333
FXUS63 KMKX 210948
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
448 AM CDT Tue May 21 2024

.KEY MESSAGES...

- Dense fog will persist across south central and eastern
  Wisconsin through sunrise this morning.

- Marine Dense Fog early this morning across the southern half
  of Lake Michigan is expected to continue through this evening.

- A complex severe weather event is expected today, with
  multiple rounds of thunderstorms expected. The greatest severe
  weather threat continues to be this evening.

- All severe weather hazards will be possible this evening,
  including strong winds, large to very large hail, and
  tornadoes.

&&

.SHORT TERM...
Issued 448 AM CDT Tue May 21 2024

Today and Tonight:

A busy, rain and stormy, day is in store for Wisconsin today.
The Storm Predictions Center`s Severe weather outlook does a
good job of reflecting this busy day with a Moderate Rick (4 out
of 5 risk) covering portions of southwestern Wisconsin.

With high dewpoints this morning and cooling temperatures, fog
has developed across the forecast area with many locations
experiencing dense fog. As southerly winds increase and diurnal
heating kicks in after sunrise this fog should burn off rather
quickly.

Kicking the rain/storm discussion off early this morning there
is ongoing convection across northeast Iowa and far western
Wisconsin. This ongoing convection is on the leading edge of the
Low level jet. Much of this early morning convection is well
ahead of these features and is slowly moving northeast.
Southwestern and western Wisconsin will have the best chances
the ongoing and slightly developing blob of showers/storms this
morning. Much of eastern and southeastern Wisconsin will remain
dry with this morning "round".

This afternoon and evening will be the main concerns for any
severe weather to develop. The afternoon round of storms will
likely be along the leading edge of the warm front. As warm
moist air surges northward a few showers and storms are likely
to develop. The exact location that storms could fire is a bit
muddled due to many models have a very shallow cap in place
which limits the location and coverage of any convection during
the afternoon. This cap does look to be pretty weak, which
means anything that does break it could grow quickly. Strong to
severe storms during this afternoon would mostly pose a wind and
hail threat. A brief lull between this afternoon and evening
rounds will prep the stage for the severe weather potential this
evening.

As the cold front passes later this evening the next round of
rain and storms will move through. Timing with this has the cold
front beginning to move through as early as 6 PM with it
exiting the region as late as midnight. While the exact outcome
will depend on the duration of the lull between the passage of
the warm front and cold front. The air mass in place and the
dynamics within this strengthening low pressure system are
fantastic. This means that supercells and squall line storm
modes are on the table. Lapse rates are steep, CAPE is high, and
low level shear/helicity is also very good. Hodographs continue
to show the nice curved features you would be looking for on
days with good tornado potential. Overall the threat with this
evening round is strong winds, large hail and tornadoes.

Patterson

&&

.LONG TERM...
Issued 448 AM CDT Tue May 21 2024

Wednesday through Monday:

As the low pressure system bringing all of our rain and storms
today moves northeast across Lake Superior and into Canada, high
pressure will be on its heals for Wednesday and Thursday. The
upper level ridging will be building into the Midwest Wednesday
afternoon and will continue to influence the region through
Thursday. The pressure gradient will remain tight between the
exiting low and incoming high pressure resulting in some gusty
west winds, and decent cold air advection. Cloud cover should be
decreasing throughout the day Wednesday. Considering the warmer
temperatures over the previous few days, Wednesday is likely to
feel much cooler with the 70 degree high temperatures feeling
slight deceiving for some.

Dry weather will continue through Friday morning. Precipitation
chances will increase as the next approaching shortwave moves
toward the state. Showers and thunderstorms will be possible
Friday afternoon through Saturday morning. There is still quiet
a bit of uncertainty with this system especially with timing
and strength. The GFS is still pretty rambunctious in
comparisonsto other long range models. Its likely that timing
of rain will tighten up a bit and that some of the finer details
such as QPF and exact location as this system gets closer in
time.

Another shortwave looks to be on the horizon as well for
Saturdaywhich could be yet another round of showers and
storms. Almost like a round two if you will. Showers and storms
Friday into Saturday and again Saturday will be supported by
two separate shortwave troughs. Still a lot of details to be
hashed out here. Thankfully Sunday continues to show promise for
being dry as a weak ridge quickly moves through the Great Lakes
Region.

Patterson

&&

.AVIATION...
Issued 448 AM CDT Tue May 21 2024

VFR to LIFR conditions are expected through the period. Early
this morning for south central and eastern Wisconsin there is
dense fog that dropping visibilites down to a mile or less.
Many terminals will see quarter mile visibilities with ceilings
around 200 to 500 feet until after sunrise this morning.
Multiple rounds of showers and storms are expected to move
through southern Wisconsin today. The first of these round
moving through this morning. Ongoing convection to our west is
gradually moving northeast this morning. Areas of west central
and south central Wisconsin will have the best chance for
showers and storms with this morning round, while the rest of
southern Wisconsin remains dry. MVFR fusillades and ceilings
will be possible during this round of showers/storms.

There is a small chance for an afternoon round of showers and
storms as the warm front moves through. MVFR to IFR visibilities
will be possible any of the moderate to heavy rainfall. Then the
last round would be this evening along the cold front. Again
MVFR to IFR visiblies will be possible. For both of these rounds
ceilings are expected to be around 3-6 kft. Severe storms will
be possible for both the afternoon and evening rounds with large
hail, strong winds and tornadoes all being possible.

Southwest to southeast winds are expected today. These southerly
winds will increase becoming breezy this afternoon. The breezy
south winds will persist through Wednesday morning with gusts
of 20 to 25 kts likely. Stronger gusts will be possible with
any convection.

Patterson

&&

.MARINE...
Issued 448 AM CDT Tue May 21 2024

With dewpoints near the air and water temperatures across the
southern half of the Lake this morning dense fog has developed.
As dewpoints increase with the passage of the warm front later
today, its likely that the dense fog will persist until the
cold front moves across the open waters, bringing with it rain
and thunderstorms.

South to southeast winds this morning will become breezy as a
deepening low pressure system advance from the central plains
northeastward toward the upper Great Lakes Region. There will be
periods of thunderstorms over the lake, especially the southern
portions through Wednesday morning. A Small Craft Advisory is in
effect tonight through Wednesday morning due to the gusty
southerly winds.

High pressure will build into the Midwest Wednesday and Thursday
bringing quieter winds and waves through midweek.

Patterson

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory...WIZ046-WIZ047-WIZ051-WIZ052-WIZ057-WIZ058-
     WIZ059-WIZ060-WIZ063-WIZ064-WIZ065-WIZ066-WIZ069-WIZ070-
     WIZ071-WIZ072 until 10 AM Tuesday.

LM...Small Craft Advisory...LMZ643-LMZ644...10 PM Tuesday to 4 PM
     Wednesday.

     Small Craft Advisory...LMZ645-LMZ646...10 PM Tuesday to 10 AM
     Wednesday.

&&

$$

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