NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 150600
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
100 AM CDT Fri May 15 2026

.KEY MESSAGES...

- A complex of thunderstorms is expected to roll across at least
  a portion of southern WI Friday night. There is a chance for
  damaging winds if the storm complex is well-organized.

- Warm and increasingly humid conditions will bring rounds of
  storms Saturday night through Tuesday. Storms may be severe.

&&

.SHORT TERM...
Issued 100 AM CDT Fri May 15 2026

Overnight through Saturday:

The thunderstorms diminished late in the evening but light
showers are still crossing southern and central WI during the
overnight hours. Temperatures will remain mild due to increasing
southerly winds, with lows ranging from the mid 40s near the
lake to the lower 50s west of Madison.

Breezy southerly winds with gusts up to 30 mph are expected
Friday. The south component should allow a lake breeze to
develop but remain close to the shoreline. With sunny skies,
highs will range from the mid 70s east to the lower 80s near
Wisconsin Dells.

A thunderstorm complex should develop in northwest IA Friday
afternoon along the warm front, with support from the nose of a
low level jet, a mid level shortwave, and the right entrance
region of an upper jet. This is expected to track east through
northern IA and into southwest WI during the evening hours.
The southern WI environment should be primed with around 1000
j/kg of CAPE and very high shear (high-shear/low-cape
situation). The complex should weaken as the LLJ veers, and
also trend southeast into IL toward the better instability
overnight. Severe storms will be possible if the storm complex
has a well- organized line along the leading edge, but model
soundings are hinting at a stable layer near the surface (below
900mb). Damaging winds are the main threat, although isolated
hail and locally heavy rain are also possible. If a well-organized
line tracks into southern WI, the 0-3km shear vectors will be
around 30 kt out of the WSW, so we would need to watch for QLCS
tors if the system became surface-based.

Lingering clouds over southern WI Sat from the decaying complex
will keep temps modest during the morning, but expect a quick
jump into the lower 80s by the afternoon with the sunshine.
Dewpoints should be in the mid 50s which keeps us at fairly
comfortable humidity levels.

Cronce

&&

.LONG TERM...
Issued 100 AM CDT Fri May 15 2026

Saturday night through Wednesday:

Another thunderstorm complex (or two) is expected to develop in
the Plains Saturday night where the low level jet, warm front,
shortwave trough, and upper jet are all situated. This complex
should track eastward and remain south of WI overnight.

With the upper trough amplifying over the west Sunday morning,
the warm front over IA will push into MN and WI. Showers and
thunderstorms will be possible along this front, and a few
severe storms cannot be ruled out. However, the stronger forcing
and better chance for severe will be over MN and western WI
with the better dynamics, especially in the evening when the LLJ
kicks in and the upper trough gets closer.

Southern WI may see remnants of any upstream storm complexes
late Sunday night or Mon morning, but there is not a lot of
confidence here. If there are remnants, clouds may inhibit some
degree of instability for Monday afternoon. The stronger storms
still look like they will develop in MN and western WI Monday
afternoon/evening but we could be in their path and get severe
storms out of it.

The main cold front will track through WI on Tuesday and bring
one last chance for storms. Timing of this front is still
uncertain and the severity of storms will depend on that timing.
Cooler temps will briefly return Wed.

Cronce

&&

.AVIATION...
Issued 100 AM CDT Fri May 15 2026

Showers along a wing of warm air advection are diminishing as
they move eastward into southeast WI overnight. Cloud bases are
between 8000 and 120000 ft, so only light rain/sprinkles are
reaching the ground. There used to be a signal for MVFR ceilings
along the lakeshore Friday morning, but it looks like dry air is
going to win and keep VFR conditions through the day.

A thunderstorm complex is expected to track into south central
WI during the evening and weaken or track south of southeast WI
around midnight Fri nt. If the complex is well-organized, severe
winds are possible.

Cronce

&&

.MARINE...
Issued 100 AM CDT Fri May 15 2026

High pressure over Lower Michigan will continue to shift
eastward overnight, with southerly winds developing on the back
side of the high. These winds will increase on Friday behind
the departing high and low pressure moving from central
Manitoba into Ontario. Confidence is increasing in gale force
gusts over the northern third of the lake Friday afternoon and
evening, so we will be issuing a Gale Warning.

Southerly winds will gradually diminish on Saturday as the low
pulls away to the northeast. Southerly winds will then pick back
up Sunday into Monday ahead of approaching low pressure. Gales
are possible Monday and Tuesday. Multiple rounds of showers and
storms will be possible this weekend into early next week.

Cronce

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...10 AM
     Friday to 4 AM Saturday.

&&

$$

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