Janesville, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

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FXUS63 KMKX 182346
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
646 PM CDT Thu Jun 18 2026

.KEY MESSAGES...

- Isolated to scattered thunderstorms are possible this evening
  (10-25%) and again Friday evening (30-50% Chance).

- Additional shower chances return on Sunday (40-60%).

&&

.UPDATE...
Issued 635 PM CDT Thu Jun 18 2026

Previous forecast remains on track as isolated to scattered
light showers trek southeastward across portions of southern WI
this evening with the mid-level shortwave. While a few pulse
thunderstorms briefly develop, they quickly collapse as not
much support for them to grow upscale exists. Much of this
activity will linger through sunset, but loss of daytime heating
will limit activity after sunset.

Wagner

&&

.SHORT TERM...
Issued 245 PM CDT Thu Jun 18 2026

Tonight and Friday:

Partly cloudy skies and dry weather early this afternoon may
give way to some light rain showers later this evening. The sfc
low pressure continue to move east with a mid level shortwave
lagging behind a bit this evening. The last of this mid level
lift combined with some mid level moisture should give there
state just enough lift to get isolated to scattered rain
showers. Chance for these showers late afternoon through the
evening are around 20%. There are already a few showers
developing across southeastern MN and western UP of Michigan.
Shear isn`t great and instability isn`t much better across
southern Wisconsin so lightning or any storms are not expected.
As the sun goes down and the mid level shortwave pulls to the
east, rain chances will end and skies should become mostly
clear.

For Friday, mostly dry weather is expected into the afternoon
ahead of another approaching mid level shortwave. This shortwave
looks to have better instability and shear in the low level to
support thunderstorms. The better chance for stronger storms
will largely be to our north in west central Wisconsin and
Minnesota, where the better instability and lift looks to
reside. The northwestern corner of the MKX forecast area
including Sauk, northwest Columbia and Marquette County have the
best chances for seeing any strong storms. Main hazards with any
strong storms are expected to be brief gusty winds and
lightning. As storms move southeast overtime they are expected
to weaken, which will make sporadic lightning the largest
concern for southeastern Wisconsin.

Patterson

&&

.LONG TERM...
Issued 245 PM CDT Thu Jun 18 2026

Saturday through Thursday:

As low pressure exits to the east Saturday morning, dry conditions
and northwesterly breezes will bring in temperatures in the mid to
upper 70s. A weak cold front stalling across northern Illinois
Saturday night into Sunday will phase with a deepening ejecting
low pressure system from the central Plains. Northeasterly winds
will increase through the day as low pressure approaches from the
south, keeping southern WI on the cool side (low 70s to upper
60s), and keeping any severe potential at bay. Rain will spread
northeastward through Sunday into Sunday night as low pressure
makes its closest approach through northern Illinois. Northern
extent of rainfall will depend on exact track of the low, so
probabilities are lower toward central WI (~30% chance) and higher
toward IL (60-70%). Precipitation tapers off overnight as low
pressure propagates into the Northeast U.S., with strong high
pressure pushing into the Midwest and keeping WI dry through
Monday night.

Pattern becomes much more complex Tuesday through Thursday, with
impulses from the Gulf Coast and the northern High Plains
interacting with each other to produce precipitation chances
across the Mississippi Valley into the Upper Midwest. Highest
confidence is in Wednesday afternoon (PoPs 40-60%) as the
northern High Plains low propagates through the Upper Midwest, but
prefrontal convection and shortwaves will produce on and off
thunderstorms across the region throughout the timeframe (PoPs of
20-40% for most timeframes).

MH

&&

.AVIATION...
Issued 635 PM CDT Thu Jun 18 2026

VFR conditions prevail through the period with light westerly
winds overnight. May be a few sporadic isolated to scattered
showers that may impact MSN and JVL terminal along with a low
potential fro a brief rumble of thunder. SBM may also see some
brief light showers as well. However, this activity remains
light and will diminish after sunset and unlikely to impact
southeastern WI terminals. Otherwise high pressure builds across
the Midwest through Friday morning withe VFR ceilings and
lighter winds through much of the day. Then looking at
additional shower and thunderstorms to develop Friday evening as
weak surface low tracks across central WI.

Wagner

&&

.MARINE...
Issued 245 PM CDT Thu Jun 18 2026

As low pressure of 29.3 inches in northern Michigan will move
northeast into eastern Quebec today. Winds will shift to
northwesterly and diminish as this low pressure exits. High
pressure around 30.0 inches will build into the mid Mississippi
valley behind the exiting low, keeping northwest winds light
through Friday. Winds may briefly turn southwesterly Friday night
as weak low pressure around 29.9 inches moves through the region,
but high pressure will rapidly regain dominance by Saturday,
keeping winds light and variable. Stronger low pressure will
approach from the central Plains on Sunday, bringing more
widespread rain and thunderstorms and turning winds to
northeasterly. Northeast winds will continue into early next week.

Patterson

&&

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

$$

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