515
FXUS63 KMKX 021725
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1225 PM CDT Tue Sep 2 2025

.KEY MESSAGES...


- Showers and storms likely (~60-80% chances) late tonight
  through Wednesday ahead of an approaching cold front.

- Below normal temperatures expected Wednesday night through the weekend.

- Shower and isolated storm chances (now ~50-70%) trending up
  Thursday night into Friday morning.


&&

.UPDATE...
Issued 1225 PM CDT Tue Sep 2 2025

Partly cloudy to brief periods of mostly cloudy skies will
continue through the afternoon via daytime heating and fair
weather cumulus. A broad trough of low pressure just north of
Lake Superior will deepen tnt when a deep upper trough over nrn
Manitoba digs toward it. The cyclogenesis will deepen to nearly
996 MB by late afternoon Wed as the low tracks from just north
of Lake Superior to nearly James Bay, Canada.

Farther south over srn WI, a weak pre-frontal trough and/or
outflow boundary currently over se MN will shift into areas
northwest of Madison along with a band of PVA. PoPs will
increase to 30-50 percent over this area this evening. After
midnight, PWs will increase to 1.2-1.3 inches within the 850 mb
thermal ridge, ahead of the approaching cold front. Fcst
soundings become fairly saturated above the boundary layer with
very minimal CAPE for the night and through Wed. The warm, moist
advection followed by low level frontogenesis along the cold
front is expected to provide enough lift for showers to become
likely with embedded thunder. The likely PoPs will be within a
narrow band from nw to se across the area and long duration
rainfall is not expected.


Gehring

&&

.SHORT TERM...
Issued 351 AM CDT Tue Sep 2 2025

Today through Wednesday Night:

Synopsis/Mesoanalysis: High pressure continues to linger across the
western Great Lakes this morning, resulting in clear skies and
light/variable winds across southern Wisconsin. Similar to previous
nights, the combination of light winds and clear skies has allowed
for efficient radiational cooling, with nighttime microphysics
imagery showing areas of ground and valley fog forming along/west of
the Kettle Moraine. Said areas of fog will linger through sunrise,
and could briefly drop visibilities to and below a mile. Northwest
of the region, surface observations show a cold front extending from
the Winnipeg vicinity southwest into the SD Black Hills. Water vapor
imagery shows an upper disturbance moving into northern Manitoba
from Nunavut & the Northwest Territories. The disturbance will
continue to drive southeast today, beginning to pull the
aforementioned cold front south in the process. Both features will
move into the Mississippi Valley tonight, approaching southern
Wisconsin by predawn Wednesday morning. Shower and thunderstorm
chances thus increase across the region later tonight, and continue
through most of the day Wednesday as the front pushes through.
Breezy northwest winds will become established Wednesday evening
behind the departing cold front, leading to chilly overnight lows
Wednesday night.

Rest Of Overnight: Areas of patchy fog will continue through
daybreak, particularly along and west of the Kettle Moraine. Similar
to prior nights, fog is largely shallow due to a very small layer of
near-surface saturation. Thus expect fog to behave much like
previous nights, with abrupt visibility reductions tending to focus
near marshes, lakes, rivers, and other low-lying locations. The
localized, hit/miss nature of the fog will thus create the potential
for brief but abrupt drops in visibility to/low below a mile. Have
addressed this potential in a Special Weather Statement running
through sunrise. Budget a few extra minutes of travel time if
heading out this morning. Use low beam headlights and allow for
extra following distance if encountering areas of fog.

Tonight through Wednesday: Shower and thunderstorm chances increase
ahead of the approaching upper disturbance and cold front. Likely
due to increasing 850 mb flow & WAA ahead of the cold front tonight,
rain arrival times have trended a touch earlier in the overnight
forecast, with showers & isolated storms now possible as early as
predawn across all of southern Wisconsin. Shower and storm chances
will continue through the daytime hours Wednesday as the cold front
crosses the area. Strong to severe storm potential is low, though a
few storms could produce gusty winds given strong gradient winds at
the 850 mb level. Brief heavy downpours will also be possible in
storms, though progressive storm motions should keep flooding
concerns low in any given location. Current forecast indicates a
widespread 0.25-0.50" of new rainfall across the area, with
streaks/pockets of 0.50-1.0" totals where deeper storms focus.

