Fond Lac, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

454
FXUS63 KMKX 142114
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
414 PM CDT Wed May 14 2025

.KEY MESSAGES...

- A Marine Dense Fog Advisory is in effect for all open waters
  of Lake Michigan and all nearshore waters adjacent to
  Wisconsin through late Thursday afternoon. This fog may drift
  into eastern WI once again tonight through early Thursday
  morning.

- Isolated pop-up thunderstorms inland from Lake Michigan will
  continue this afternoon, then dissipate this evening.

- There is a level 3 out of 5 threat for severe thunderstorms
  Thursday afternoon and evening, with a threat for very large
  hail, tornadoes, and strong wind gusts. Initial storm
  development around 2 to 4 PM, peak intensity between 4 and 8
  PM, then storms push east of the region after 8 PM CDT.

- Additional isolated to scattered (15 to 40 percent chances)
  showers and thunderstorms are possible for Friday afternoon
  and evening. A couple of these storms may reach severe levels.

- Gusty southwest winds are expected Friday in the late morning
  and afternoon hours. Gusts of 35-45 MPH. This will usher in
  cooler temps for Saturday and Sunday, with inland high temps
  in the 60s.

&&

.SHORT TERM...
Issued 415 PM CDT Wed May 14 2025

Tonight through Thursday night:

Isolated pop-up showers and thunderstorms look to persist
through the next few hours inland, dissipating this evening. The
majority of the activity thus far has been north and west of
Madison.

Existing areas of low stratus and fog over Lake Michigan are
expected to drift into eastern WI tonight through early Thursday
morning due to a weak synoptic easterly wind. Similar to last
morning, the worst of the fog is likely to setup along and east
of the Kettle Moraine hills. Fog is less likely to push past
Fond du Lac / Watertown / Janesville this time (compared to this
past morning) based on model guidance, though I do note the
synoptic setup is quite similar. A Dense Fog Advisory may be
needed for eastern WI again.

Thursday`s Severe Thunderstorm Environment:
As the eastern WI fog erodes a few hrs after sunrise, southeast
winds setup across the region, forming a region of stable air
(with the fetch off of Lake Michigan) covering areas along and
east of line from the city of Kenosha to Fond du Lac (either the
eastern or western edge of Fond du Lac County). West of said
line, very warm temperatures (highs in the mid to upper 80s) are
expected, along with a field of scattered cumulus clouds (with
plenty of sunshine likely to get through). Forecast soundings
show steep lapse rates (all levels, with the only solid
stability in the aforementioned marine layer), HREF mean SBCAPE
3000 to 4000 joules and peak 0-3 KM SRH around 300 m2/s2. This
environment poses a threat for semi-discrete supercells capable
of producing very large hail, tornadoes, and damaging wind
gusts. The hail threat is the strongest signal, and is present
across the whole region. The tornado and wind parameter space is
similarly impressive, except for the LCL heights (cloud bases)
being ever so slightly higher than ideal for tornado-genesis
(with the caveat that storm-to-storm outflow ingestion /
interaction and the initial contact with the marine layer could
easily knock LCLs closer to the ground). As storms progress
further east and slide over the marine layer, the tornado and
wind threats will gradually decrease, but the hail threat will
persist. Exactly when/where this elevation of the storm inflow
will occur may be subject to change.

Timing and Confidence:
Initial storm development 2 to 4 PM CDT Thursday, somewhere
along or west of a Janesville to WI Dells line. Highest
confidence in storm formation / initiation further north. Thus,
areas in far southwestern WI could potentially be missed
entirely. Though confidence is lower in initiation further
south, if storms do fire, the environment is even stronger
thermodynamically, and storms may have more space to consume
said energy independently.

Peak storm intensity / coverage from 4 to 8 PM CDT.
Northeastward storm motions expected (Bunkers RM vector), with
additional storm development on the southern flanks leading to a
somewhat west-to-east propagation of the overall convection.

Storms move east of the region (likely passing Sheboygan last,
before moving over the lake) after 8 PM CDT.

Sheppard

&&

.LONG TERM...
Issued 415 PM CDT Wed May 14 2025

Friday through Wednesday:

A low (but existent) severe threat for Friday:
As strong low pressure over the northern Plains drifts east into
northern WI on Friday (and weakens slightly), gusty south to
southwest winds are expected across the region, veering further
west as a cold front passes in the afternoon and evening,
accompanied by 15-40% chances for scattered / isolated
thunderstorms. Though LCLs remain fairly high and CAPE is far
less than what we are dealing with Thursday, lapse rates do
remain favorable for a few storms to become strong to severe,
particularly in the GFS model solution. A lower end (perhaps
level 1 out of 5) threat for hail and gusty winds is possible,
particularly further south and east in the state of Wisconsin on
Friday. Main timeframe of concern would be the afternoon /
evening frontal passage, with instability dwindling into the
evening. Even without the thunderstorms, 35 to 45 MPH wind gusts
are looking likely through the daytime hours of Friday, and a
Wind Advisory may become necessary on future forecast
iterations.

The secondary cold front ushers in cooler air for Saturday and
Sunday, with inland daytime highs in the 60s.

Sheppard

&&

.AVIATION...
Issued 415 PM CDT Wed May 14 2025

Isolated pop-up thunderstorms well inland from Lake Michigan
will continue over the next several hours, dissipating shortly
after sunset along with the majority of the low-level cumulus
clouds (currently SCT/BKN around 4,500 ft). For Lake Michigan
shoreline terminals, though we currently observe mostly clear
skies and VFR, marine fog and low ceilings over the lake are
expected to drift into eastern Wisconsin after sunset tonight,
lingering through early Thursday morning (a few hrs after
sunrise). Similar to the previous night, this will likely
feature LIFR ceilings and visibilities for first and second tier
counties away from Lake Michigan.

After the eastern WI fog / low stratus erodes Thursday morning,
building southeast winds overspread the entire region. Diurnal
cumulus at SCT to BKN coverage redevelop around 3,000 ft, rising
1 to 3 thousand feet higher throughout the course of daytime
heating (remaining lowest further east). There is a level 3 out
of 5 threat for severe storms Thursday afternoon and evening,
with a threat for very large hail, tornadoes, and strong wind
gusts. Initial storm development around 2 to 4 PM, peak
intensity between 4 and 8 PM, then storms push east of the
region after 8 PM CDT. As the associated front passes in the
afternoon and evening, expect winds to veer from southeast to
southwest. 20 to 30 kt wind gusts expected through the day
Thursday.

Sheppard

&&

.MARINE...
Issued 415 PM CDT Wed May 14 2025

Dense fog will remain possible through Thursday afternoon as a
moist airmass lingers over the chilly waters of Lake Michigan. The
Dense Fog Advisory now covers all open waters of the lake, and
remains in effect through 7 PM CDT Thursday. This also includes
all nearshore zones adjacent to Wisconsin.

Winds will remain light and somewhat variable into Tonight, due
to a weak pressure gradient between developing low pressure of
29.2 inches just east of the Rockies and exiting high pressure
centered over the Atlantic Ocean. South to southeast winds will
then increase on Thursday as low pressure lifts through the
Northern Plains while deepening to 28.9 inches. While breezy at
times, winds are expected to remain well below gale levels due to
a strong inversion layer with the warmer air over the cold lake.
Thunderstorms will be likely along a cold front Thursday evening.
A few strong to severe storms with large hail will be possible.
Winds turn southwest behind the front.

Low pressure will then move through northern Minnesota and northwest
Wisconsin Friday, while weakening a bit to around 29.2 inches. Winds
will remain southerly over the open waters, but will be more
southwest across the nearshore waters. Could see gusts approach gale
force over the western nearshore waters ahead of the main cold
front Friday afternoon. An additional round of thunderstorms will
be possible with this secondary front, with a few strong to severe
storms possible again, especially across the south half of the
lake. Breezy westerly winds are likely Saturday behind the cold
front and as low pressure passes by to the north. Winds veer north
Saturday night into Sunday as high pressure builds in north of the
region.

Sheppard

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ643-LMZ644-LMZ645-LMZ646-LMZ669-LMZ671-
     LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-
     LMZ876-LMZ878 until 7 PM Thursday.

&&

$$

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