775
FXUS63 KMKX 041556
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1056 AM CDT Sat May 4 2024

.KEY MESSAGES...

- A few strong thunderstorms with hail and gusty winds are
  possible near & east of I-39 this afternoon.

- Additional showers and thunderstorms are expected during the
  middle portions of next week.


&&

.UPDATE...
Issued 1030 AM CDT Sat May 4 2024

Warmer air and dewpoints over the cooler Lake Michigan waters
temps have resulted in a patchy of lower ceilings and some
patchy fog, which has crept inland along the lake. With temps
continuing to warm and winds picking up, latest visible
satellite and webcams trends suggest conditions improving.
However, with persisting onshore flow, it will likely play a
role in keeping the lakeshore areas more stable limiting how far
east the afternoon/evening storm activity may make it.

Radar continues to show this line holding together late this
morning, while the 12z CAMs continue to show a
weakening/decaying trend. However, this activity continues to
show signs on IR satellite of becoming shallower as it moves
into the western portions of the CWA. And paired with drier
dewpoints, may continue to see it weaken as it moves into our
neck of the woods, but scattered, light showers will still be
possible for areas west of Madison through the remainder of the
morning.

Have been chasing inland temps all morning as they have trended
warmer even with the encroaching cloud cover. Given the warmer
trends, this will bode more in favor of higher instability this
afternoon/evening for any thunderstorms to tap into. Pockets of
clearing this afternoon will also aid in the warmer trend. Would
not be surprised to see a few spots creep toward 80F this
afternoon, especially across southeastern areas closer to the
WI/IL border.

Strong Storm Potential this Afternoon/Evening:
Continue to see the ingredients present themselves late this
morning for the line of showers and thunderstorms to redevelop
along the cold frontal boundary this afternoon and evening. The
focus of the redevelopment may be associated with a remnant MCV
currently located over northeastern MO as it moves northeast
into IL paired with the cold front. The 12z HRW NSSL and NAM
nest seem to pick up on the northeast MO MCV best and will lean
more on those solutions, which timing wise redevelops the
shower/thunderstorm activity for southern WI between 20-22z and
push east through 00-02z.

Given warmer temps along with dewpoints in the 50s and 60s,
SBCAPE is looking increasingly likely to build to the 500-1000
J/kg as the morning models have suggested. Meanwhile shear
continue to remain parallel to the front. Thus, still cannot
rule out to see a few stronger storms develop along the front.
May see a small window as things re-initiate for some small
hall, but given the steeper low-level lapse rates and inverted V
model soundings thing the main threat will be pockets of gusty
to damaging winds. Would not be surprised to see a severe storm
or two embedded within the line, especially for areas along and
just north of the WI/IL border. While it is not out a realm of
possibility to see a brief spinup within the line, the chances
remain very low at this time, up we see some bow feature develop
along the line.

Overall, the line of showers and thunderstorm potential
continues this afternoon and evening. The main area of concern
looks to be a slice from Monroe up through Fond du Lac County
down through Lake Geneva/Twin Lakes, excluding the lakefront due
to more stable conditions.


Wagner

&&

.SHORT TERM...
Issued 401 AM CDT Sat May 4 2024

Today through Sunday:

Synopsis/Mesoanalysis: Early morning surface observations place a
surface cold front along an approximate Wichita, KS to Omaha, NE to
Rochester, MN axis. Regional radar mosaics show a line of convection
extending from southwest IA to northeast KS, with light to moderate
rainfall covering much of northwest IA and southwestern MN. This
activity has developed thanks to frontogenetic forcing from the
aforementioned surface front, as well as upper divergence within an
upper jet streak currently analyzed from the Northern Plains to Lake
Superior. This area of precip will continue to pivot northeast
toward the Mississippi River through sunrise, gradually weakening as
it drifts off the most favorable upper jet dynamics & encounters a
more stable air mass with eastward extent. A weak surface low will
organize over central IA this morning, dragging the previously
mentioned cold front across southern Wisconsin later this afternoon
and evening. Scattered shower and thunderstorm redevelopment is
anticipated along the advancing surface boundary, with the bulk of
activity expected to focus near and east of the Interstate 39
Corridor. While widespread severe weather chances are low, an
isolated strong to severe thunderstorm can`t be ruled out. Precip
chances will quickly shift east with the departing surface front
this evening. Shortwave ridging will become established in the mid-
levels over the Northern Plains on Sunday, with weak high pressure
moving across the state at the surface. This will translate to
pleasant & quiet weather tomorrow.

Today: Anticipate that at least some of the rainfall currently
ongoing to our west will survive to our western zones later this
morning/early this afternoon. Given well-established weakening
trends, don`t envision any of this activity amounting to much more
than scattered showers and perhaps an isolated thundershower. With
the surface front discussed above pushing in from the west, and peak
heating of the day beginning to be realized, anticipate scattered
redevelopment of showers and thunderstorms moving into the mid to
late afternoon hours. Given frontal positioning near or just east of
the I-39 Corridor, most 00Z and 06Z CAM guidance suggests that said
redevelopment will focus over the eastern half of the area. While
widespread severe weather is not expected, an isolated strong to
severe storm can`t be ruled out given the presence of ~500-1000 J/kg
of surface-based CAPE in a warm sector bounded by the advancing
front and the westward-mixing lake breeze. A sampling of forecast
hodographs depict modest & largely unidirectional shear profiles,
with shear vectors oriented predominantly parallel to the
approaching cold front. Thus expect a clustered/messy mode in any
redeveloping storms, with hail and gusty winds being the primary
hazards in any isolated strong/severe activity given the mid-level
lapse rates and deeply-mixed boundary layers sampled in area
forecast soundings. Keep an eye on the sky if planning to be
outdoors this afternoon, and be sure to move inside if a
thunderstorm approaches your area.