Wednesday Night: Conditions dry out, with breezy northwest winds
expected behind the departing cold front. The combination of breezy
winds, in addition to a strong push of cold advection, will lead to
chilly overnight temps in the lower 40s. A few low-lying spots could
fall into the upper 30s away from Lake Michigan. The combination of
air temps and winds will lead to feels-like temps in the upper 30s
across most of the area. Be sure to grab a jacket if heading out
late tomorrow night.

Quigley

&&

.LONG TERM...
Issued 351 AM CDT Tue Sep 2 2025

Thursday through Monday:

Models have come into general agreement that a reinforcing cold
frontal feature turned clipper-type low pressure system will swing
southeastward through the Canadian Prairies on Thursday, bringing an
additional round of rainfall to southern Wisconsin Thursday night
into Friday as it hooks around the back of the stronger, occluded
low pressure system in northern Ontario (60-70% POPs). Not expecting
thunderstorms with this system, but definitely will bring in an
additional cool airmass and gusty winds. Expect highs in the lower
60s and lows in the lower 40s Friday through Saturday.

The clipper system will work its way into the main occluded low into
Friday night, keeping gusty northwesterly winds across the area
throughout the overnight hours into Saturday morning. The
combination low will then propagate eastward as high pressure builds
into the western Great Lakes region, allowing for temperatures to
rise back into the upper 60s to low 70s Sunday and Monday.

MH

&&

.AVIATION...
Issued 1225 PM CDT Tue Sep 2 2025

Sct-bkn035-050 fair wx cumulus today, then showers becoming
likely late tnt into Wed as a Canadian cold front passes through
srn WI. MVFR Cigs will develop north and west of a line from
Mineral Point to Madison to Sheboygan during the early morning
hours of Wed, with areas of Cigs below 1 kft in this same
region. The MVFR Cigs will then expand into se WI by late
morning. Cigs will then rise to 3.5-4.0 kft during the early
afternoon.


Gehring

&&

.MARINE...
Issued 351 AM CDT Tue Sep 2 2025

1020 mb high pressure remains focused over the western Great Lakes
early this morning, resulting in east-northeast winds over the
southern half of Lake Michigan and east-southeast winds further
north. Prevailing south to southwest winds will become established
across the waters by this afternoon as low pressure begins to
develop over central Ontario. The low will move into Lake Superior
tonight, deepening to near 1004 mb in the process. The low will
continue to deepen to near 996 mb during the day on Wednesday as it
slowly progresses toward the Ontario-Quebec border. Southwest winds
will thus become gusty across Lake Michigan tonight into Wednesday
morning. Highest gusts are anticipated over the northern third of
the waters, where a few gusts approaching gale force are possible
Wednesday morning. Said gusts aren`t expected to be persistent or
widespread, making Gale Warnings unlikely at this time. Trends will
continue to be monitored through today.

A cold front will cross Lake Michigan Wednesday afternoon & evening,
resulting a gusty northwest wind shift across the waters. Currently
anticipate that gusts will remain below gale thresholds, though
trends will continue to be monitored. Showers and storms will
accompany the approaching/passing front Wednesday morning and
afternoon. Widespread strong to severe storms aren`t expected,
though a few storms could produce gusty winds. A few waterspouts are
also possible, particularly Wednesday morning and afternoon across
the northern half of the open waters.

1016 mb high pressure will settle into the northern Great Plains
early Thursday morning, migrating into the western Ohio River Valley
by Thursday evening. The feature`s progression will result in a
southwest wind shift across the waters during the day Thursday.
Winds will become gusty Thursday night as a second area of 1000 mb
low pressure quickly develops in the northern Great Plains. The low
will move across Lake Michigan Friday morning, with gusty northwest
winds becoming established during the afternoon hours. Wind gusts
could thus approach gale thresholds once more Thursday night through
Friday afternoon. Showers and isolated storms will accompany the
passing low, particularly late Thursday night into early Friday
morning.

Northwest winds will become gusty in nearshore zones Wednesday
evening behind a departing cold front. A few gusts approaching Small
Craft Advisory thresholds are possible. Winds will briefly taper as
they shift out of the southwest during the day on Thursday, quickly
becoming gusty once more Thursday night through Friday afternoon.
Additional Small Craft Advisory conditions are possible during this
time frame, with trends being monitored in the coming forecasts for
potential headlines. Periods of showers and storms are expected
during the day on Wednesday and once more Thursday night into
Friday.

Quigley

&&

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

$$

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