000
FXUS63 KMKX 252018
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
318 PM CDT Thu Apr 25 2024

.KEY MESSAGES...

- Active pattern Friday afternoon through this weekend.
  Multiple rounds of showers/storms will result in locally heavy
  rainfall.

- Severe storm risk possible Friday through this weekend, with
  uncertainty remaining in exact timing and placement.

- Additional chances for precipitation mid to late week next
  week.

&&

.SHORT TERM...
Issued 318 PM CDT Thu Apr 25 2024

Tonight through Friday night:

Low pressure deepening in the lee of the Colorado Rockies
overnight will increase the PGF across southern Wisconsin as a
warm frontal feature lifts slowly towards the region. Expecting
mainly dry conditions throughout the overnight hours, although
cloud cover and southeasterly winds are expected to increase from
west to east overnight into Friday morning.

The first rain shower activity looks to be lacking in CAPE and
favorable lapse rates, so expecting an initial round of light to
moderate rainfall Friday morning into Friday afternoon. Late
Friday afternoon into Friday evening as the surface warm front
lifts northward into central Wisconsin and low pressure pushes
northeastward into the northern Great Plains, MUCAPE above 500
J/kg and mid level lapse rates (700 to 500 mb) between 6.5 and 7
degrees C/km may lead to elevated thunderstorms hail cores. 0 to 3
km helicity is also quite high (300 to 500 m2/s2), but a thick
stable layer near the surface should keep convection elevated. Mid
level lapse rates continue to increase overnight to 7 to 7.5
degrees C/km, while MUCAPE in far southern Wisconsin increases to
near 1000 J/kg. However, the warm front progressing farther
northward will remove a trigger from the region late Friday night
into Saturday morning. Any convection that does develop will be
isolated during this time period.

MH

&&

.LONG TERM...
Issued 318 PM CDT Thu Apr 25 2024

Saturday through Thursday:

Saturday, some clearing is possible as southern Wisconsin remains
in the warm sector. GFS indicates potential for an outflow
boundary from overnight Plains convection to produce
thunderstorms across southwestern Wisconsin as early as Saturday
morning, although confidence in this feature is low due to the
necessitation of precursory convection. Southerly winds and
increasing temperatures within the warm sector will result in high
temperatures in the upper 70s and dewpoint temperatures in the
lower 60s. Plenty of MUCAPE (global models are noting a potential
of over 1500 J/kg), a warm and moist surface layer, and bulk shear
of 40 to 45 kt all support sustained convection. However, trigger
placement and timing is the main question for convective
potential on Saturday.

As the original parent low moves northward into Ontario, its weak
cold front interacts with a developing warm frontal feature
associated with a second low developing off the lee of the
Colorado Rockies. This frontal feature is modeled to remain
hovering over central Wisconsin to central Iowa, but its exact
location remains in question. As the main trigger to convection
for the Saturday time period, the timing and placement of this
feature will be pivotal in the intensity and placement of
widespread convection.

As the second low pressure system propagates along its warm front
into the Upper Midwest on Sunday, WAA continues across southern
Wisconsin. Disparities from run to run and model to model continue
into Sunday as well as far as the northern extent of the warm
frontal boundary, and therefore how far north into central
Wisconsin warm, moist, unstable air is able to remain in place.
The cold frontal passage of this second low pressure system Sunday
afternoon into Sunday night will be the main trigger for
convection. This day remains most in question as far as intensity
of any severe weather, due to its dependence on frontal timing.
Will continue to monitor as the event approaches.

From Saturday through Sunday, PWATs of 1 to 1.5 inch are
forecast across the region, leading to locally heavy rain
concerns. Places that see multiple rounds of thunderstorms will
be more prone to heavy rain impacts.

Cold front moves out by Monday morning, with southwesterly winds
and quieter weather expected through Tuesday before additional
shortwaves progress across the region midweek.

MH

&&

.AVIATION...
Issued 318 PM CDT Thu Apr 25 2024

VFR conditions continue throughout today and into tonight, with
increasing VFR cloud cover late tonight through Friday morning.
Showers look to progress southwest to northeast Friday morning
through Friday evening, with a few rumbles of thunder developing
Friday evening in southwestern Wisconsin. Friday afternoon into
Friday evening, ceilings will rapidly fall as a warm front with
widespread showers pushes northeastward into southern
Wisconsin late Friday afternoon through Friday night. Chances for
scattered thunderstorms push northward into much of southern
Wisconsin Friday night.

MH

&&

.MARINE...
Issued 318 PM CDT Thu Apr 25 2024

Light winds continue into this evening as high pressure of 30.4
inches remains in place over the northern Great Lakes region. As
this high exits eastward and low pressure of 29.3 inches develops
in the central Great Plains overnight, southeast winds will begin
to increase. As low pressure approaches Minnesota Friday into
Friday night, expect southeasterly winds to continue to increase,
with some gusts approaching gales possible Friday night into
Saturday. A Small Craft Advisory for wind and waves is in effect
for nearshore regions throughout this time period. Another low
pressure system around 29.5 inches will move northeast across
the Great Lakes Region Sunday into Monday, which will bring
gusty southerly winds to the southern half of the Lake and
northeasterly winds to the northern half.

Showers and thunderstorms are possible Friday night through Sunday
night, with the best chances for thunderstorms Friday night,
Saturday afternoon and night, and Sunday afternoon and night.

MH

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...7 AM
     Friday to 7 PM Monday.

&&

$$

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