NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 131122
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
622 AM CDT Thu Aug 13 2026

.KEY MESSAGES...

- Dense fog will continue over the next few hours. A

- Unsettled weather continues this week, with on and off chances
  for showers and weak thunderstorms. The highest rain chances
  Today and Friday (35-80%) are found over far southern and
  southwestern WI.

- Potential for stronger and more widespread storm activity this
  weekend, but timing and intensity remain uncertain at this
  time.

- Drier & more comfortable early next week, with storm chances
  returning by mid-week.

&&

.UPDATE...
Issued 608 AM CDT Thu Aug 13 2026

Areas of dense fog have cropped up this morning out ahead of
some approaching cloud cover. A Dense Fog Advisory has been
issued for counties inland from Lake Michigan until 9am. The
high clouds have grown thicker with time, so the fog may
dissipate before 9am. Otherwise forecast details for today
largely remain on track. An MCS is expected to track south of
the state through today. We will likely experience stratiform
rain from this MCS and some rumbles of thunder, but severe
weather is expected to stay south of the Wisconsin and Illinois
border.

CMiller

&&

.SHORT TERM...
Issued 1250 AM CDT Thu Aug 13 2026

Today through Friday night:

The fog over eastern WI should become more widespread and continue
to thicken through predawn this morning, with dense fog possible
across eastern WI and low-lying marshy areas inland. The nearly calm
winds and humid airmass make for great antecedent conditions for fog
development, the only thing that could slow it down at this point is
the remnant anvil material (high altitude clouds) from convection in
the Dakotas drifting into WI. With a light onshore breeze expected
to develop post-dawn, portions of southern WI (particularly further
east) could easily hang onto this fog through mid-morning. If you
encounter dense fog on your commute this morning, remember to slow
down, use low-beam headlights, leave plenty of space between you and
the vehicle in front of you, and allow yourself extra time to reach
your destination.

As a surface trough of low pressure extends northeast from the
central Great Plains towards IA today, and weak high pressure
remains over southern Canada and the upper Great Lakes, the stalled
surface front will remain well south of the region (from the IA/MO
border to south-central IL), with one or two rounds of thunderstorms
igniting along it. Showers and perhaps some weak thunderstorms north
of the boundary are expected in southern WI, with the first round of
them tracking west to east from late morning through midday,
followed by a chance for lingering activity along and south of the I-
94 corridor (MKE-MSN) as well as west of the I-39 / I-90 corridor
into the afternoon and early evening. 00z CAM guidance remains quite
dispersed on the exact placement / duration of this activity.

For Friday, models allow the surface boundary to lift further north
in IA / IL, which could bring the instability and stronger storms
closer to southern WI, but the overall consensus is that Friday
plays out similar to today, with the majority of the activity
remaining south of the state borderline and some weaker storms
and showers clipping the southern and southwest CWA. Sticking
with meager 25-55% precip chances for the southwest half of the
CWA Friday, with higher and more widespread chances arriving
Friday night as weak low pressure lifts out of the central
plains and into WI.

Sheppard

&&

.LONG TERM...
Issued 1250 AM CDT Thu Aug 13 2026

Saturday through Wednesday:

Synopsis: Tied to a surface front lingering just south of southern
Wisconsin, leftover thunderstorms may be ongoing across parts of the
region on Saturday morning/the beginning of the long term period.
The responsible boundary will attempt to work north/into southern
Wisconsin as a warm front on Saturday afternoon, with its ultimate
progress being dictated by lingering clouds & precipitation. An
upper wave will swing through the Great Lakes Saturday night into
Sunday, pushing the boundary back southward as a cold front. With
the front in the vicinity & the aforementioned wave moving through,
shower and thunderstorm chances will thus continue Saturday night
into perhaps Sunday. The surface front will shift south of the
region by Sunday evening, bringing a noticeably drier air mass into
the area for Monday. Moisture will gradually work back into southern
Wisconsin Tuesday through Wednesday, bringing returning shower and
thunderstorm chances along with it.

Saturday Night through Sunday: Anticipating at least one window of
shower/storm potential as a surface front moves through southern
Wisconsin. Most global guidance points to a Saturday overnight
frontal passage, which would combine with ascent from the passing
mid-level wave to support the best overall window of opportunity for
thunderstorms. Have thus maintained precip probabilities from the
NBM, which reach their highest values Saturday night/during the
passage of the overlapping forcing mechanisms. Depending on the
front's forward speed, could then see some additional development on
Sunday afternoon. Details regarding any severe storm potential
(particularly Saturday evening/night) remain murky at this time,
with lingering clouds/precip on Saturday afternoon being the key
influence on the amount of instability that can build back into the
area with the warm front. Will be monitoring trends & providing
updates over coming forecasts.

Quigley

&&

.AVIATION...
Issued 615 AM CDT Thu Aug 13 2026

Dense fog is expected to linger for the next couple of hours
before lifting. Clouds will linger today and rain and a few
rumbles of thunder will move through Wisconsin during the late
morning and into the afternoon as the stratiform region from an
MCS to our south moves overhead. Winds will remain light and
easterly to southeasterly.

CMiller

&&

.MARINE...
Issued 1250 AM CDT Thu Aug 13 2026

Light and variable winds expected to continue this morning
through this evening, with low pressure around 29.6 inches over
the central Plains and broad high pressure across Canada.
There are chances for showers and thunderstorms across the
southern third of the lake from midday today through Tonight,
but severe storms are not anticipated.

A light northeast breeze is expected into Friday as Canadian
high pressure around 30.2 inches spreads east. Occasional shower
and storm chances continue for the southern third of the lake
due to a stalled frontal boundary south of the lake. Low
pressure around 29.9 inches will lift this boundary northward as
a warm front into this weekend, leading to increased chances for
showers and thunderstorms across the lake.

Sheppard

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Dense Fog Advisory...WIZ046-WIZ047-WIZ051-WIZ056-WIZ057-WIZ058-
     WIZ059-WIZ062-WIZ063-WIZ064-WIZ065-WIZ067-WIZ068-WIZ069-
     WIZ070 until 9 AM Thursday.

LM...None.
&&

$$

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