Tonight: Precip chances will taper quickly this evening as the cold
front pushes east of the region. Some patchy fog is possible near
daybreak, particularly over the Wisconsin River Valley.

Quigley

&&

.LONG TERM...
Issued 401 AM CDT Sat May 4 2024

Sunday night through Friday:

High pressure is anticipated to expand over the Upper Great Lakes
Sunday night ahead of approaching ridging from the Central
Plains. This should keep Sunday night through Monday mostly dry,
as rain from a weak shortwave in the middle Mississippi Valley
will likely stay south, owing to dry air from the high pressure
center.

By Monday Night, rain chances will begin to increase as WAA and a
weak frontal boundary bring a dying line of storms toward
southern Wisconsin. Overnight into Tuesday morning, this line will
pass from west to east, with models depicting coverage becoming
spotty by the time the line hits the Lake Michigan shoreline.

Through the day on Tuesday, a secondary warm front is then
expected to lift north, with another round of thunderstorms
forming Tuesday afternoon as a strong 500mb wave and intensifying
850mb jet provides lift over the region. ECMWF and GFS solutions
show favorable shear for this event with modeled sfc to 500mb
shear around 50 knots, but both models depict differing positions
for the secondary warm front Tuesday afternoon. The ECMWF brings
it north through most of WI, while the GFS keeps it parked over
northern IL, owing to differing evolutions of the formation of a
sfc low during that time period. The positioning of this warm
front will determine the area of better instability and mode of
potential severe weather hazards on Tuesday. For what its worth,
00z CIPS analogs based on the GEFS favor a hail threat (10%
chance) mainly along and south of I-94, with no signals in the
GEFS for a wind or tornado threat at the moment.

Whatever convection develops over the middle to upper Mississippi
Valley on Tuesday is expected to push the effective warm front
farther south into central IL. At this time, models depict
thunderstorm activity staying south of the Wisconsin-Illinois
boarder, though some benign showers and a rumble of thunder may
occur Wednesday evening as an inverted trough/cold front sinks
south over the upper Midwest. This could all change by Wednesday,
however, if that warm front isn`t pushed as far south as models
currently anticipate.

Beyond, details get fuzzy, with the NBM painting broad slight
chance to chance PoPs (15% to 35%) into Friday evening, as long
range models diverge in their handling of an upper level trough
going into the upcoming weekend.

CMiller

&&

.AVIATION...
Issued 1030 AM CDT Sat May 4 2024

Onshore flow with warmer temps over cooler Lake Michigan water temps
have resulted in low ceilings pushing inland for our near lake
terminals along with some patchy fog. This is bring MVFR to LIFR
ceilings and visibility to a few spots and may continue for
another couple of hours. However, the increasing winds will help
limit the visibility impacts, keeping it mostly patchy.
Satellite trends show the thin cloud deck continuing to erode
and thinking it should mostly lift or break up through the
afternoon.

Otherwise a line of showers and few thunderstorms across
southwestern WI continue to show a downward trend in activity as
the push east, but may be organized enough for scattered
showers move in through the remainder of the morning. Overall
not expecting much in the way of aviation impacts as they stay
west of the terminals. However, expecting this line to redevelop
this afternoon as it works east with the cold front. Looking a a
line of showers and thunderstorms likely impacting most southern
WI terminals bring moderate to heavy rain, lower visibility and
ceilings, and potentiall brief stronger gusty and even some
small hail.

Otherwise, expect south-southeasterly winds today through the
afternoon before turning west-northwest by the afternoon with
the cold frontal passage.

Wagner

&&

.MARINE...
Issued 401 AM CDT Sat May 4 2024

Areas of patchy fog are possible from predawn through the morning
hours today over the open waters, though confidence regarding the
precise placement of any development remains low. Will monitor
trends over the next several hours and make forecast adjustments as
necessary. A weak, 1012 mb low pressure center will approach from
the west today, dragging a cold front across the open waters in the
process. Scattered showers and thunderstorms will be possible along
and ahead of the front. Most activity is expected to remain sub-
severe, though an isolated strong storm with small hail and gusty
winds can`t be ruled out. A 1020 mb high pressure will approach from
the northern Great Plains on Sunday, resulting in light & variable
surface winds across the open waters. Winds will begin to shift out
of the east-southeast Monday afternoon & evening as a 984 mb low
pressure center develops over the northern Great Plains. Winds will
pivot between southeasterly and southwesterly through mid-week,
prior to turning out of the north and northwest on Thursday & Friday
as a 1002 mb low pressure center moves east of the open waters.
Periods of showers and thunderstorms are forecast from early to mid
week, with conditions drying out by the end of the week & beginning
of next weekend.

Quigley

&&

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

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSMilwaukee
www.twitter.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee