Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 280949 AAA

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
449 AM CDT Wed Jul 28 2021

(Issued 246 AM CDT Wed Jul 28 2021)

Today and Tonight:

The primary forecast concern and focus is on the increasing threat
of a significant severe weather event that looks to unfold across
the area this evening. This threat will include all severe hazards,
most notably the increased potential for significant damaging winds
(70-80+ mph) and even tornados.

We do have some ongoing convection across southwestern sections of
the forecast area. This activity is expected to continue shifting
southward into northern IL early this morning. Some brief gusty
winds of 50 mph will be possible with the strongest storms.
Otherwise, expect very warm and humid weather today as we await the
main threat of severe thunderstorms this evening. Expect highs
temperatures today to top out well into the 80s north, to around 90
south, and with dew points in the lower 70s we will see heat
indices into the mid 90s to around 100. Areas near the lake will be
cooler, however, due to persistent onshore winds, expect highs here
to remain in the lower to mid 80s.

We could see a few scattered showers/storms this afternoon as a
disturbance now leading to some storm development across parts of
the Dakotas shifts across the area. We continue to mention some low
end chances for a period this afternoon as this disturbance
approaches. Otherwise, our main period of concern is during the
evening, roughly from 9 PM through around 2 am. A forward
propagating MCS is expected to develop to the northwest of the area
early this evening in response to another disturbance shifting
southward across the Upper Midwest. The thermodynamic and kinematic
environment is forecast to become quiet impressive, and more than
supportive of severe thunderstorms. In fact the ingredients look
favorable to support a potential derecho, which would be capable of
producing 75+ mph winds. Low to mid level shear will also be
sufficient to support a notable tornado threat associated with
mesovortices developing within the bow. For these reasons, the SPC
has put our area in an enhanced to moderate risk (level 3 to 4 out
of 5 severe risk). Stay tuned for updates on this potentially
dangerous weather situation later this evening.

The threat of storms will come to an end overnight as the forward
propagating complex shifts to the southeast. Torrential downpours
are likely with these storms, and this could cause some hydro
concerns, though the storms fast movement will likely limit this
threat outside of the urban centers.



(Issued 448 AM CDT Wed Jul 28 2021)

Thursday through Tuesday:

Northerly winds will usher cooler and drier air into southern WI
on Thursday. This may take a bit, so not expecting immediate
relieve from the humidity (higher dewpoints). The steady northerly
winds will cause higher waves along the shoreline from Milwaukee
south, so we may need a Beach Hazards Statement Thu nt into Fri
morning. Lows Thu nt should make it down to around 60, and Fri
highs will only be in the upper 70s to around 80.

We will have a brief return of moisture and heat on Saturday with
a weak wave moving through the Midwest. Convection with this wave
is expected to stay to our southwest. The main upper trough will
swing down through WI Saturday night. There is a chance for
storms with this. Much cooler and drier air will spread in Sunday
and stick around through the middle of next week.



(Issued 448 AM CDT Wed Jul 28 2021)

Look for SCT to BKN low clouds with bases around 4500 ft this
morning. Expect these to dissipate shortly after sunrise. There
could be some cu development later today, but we will mainly see
mid level clouds start to stream into the area.

A complex of strong to severe thunderstorms is expected to roll
southward into southern WI mid to late evening. Damaging winds are
the main threat, but hail and a tornado are also possible. Best
chances would be between 02Z and 08Z Thursday across terminals.
MVFR/IFR ceilings and visibility values may occur at times with
any storms and during the overnight hours behind the complex.



(Issued 448 AM CDT Wed Jul 28 2021)

Look for variable winds to become southerly today. A complex of
strong to severe thunderstorms is expected to track across
northern Wisconsin late this afternoon and then drop into central
and southern Wisconsin and Lake Michigan this evening. It should
exit southern Lake Michigan by 4 AM.

Persistent northerly winds on Thursday will build higher waves
over the south half of Lake Michigan Thursday afternoon through





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