Sullivan, Wisconsin Weather Forecast Discussion

628
FXUS63 KMKX 222003
AFDMKX
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
303 PM CDT Mon Sep 22 2025
.KEY MESSAGES...
- Scattered showers & storm (~40-60% chances) redevelopment
  expected late this afternoon through this evening. An
  isolated strong storm with gusty winds & small hail remains
  possible.
- Areas of fog possible tonight.
- Additional periods of showers & isolated thunderstorms
  (~15-35% chances) continue during the afternoon periods
  Tuesday through Thursday primarily south of US-151.
- Conditions drying out by the weekend.
&&
.SHORT TERM...
Issued 305 PM CDT Mon Sep 22 2025
Tonight through Tuesday night:
Synopsis/Mesoanalysis: Earlier day showers & storms have dissipated
across southern Wisconsin. An outflow boundary affiliated with the
departed precip lingers over far southeastern Wisconsin, but has
otherwise steadily washed out under mostly sunny skies in south-
central and southwestern Wisconsin. Surface winds are thus returning
to a subtle area of low pressure over southeastern Minnesota,
allowing for air mass recovery over south-central and southwestern
portions of the area. A wavy/effective warm front has been analyzed
to the east of the surface low, with surface observations and model
moisture convergence placing the boundary along an approximate
Rochester, MN - Viroqua - Dells axis. A severe storm has developed
along the boundary to the south of La Crosse, with additional
scattered storm redevelopment anticipated along/north of the front
late this afternoon & evening as it slowly sags southeast. Thus
expect a second round of scattered showers and storms across
southern Wisconsin late this afternoon & evening. A few strong to
severe storms remain possible, with gusty winds and small hail being
the primary concerns. Areas of fog are possible later tonight, with
some dense fog possible. Scattered showers and isolated
thunderstorms are possible once more on Tuesday afternoon as an
upper disturbance lingers over the western Great Lakes, though
severe weather is not expected.
Rest Of This Afternoon through Tonight: Anticipate re-development of
scattered showers and thunderstorms. Coverage of redeveloping storms
remains uncertain, which has resulted in precip probabilities being
capped in the 40-60% range in the afternoon forecast update. Upward
adjustments will likely become necessary later this afternoon/early
this evening as radar trends clarify. Several hours of recovery
behind early morning showers/storms has allowed for MLCAPE to build
back into the 500-1500 J/kg range regionally, with the greatest
values evident west of I-39 where the sun has been out for the
longest. Given the recovery, in addition to an approximate 20-35 kts
of deep layer shear being estimated in regional VWPs, an isolated
strong to severe storm thus can`t be entirely ruled out through
early evening. Gusty winds will be the primary concern, in addition
to some potential for small hail and cloud to ground lightning.
Precipitable water values in the 1.1-1.4" range will support the
potential for heavy downpours as well, though relatively progressive
storm motions should preclude widespread hydro concerns. Expect
additional rainfall totals to generally fall in the 0.1-0.5" range,
with corridors of locally higher 1"+ totals possible where heavier
storms track. Stay weather aware if heading outdoors through this
evening, and be sure to move indoors if storms approach your area.
Areas of fog are possible near/after midnight, particularly where
storms push out earlier & winds fully decouple. Dense fog can`t be
ruled out, with trends being monitored through the overnight
period.
Quigley
&&
.LONG TERM...
Issued 305 PM CDT Mon Sep 22 2025
Wednesday through Monday:
The trough meandering across the Great Lakes Region will ever so
slowly begin to exit to our east as we head into mid to late this
week. Similarly to what we saw when this cut off low began moving in
with POPs being delayed run after run, its possible we could see the
same thing on the back end. As this meandering low moves into
eastern WI and western MI, a shortwave will advance from the Rocky
Mountain west and advance east into the Great Lakes and Ohio River
Valley. These two troughs will likely merge and further delay any
movement further east. Thus low chance POPs(10-20%) do linger into
Thursday. Now this upper level trough will be positively tilt and
therefore much weaker overtime. The other item worth mentioning is
there remains uncertainty with the exact track and timing of the
trough after the merger with the shortwave. For example the NAM and
CAN are much further east versus the GFS and the Euro is somewhere
in between. Overall, just keep an eye on POPs through the week as
there will likely be additional changes over the next couple of
days.
As we head into the weekend, a ridge will begin to build in and
bring a drier, more quiet pattern. As this ridge builds in, one more
trough will try to descend down from Canada Saturday, but guidance
keeps this trough further to our east. This largely keeps POPs out
of our area of concern, but we could see some slightly cooler temps
as an associated cold front may move down the state. In the event
that this occurs, we will again remain mostly dry. There is a lack
of moisture and upward lift under the growing ridge to our west.
This ridge then looks to remain in place into early next week.
Patterson
&&
.AVIATION...
Issued 305 PM CDT Mon Sep 22 2025
Earlier line of -TSRA and -SHRA has shifted over Lake Michigan early
this afternoon, resulting in mostly VFR conditions across southern
Wisconsin. Currently ongoing from La Crosse into southern Minnesota,
additional -SHRA and -TSRA development is anticipated along an
approaching front from the late afternoon into the evening hours.
Evolution of said development remains highly uncertain do to
lingering impacts from earlier day activity. Have thus handled later
precip potential with PROB30 groups at all terminals, and will
insert TEMPO/prevailing groups as radar trends warrant later this
afternoon/evening. -SHRA/-TSRA potential will conclude prior to
daybreak Wednesday, with BR/FG and MVFR CIGs possible in their wake.
CIGs could drop lower than the current forecast of FL020, with
forecast uncertainties precluding lower mentions at this time. Will
continue to watch observational and forecast guidance trends through
this evening.
Quigley
&&
.MARINE...
Issued 305 PM CDT Mon Sep 22 2025
Light southerly winds, variable at times, will prevail through this
evening. A weak cold front will slowly move north to south across
the lake late tonight into Tuesday morning with a light wind shift
to northerly expected. Scattered showers and thunderstorms will
occur at times during this period. Moist conditions, in addition to
light overall winds in the vicinity of the passing front, will
support additional periods of fog through Tuesday morning,
particularly across the northern half of the open waters. The Dense
Fog Advisory has been extended until 4 AM CDT Tuesday morning over
the northern third of Lake Michigan. An isolated stronger storm with
gusty winds is possible this afternoon and evening, particularly
across the southern half of Lake Michigan.
Northeast winds will pick up Tuesday afternoon through Wednesday as
high pressure around 1023 mb forms near the Hudson Bay and low
pressure around 1009 mb develops in the middle Mississippi Valley.
The low will slowly pass near or just southeast of southern Lake
Michigan Wednesday night through Thursday. Wind gusts are expected
to remain below gale thresholds during the low`s approach and
passage, though trends will be monitored in coming forecasts.
Additional periods of showers and isolated thunderstorms are
expected Tuesday afternoon through Thursday, with severe weather not
anticipated at this time.
Earlier day dense fog has improved in nearshore zones, though
additional fog is possible this evening through mid-day Tuesday
given moist low level conditions and generally light surface winds.
Additional Dense Fog Advisories are possible, with visibility trends
being closely monitored this evening through Tuesday morning.
Additional showers and thunderstorms are possible late this
afternoon through this evening as a cold front slowly works through
nearshore zones. An isolated stronger storm is possible. Additional
periods of showers and isolated thunderstorms are possible Tuesday
afternoon through Thursday, with strong/severe storms not
anticipated at this time.
Quigley
&&
.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565
     until 4 AM Tuesday.
&&
$$
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NWS MKX Office Area Forecast Discussion