Janesville, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

457
FXUS63 KMKX 050357
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1057 PM CDT Sat Jul 4 2026

.KEY MESSAGES...

- Areas of fog possible through the remainder of the overnight
  hours. Slow down & allow for extra time if encountering fog on
  the roads.

- Small chances (~15-20%) for a few thundershowers Sunday
  afternoon west of Madison. Isolated lightning would be the
  main impact in any activity.

- Quieter & less humid through the beginning of the work week.

- Next opportunity for widespread showers and thunderstorms
  arrives Wednesday into Thursday.

&&

.SHORT TERM...
Issued 1100 PM CDT Sat Jul 4 2026

Rest of Overnight through Sunday night:

Synopsis/Mesoanalysis: Thundershowers have diminished late this
evening thanks to the loss of daytime heating & easterly surface
flow pulling stable air inland from Lake Michigan. A diffuse surface
pressure gradient is resulting in calm to light/variable surface
winds across the area, with observations suggesting that decoupling
of the boundary layer is in-progress across southern Wisconsin. With
near-surface moisture still elevated regionally, said decoupling
could result in fog development through the remainder of the
overnight hours. Some dense fog can`t be ruled out, with trends
being monitored for possible headlines through tonight. Slow down,
use low beam headlights, and allow for extra following distance if
encountering fog on the roads. To the northwest of the area, a
complex of thunderstorms continues from Eau Claire southwest toward
the Albert Lea, MN vicinity. These storms will continue to drift
south toward the Iowa-Minnesota border near-term, though stable air
will impede any eastward progress into southern Wisconsin. A few
showers are possible west of Madison Sunday afternoon. Apart from an
isolated flash of lightning & clap of thunder, hazards aren`t
expected in any showers that develop Sunday afternoon.

Rest of Overnight: Will be monitoring visibility trends as areas of
fog attempt to fill in across southern Wisconsin. Can`t rule out
some areas of locally dense fog given light winds in place
regionally & an inversion above the boundary layer. If necessary,
will address any such areas of dense fog with appropriate headlines.
Can`t entirely rule out an isolated shower in far southeast
Wisconsin through daybreak as a remnant shortwave/MCV from afternoon
storms lingers over southern Lake Michigan. Apart from the HRRR,
most high-res guidance points toward dry conditions in the vicinity
of this feature. Have thus capped precip probabilities below
15%/mentionable thresholds in the evening forecast, but will be
monitoring for possible adjustments in the event that the HRRR
solution verifies.

Quigley

&&

.LONG TERM...
Issued 1100 PM CDT Sat Jul 4 2026

Sunday night through Friday:

A quieter weather pattern will settle over the region early in the
week as a western CONUS ridge builds, with an eastern CONUS trough.
Nestled between these two features, we will experience northwest
flow aloft. Will need to monitor for occasional passing waves
embedded in this northwest flow, but there will be more dry time
than active time next week.

Overall expect dewpoints to lower a bit, trending a bit more
comfortable than the past week. Lows will be in the 60s and highs in
the low/mid 80s. A signal is starting to hone in on better rain
chances later Wednesday into Thursday.

Looking a bit longer term, the GEFS supports keeping this western
ridge/eastern trough pattern into next weekend and beyond.

Gagan

&&

.AVIATION...
Issued 1100 PM CDT Sat Jul 4 2026

Mainly VFR flight categories prevail across southern Wisconsin late
this evening, with the expectation that pockets of MVFR VIS and CIG
readings will develop through daybreak. Reductions would be driven
primarly by reduced VIS readings inland, with a combination of low
CIGs backing off Lake Michigan & reduced VIS readings driving
reductions near the lakeshore terminals. Have included prevailing
MVFR mentions at all Lake Michigan terminals, with lower forecast
confidence precluding any prevailing mentions further inland. Will
be monitoring trends through tonight & making adjustments where
necessary. Flight categories will improve areawide through the first
half of Sunday morning. Isolated -SHRA/-TSRA are possible in the
Wisconsin River Valley Sunday afternoon. Currently expect activity
to remain west of MSN and JVL, but will be monitoring trends for
potential adjustments through Sunday morning.

Quigley

&&

.MARINE...
Issued 1100 PM CDT Sat Jul 4 2026

1024 mb high pressure is centered over the Hudson Bay this evening,
resulting in light north-northeasterly winds across the open waters
of Lake Michigan. Light winds will continue through the overnight
hours, with areas of fog continuing over the southern two-thirds of
the lake into early Sunday morning. A Dense Fog Advisory remains in
effect until 10 AM CDT given this potential. Expanded the advisory
into the far southern waters in the evening forecast update given
the potential for southward expansions of fog through the overnight
period. Fog is expected to dissipate early Sunday morning as wind
speeds pick up across the lake. Isolated showers and thunderstorms
are possible over the southern third of the waters Sunday afternoon,
with severe weather not anticipated.

North-northeast winds will continue through the day Monday as the
aforementioned high drifts into northern Quebec. Winds will trend
light and variable Monday night into Tuesday, ultimately shifting
out of the southwest Tuesday night into Wednesday as 998 mb low
pressure moves into the Hudson Bay. Said low will drag a cold front
across the open waters Wednesday night into Thursday, bringing the
next chances for widespread showers and thunderstorms. It remains
too early to tell if any storms could be severe, with trends being
monitored over coming forecasts.

Small Craft Advisory conditions aren`t anticipated through the
period in nearshore zones. Areas of fog will continue through the
remainder of the overnight into early Sunday morning, with pockets
of dense fog anticipated. A Dense Fog Advisory remains in effect
until 10 AM CDT Sunday given this potential. The next chance for
thunderstorms arrives during the Wednesday-Thursday time frame. It
remains too early to tell if any storms could be severe, with trends
being monitored over coming forecasts.

Quigley

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ080-LMZ366-LMZ565-LMZ567-LMZ643-LMZ644-
     LMZ645-LMZ646-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 until 10 AM
     Sunday.

&&

$$

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