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191
FXUS63 KMKX 220255 AAA
AFDMKX

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

.KEY MESSAGES...

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- Tornado Watch continues until midnight CDT for all of
  southern Wisconsin. Severe thunderstorms will continue to
  shift northeastward this evening across the area. Damaging
  winds will be the primary concern, though large hail and
  isolated tornadoes remain possible.

- Gale Warning in effect for the southern two thirds of the open
  waters of Lake Michigan, as well as for the nearshore waters,
  for strong south winds ahead of the cold front.
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&&

.UPDATE...
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Issued 955 PM CDT Tue May 21 2024

Severe storms will continue to shift northeast across the area
this evening, exiting to the east around or soon after midnight.
Damaging winds are the main concern with these storms, with
large hail and brief spin-up tornadoes still possible. There is
still strong upward vertical motion with the cold front and
associated low level frontogenesis response. The passing 500 mb
shortwave trough will also provide some upward vertical motion,
with strong low layer and deep layer bulk shear in place. Mean
Layer CAPE of 1500 to 2000 J/kg remains as well ahead of the
front, so think that severe storms should continue through most
of the rest of the area late this evening.

Wood
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&&

.SHORT TERM...
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

&&

.LONG TERM...
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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.

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

.AVIATION...
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Issued 955 PM CDT Tue May 21 2024

Severe storms should continue to push northeast across the area
late this evening, exiting to the east around or soon after
midnight CDT. Damaging winds are the main hazard, though large
hail and a brief spin-up tornado are still possible. May see IFR
visibility and MVFR ceilings in any storms.

Gusty south winds may increase until the cold front passes, with
gusts to 30 knots or so expected, especially for terminals
closer to Lake Michigan. Low level wind shear is also expected
ahead of the front, with southwest winds at 2000 feet AGL around
45 to 50 knots.

Winds will shift to the southwest behind the cold front later
tonight, remaining gusty into Wednesday and slowly veering to
the west. A period of MVFR category ceilings below 2000 feet AGL
are possible later tonight and into Wednesday morning, before
becoming VFR again by Wednesday afternoon. Skies should scatter
out in the late morning or early afternoon.

Wood
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&&

.MARINE...
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Issued 955 PM CDT Tue May 21 2024

Low pressure around 29.3 inches near the Twin Cities will
strengthen to 29.1 inches and track to north of Lake Superior
overnight. South gales are expected into the overnight hours
over the southern two thirds of the lake. Waves will increase as
well during this time.

Widespread thunderstorms are expected to move across the lake into
the overnight hours, and may contain damaging winds.

A strong cold front will then veer the winds to southwesterly
late tonight, with the gusty winds continuing over the north half
of the lake through Wednesday. A Small Craft Advisory is in
effect for the nearshore waters after the Gale Warning expires
and into Wednesday afternoon.

Light to modest southwest winds will then prevail over the
entire lake for Wednesday night and Thursday.

Wood
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&&

.MKX WATCHES/WARNINGS/ADVISORIES...
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WI...None.
LM...Gale Warning...LMZ080-LMZ366-LMZ565-LMZ567-LMZ643-LMZ644-
     LMZ645-LMZ646-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 until 4 AM
     Wednesday.

     Small Craft Advisory...LMZ645-LMZ646...4 AM Wednesday to 10 AM
     Wednesday.

     Small Craft Advisory...LMZ643-LMZ644...4 AM Wednesday to 4 PM
     Wednesday.
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&&

$$

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