still
possible underneath the LLJ and strong WAA in the region late
tonight into early Thursday morning. That being said, plenty of
dry air will need to be whittled away before those showers can
develop and reach the ground.

00Z mesoscale modeling has continued to indicate potential for
snow squalls during the evening commute timeframe Thursday.
Strong frontogenesis and pockets of instability along a cold
front pushing eastward as large scale troughing tilts briefly
neutral to negative, lending to intense forcing along a narrow
region. As temperatures fall quickly from the mid-30s into the
teens along this frontal passage as well, even if snow squalls
fail to become intense enough to produce visibilities below 1
mile, a flash freeze is looking likely and slick conditions
would develop on untreated surfaces.

MH

&&

.SHORT TERM...
Issued 300 PM CST Wed Dec 17 2025

Tonight through Thursday night:

High pressure will push out tonight as a fairly strong system
slides in late tonight. The low pressure with this system will
be around 985mb with strong southerly winds ahead of the initial
front. Models have some initial precip potential ahead of the
majority of the forcing primarily due to strong WAA, with the
very strong LLJ in place, though the strongest forcing will
remain in northern WI where the LLJ is upwards of 70-80 kts.
However, as we get toward daybreak we will start to see
significant forcing push in from the south and west. To the
south we will likely see bands of light precip associated with
the LLJ and associated WAA being directly overhead (though not
as strong as in northern WI). This precip will be particularly
maximized in northern IL but will likely leak into parts of
southern WI where the omega shown in soundings really ramps up.

On the western side of the CWA, we expect to see significant
overlapping forcing along the axis of the initial front. The
surface front in combination with strong 850mb WAA, very strong
PVA at 500mb, and strong Fgen throughout the column. This should
lead to a period of decent rainfall Thursday morning across the
CWA. This will however be fairly short-lived given how most of
the forcing is co-located in a narrow area. It almost looks like
just a band of precip in most of the CAMs.

Rain will likely push out by the late morning to the west and
early afternoon to the east with dry conditions temporarily.
However, we will then transition to the secondary front that
will bring in the colder temperatures behind it. This will bring
potentially significant impacts to southern WI. This front is
looking increasingly more like a snow squall situation. The
front, in combination with some instability and strong Fgen,
looks likely to bring a band of snow, perhaps heavy, across at
least parts of southern WI late Thursday afternoon during the
evening commute. While there remains some uncertainty regarding
what this may look like, how expansive it is and what the impact
might be the concern has been heightened for this given the
models showing a period where the snow squall parameter is on
the higher side. We will continue to monitor this but rapid
onset snow with potential for brief heavy snow, low visibilities
and gusty winds would be possible. While these are short-lived
the impacts can be significant for travel. In addition,
following the frontal passage temperatures are expected to fall
rapidly with lows in the single digits overnight. This will lead
to concerns for flash freeze with any remnant water on roads
likely freezing. This would make for potentially very slick road
conditions into Friday morning.

Kuroski

&&

.LONG TERM...
Issued 300 PM CST Wed Dec 17 2025

Friday through Thursday:

Friday will be chilly to start with potentially slick roads from
overnight flash freeze potential but high pressure will move
back in for Friday with no concerns for precip though
temperatures will remain fairly chilly with highs in the 20s
for the most part. Friday night through Saturday another system
will push through but there remains uncertainty on what we may
see, if anything, as models keep the system fairly dry given the
absence of significant moisture. But if some moisture can be
added to that system we could easily see some precip with it,
likely a rain/snow mix with the current track and exactly where
the 540 line lines up. High pressure then is expected to develop
and strengthen later in the weekend.

Into early next week things become a bit more uncertain with a
chance for precip Monday and again Wednesday night into
Thursday. Ensembles show at least a 50% chance for 0.01 inches
of precip for both days and thus it appears that various
differences in tracks, moisture and intensity of these various
system there is at least a decent chance for precip for these
periods but likely heavily rely on the development of a few
shortwaves in the upper levels that likely will not carry any
significant precip with light rain or snow possible given the
placement of the 540 line in models and corresponding surface
temps.

Kuroski

&&

.AVIATION...
Issued 1003 PM CST Wed Dec 17 2025

Southwesterly winds will continue to increase tonight, with
gusts near 25 kt expected by the early morning hours. A wave of
steady precipitation will work its way west to east during the
early morning hours Thursday, bringing ceilings as low as IFR
and visibilities as low as 2 SM. Trends will be monitored
tonight for potential improvements with dry air ahead of this
line of rain. As rain tapers off into Thursday afternoon, winds
shift westerly and increase again. Gusts near 30 kt are
expected. A quick-hitting line of snow showers is expected to
move west to east Thursday late afternoon and evening, dropping
visibilities rapidly to 1 SM or lower for up to half an hour
before exiting each terminal. In addition, this line will drop
temperatures from the mid-30s to the teens within a short
period, leading to refreeze on any untreated surfaces. Gusty
northwest winds are expected behind this line, with ceilings
slowly improving Thursday night.

MH

&&

.MARINE...
Issued 300 PM CST Wed Dec 17 2025

Low pressure will track eastward along the Canadian border
tonight into Thursday, bringing southerly gales from late evening
through Thursday morning. A lull in the gales may occur Thursday
afternoon as low pressure crosses the Upper Peninsula of Michigan.
Winds become west and accelerate back to gale force behind a
strong cold front Thursday evening, then eventually turn northwest
Thursday night. A Gale Warning is in effect for all open waters
of Lake Michigan late this evening through early Friday morning.

Westerly gales are expected in the nearshore areas from early
Thursday evening through Friday morning.

Moderate freezing spray is expected to accompany the gales late
Thursday night into Friday morning as a bitter cold airmass
briefly enters our region.

Friday night, another low pressure system swings through southern
Canada, bringing gusty south-southwest winds once again. Gales are
possible, but confidence is lower with timing and intensity at
this time.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 6 PM
     Thursday.

     Gale Warning...LMZ643-LMZ644-LMZ645-LMZ646...6 PM Thursday to
     9 AM Friday.

     Gale Warning...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 until 9 AM
     Friday.

&&

$$

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