233
FXUS63 KMKX 211812
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
112 PM CDT Tue May 21 2024

.KEY MESSAGES...

- Marine Dense Fog will continue to decrease in coverage through
  the afternoon.

- A complex severe weather event is expected today, with
  multiple rounds of thunderstorms expected. All severe hazards
  are possible.





&&

.UPDATE...
Issued 112 PM CDT Tue May 21 2024

Low to mid level warm, moist advection has been maintaining the
convection from Iowa into south central WI today. The sfc warm
front is beginning to move nwd with a weakening supercell along
it over Dane Co. with additional storms along the warm front or
outflow over ern IA. Any of these storms will be capable of
becoming supercells given deep layer shear of 50 kts and 0-1KM
SRH of 200-300 m2/s2 with all hazards possible including
tornadoes.

The warm front should move into central WI by early evening as
the deepening sfc low over the Mid MO River Valley tracks to
just west of KMSP by 00Z Wed. The amplifying upper wave, strong
cold front, and a broken to solid line of convection will then
sweep across WI this evening. Mdt to strong deep layer shear
and strong low level shear is present but there is a limiting
factor to the severe potential this evening. A warm layer from
800-700 MB could yield a high LFC and very low 0-3 km CAPE. This
warm layer will also contribute to building MLCIN along with
the loss of diurnal evening. Although there would still be some
tornado risk, damaging winds and hail may be more probable. The
warm layer and building MLCIN could actually cause the line to
dissipate over far se WI as indicated by some CAMs.

Gehring

&&

.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
comparison to 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
Saturday which 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 112 PM CDT Tue May 21 2024

The Cigs well below 1 kft over far ern WI and nw of Madison will
dissipate by late afternoon. Otherwise scattered strong to
severe storms will move across south central WI this afternoon
followed by a north to south line moving ewd across srn WI for
the early to middle evening hours. After the cold front passes
MVFR Cigs are expected to develop over much of srn WI and
continue into Wed AM before dissipating by afternoon.


Gehring

&&

.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...None.

LM...Dense Fog Advisory...LMZ080-LMZ643-LMZ644-LMZ645-LMZ646-LMZ669-
     LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ870-LMZ872-LMZ874-
     LMZ876-LMZ878 until 7 PM Tuesday.

     Small Craft Advisory...LMZ643-LMZ644...7 PM Tuesday to 4 PM
     Wednesday.

     Small Craft Advisory...LMZ645-LMZ646...7 PM Tuesday to 10 AM
     Wednesday.

&&

$$

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