199
FXUS63 KMKX 010831
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
331 AM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Areas of fog possible (~20-30% chances in a given spot)
  through sunrise and once again tonight along & west of the
  Kettle Moraine.

- Shower and storms likely (~60-80% chances) late Tuesday night through
  Wednesday along a cold front.

- Below normal temperatures expected Wednesday night through the
  end of the week.

- Additional periods of showers and isolated storms possible
  (~20- 40% chances) Friday.

&&

.SHORT TERM...
Issued 333 AM CDT Mon Sep 1 2025

Today through Tuesday:

Synopsis/Mesoanalysis: A broad area of high pressure extends from
the Saint Lawrence River west to the Upper Mississippi Valley this
morning, maintaining clear skies and light surface winds across
southern Wisconsin. Efficient radiational cooling has occurred in
the presence of the clear skies and winds, with areas of mostly
shallow ground fog having been noted in recent observations.
Slightly deeper valley fog has developed from Sauk City west to
Prairie du Chien, and is well-defined in current nighttime
microphysics imagery. Areas of patchy ground fog, in addition to
valley fog near the Wisconsin River, will continue through daybreak,
with visibilities rapidly improving after sunrise. Well to the north
of the region, surface observations show a nearly stationary surface
front extending from the Hudson Bay into Saskatchewan. Even further
northwest, water vapor imagery shows an upper trough along the
border of Alberta and the Northwest Territories. The trough is
forecast to dig southeast today through Tuesday, dragging the
currently stationary Hudson Bay - Saskatchewan surface front with it
by Tuesday afternoon. The pair of features will continue to drive
toward the international border Tuesday evening, reaching the Upper
Mississippi Valley by predawn Wednesday morning. Shower and storm
chances thus return to the forecast late Tuesday night, particularly
along & north of US-151.

Rest Of Overnight: Expect current trends showing areas of fog
along/west of the Kettle Moraine to continue through daybreak.
Similar to last night, forecast soundings show an extremely shallow
layer of near-surface saturation outside of the immediate Wisconsin
River Valley, which likely helps to explain the high variation in
hour to hour visibilities being reported at impacted observation
sites (JVL, UES, ETB, and MSN to name a few). Given these trends,
don`t anticipate the need for Dense Fog Advisories through sunrise,
but will nevertheless be closely watching surface ob & webcam
trends. If < 1 mile visibilities become more prevalent outside of
low-lying spots, Special Weather Statements may be considered. Slow
down, use low beam headlights, and allow for extra following
distance if encountering areas of ground fog through daybreak.

Tonight: With largely unchanged surface conditions, expect another
round of ground fog development along and west of the Kettle
Moraine. Budget a few extra minutes of travel time if taking to the
roads late tonight/early Tuesday morning.

Tuesday Night: Shower and thunderstorm chances will begin to
increase after midnight as the aforementioned upper trough and
surface front begin to approach the region. Expect that the majority
of precip potential will remain along and north of US-151, where
proximity to the approaching features will be greatest through
sunrise. Don`t currently anticipate any strong/severe storms in this
activity given overnight timing, though storms could produce brief
heavy downpours.

Quigley

&&

.LONG TERM...
Issued 333 AM CDT Mon Sep 1 2025

Tuesday night through Sunday:

A robust mid level shortwave trough over central Canada will swing
across the MN/Ontario border Wednesday morning and bring us our
first glimpse of Fall. Ahead of this wave, surface low pressure will
develop over Ontario, and the associated cold front will approach
northwest Wisconsin Tuesday and Tuesday night. We can expect
increasing southerly winds ahead of this front. The cold front will
cross southern WI on Wednesday, although the timing is uncertain.
Showers and thunderstorms are likely along the front. If it is later
in the day, there will be time for temps to reach 70s one more time,
and also a potential for a few stronger storms.
If it crosses in the morning, there will be less instability and
weaker convection.

Brisk northwest winds will usher colder air into the area behind the
front Wednesday night into Thursday. Highs Thursday will be around
60. Another shortwave trough is expected to swing across MN and WI
Thursday night and bring a reinforcing blast of cool air on gusty
WNW winds on Friday. We should see some showers along this secondary
cold front. The upper trough will begin to move out on Saturday,
although a few light showers are possible before it completely
exits.

Cronce

&&

.AVIATION...
Issued 333 AM CDT Mon Sep 1 2025

Mostly SKC conditions prevail across southern Wisconsin early this
morning. The combination of clear skies and light surface winds is
leading to a favorable environment for another round of shallow FG
development tonight, with several sites reporting visibilities
at/below 1 SM as of 2:30 AM CDT. Similar to previous overnight
periods, near-surface saturation is very shallow, leading to
scattered FG pockets & highly variable fluctuations in VIS readings
at any given location. Given these factors, have accounted for FG
potential with TEMPO groups through daybreak at terminals along and
west of the Kettle Moraine. FG will quickly dissipate after sunrise,
allowing for the return of prevailing VFR conditions at all
terminals. Currently VRB winds will become generally easterly this
morning, with VRB conditions re-establishing after sunset. Given
anticipated similar sky & wind conditions tonight, expect that
additional FG development will be possible. Will address this
potential with TEMPO groups in future updates as forecast trends
clarify.

Quigley

&&

.MARINE...
Issued 333 AM CDT Mon Sep 1 2025

1026 mb high pressure is centered over Lake Huron this morning,
resulting in generally light northeasterly winds over the southern
third of Lake Michigan, light/variable winds over the central third,
and light/southeasterly winds over the northern third. This general
pattern will persist into Tuesday morning as the broad area of high
pressure slowly migrates into Ontario. South to southwest winds will
become established late Tuesday afternoon through Tuesday night as
low pressure of at least 1004 mb develops across Lake Superior. Said
area of low pressure will slowly move east toward the Ontario-Quebec
border Wednesday, dragging a strong cold front across Lake Michigan
in the process. Gusty northwest winds will become established along
and behind the passing front Wednesday evening through Thursday
morning. Widespread gale-force gusts are not anticipated at this
time, though forecast trends will be closely monitored through the
beginning of this week. Winds are forecast to turn west-
southwesterly Thursday afternoon and night as second area of low
pressure develops across the western Great Lakes. Central pressure
of the low, in addition to its precise location, remain a source of
uncertainty at this time, with forecast trends being monitored
through this week. Additional gusts in the 20-25 knot range will be
possible during this time frame. The second area of low pressure
will cross over or just to the north of Lake Michigan during the day
on Friday, resulting in a northwest wind shift Friday night into
Saturday.

Showers and thunderstorms are likely along the advancing cold front
Wednesday and Wednesday evening. Widespread severe thunderstorms
aren`t anticipated, though a few storms could produce gusty winds.
Forecast trends will also be monitored for waterspout potential
during the day on Wednesday, particularly across the northern half
of the open waters. Additional showers and isolated thunderstorms
will be possible ahead of the second low on Friday. Whether or not
gusty winds or waterspouts will accompany this activity remains
uncertain at this time.

Light and variable winds continue in nearshore zones through Monday
night with a broad area of high pressure lingering across the Great
Lakes. Prevailing west-southwest winds will become established
Tuesday night as low pressure develops across Lake Superior. The low
will drag a front through the region Wednesday, bringing a gusty
northwest wind shift and chances for showers and storms. Winds will
briefly turn out of the west-southwest Thursday afternoon and night
as a second area of low pressure forms across the western Great
Lakes. Said low will pass over or just to the north of Lake Michigan
on Friday, bringing additional chances for showers and isolated
storms. Winds will shift out of the northwest once again Friday
night into Saturday as low pressure shifts into Ontario. Periods of
Small Craft Advisory conditions are possible Wednesday through
Friday, with trends being monitored in the coming forecasts.

Quigley

&&

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

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, X, and YouTube at:
www.facebook.com/NWSMilwaukee
www.x.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee