229
FXUS63 KMKX 300856
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
356 AM CDT Tue Apr 30 2024

.KEY MESSAGES...

- Showers expected this evening into tonight, with some thunder
  also possible

- Additional rounds of showers and storms Wednesday night
  through Thursday night

&&

.SHORT TERM...
Issued 356 AM CDT Tue Apr 30 2024

Today through Wednesday:

Clouds should gradually decrease across the north today under
high pressure. With plenty of sunshine anticipated by afternoon,
high temps should reach or approach 70 most places. Winds will
likely turn onshore by the lake in the afternoon, bringing some
cooler temps to lakeshore areas.

A shortwave will swing through the area this evening into
tonight, bringing showers and a few thunderstorms to southern
Wisconsin. Instability will be decreasing as the area of precip
approaches, with models showing a lessening chance for thunder
and also decreasing precip amounts. Still, looks like enough
forcing and moisture for high precip chances (60-100% most
places), so confidence is high in rain this evening/overnight.
The higher chances will be in the north closer to the track of
the surface low.

High pressure will then bring mostly sunny skies and mild temps
to the area on Wednesday. Offshore winds should be strong
enough through the day to keep the lake breeze away.

DDV

&&

.LONG TERM...
Issued 356 AM CDT Tue Apr 30 2024

Wednesday night through Monday:

Wednesday night marks the approach of our next active weather
pattern, with a neutrally tilted trough over the rockies deepening
and becoming more negatively tilted and the corresponding ridge
axis building over the eastern Great Lakes region, obtaining
stronger supergeostrophic flow. The corresponding upper air
divergence and lee cyclogenesis develop a deep low pressure in
Colorado Wednesday evening, which then elongates meridionally into
two separate lows, with the northern low tracking from southeast
Nebraska Thursday morning to northern MN / WI by Thursday night.
As it travels, it occludes, and a triple- point low develops to
its southeast, which may track as close as central-WI Friday
night. Showers (and eventually thunderstorms) associated with this
event are expected to arrive Wednesday night / Thursday morning,
peak in intensity Thursday afternoon / evening, weaken Thursday
night, then clear out into Friday.

The severe thunderstorm threat for Thursday afternoon and evening
is conditionally dependent on the positioning of the warm sector /
warm front and wind shear from the jet streak. For example, the
ECMWF produces 40 to 55 kts of surface to 500mb bulk shear across
the CWA at 1 PM Thursday (sufficient for organized convection and
supercells). Then, as the ridge continues to build northward and
the jet lifts with it, the shear decreases to 20 to 35 kts at 7
PM (marginally sufficient for organized convection, but supercells
much less likely). The GFS exhibits similar behavior, while the
NAM allows more consistent favorable shear (jet stays closer to us).
Until model guidance converges on a solution, either scenario is
in play. For instability, global models have suggested roughly 500
j/kg CAPE (relatively weak) in southern portions of our CWA, with
lower values to the north. Depending on the exact track of the
system, and how strong the triple point low becomes, CAPE > 1000
j/kg deeper within the warm sector could easily be pulled into our
CWA. On the other hand, said triple point low could also
strengthen the easterly component of the wind field off of Lake
Michigan, advecting cool stable air over portions of the CWA and
minimizing the severe threat. Both the warm frontal surge
(late Thu morning through Thu afternoon) and the cold front
passage (late Thu evening / nighttime) should be capable of
triggering ascent, hence our PoPs are 80% and rain is likely in
any scenario.

Shower and thunderstorm chances continue into Friday behind the
cold front, but chances have decreased (25 to 50% PoP in the
morning, only 25% in the afternoon) and may continue to trend
down. This is due to model guidance converging on a sooner than
anticipated passage of the cold front and a dry slot wrapping into
the departing low pressure.

A shortwave trough approaches Saturday, bringing a small/brief
push of moisture and PVA, delivering some rain showers to the
area. Our forecast features broad-brushed 30% PoPs due to model
guidance disagreeing on the exact arrival time. Dry / quiet
weather is the most likely scenario for Sunday, with a high
pressure system residing over WI.

Sheppard

&&

.AVIATION...
Issued 356 AM CDT Tue Apr 30 2024

A mix of VFR and MVFR clouds continue mainly north of I-94
early this morning. There should be gradual clearing in the
north the remainder of the morning under high pressure. Low
pressure will pass by to the north this evening into tonight,
with showers likely as this system moves through. A few rumbles
of thunder will also be possible, especially in the evening.
Ceilings could briefly dip below VFR as the trough swings
through tonight, with skies clearing early Wednesday behind the
trough. Low level wind shear is expected for a time later this
evening into tonight as the the low level jet moves overhead.

DDV

&&

.MARINE...
Issued 356 AM CDT Tue Apr 30 2024

Southerly winds will be generally under 15 knots today, as high
pressure slides through the area. Southeast to south winds will
increase tonight, as low pressure lifts northeast through
northern Wisconsin. Breezy west to southwest winds are expected
on Wednesday behind the departing low and as high pressure
builds in from the west. Another low will lift through
Wisconsin Thursday into Thursday night, bringing breezy east to
southwest winds to the lake.

Winds will approach Small Craft Advisory levels on Wednesday,
especially north of Milwaukee. Onshore winds Thursday may push
waves over 4 feet, with advisory conditions possible then as
well.

DDV

&&

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

$$

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