NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 130552
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1252 AM CDT Thu Aug 13 2026

.KEY MESSAGES...

- Widespread fog is expected overnight through early / mid
  morning Thursday, with areas of dense fog possible, especially
  along Lake Michigan and in low-lying marshy locations.

- 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.

&&

.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 1250 AM CDT Thu Aug 13 2026

Fog will continue to spread and thicken across southern WI
predawn this morning, with areas of dense fog possible in low-
lying marshy areas and in eastern WI (where a lake breeze left
from last evening left residual moisture). Fog should begin to
thin out after sunrise Thursday morning, though some developing
light onshore winds may allow it to linger into mid morning for
portions of eastern WI.

Through the daytime hours Thursday, the majority of thunderstorm
activity should progress eastward across IA and IL, with showers
(and potentially weak storms) tracking across southern WI. Model
guidance suggests VFR-altitude overcast cloud ceilings through
the day, with the rain standing a chance to (briefly) drop
visibility to MVFR at times. A light east to southeast breeze.

Sheppard

&&

.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...None.
LM...None.
&&

$$

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