NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 121140
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
640 AM CDT Sun Jul 12 2026

.KEY MESSAGES...

- Hot temperatures will return early in the week, with highs in
  the low to mid 90s Monday through Wednesday. Heat indices may
  reach 100 at times.

- Dry weather is expected through Wednesday, with thunderstorm
  chances returning late in the week.

&&

.UPDATE...
Issued 645 AM CDT Sun Jul 12 2026

Warming up into the upper 80s today as high pressure remains
squarely over the region. Perhaps a lake breeze today given very
light surface winds but overall the forecast remains on track.

Kuroski

&&

.SHORT TERM...
Issued 1259 AM CDT Sun Jul 12 2026

Overnight through Tuesday:

We could see some fog in the Wisconsin River valley early this
morning.

Surface high pressure will set up across IA, IL, southern WI,
and Lower MI today and remain stationary through Monday. Winds
will be fairly light and variable today so we can expect a lake
breeze. High temperatures are expected in the upper 80s, except
lower- mid 80s near Lake Michigan. With dewpoints topping out
in the lower 60s, the heat indices will end up close to the
temperatures.

Monday, look for a westerly breeze and therefore only a
potential wind shift right along the lakeshore. Warmer air will
be advecting in from the Northern Plains, with highs in the
lower 90s. The dewpoint values are also expected to creep up
into the 68-71F range. The calculated heat index looks to top
out over 100 toward east central WI Monday.

Tuesday conditions will be similar, but this is the day that the
highest 500mb height anomalies will be overhead and the
westerly surface return flow occurs. With the steady westerly
wind, the forecast highest temps along the Kettle Moraine toward
Lake Michigan make sense due to subtle downsloping, but this
may be a little overdone due to bias correction in the models.
Took a compromise between the higher and lower values, but this
is something we can re-evaluate today-tomorrow as we see the
upstream values. The hot temps forecast in the mid to upper 90s
can only occur if we get at least a little subtle mixing for
dewpoints to drop below 70. Therefore, the current forecast max
heat indices for Tuesday are looking like 100-104 in the east
half of the county warning area, and just shy of 100 for the
west half.

Models vary widely in max/min temp and dewpoint values and this
is mainly due to bias correction, but also to the degree that
evapotranspiration is taken into account. We are getting into
the peak crop growth period and this could boost our dewpoint
temps a bit.

All this is to say that we will likely need a heat advisory for
at least the eastern portions of southern WI Monday and Tuesday.

Cronce

&&

.LONG TERM...
Issued 1259 AM CDT Sun Jul 12 2026

Wednesday through Saturday:

With the surface high nudging southeastward on Wednesday and low
pressure approaching from the northern Plains, a subtle front is
expected to drop halfway down lake Michigan and Wisconsin. Most
models depict that boundary to stall from northwest WI to
southeast WI Wed afternoon through Friday.

A wind shift to the northeast along the lakeshore Wed will help
cool the temps, but inland areas will be stuck in the lower 90s.
This boundary between easterly westerly winds that is also
reinforced all the way into the upper levels will become focus
for some shower and thunderstorm activity Thursday evening
through Friday (or Saturday if the GFS pans out). Weak
shortwaves in the 500mb flow and a southerly low level jet could
produce storms upstream in nrn MN that track down through WI.

Saturday-Sunday is much more uncertain, as the GFS holds on to
that upper trough over the Great Lakes longer than the ECMWF.

Cronce

&&

.AVIATION...
Issued 645 AM CDT Sun Jul 12 2026

VFR conditions expected through the TAF period with mostly clear
skies and light winds today with perhaps some spotty valley fog
tonight but otherwise modest west winds Monday under continued
clear skies for the most part.

Kuroski

&&

.MARINE...
Issued 1259 AM CDT Sun Jul 12 2026

High pressure over the Great Lakes region will maintain an axis
roughly from northern Iowa to southern Lower Michigan through
Monday and then sink into Illinois and Indiana Tuesday and
Wednesday while weakening. Low pressure will approach from the
Northern Plains Thursday into Friday. Look for winds over Lake
Michigan to become southerly across the north half today and
light and variable in the south. Winds will become south-
southwesterly Monday and increase a bit by Tuesday. A weak cold
front will bring a wind shift to the north- northeast Wednesday
into Thursday.

Cronce

&&

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

$$

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