River Flood Warning 38, NWS Milwaukee, WI

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
248 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

-  A strong to severe line of fast moving thunderstorms is
   expected to move across southern WI late this evening and
   overnight. Damaging winds will be the main threat.

-  Urban and small stream flooding will be possible after
   midnight due to the already saturated conditions and a quick
   burst of torrential rainfall.

-  River rises will continue early this week and may receive a
   sudden boost from heavy rain after midnight.

-  Heat index values into the 90s will be possible on Tuesday.

&&

.SHORT TERM...
Issued 248 PM CDT Mon Jun 24 2024

Tonight through Tuesday night:

Main concern heading into tonight will be MCS activity and an
associated severe wind threat. Convection is still on track to
develop in the vicinity of the Minnesota/Wisconsin state line
this evening, congealing into an MCS as it pushes southeastward
into the area. With a strongly unstable airmass aloft feeding
this complex, it will be capable of producing high winds,
especially near the apex of any bowing segments. Outside of
that, look for sporadic wet microbursts within the areas of
heaviest rain. Limited low level CAPE and shear will greatly
limit the QLCS tornado threat.

The biggest question right now remains the exact track of the
MCS, which will be highly dependent on where exactly convection
forms late this afternoon/early this evening, and how quickly
cold pools are able to conglomerate. Once cold pool
conglomeration takes place, the complex should pretty closely
follow the northwest to southeast instability gradient and the
forward propagating Corfidi vectors.

The latest forecasts suggest that this complex could arrive in
our north as early as 10 PM, but more likely close to midnight.
It should clear the area by 4 or 5 AM. This should be a fast
enough motion to limit any widespread flooding issues, but with
high rainfall rates and already saturated ground, there could be
some localized issues.

Heading into Tuesday, it seems increasingly likely that the
outflow from tonight's activity will be far enough south to keep
the vast majority of the convection south of the state line
through the day. We will still get quite warm and humid,
especially south of I-94, with highs in the upper 80s to around
90, and heat indices between 90 and 95. A cold front brings a
cooler and drier airmass into the region Tuesday night into
Wednesday.

Boxell

&&

.LONG TERM...
Issued 248 PM CDT Mon Jun 24 2024

Wednesday through Monday:

Mid-level and surface troughing still look to move across
Wisconsin on Wednesday in the wake of the low pressure moving
across the state Monday and Tuesday. GFS and NAM soundings show
dry mid to upper levels but a well mixed boundary layer, so
expecting just cumulus to develop across southern Wisconsin
Wednesday afternoon and have kept the forecast dry with highs near
80F. However, given dynamic forcing via the troughing, moisture
in the lower levels, and the well mixed boundary layer I wouldn't
be surprised to see a stray shower or two. High pressure then
sinks south into Wisconsin Wednesday night which will bring clear
skies and potentially allow fog to develop given radiational
cooling and the abundant amount of moisture across the southern
part of the state. Upper level ridging and high pressure will
remain in place across Wisconsin on Thursday allowing for quiet
weather and temperatures in the 70s before moving east Thursday
night.

Southerly flow will return Thursday night into Friday morning,
bringing strong warm and moist advection into the state. Soundings
indicate a very saturated column Friday morning with PWATs around
2in which combined with a weak shortwave trough at 500hPa could
provide for heavy rainfall. A strong cold front will then move
across the state Friday evening. There is some uncertainty with
the timing of the front as the GFS/Euro/Canadian differ slightly
with when it comes through, but steepening mid-level lapse rates
and modest MUCAPE may allow for some elevated, but strong to
severe storms Friday night into Saturday.

High pressure will then again sink south Saturday behind a weak
surface trough. This will allow for drier and cooler weather
across southern Wisconsin for the beginning of next week.

Falkinham

&&

.AVIATION...
Issued 248 PM CDT Mon Jun 24 2024

South winds are expected into this evening, with low level wind
shear developing as a low level just noses into the area. A
complex of thunderstorms is then expected to affect most, and
perhaps all, of the terminals overnight, bringing reduced
visibilities, lower ceilings and strong gusty winds.

The complex should clear the terminals by daybreak with westerly
winds through much of the day on Tuesday.

Boxell

&&

.MARINE...
Issued 248 PM CDT Mon Jun 24 2024

Modest south winds will develop this evening, becoming breezy
late tonight into Tuesday morning as low pressure inches moves
across northern Ontario. A Small Craft Advisory is in effect
overnight for the nearshore waters. A line of thunderstorms
with very gusty winds will move across Lake Michigan late
tonight through early Tuesday morning. West winds on Tuesday
will then shift to northerly on Wednesday following the passage
of a cold front. High pressure will move across the lake
Wednesday night through Friday morning, bringing pleasant
weather.

Boxell

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 AM
     Tuesday to 7 AM Tuesday.

&&

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