Sun Prairie, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

629
FXUS63 KMKX 260236
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
936 PM CDT Fri Jul 25 2025

.KEY MESSAGES...

- Heavy rainfall potential overnight into daybreak tomorrow
  morning. Could lead to isolated flooding in southeast
  Wisconsin.

- Hot and very humid Sunday and Monday with upper 90s to triple
  digits heat indices.

- Periodic shower/storm chances through later Sunday and into
  early next week before an eventual cold front passage midweek.

&&

.UPDATE...
Issued 936 PM CDT Fri Jul 25 2025

The main focus is on the storm/heavy rainfall potential
overnight into Saturday morning.

Currently, an MCV is propagating across northern Illinois along
and north of a boundary that extends from central Missouri
through central Illinois. Most of the convection associated with
this feature is tracking in a similar motion from SW to NE.
However, there`s enough lift on the northern fringe of the
feature that a west to east band of convection is developing
across NW Illinois with individual cells drifting N-NWward. That
orientation and band of convection has been the concern for the
late evening and early overnight hours for whether or not it
would get into southern Wisconsin and still have the heavy rain
aspect to it or if it`d be in weakening phase. Current thinking
with this first wave is that we have a window from about 11pm
through about 3am where these slow moving isolated to scattered
storms will be tracking into southern WI and could have some
locally heavy rainfall of about an inch or two. The
secondary/final feature appears to be going through eastern
Kansas/NW Missouri and should reach eastern Iowa/northern
Illinois around daybreak. Thinking that this will be the main
period for when heavy rainfall would be more possible. PWs are
around 2" and the RAP forecast soundings show a moist profile as
this lift comes in.

With NWS Chicago lifting the Flood Watch up to along the WI/IL
border, considering adding a few counties to the watch but
wasn`t confident enough in widespread/training storms to even
occur to put it up. The past few runs of the RAP have shown that
the main 925-850mb moisture transport/focus aims more for
southern Lake Michigan than SE WI, so the support may not be
there.  That said, can`t rule out that a small area could see
some heavy rainfall if things come together.

The mid level shortwave looks to be through the region by
Saturday evening, so am expecting a downtick in POPs from west
to east through the afternoon and evening hours. Considered
removing the POPs from 7pm onward, but wanted to get a look at
the 00z guidance before making that move.

Halbach

&&

.SHORT TERM...
Issued 253 PM CDT Fri Jul 25 2025

Tonight through Saturday night:

High pressure remains centered over the upper Great Lakes with
the stalled frontal boundary set up south across IL/IN. This
afternoon is still fairly warm with not much relief in dewpoints
(upper 60s- low 70s) even with easterly winds off of the lake.
The high will gradually slide east this evening/tonight with
overnight lows in the mid to upper 60s before southerly flow
gradually builds back into southern WI and will see the stalled
boundary lift back northward as well. Could see a few showers
and storms later this evening as the elevated humidity level
paired with a lifting warm frontal boundary and MCV (currently
centered across southern IA) may trigger development across far
southern WI. However model trends are leaning more in favor of
the late evening activity either hugging the WI/IL border or
staying south where the front lingers a bit longer with the
sub-30 kt LLJ.

Expecting more widespread shower and storm activity to develop
into Saturday morning as another MCS/MCV, currently centered
over NE/KS border, lifts northeastward into the region. With the
return of higher moisture and PWATs creeping back above 1.5 to
around 2 inches, expecting increased shower chances through
Saturday morning as a mid-level shortwave trough lifts in from
the southwest across WI/IL. Latest model trends continue to
favor the southern half of the CWA (along and south of I-94) to
see much of this activity, but could see it as far north as
HWY-151, with areas northwest remaining mostly dry. However
given the uncertain nature of an MCS, could see things shift
depending on where the features ends up tracking. Given the
increasing moisture, will see instability climb with the 12z
HREF progging at least 500-1000J/kg of MUCAPE accompanying the
incoming MCS. Thus few embedded thunderstorms will be possible
Saturday morning into the early afternoon. Any delay in the
timing of the MCS and morning shower activity will help
instability climb upward and increase the thunderstorm
potential into the afternoon. If this scenario ends up panning
out, then cannot rule out seeing a storm or two grow tall enough
and produce gusty winds and even some small hail. However,
continue to see the better potential for stronger storm further
south into IL where the greater instability and deep layer shear
will be in associated ahead of the MCS.

Much of the shower and storm activity does look to be through
the area by the later half of the afternoon. While looking at a
drier evening, not expecting much of a change in airmass so the
humidity will linger into Saturday night with lows in the upper
60s to low 70s.

Wagner

&&

.LONG TERM...
Issued 253 PM CDT Fri Jul 25 2025

Sunday through Friday:

Upper-level high pressure remains established over southeastern
CONUS into early next week. This will place southern WI at the
top of the upper ridge with southwesterly flow advecting in a
more tropic airmass into southern WI Sunday through the start of
next week. Given this pattern, it lends way to another hot and
humid stretch with temps in the upper 80s into the 90s and even
hotter heat indices ranging from the mid-90s into triple digits,
especially for Monday and may even see the heat continue into
Tuesday. Thus heat headlines may be needed early next week.
However, there continues to be uncertainty with temps as periods
of showers/storms from upper-level waves overrunning the ridge
and bringing an MCS or two across the region may present a
wrinkle in the forecast limiting the heat potential. Difficult
to pinpoint the cloud cover and shower/storm chances from a wave
or two this far out, but mid-range models hint a few
opportunities one being Sunday night into Monday and again on
Monday night into Tuesday. Nevertheless will be the potential
for wave of showers/storms to accompany the hot and humid
stretch into early next week.

Upper-level high gradually meanders back westward midweek and
will allow for the upper-level trough to work its way across the
Upper Midwest. With the ridge to the west, northwesterly flow
and cooler pattern then looks to set up across the Great Lakes
for the second half of next week. Long-range models also show
(fairly consistently) a surface high pressure set up over the
region through the end of the week, which would support near-
normal if not slightly below normal temps.

Wagner

&&

.AVIATION...
Issued 936 PM CDT Fri Jul 25 2025

VFR conditions currently across southern WI as the low cloud
deck near Lake Michigan has dissipated. As rain moves in
overnight, expect that some lower visibility and ceilings will
accompany it with light winds and high pressure in place.
Improvement will likely come on Saturday afternoon as the system
moves off to the east and drier air pushes in. Otherwise,
conditions may be highly variable through Saturday morning as
the rain and possibly storms move through.

Halbach

&&

.MARINE...
Issued 251 PM CDT Fri Jul 25 2025

High pressure centered over Lake Superior and northern Lake
Michigan will gradually slide east tonight. Then a frontal
boundary stalled south of Lake Michigan this afternoon is
expected to gradually lift northward overnight into Saturday.
Will see lighter north and easterly winds north of the boundary,
but will begin to shift more southerly behind it. Light
southerly winds will prevail by Saturday afternoon/evening
across all of Lake Michigan. Will continue to see light to
occasionally moderate southerly winds prevail through the
weekend into early next week. There will be a few windows for
shower and thunderstorms to track across the Lake
tonight/Saturday and again Sunday night into Monday and again
midweek. May see more variable winds accompanying any storm
complex that traverses the Lake through early next week.

Wagner

&&

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

$$

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