Janesville, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

404
FXUS63 KMKX 190240 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
940 PM CDT Fri Jul 18 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms (40 to 60 percent chance)
  are forecast to move southeast into south central Wisconsin
  early Saturday morning and exit southeast Wisconsin by midday.
  Damaging winds are possible with stronger storms, along with
  some hail. There is uncertainty with how much in the way of
  showers and storms the area will see during this time.

- Additional showers and thunderstorms are possible Saturday
  afternoon along a cold front. Storms may produce damaging
  winds and hail.

- Chances for storms develop on and off early through late next
  week, but timing and intensity remains uncertain at this time.

- Heat builds back into the region, with highs in the upper 80s
  to lower 90s Tuesday into the end of the week.

&&

.UPDATE...
Issued 940 PM CDT Fri Jul 18 2025

Showers and thunderstorms have developed over central to west
central Minnesota, near the cold front and the developing
southwesterly low level jet. CAMs have generally been trending
with the northern portions of this convection moving east along
the developing warm front in northern Wisconsin overnight into
Saturday morning.

They have the rest of the convection shifting southeastward and
either missing the area to the southwest or having scattered
convection move through the area during the early to middle
morning hours on Saturday. This generally follows the
instability gradient from Minnesota into eastern Iowa and
northern Illinois. Recent CAM runs have been back and forth
with the areal extent of the convection, so uncertainty remains
fairly large with this aspect of the thunderstorm potential.

CAMs have slowed a bit more with the timing of these storms,
with the main window appearing to be in the 6 AM to Noon CDT
time period through the area.

For now, will maintain the current expectations for scattered
storms to move through the area in the early to middle morning
hours on Saturday. There is enough elevated CAPE and deep layer
bulk shear for strong winds to occur with the storms, and
perhaps some hail and brief heavy rainfall.

The potential second round of more isolated to scattered
showers and storms with the cold frontal passage Saturday
afternoon lingers as well. However, the later timing of the
exiting storms may leave cloud debris around long enough to
limit sunshine and instability for this next potential round.
This will be the key for additional storms Saturday afternoon.
Again, if the storms develop, there is the potential for strong
winds and some hail with the stronger storms.

Wood

&&

.SHORT TERM...
Issued 336 PM CDT Fri Jul 18 2025

Tonight through Saturday night:

Light winds and lows in the mid to upper 60s through midnight,
as high pressure exits to the east and winds kick southeasterly
and bring a return to warm, moist conditions.

Exiting 200 mb jet will continue to produce showers and
potentially thunderstorms across northern Minnesota and northern
Wisconsin into tonight. Warm frontogenesis developing across
the same region will bring additional lift and allow storms to
progress southeastward through the overnight hours as the front
sags southward. A second area of storms will develop early
tonight across northern Nebraska at the apex of the 850 mb LLJ,
following bulk shear vectors east-southeastward through Iowa
overnight. Placement and extent of these features remain
uncertain, and likely will continue to be uncertain until they
complete their development tonight.

Two main solutions arise, with the first, more intense scenario
indicating that plenty of moisture and elevated instability
indicated by MUCAPE of 1000 to 1500 J/kg will only require a
trigger to fire off storms across southern Wisconsin, allowing
the two storm systems to connect through southern Wisconsin due
to phasing of their respective shortwaves. this would allow for
lightning and locally heavy rain, with potential south of I-94
to produce strong to severe storms as the southern MCS taps into
better instability along the Wisconsin/Illinois border and
intensifies into the Saturday morning timeframe. The second,
less intense scenario depicts only isolated to scattered storms
across southern Wisconsin with each MCS remaining separated
throughout the overnight hours into Saturday morning. Regardless
of solution, morning convection ends by noon at the latest.

