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875
FXUS63 KMKX 191537 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1037 AM CDT Wed Jun 19 2024

.KEY MESSAGES...

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- There will be chances for showers and thunderstorms this
  afternoon into this evening for all of southern Wisconsin. May
  see gusty winds with the stronger storms over southeast
  Wisconsin. On and off thunderstorm chances will then continue
  into this weekend.

- Heat index values will be in the middle 90s over southeast
  Wisconsin today. Head index values will be back in the middle
  90s Friday and Saturday.

- A moderate swim risk may occur Thursday morning at Sheboygan
  County beaches.
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&&

.UPDATE...
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Issued 1037 AM CDT Wed Jun 19 2024

Cold front is expected to continue to shift southeast into the
area this afternoon and into northern Illinois tonight. CAMs are
generally showing widely scattered to scattered showers and
storms developing after 1 to 2 PM CDT this afternoon and
continuing ahead of the front into at least early this evening.

The best instability will be toward southeast Wisconsin, where
daytime heating should bring mean layer CAPE into the 1000 to
1500 J/kg range, perhaps higher in spots. Areas further
northwest may have more clouds move in with the front, so mean
layer CAPE there will be lower. 0 to 6 km bulk shear values are
weak into early afternoon, perhaps 15 to 20 knots. They are
expected to increase by later this afternoon and early evening
into the 20 to 25 knot range, though the southeast parts of the
area will be on the lower end of this range.

This would mean short-lived airmass thunderstorms that have
some downburst wind potential, as forecast soundings are showing
some inverted V structures to them in the low levels. Heat index
values in the lower to middle 90s are expected in southeast
Wisconsin, with highs in the upper 80s to lower 90s.

Wood
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&&

.SHORT TERM...
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Issued 441 AM CDT Wed Jun 19 2024

Today through Thursday:

A cold front is expected to slowly sink southeast over the state
today. Currently, a weak 500mb wave along the front is causing
an area of shower and storm activity over NE IA. This activity
should continue northeast into central WI this morning and fade
with time. There should be a bit of a lull in activity as the
front continues southeast, but by the mid afternoon, convergence
along the front and the breaching of convective temps should
allow for scattered thunderstorms to form over much of southern
WI. Shear will be weak with effective bulk shear only around 10
knots, but shallow inverted v soundings in the lowest 1 to 2 km
and PWATs in excess of 1.6 to 1.8 inches will cause torrential
downpours and the possibility of downbursts with any storms
that form.

Scattered shower and storm activity will continue into the
overnight hours and into Thursday morning as the front slowly
sags south and stalls in northern IL. Thursday will actually
feel cool in comparison to the past few days, as cloud cover,
rain and northeasterly flow off of Lake Michigan will dull
daytime highs. Highs will be in the 70s over most of southern
WI, with 80s near the WI/IL border. Dew points will remain
elevated however, keeping some soupiness in the air.

CMiller
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&&

.LONG TERM...
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Issued 441 AM CDT Wed Jun 19 2024

Thursday night through Tuesday:

Lee troughing along the Rockies is anticipated to create an
area of low pressure over the Nebraska panhandle by Thursday
night. WAA in association with circulation around this low will
bring another surge of warmth north for Friday and Saturday
with daytime highs in the mid to upper 80s for Friday and the
upper 80s to low 90s for Saturday. Heat indices will reach the
90s both days owing to lingering dew points near 70. The broad
WAA over the upper midwest to central plains is expected to
promote further chances for convection Thursday night into
Saturday morning with the NBM painting broad PoPs of 30 to 45%
over southern WI.

Models are still keying in on a cold frontal passage Saturday
evening with 60 to 70% PoPs as the aforementioned low deepens
and approaches Lake Superior. Timing of the front would suggest
some of the storms would be strong, but GFS soundings are
currently ho-hum, with only 25 knots of effective bulk shear,
mid level lapse rates around 6 C/km, 1600 J/kg of SBCAPE, and
weak flow evident in the hodographs. This paired with boundary
parallel shear would drive quick upscale growth into a squall
line along the front Saturday night. We`ll continue to monitor
the storm threat as the weekend draws closer.

Beyond, temperatures "cool" in the low 80s Sunday and Monday as
high pressure sink south into the area behind the front, but
heat may return by Tuesday as ridging returns.

CMiller
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&&

.AVIATION...
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Issued 1037 AM CDT Wed Jun 19 2024

Gusty southwest winds this afternoon will shift west to
northwest and weaken later this afternoon and early this
evening, as a cold front moves southeast through the area.
Widely scattered to scattered showers and thunderstorms may
develop with the front during the afternoon and early evening,
and may bring gusty winds and locally reduced visibility values.

Light winds will shift north this evening and northeast later
tonight, with east to northeast winds on Thursday. Cooler
temperatures are expected tonight into Thursday, especially near
Lake Michigan. A few showers and storms may occur at times
overnight into Thursday, perhaps more toward the Illinois border
areas on Thursday.

General VFR ceilings overnight should drop to 800 to 1500 feet
AGL Thursday morning and slowly rise Thursday afternoon. In
addition, fog with 2 to 5 mile visibility may form overnight
into Thursday morning, or move onshore from Lake Michigan for
terminals nearby. Locally lower values are possible.

Wood
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&&

.MARINE...
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Issued 415 AM CDT Wed Jun 19 2024

A cold front will gradually sink east-southeast over Lake
Michigan through today as low pressure approaches James Bay in
Canada. Modest southerly to southwesterly winds will prevail
through today until winds come around to northerly tonight
following the front. In the post-frontal air mass, some areas of
marine fog may form tonight.

North to northeast winds should then linger into Thursday
night, as high pressure moves toward Lake Superior.

CMiller
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&&

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

$$

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