Sun Prairie, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

491
FXUS63 KMKX 260944
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
444 AM CDT Thu Jun 26 2025

.KEY MESSAGES...

- Patchy fog will continue this morning in scattered spots
  inland and along the Lake Michigan shoreline.

- Scattered thunderstorms will continue this morning. There may
  be a bit of a lull in the late morning and early afternoon,
  before more storms develop over central WI during the mid
  afternoon and then a line of storms moves through from west to
  east during the evening. Storms will feature mainly gusty
  winds. A conditional threat for an isolated tornado does exist
  over central WI and areas west of Madison.

- Rivers are currently rising, with additional rounds of rain
  and storms bringing potential rises to action stage and minor
  flood stage into the weekend.

- A brief heatwave returns for Sunday, with heat indices once
  again approaching 100 degrees.

&&

.SHORT TERM...
Issued 406 AM CDT Thu Jun 26 2025

Today through Friday:

Scattered thunderstorms and patchy fog, both inland and along
the Lake Michigan shoreline, will continue this morning as dew
points pool along a stationary front at the surface, and low
level WAA continues at the 925 to 850mb level aloft. Guidance
suggests inland fog will dissipate after dawn, but some
nearshore fog along the Lake Michigan shoreline will remain
through the day.

After dawn and through the remaining morning hours, models
depict the stationary front lifting north as a warm front to
about Fond du Lac County through Marquette County, as a weak
surface low moves into western Iowa. As lift from this surface
low approaches this afternoon and some PVA from a 500mb trough
aloft spreads over the region, storms are expected to blossom
near the surface low and cold front over Iowa, as well as along
portions of the warm front closer to the surface low.

This afternoon, CAMs depict storms forming along the warm front
over central Wisconsin to varying degrees of coverage and
timing, but the main consensus seems to focus a potential storm
or two forming along the warm front through Sauk, Marquette,
Green Lake, and Fond du Lac Counties. This would likely occur
somewhere around 2 to 4pm. With partly cloudy skies in the
morning, HRRR soundings show that enough instability should
build along and south of the warm front to support 2500 J/kg of
SBCAPE, with some really good 0-3km CAPE around 150 J/kg. In
addition to the enhanced low-level stretching potential,
the presence warm front will support >200 m2/s2 of effective
storm relative helicity. Hodographs, while lacking in flow
aloft, do show streamwise helicity near the surface and
effective shear will be around 40 knots, supporting a
supercellular mode. LCLs will be around 500m as well. If a storm
forms in central WI and latches onto the warm front as some
CAMs suggest, a localized tornado threat may exist this
afternoon in central WI.

Turning our attention back west, storms along the cold front
will be ongoing over Iowa and Minnesota during the late
afternoon and will likely cross the Mississippi as a squall line
around 6pm. This line will approach our far western counties
during the early evening with CAMs showing a weakening trend as
the line moves into our CWA. Even so, soundings remain uncapped
enough west of Madison and a gusty wind threat may occur with
the line as it moves in, as model soundings show just a bit more
dryness to the low levels in southwest WI. There may
also be a conditional brief QLCS tornado threat in central WI as
the squall line moves in, given the lingering presence of the
warm front before the line gusts out as the boundary layer
decouples after dusk. Much like this past evening, a then
severely weakened line of storms will then travel east and exit
over Lake Michigan during the overnight hours.

Friday, the cold front will pass during the morning hours. There
may be a few lingering weak showers for the first half of the
day as the front passes, but the afternoon hours look mostly dry
at this time.

CMiller

&&

.LONG TERM...
(Issued 343 AM CDT Thu Jun 26 2025)

Saturday through Wednesday:

Weak ridging over southern WI should help us to remain dry through
the day Saturday. The better forcing with warm air advection and
vorticity advection is expected to be over northern MN. Any
lingering frontal boundary from the Friday front should be well
into Illinois. That puts southern WI in the non-eventful sector.
Of course, this can change if any upstream convection tracks into
our area late in the day, but at this time we are not expecting
anything.

Heat will begin to build back into the area Saturday, with highs
in the upper 80s for inland areas. With dewpoints around 70, heat
indices should be in the lower 90s. The winds look much lighter
than they were this past weekend, which will make it feel more
muggy.

Sunday will remain warm and muggy until a thunderstorm complex
potentially rolls in during the afternoon or evening. A potent
shortwave within the right entrance region of an upper jet is
expected to initiate a cluster of thunderstorms over central MN
Sunday. This cluster will likely ride the CAPE gradient which
should be over a portion of south central WI. Areas along and west
of I-94 have the higher chance of seeing storms, possibly severe.

An upper trough will swing across the Upper Great Lakes Monday. A
few showers and thunderstorms may be possible. The upper ridge is
going to strengthen over the Northern Plains from Tuesday through
Thursday. Models start to diverge then, with the GFS trying to
break down the ridge and the ECWMF maintaining its strength.
Either way, a ridge rider or two look possible later in the week,
which would include Independence Day. Still a lot of uncertainty
here.

Cronce

&&

.AVIATION...
Issued 343 AM CDT Thu Jun 26 2025

IFR to LIFR ceilings and patchy dense fog continue early this
morning along the Lake Michigan shoreline. Once we get some
daytime heating, any marine fog over the land areas will mix out,
despite a breeze of the lake persisting all day.

Expect ceilings to slowly lift through the day and develop more
breaks in the clouds. Isolated to scattered showers and
thunderstorms may develop along a warm frontal boundary north of
I-94 in the afternoon. There is a small risk for severe storms
with all hazards in this round.

Then a north-south oriented line of storms along a cold front
should bring additional storms as it tracks from northwest to
southeast in the evening. Gusty winds are the primary threat. IFR
ceilings are possible overnight into Friday morning in the wake
of the front.

Cronce

&&

.MARINE...
Issued 343 AM CDT Thu Jun 26 2025

A stationary front will continue to linger over the center of Lake
Michigan, roughly from Port Washington to Ludington. A few showers
and storms are possible along this front during the afternoon as
low pressure of 29.8 inches approaches from central Wisconsin. A
a weakening line of storms oriented north to south along the
associated cold front over Wisconsin is expected to reach Lake
Michigan around midnight.

Winds will gradually become westerly on Friday in the wake of the
front, with gusts remaining below 20 kt. High pressure around 30.0
inches will drift across the Upper Great Lakes on Saturday. A
storm complex may roll across Lake Michigan Sunday evening. Then
the high is expected to sit over the region through the middle of
the week.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory...LMZ644-LMZ645-LMZ646-LMZ671-LMZ673-LMZ675-
     LMZ777-LMZ779 until 7 AM Thursday.

&&

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSMilwaukee
www.twitter.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee