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378
FXUS63 KMKX 212121
AFDMKX

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

.KEY MESSAGES...

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- A Tornado Watch has been issued for most of southern Wisconsin
  until midnight, with multiple rounds of strong to severe
  storms possible.

- Isolated thunderstorms have developed over south-central and
  southwestern Wisconsin late this afternoon. Some of these
  storms could be severe through early evening. Large hail,
  damaging winds, and isolated tornadoes are all possible.

- Additional showers and thunderstorms are expected will move in
  from the west this evening. Severe weather will also be
  possible in this activity. Damaging winds will be the primary
  concern, though hail and isolated tornadoes are also possible.


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

.UPDATE...
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Issued 420 PM CDT Tue May 21 2024

...TORNADO WATCH 279 IN EFFECT UNTIL MIDNIGHT FOR MOST OF
SOUTHERN WISCONSIN...

In coordination with the Storm Prediction Center, a tornado
watch has been issued for most of southern Wisconsin until
midnight. This watch includes the Madison metro. The city of
Milwaukee/Milwaukee County are not included in this initial
watch. A weak surface warm front is draped across the region
late this afternoon, with current analyses placing the boundary
along an approximate Lone Rock - Madison - Burlington line.
Winds have turned out of the southeast along/south of the
boundary, with stations in the warm sector reporting
temperatures in the 80s and dew points in the mid-upper 60s.
Likely encouraged by this boundary, widely scattered
thunderstorms have initiated & tracked into southwestern
Wisconsin over the last 30 mins, with severe warnings currently
in effect for Iowa and Lafayette Cos. A near term (next 1-2
hours) large hail and damaging wind threat will persist with
this activity, though the longevity of the threat deeper into
the evening/when storms move north of the front is unclear.
Given an environment characterized by abundant low level shear
south of the warm front, a tornado threat will exist in storms
remaining south of the front.

A several hour lull between this leading batch of storms and
additional activity over Iowa is anticipated. We expect these
storms to begin moving in following 7 PM, with activity pushing
through the region through midnight. Damaging winds will be a
concern in these storms, in addition to the potential for line-
embedded/spin up tornadoes. Have multiple ways to receive
warning information through this evening, and be prepared to
move to shelter if a warning is issued for your area.

Quigley
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&&

.SHORT TERM...
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Issued 244 PM CDT Tue May 21 2024

Tonight through Wednesday night:

Low to mid level warm, moist advection continues from IA into
WI. The sfc warm front is currently stalled and stretches from
near Lake Geneva to just south of Madison. This area of 1000-925
mb frontogenesis then extends south through ern IA into ne MO.
A strong storm has developed along this boundary west of
Dubuque. Isold SVR storms will continue to be possible until
the more widespread convection arrives this evening.

The warm front should still move toward central WI by early
evening as the deepening sfc low over wrn IA 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 are limiting factors
to the severe potential this evening. An area of high MLCIN
exists over far wrn WI into ne IA where rounds of storms have
kept the warm front from advancing nwd. Also, an incoming warm
layer from 800-700 MB could yield a high LFC and very low 0-3 km
CAPE even after the warm front advances. In addition, boundary
layer cooling will begin to occur as sunset approaches. Although
there would still be some tornado risk over south central WI,
damaging winds and hail may be more probable. The warm layer and
building MLCIN could then actually cause the line to dissipate
over far se WI as indicated by some CAMs.

Cold advection to then take hold into Wed AM with a shortwave
trough to pass in the afternoon. Despite the trough, drying
conditions should bring some sunshine for the afternoon and high
temps in the lower 70s. High pressure will then pass to the
south Wed nt with lgt swly winds over srn WI.

Gehring
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&&

.LONG TERM...
Issued 244 PM CDT Tue May 21 2024

Thursday through Tuesday:

Height rises associated with an upper level ridge will propagate
eastward across Wisconsin on Thursday which combined with surface
high pressure and dry air throughout the column will allow for dry
and sunny weather with highs in the upper 70s.

Showers and storms are expected to return Friday as the next
500hPa shortwave trough ejects off the Rocky Mountains and
traverses the northern Great Plains Thursday afternoon and
overnight. Current model guidance depicts this trough taking on
more of a negative tilt as it moves towards Wisconsin with a
deepening low pressure system at the surface moving northeastward
across Minnesota. Model soundings indicate decent mid-level lapse
rates and CAPE values as well as modest 0-6km wind shear in the
afternoon with a surface cold front progged to move across the
state throughout the day which would prove to be a forcing
mechanism. The mesoscale parameters combined with the upper level
dynamics suggests there may be potential for stronger storms on
Friday. However, there is the issue of potential morning
convection depleting the environment of these better conditions,
leading to uncertainty in the potential strength of Friday storms.
Discrepancy between the models still exists with the GFS
indicating a faster and stronger solution as compared to the
Euro/Canadian which would impact the strength of storms. These
variations will dissipate over the next few days though and we
should get a clearer picture as we get closer to Friday.

Upper level ridging and surface high pressure will briefly pass
through Wisconsin Saturday before yet another upper level
shortwave trough and associated surface low deepen across the
Plains before moving towards Wisconsin. There is again
discrepancy between the models with the location and path of this
low on Sunday with the Euro/Canadian bringing the low into
southern Wisconsin allowing for shower/storm chances across our
area while the GFS keeps the low further south across Illinois and
Indiana with the Wisconsin/Illinois border perhaps seeing a
little precipitation. Have gone with 30%-40% PoPs Sunday into
early Monday given the uncertainty associated with this system.
Weak upper level ridging will move through Wisconsin Monday and
should provide for drier conditions early next week.

Falkinham

Gehring

&&

.AVIATION...
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Issued 244 PM CDT Tue May 21 2024

The Cigs well below 1 kft north of the MKE metro area will
dissipate by late afternoon or early evening. Otherwise
isolated 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 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. LLWS
is expected this evening due to a strong swly low level jet
stream.

Gehring
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&&

.MARINE...
Issued 244 PM CDT Tue May 21 2024

Low pressure around 29.3 inches over western Iowa will deepen to
29.1 inches by early evening just northwest of Minneapolis, then
track to western Ontario by sunrise Wednesday. East to southeast
winds will increase this afternoon as a warm front approaches,
becoming breezy south winds, possibly approaching gale force, as
the front moves northward across the lake this evening. Areas of
dense fog should dissipate by early this evening over the south
half of the lake.

A strong cold front will then veer the winds to southwesterly
late tonight with the breezy winds continuing over the north half
of the lake through Wednesday. Light to modest southwest winds
will then prevail over the entire lake for Wednesday night and
Thursday. Widespread thunderstorms are expected tonight and may
contain strong, damaging winds.

A Small Craft Advisory is in effect from Sheboygan to Winthrop
Harbor tnt-Wed for breezy southerly winds and high waves.

Gehring

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
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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...LMZ645-LMZ646 until 10 AM Wednesday.

     Small Craft Advisory...LMZ643-LMZ644 until 4 PM Wednesday.
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&&

$$

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