Delafield, Wisconsin Weather Forecast Discussion

231
FXUS63 KMKX 130321
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1021 PM CDT Fri Sep 12 2025
.KEY MESSAGES...
- Dense fog is lingering over portions of east-central Wisconsin
  and northern Lake Michigan. This will gradually dissipate late
  tonight through mid Saturday morning.
- Chances (30 to 50 percent) for showers and thunderstorms
  tonight through Saturday morning. Heavy rain, small hail and
  localized gusty winds are possible.
- High temperatures climbing above normal through the weekend,
  with humidity increasing as well.
&&
.UPDATE...
Issued 901 PM CDT Fri Sep 12 2025
Current forecast largely on pace, but a few things to tweak
heading into the overnight hours. Mid/high level clouds are on
the increase, but SBM quickly cooled to their crossover
temperature in the past hour, resulting in a plummeting ceiling
and visibility. Prior to higher clouds moving in, the spatial
extent of this low stratus/fog was limited and given slight
warming due to the influence of higher clouds, not expecting
much of an expansion. With time, dense fog should shift to a
more predominate low cloud deck, but will continue to monitor.
Narrow, north to south oriented zone of isentropic upglide
continues to approach southern Wisconsin from the west.
Meanwhile, a mid level shortwave over northwestern WI continues
to move to the southeast. These features will converge over the
area tonight through at least Saturday morning, sparking
scattered showers and storms. Looking at guidance run to run to
run, output has been all over the place. One run has barely any
coverage, then next has sporadically placed pockets of high QPF.
This results in a higher than average forecast uncertainty.
The two main things to hone in on are the aforementioned forcing
mechanisms. Radar over the past two hours shows mainly light
showers with the band of isentropic upglide. With the vort max
to the northwest, activity was a bit more robust earlier today,
but the general trend has been weakening and a broadening of
light and perhaps some moderate showers.
While there is some dry air to fight, advection will win out as
a southerly low level jet this evening veers to more westerly
through the overnight hours. That veering to the west is
actually beneficial as it helps to maintain if not improve
isentropic upglide. At the very least this band of showers
should maintain itself as it heads east, with some increase in
embedded thunder as warming due to the influence of the low
level jet increases lapse rates a bit.
Incoming 00z guidance continues the above mentioned varying run
to run trends in the output. The 00z NAM focuses most on the
approaching vort max, the HRRR hones in more on the isentropic
upglide. Both indicate scattered showers and storms and will
continue hone PoP updates based on satellite and radar trends.
With at least some modest increase in MUCAPE, a few storms will
have the potential to produce small hail, during the latter half
of the overnight hours.
Heading into the daylight hours of Saturday, shower/storm
chances will be most tied to the vort max moving over the
region. Current timing has this exiting to the southeast around
midday. That said, there are still indications of a low level
boundary hanging nearby into the afternoon. This could spark
widely scattered showers/storms through the afternoon. As the
low level jet pushes the low level boundary through the area, to
the west, CAPE increased, but so does the cap. As a result it
appears shower/storm chances drop by early evening.
Gagan
&&
.SHORT TERM...
Issued 304 PM CDT Fri Sep 12 2025
Tonight through Saturday night:
We may see dense fog develop toward Sheboygan once again late
this evening as this area will still be under a moist marine
influence. Fog will be less of a concern elsewhere tonight.
There are several clusters of thunderstorms ongoing over many
areas of Minnesota this afternoon, and also a weaker area of
convection over northern Iowa. They are within an area of low
level warm air advection, the nose of the low level jet, a
shortwave trough (and possible MCV), and the entrance region of
an upper jet. The clusters of storms should generally track
eastward across central and southeast MN (and eastern IA) this
afternoon, right along the CAPE gradient.
For this evening, the convection should weaken as it gets into
western WI and especially south central WI because it will be
drifting out of the favorable instability and shear region.
However, the GFS weakens the LLJ but still gradually leans it
over into south central WI just prior to midnight and then
strengthens and veers the LLJ through southern WI Saturday
morning. It therefore brings the area of showers and
thunderstorms through southern WI slowly overnight through
Saturday morning. This scenario generally makes sense and our
forecast precip (PoPs) follow this idea.
The meso models have a general sense of this scenario, with
mixed degrees of weakening and strengthening through the period.
