359
FXUS63 KMKX 040904
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
404 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.

&&

.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 401 AM CDT Sat May 4 2024

Expect primarily VFR conditions to prevail through the remainder of
the overnight and AM hours today. East-southeast winds will begin to
increase ahead of an approaching surface low near/just prior to
daybreak, allowing moisture to begin increasing across the region.
Given the timing of the wind shift/onset of moisture returns, will
be closely monitoring obs for any possible CIG/VIS reductions,
particularly at SBM where surface temp & dew point spreads are
approaching zero. Anticipate improvements in any isolated
categorical reductions by mid-late morning. Chances for SHRA and
TSRA will increase this afternoon along and ahead of an approaching
cold front. Mentions of said chances have been maintained in the 06
and 09Z updates. Expect a period of prevailing MVFR behind the
departing frontal boundary early this evening, with improvements
occurring closer to midnight as west-northwest winds pick up
regionally.|

Quigley

&&

.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.
&&

$$

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