Going into Saturday afternoon, a cold front from a weak low
pressure system traversing northern Wisconsin into Michigan will
drag across southern Wisconsin. Due to the uncertainties
lingering for overnight convection, uncertainties continue into
Saturday afternoon. If phasing occurs and more widespread
convection develops across southern Wisconsin Saturday morning,
overcast skies will likely linger and prevent diurnal heating
from destabilizing the atmosphere. This would allow for weak,
pulse- type thunderstorms along the front. However, if no
phasing occurs overnight and conditions remain relatively dry,
clearing skies and a redevelopment of convection is possible.
This would lead to stronger storms along the front, capable of
producing gusty winds and small hail. All storms will exit into
Lake Michigan going into late Saturday evening.

CAMs depict potential for thunderstorm development along the
Wisconsin/Illinois border once again Sunday night along the now-
stationary front, bringing slight chances for precipitation
across far southern Wisconsin (20-30 percent). Lows in the lower
60s.

MH

&&

.LONG TERM...
Issued 336 PM CDT Fri Jul 18 2025

Sunday through Friday:

Stationary front remains just south of the Wisconsin border
through Sunday and into Monday as high pressure settles into the
Great Lakes region once again. On and off chances for showers
and storms are expected across far southern Wisconsin, but
chances remain low (15-30 percent). Low pressure develops and
pushes eastward into the Upper Midwest on Tuesday, bringing
stiff southerly winds and heat back to southern Wisconsin
through the day (highs in the mid to upper 80s). Warm frontal
feature will lift into the region Tuesday night, with potential
for storms along it (30-50 percent chance). Heat continues into
Wednesday, with highs in the upper 80s to lower 90s within the
warm sector. Timing is in question for the low`s progression
eastward, but best chances for thunderstorms in the evening to
overnight (40-50 percent chance).

Ridging continues to build across the southern U.S. Wednesday
through Friday, putting southern Wisconsin firmly into the ridge
riding MCS setup. Therefore, NBM PoPs of 20-40 percent linger
through the rest of the week. Still, expecting future
refinements to the forecast to nail down specific timeframes of
interest with future modeling. Regardless of exact timing of
storms, expect heat and humidity to continue into Friday.

MH

&&

.AVIATION...
Issued 940 PM CDT Fri Jul 18 2025

There is the potential for scattered showers and storms
shifting southeastward and either missing the area to the
southwest or moving through the area during the 11Z to 17Z
period on Saturday. Uncertainty remains fairly large with this
aspect of the thunderstorm potential, so keep up with the
forecast. If storms move through, strong winds and some hail are
possible.

The potential second round of more isolated to scattered
showers and storms with the cold frontal passage Saturday
afternoon lingers as well. This would generally be in the 19Z
Saturday to 00Z Sunday period. However, the later timing of the
exiting storms may leave clouds around long enough to limit
sunshine. This will be the key for additional storms Saturday
afternoon. Again, if the storms develop, there is the potential
for strong winds and some hail with the stronger storms.

Otherwise, light south winds overnight will become southwest on
Saturday, then west to northwest behind the cold front during
the afternoon and northwest to northeast Saturday night. Middle
to high clouds should move into the area overnight into Saturday
morning, with some ceilings down to around 2500 to 3000 feet AGL
at times if any thunderstorms develop and move through. May see
brief visibility reductions to 2 to 4 miles with storms as well.
There is some potential for lower ceilings down to or below
2000 feet AGL later Saturday evening and night to develop.

Wood

&&

.MARINE...
Issued 940 PM CDT Fri Jul 18 2025

High pressure around 30.1 inches over Lake Erie will continue
to move east tonight, as low pressure around 29.8 inches
develops in the lee of the Colorado Rockies. A warm front will
develop across northern Wisconsin and the Upper Peninsula of
Michigan overnight, bringing showers and thunderstorms to the
northern half of the lake. Additional thunderstorm development
is possible across the southern half of the lake into Saturday
morning. Light south to southeast winds will become south by
Saturday morning.

Winds become southwesterly as the showers and storms end by
midday Saturday, then become northerly behind a cold front
Saturday afternoon and evening. A few thunderstorms are possible
along this front. High pressure around 30.0 inches will settle
back into the region on Sunday, slowly departing into Monday and
shifting winds to easterly. A low pressure trough around 29.8
inches will cross the Upper Midwest on Tuesday, bringing
southeasterly winds.

MH/Wood

&&

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

$$

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