394
FXUS63 KMKX 210302
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1002 PM CDT Mon May 20 2024

.KEY MESSAGES...

- Patchy to areas of fog will be possible overnight into Tuesday
  morning, especially fro areas that saw rainfall today.

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

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

&&

.UPDATE...
Issued 945 PM CDT Mon May 20 2024

Light winds and lingering moisture behind today`s thunderstorms
is resulting in patchy to widespread fog development now through
the early morning hours. Could see areas of dense fog develop as
well. Otherwise, focus is on Tuesday where multiple rounds of
showers and storms are expected to impact southern WI.
Developing/ongoing storms upstream in IA still look to move into
southwestern WI and decaying early Tuesday morning. This first
round will mainly impact areas north and west of Madison and
while chances are lower, cannot rule out some of these elevated
storms producing some small hail and gusty winds. Then a second
round looks possible late morning early afternoon as the warm
front lift northward with the deepening low. Given the
developing convection near the frontal boundary, could not only
see hail and damaging winds with this second round, but also
cannot rule out tornadoes given better low-level shear along the
boundary. CAMs have this activity moving out and another brief
lull allowing the environment to recover before the main line of
storms develops and moves through ahead of the cold front in the
evening. Will see all severe hazards possible with the third
round of activity. Large hail and tornadoes will be more likely
when storms are isolated/developing and more supercellular, but
are progged to merge into a large squall line where damaging
winds and embedded QLCS tornado threat increase as the
convective modes change/congeal and surge east.

While the severe potential continue to look favorable,especially
Tuesday evening will need to monitor as storms earlier in the
day storm may impact later development. Nevertheless given the
dynamics of this system, things continue to look favorable for a
few rounds of severe weather.

Wagner

&&

.SHORT TERM...
Issued 248 PM CDT Mon May 20 2024

Rest of this Afternoon through Tuesday night:

Convection is ongoing across the region this afternoon,
associated with a convectively enhanced shortwave/MCV working
through the area. Strong southerly flow associated with this
feature has helped bring a warm front north into extreme
southeastern Wisconsin, with reinforcing east to northeast flow
along and north of the track of the MCV. Convection will
continue to develop and push east through early evening, with
occasional strong/severe storms producing large hail and gusty
winds.

The evening hours tonight should be fairly quiet, with the
region within an area of subsidence behind the departing MCV. A
weak pressure gradient combined with the moist airmass will pose
a fog threat overnight, especially over the eastern half of the
area. Some areas of dense fog will be possible.

The nose of a low level jet then begins to push into the area
from the west and southwest late tonight/early Tuesday. An
initial area of elevated thunderstorms will likely push into
the area during the predawn hours. Locations north and west of
Madison will have the greatest chance of seeing convection, with
considerable uncertainty as to how far east this activity makes
it before pushing north.

By late morning, a warm front will lift into the region as low
pressure deepens across Minnesota. Despite the convection
along/north of the warm front, very deep and strong southerly
flow will favor a more progressive northward movement to the
front. This should put nearly all of the CWA solidly within the
warm sector by mid afternoon. From that point forward, things
will really depend on where exactly convection fires east of the
cold front in Iowa. There could be one round as early as mid
afternoon, if storms develop along a prefrontal trough just west
of the Mississippi River, but this is uncertain. The front will
eventually surge eastward during the evening, clearing the area
around midnight. Storms are very likely along the front as it
moves east.

While the outcome will ultimately depend on "game day" mesoscale
details, this is a very dynamic system with a very favorable
airmass ahead of it. Some combination of supercells and QLCS(s)
are probable. Very steep mid level lapse rates and appreciable
low and mid level shear will pose a threat for tornadoes and
very large hail with any supercells. If/when cold pools begin to
congeal, one or more strong QLCSs could develop, with an
attendant wind and QLCS tornado threat.

Boxell

&&

.LONG TERM...
Issued 248 PM CDT Mon May 20 2024

Wednesday through Monday:

The low pressure associated with Tuesday`s thunderstorms will
continue propagating northward into Canada on Wednesday, with
gusty west winds, cold air advection, and decreasing cloud
coverage across southern Wisconsin in response. Upper level
ridging and high pressure will build into the Midwest Wednesday
afternoon into Thursday allowing for drier weather through Friday
morning.

A shortwave trough and associated surface low pressure system
will approach Wisconsin on Friday, leading to the next chance for
showers and thunderstorms Friday afternoon through Saturday
morning. The GFS and Euro look to be in better agreement regarding
timing of this system, but the GFS continues to be a little more
rambunctious regarding shower/thunderstorm development and QPF
Saturday morning, especially near the Wisconsin/Illinois border.

Another shortwave looks to move across the state during the day on
Saturday which will help support chances for showers and
thunderstorms. Weak ridging moves into the region on Sunday and
Monday leading to lower precipitation chances before another upper
trough propagates towards the region Monday afternoon.

Falkinham

&&

.AVIATION...
Issued 945 PM CDT Mon May 20 2024

Expecting to see lower ceilings and fog develop tonight given
the light flow and saturated low-levels. Most terminals can
expect to see MVFR to IFR visibilities and ceilings and could
see LIFR/dense fog develop in some spots as well. Fog will
persist through the early Tuesday morning and maybe a bit longer
closer to the Lake before the first round of showers and storms
push into southwestern WI and decay around daybreak. Then the
warm front lift north and will see winds shift an a second round
of showers and storms develop late morning into the early
afternoon. Then expecting to see a few lull before the main line
of showers and strong to severe storm pushes west to east
across WI/IL Tuesday evening. With each round of storms, expect
terminals to experience drops in visibility and ceilings before
recovering. Also could see strong gusts and hail as well.

Wagner

&&

.MARINE...
Issued 248 PM CDT Mon May 20 2024

Southeast winds will turn southwesterly for a time late this
afternoon over the southern third of the lake, as a compact area
of low pressure moves through the area. Winds then turn
westerly tonight.

Winds will turn more south to southeasterly again Tuesday. Breezy
southerly winds are expected as a deepening low pressure approaches
the Upper Great Lakes Region and tracks northeast into
Wednesday. There looks to be periods of thunderstorms over the
lake, especially southern portions Monday through Wednesday
morning. Small Craft conditions are likely Tuesday afternoon
and night.

Boxell

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ645-LMZ646...10 PM Tuesday to 10 AM
     Wednesday.

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

&&

$$

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