Severe Thunderstorm Warning 23, NWS Milwaukee, WI

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
936 PM CDT Sat Apr 15 2023

.UPDATE...
(Issued 936 PM CDT Sat Apr 15 2023)

Thunderstorms are moving into southern WI now. The environment is
not favorable for severe with low CAPE and shear, although we
still have some weak elevated CAPE over southeast WI which could
allow for some gusty winds as the storms roll through.

The storms should lift northeast through southern and central WI
from now through 2 AM. The HRRR seems to have a decent handle on
the coverage. Lightning risk will be highest on leading edge of
this convective area.

Cronce

&&

.SHORT TERM...
(Issued 327 PM CDT Sat Apr 15 2023)

This Afternoon through Monday:

A broken area of thunderstorms has developed across southern
Wisconsin this afternoon, in association with a surface trough
moving through the area. There remains a limited severe weather
threat with this convection, mainly tied to marginally severe
hail, though a few instances of gusty winds are possible as well.

This initial round of showers and thunderstorms will likely
persist through late afternoon and early evening. After that,
another area of showers and thunderstorms will push into the area
mid to late evening, as the main surface low begins to lift
northward into the region. Could also see some marginally severe
hail with this activity, but not terribly impressed by the thermo
environment.

Rain showers will likely fill in through the morning on Sunday as
the upper level low approaches. As the surface low lifts
northeastward through the day, winds will pick up from the west
and northwest, with colder air building into the area. Precip
intensity will also increase as better upper level dynamics become
juxtaposed with low level frontogenesis, especially for locations
west of Madison. Rain will begin to change over to snow Sunday
afternoon, with snow expected Sunday evening through Monday
afternoon.

The heaviest snowfall is currently expected to occur west of
Madison, especially during the overnight hours Sunday night into
Monday morning, when snowfall rates could be rather heavy.
Accumulations are tricky this time of year, given warm ground and
road surfaces, but the overnight timing will be favorable in this
case. Have gone ahead and added Sauk, Iowa, and Lafayette to the
Winter Storm Watch Sunday evening through mid morning Monday. An
Advisory is likely to eventually be needed for another row or two
of counties further east.

It will also be quite blustery Sunday night and Monday, with
gusts to around 35-40 MPH, which could lead to some blowing snow
issues as well. And with temperatures only reaching the mid 30s on
Monday, it will feel VERY chilly compared to last week's summer-
like weather.

Boxell

&&

.LONG TERM...
(Issued 327 PM CDT Sat Apr 15 2023)

Monday Night through Saturday:

A few snow showers may linger across the eastern portion of the
area into early Monday evening, but will then end. Lows Monday
night are expected to fall into the 20s, with low 20s possible
across the west where the heaviest snow is expected.

Tuesday is looking like a fairly nice day, with diminishing winds
and sunny skies. Precip chances return Wednesday and especially
Wednesday night, as a baroclinic zone takes shape to our south and
low pressure moves across northern Missouri and Illinois.

The active pattern will continue into the weekend, with near daily
chances for rain, and perhaps even a few more snowflakes late in
the week as cooler air returns.

Boxell

&&

.AVIATION...
(Issued 936 PM CDT Sat Apr 15 2023)

An area of thunderstorms will lift northeast through southern and
central WI through 2 AM. Lightning risk will be highest on the
leading edge of the convection. There could be a break in shower
activity before another area of showers fills in early Sunday
morning. There is a distinct difference in wind direction across
southern WI- lakeshore areas will have variable to southeast to
east winds and inland areas will have steadier northwest winds.
This is due to low pressure sitting right over WI overnight.

Look for strong west to northwest winds to spread in Sunday
afternoon and persist through Monday. VFR ceilings will become
MVFR and then IFR during the overnight hours, especially with
that second batch of showers early Sunday morning.

Cronce

&&

.MARINE...
(Issued 936 PM CDT Sat Apr 15 2023)

There is enough confidence that we should have gale force gusts
Sunday night through Monday evening over the south half of Lake
Michigan to hoist a gale watch. Southwest winds just above the
surface should be around 40 kt Sunday afternoon, and shower
activity would help mix down some higher gusts, so we have the
gale watch beginning at 21z Sun. This might not be early enough.
The north half will have a chance for gales on Monday, but
confidence was not high enough to put them in the watch at this
time.

The NSH area might have gale gusts on Monday and may need a gale
warning. Not quite enough confidence in speed and timing yet.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch...WIZ056-WIZ062-WIZ067...7 PM Sunday to 10 AM
     Monday.

LM...Gale Watch...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 PM Sunday to 1 AM
     Tuesday.

     Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 PM Sunday
     to 10 AM Tuesday.

&&

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