692
FXUS63 KMKX 201801 CCA
AFDMKX

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

.KEY MESSAGES...

- Confidence in strong to severe storms has increased this
  afternoon. A Severe Thunderstorm Watch is in effect for portions
  of the area until 5 PM.

- Large hail and damaging winds are the primary concerns in this
  afternoon`s storms, though a few spin-up tornadoes can`t be
  ruled out.

- While there remains uncertainty on the exact specifics of the
  severe weather threat Tuesday, there remains a higher chance
  (risk 3 out of 5) for severe weather on Tuesday with all modes
  of severe weather (large hail, damaging winds, and tornadoes)
  possible. Overnight storms Monday into Tuesday and how they
  track/evolve over IA/IL will impact the development and
  environment Tuesday afternoon and evening.

&&

.UPDATE...
Issued 1245 PM CDT Mon May 20 2024

.SEVERE THUNDERSTORM WATCH 267 IN EFFECT UNTIL 5 PM THIS EVENING
FOR PORTIONS OF SOUTHEASTERN WISCONSIN...

In coordination with the Storm Prediction Center & neighboring
offices, a severe thunderstorm watch has been issued for the
southeastern corner of the area until 5:00 PM this evening. This
watch includes the entirety of the Milwaukee metro. Madison &
Dane County are not included in the watch. Developing along &
ahead of an MCV approaching from the west, scattered
thunderstorm development is anticipated through early to mid
afternoon, particularly within within an area of clearing skies
that has materialized from Janesville to Watertown & points east
to the lakeshore. Satellite & radar trends have shown multiple
attempts at initiation over the last 45-60 minutes, with
preliminary storms struggling to maintain intensity. Expect that
strength will steadily increase with continued surface heating
over the watch area, with large hail and damaging wind gusts
being the primary concerns. Despite the primary wind/hail
hazards, low level shear is supportive for isolated tornadoes,
with the MKX VWP depicting clockwise-turning hodographs and 200+
m2/s2 of storm-relative helicity in the lowest kilometer. Any
persistent cells will thus need to be monitored for this
isolated potential, particularly in any locations where winds
are backed out of the southeast. Have multiple ways to receive
warning information through this afternoon over southeastern
Wisconsin.

Quigley

&&

.SHORT TERM...
Issued 423 AM CDT Mon May 20 2024

Today through Tuesday night:

Early this morning a band of rain/storms is moving through
southern Wisconsin. This initial band of showers is expected to
be on the weaker side and will continue to diminish/weaken as it
traverses east away from the LLJ and shortwave trough. This line
of showers is currently supporting this thought process well as
it has been very outflow dominate over the last few hours.
Behind this band, further up stream, is the MCV feature that
brings our concern for severe weather today. The lull between
the ongoing rain the MCV will be a big determining factor in how
much sfc instability we will have. The MCV is currently being
supported by the LLJ and shortwave trough approaching the state.
The best chances for strong to severe storms late this morning
into the afternoon will likely be across southeastern and
eastern Wisconsin where conditions are currently dry. The
ongoing line is likely to weaken significantly early this
morning. This should keep the environment primed for when the
MCV rolls through. Overall the biggest threat from any stronger
storms will be hail. Can`t rule out some gusty winds, but thats
going be more likely from towering storms that fall apart
quickly than anything else.

Tuesday brings the next chance for rain and storms as the next
upper level shortwave moves through. This next system will be
more robust than the previous provide southern Wisconsin with a
greater chance for severe weather. There are two "rounds" of
rain/storms expected Tuesday, one along the warm front and a
second along the cold front. The cold front will be the main
driver for our severe potential. Overall the environmental setup
will have decent moisture, great low level instability and some upper
level synoptic support. 0-3km shear will be high and hodographs
are taking on that nice curved feature. This allows all storm
modes to be possible with the main hazard concerns being winds
and tornadoes. Tornadic potential at this point leans toward the
short-lived quick spin up type.

Now the bigger issues with the amount of synoptic support with
this shortwave and the warm front. Uncertainty in how far north
the warm front will move north and the timing this will occur
are the biggest factors. If these two "rounds" run together then
it would be hard for the environment to recover and it would
reduce the severe potential. On the other hand, if the warm
front surges northward with a significant break between it and
that cold front. Then the door opens up for more supercellular
like behavior along and ahead of the cold front. Behind the
front, quieter weather is expected to return.

Patterson

&&

.LONG TERM...
Issued 423 AM CDT Mon May 20 2024

Wednesday through Sunday:

The cold front and dry slot will be clear of southern WI by
Wednesday morning, per the majority of models and ensembles. There
may be a few strato-cu showers toward central WI with any wrap-
around precip from the exiting upper low. Otherwise, expect gusty
westerly winds and cooler temperatures around 70.

Thursday through Sunday high temps will also be in the lower to
mid 70s, with lows in the lower 50s, much more seasonal for this
time of year. The next chance for showers and thunderstorms will
arrive Friday afternoon or night to kick off Memorial Day Weekend.
This is associated with an upper low tracking across southern
Canada and remnant vorticity advection over southern WI. As the
case has been lately, the GFS goes crazy with the QPF and also
brings the front through WI earlier than the ECMWF (by at least 12
hours). The low level jet, warm air advection, and a weak
shortwave justify our small chances for showers and storms Fri
evening.

One more shortwave digging through the Plains is expected to swing
across WI on Saturday. The ECMWF came in with a similar idea to
the GFS for the 00z run. While there is still plenty of time to
work out the details, the risk of showers and storms sometime
Saturday-Sat nt is there. Weak ridging moves in Sunday, so precip
chances are much lower for that period.

Cronce

&&

.AVIATION...
Issued 917 AM CDT Mon May 20 2024

Convection will impact the terminals at times today, with the
highest chance for stronger storms occuring this afternoon at
Janesville, Kenosha, and Milwaukee. MVFR/IFR will be possible in
and around any convection, with VFR otherwise prevailing. Winds
will briefly become gusty from the southwest over southeastern
Wisconsin this afternoon as well.

Limited shower/thunderstorm coverage is expected this evening
and overnight. Winds will be light from the west, trending light
and variable at times overnight.

Boxell

&&

.MARINE...
Issued 423 AM CDT Mon May 20 2024

Light and variable winds over Lake Michigan will continue early
this morning before shifting to southeasterly. Winds will become
southwest to westerly by this afternoon as a weak low pressure
system traverses the Great Lakes Region. Monday night into
Tuesday southeast winds return as another stronger low pressure
system advances from the Central Plains. This low pressure
system will deepen as it moves into the Great Lakes Region
causing southerly winds to increase. A Small Craft Advisory will
likely be needed Tuesday night into Wednesday for the breezy
southwest winds.

Patterson

&&

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

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSMilwaukee
www.twitter.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee