Plymouth, Wisconsin Weather Forecast Discussion

148
FXUS63 KMKX 300231
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
931 PM CDT Mon Sep 29 2025
.KEY MESSAGES...
- Patchy fog possible later tonight.
- Slightly cooler Tuesday & Wednesday, with temperatures
  climbing well above normal Thursday through Friday.
- Isolated to scattered shower & thunderstorm chances (~15-30%)
  return Saturday evening through Monday.
&&
.UPDATE...
Issued 930 PM CDT Mon Sep 29 2025
The area of highest ground fog potential has shifted from prior
expectations. Short term model guidance and ongoing RH
measurements suggest that some of the best potential later
overnight through early Tuesday morning may be located towards
eastern WI, including areas along and east of the Kettle Moraine
hills and near Lake Michigan. Waukegan IL airport (south of
Kenosha) has already reported intermittent visibility dropouts
to 1/4 SM, and Kenosha airport is indicating 100% humidity
(though visibility has not yet fallen). There is still some
signal amongst model guidance for fog to develop further west as
well (particularly further north towards central WI). Areas
south and southwest of the I-94 corridor are looking noticeably
less humid than the aforementioned areas, and may struggle to
see fog development.
It`s tough to say how intense the fog may get, but as Waukegan
IL has demonstrated, it could easily reach dense criteria in
localized areas. Similar to the past few nights, the fog will
burn off rapidly after sunrise.
Sheppard
&&
.SHORT TERM...
Issued 206 PM CDT Mon Sep 29 2025
Tonight through Tuesday night:
Synopsis/Mesoanalysis: High pressure is centered over the Lakes
Huron & Ontario vicinity this afternoon, resulting in variable to
light southwesterly winds across southern Wisconsin. Responsible for
the scattered cumulus clouds currently over Racine & Kenosha
Counties, a lake breeze is beginning to develop near the Lake
Michigan shoreline, and will gradually work inland through the late
afternoon hours. Locations along/behind the boundary can expect an
easterly wind shift & modestly cooler surface temperatures in its
wake. Currently directly overhead, upper ridging will gradually
shift toward Lake Huron through the period, allowing surface high
pressure currently along the Manitoba-Ontario border to migrate
toward the southern Hudson Bay. The high`s progression will allow
east-northeast winds to become established across the area on
Tuesday, resulting in slightly cooler highs relative to today.
Scattered upper clouds will move into the region after midnight,
though patchy fog will be possible in locations experiencing clear
skies through the overnight hours tonight.
Rest Of This Afternoon: Well above-normal temperatures are forecast
away from Lake Michigan/the slowly-advancing lake breeze.
Temperatures should remain below record thresholds (90 in Madison in
1953), though trends will be watched through the rest of the
afternoon.
Tonight: Expect some patchy fog development after midnight,
particularly in areas experiencing clear skies and calm winds.
Forecast guidance depicts the best potential for calm winds along &
west of the Kettle Moraine, which is where patchy fog mentions have
been placed in the afternoon update. Model solutions don`t show a
robust signal for dense fog, though observations will be watched
through the overnight hours.
Quigley
&&
.LONG TERM...
Issued 206 PM CDT Mon Sep 29 2025
Wednesday through Monday:
Synopsis: Upper ridging will progress east during the second half of
the week, advancing from the western Great Lakes into Saint Lawrence
Valley & Appalachians by Friday. The ridge`s advance will allow for
surface high pressure to migrate into the Northeast by the end of
the week, with winds shifting out of the south during the Thursday-
Friday time frame. The southerly wind shift will allow a warmer air
mass to advect into southern Wisconsin from the Mississippi Valley,
with well-above normal high temperatures forecast by Friday. Upper
troughing will progress into the western CONUS Thursday through
Friday, slowly working eastward toward the Northern Plains through
the weekend. Responding to the western troughing, increasing upper
divergence will support isolated shower and thunderstorm chances
Saturday night into Sunday. Additional scattered showers and
thunderstorms will be possible Sunday night into Monday as a cold
front approaches southern Wisconsin from the west. Uncertainty
remains regarding the best timing windows for rain during the
Saturday night through Monday time period, with all-day washouts not
currently anticipated.
Thursday through Friday: High temps will trend upward, with readings
climbing into the 15 to 20 degree above normal range by Friday
afternoon. Current forecast shows highs in the low to mid-80s away
from Lake Michigan, with readings in the 70s near the water. In the
event this forecast verifies, said high temps would at least
challenge the October 3rd records in Madison (85 in 2005), with
slightly lower record potential closer to Lake Michigan in Milwaukee
(86 in 2018). Will be watching trends through the rest of this week.
Saturday through Monday: Scattered shower and thunderstorm chances
return to the forecast as upper troughing slowly works toward the
Northern Plains. With the area still on the edge of the eastern
CONUS upper ridge, tend to think that any activity will be highly
isolated through Sunday, with better precip potential holding off
until the arrival of the better-defined frontal boundary Sunday
night into Monday. Have maintained NBM precip probabilities in the
afternoon update, and will continue to monitor trends.
Quigley
&&
.AVIATION...
Issued 930 PM CDT Mon Sep 29 2025
Dry weather and VFR expected through and beyond the TAF period,
with the only exception being some potential for ground fog to
develop across low lying marshy areas later overnight into
early Tuesday morning, perhaps most focused along and east of
the Kettle Moraine hills as well as further north towards
central Wisconsin. As demonstrated by Waukegan IL airport (KUGN)
in recent observations, brief dropouts to LIFR visibility may
occur with the patchy dense fog, but we don`t expect the fog to
become widespread and dense (yet). Nearly calm wind expected
through the night.
Winds turn east-northeast and accelerate Tuesday, with periods
of scattered to broken high altitude cloud cover (VFR) and dry
weather.
Sheppard
&&
.MARINE...
Issued 206 PM CDT Mon Sep 29 2025
Light and variable winds continue across the waters this afternoon
as 1026 mb high pressure lingers over Lake Ontario. Patchy fog is
possible over far northern portions of the open waters tonight.
Currently centered over northern Manitoba, a second area of 1028 mb
high pressure will drift into Ontario tonight through Tuesday,
allowing east-northeast winds to become established over Lake
Michigan. The high will strengthen to near 1032 mb as it settles
along the Ontario-Quebec border Tuesday night through Wednesday,
maintaining generally easterly winds. The high will advance into the
northeastern United States through the end of the week, allowing
winds to turn out of the south Thursday through Friday. Broad low
pressure will form over the northern Great Plains Saturday, and will
gradually attempt to work toward the upper Mississippi River Valley
by the end of next weekend. Chances for isolated showers and
thunderstorms return to the forecast Sunday through Monday.
Light and variable winds continue in nearshore zones through
tonight, ultimately turning east-northeasterly Tuesday and Tuesday
night. Patchy fog is possible tonight. Generally easterly winds will
continue through Wednesday night. Given fetch, periods of elevated
wave heights are possible Tuesday night through Wednesday night,
though it`s uncertain if any such conditions will be widespread/long-
lasting enough to warrant Small Craft Advisories. Trends will be
monitored in coming forecasts. Winds will turn southerly through the
end of the week, with isolated shower and thunderstorm chances
returning by the end of next weekend.
Quigley
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&
$$
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NWS MKX Office Area Forecast Discussion