Most models agree that the convection will exit southeast WI by
1 PM Saturday. Warm air advection will be the dominant forcing,
and there should be elevated CAPE of up to 500 j/kg late
tonight into Saturday morning, so a few thunderstorms with hail
and some gusty winds are possible. Surface- based CAPE will
increase with the daytime heating over south central WI, but
will likely be impeded by the cooler marine- influenced air over
southeast and east central WI. However, the wind shear is
expected to be highest over east central WI during the mid
morning due to the LLJ and a passing shortwave  from nrn MN.
SPC has all of southern WI in a marginal risk for severe storms
and this seems warranted.
Additionally, the precipitable water values will be in the 1.5
to 1.75 inch range, so very efficient rainfall is expected.
Showers will be slow-moving, so any stronger cells will have the
potential to drop an inch of rain within a half hour. While
flooding is not an immediate concern, if storms can regenerate
over the same area due to the LLJ sitting over south central WI,
then heavy rain and flooding could become a threat.
Warm and more humid air will push into southern WI behind the
precip Saturday afternoon on steady southerly winds.
Temperatures will depend on how quickly our clouds clear, so our
highs are in the lower to mid 80s over southwest WI, and in the
mid 70s near the lakeshore. Lows Sat nt should be around 60.
Cronce
&&
.LONG TERM...
Issued 304 PM CDT Fri Sep 12 2025
Sunday through Friday:
The warm and humid ridge will push into southern WI by Sunday,
although a southeast wind component will keep east central and
lakeshore areas of southeast WI cooler once again. Inland areas
should reach mid 80s central (including Madison) and upper 80s
west.
The upper level ridge will be stuck over the Great Lakes, with
an upper trough over the Northern Plains, through at least the
middle of next week. Southern WI will remain in southerly flow
but with a southeast lake breeze each day. Monday and Tuesday
will be the warmest for inland areas, with highs in the mid to
upper 80s. Lakeshore areas will be in the upper 70s with a
chance for lower 80s depending on the timing of that lake
breeze.
Rounds of showers and thunderstorms associated with the
upper trough will remain over the northern Plains during this
time. We may see clouds from this system west of Madison at
times, but no precip is anticipated. The trough is expected to
finally slide across the Upper Great Lakes Thursday night
through Friday, although the GFS tries to bring this through a
little earlier.
Cronce
&&
.AVIATION...
Issued 1020 PM CDT Fri Sep 12 2025
Dense fog and low ceilings ongoing for Sheboygan (KSBM) and
portions of east-central Wisconsin. Expecting this activity to
remain confined to east-central Wisconsin overnight and
gradually dissipate late tonight through mid Saturday morning.
With overcast high clouds moving in, we expect the LIFR Fog at
KSBM to gradually transition to IFR / LIFR stratus, beginning to
lift faster after dawn Saturday.
An arc of high clouds (10,000 ft or higher) and sprinkles of
rain are gradually pushing in from the west. After 3 AM CDT, we
expect some stronger showers and eventually scattered thunderstorms
to evolve across the region, sagging southeastward across the
region through around 10 AM CDT. A few of the stronger storms
could be capable of producing small hail and briefly gusty
winds, as well as a burst of heavy rain and frequent lightning.
Instability for an additional shower or thunderstorm will still
be present into Saturday afternoon, though the odds are well
below PROB30 criterion due to a lack of ascent to trigger them.
VFR and dry weather looking likely for much of the rest of
Saturday, with a light southeast breeze.
Sheppard
&&
.MARINE...
Issued 304 PM CDT Fri Sep 12 2025
The majority of the fog between Sheboygan, Port Washington, and
mid lake as dissipated, per the latest satellite imagery. Dense
fog with visibility below 1 NM is expected to expand and persist
over much of the north half of Lake Michigan tonight through mid
Saturday morning.
Low pressure around 29.6 inches over the northern Great Plains
will remain in place through early next week. Lake Michigan will
have south to southeast flow tonight into Saturday. An area of
showers will cross WI and Lake Michigan tonight through Saturday
afternoon. Winds will gradually become northeast Saturday night
into Sunday, as a frontal boundary shifts south and high pressure
around 30.3 inches develops in Quebec. Winds will increase out of
the south early next week.
Cronce
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ643-LMZ669-LMZ868-LMZ870 until 10 AM Saturday.
&&
$$
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NWS MKX Office Area Forecast Discussion