NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 161145
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
645 AM CDT Sat May 16 2026

.KEY MESSAGES...

- Isolated thunderstorm development this evening with more
  widespread rain and storms overnight into Sunday morning. A
  storm or two could become severe, but confidence remains low
  at this time

- Active start to next week, with multiple rounds of showers
  and storms expected. Some storms could be severe & produce
  locally heavy rainfall.

- Trending quieter & cooler Wednesday into Thursday.

&&

.UPDATE...
Issued 636 AM CDT Sat May 16 2026

Confidence in storm formation remains low for tonight as the
HRRR continues to show widespread storms along the WI/IL border
this evening, but solutions from the rest of the CAMs suggest
storm formation should be centered west over Iowa. If the HRRR
solution verifies, there may be a few isolated strong to severe
storms tonight near the WI/IL border capable of hail and gusty
winds. Otherwise if that solution doesn't take shape, most of
tonight may be dry until the warm from lifts north Sunday
morning.

CMiller

&&

.SHORT TERM...
Issued 1140 PM CDT Fri May 15 2026

Tonight through Sunday:

850 mb LLJ will strengthen existent storms as they progress
southeastward tonight along and south of the I-94 corridor late
tonight through early Saturday morning. A Severe Thunderstorm
Watch is in effect for Iowa County through Milwaukee County
southward. With storms already developing linear structure,
expecting the hail threat to be lower than previously
forecasted, although a few cores may become strong enough to
produce 1 inch in diameter hail. Cloud bases do remain high,
around 4000 ft, and combined with a stable to moist adiabatic
airmass in the low levels, expecting very low tornado threat.
An isolated tornado DOES remain possible in scenarios with an
easterly bowing segment and strong rear inflow jet. Storms are
expected to maintain intensity through the Lake Michigan
Counties, but confidence decreases farther east. Regardless of
intensity, expecting storms to exit offshore by 5 AM CDT.

Lingering light showers are possible after storms exit Saturday,
with clearing conditions through the rest of the day. Low
pressure developing in the central High Plains will bring warm
frontogenesis back into the Upper Midwest late Saturday
afternoon into Saturday night. If storms develop early enough on
Saturday (HRRR favors this solution with MUCAPE around 1000 J/kg),
probabilities for an isolated severe thunderstorm increase.
However, confidence is low (1 out of 5, or Marginal on the SPC
scale). More widespread rain and storms are expected to develop
during the overnight hours along this wing of frontogenesis.
Ingredients are not favorable for severe weather overnight, with
minimal MUCAPE and mid-level lapse rates only near 6 degrees
C/km as the surface front lingers just to the south.

Early Sunday morning, warm front finally lifts northward
through southern Wisconsin, bringing increasing instability and
shear. With overrunning precipitation, still not anticipating
any organization, but storms may become briefly surface based.
Southeasterly winds expected throughout the day Sunday, keeping
a wide temperature margin from the Lake Michigan and central
Wisconsin (low to mid 70s) to southwestern and inland counties
(low to mid 80s). Sunday afternoon, low pressure ejects into the
central Plains, bringing an additional frontogenesis region to
southwestern Wisconsin. Severe storms may become possible Sunday
afternoon into Sunday evening in this region, but confidence in
timing and placement remains in question (slower low
progression would result in less severe potential).

MH

&&

.LONG TERM...
Issued 1140 PM CDT Fri May 15 2026

Sunday night through Thursday:

Synopsis: Longwave ridging will remain entrenched over the eastern
CONUS Sunday night through the beginning of next week as a broad
upper trough gradually migrates from the Great Basin to the Northern
Plains. The upper pattern will support persistent high pressure off
the Eastern Seaboard, with broad low pressure gradually building
from the Central Plains into the upper Mississippi River Valley. The
placement of surface features will support southwesterly winds and
well-above normal temperatures through the day Monday. Muggy
conditions will accompany the warm temperatures. Temperatures will
slowly begin to trend downward Tuesday as low pressure continues to
build from Michigan's Upper Peninsula into Ontario, sweeping a cold
front across southern Wisconsin. The warm/muggy conditions &
eastward progressing upper trough, surface low and cold front will
support a continued active pattern featuring multiple chances for
additional showers and thunderstorms Sunday night into Tuesday. Some
storms could be severe, with locally heavy rainfall also possible.
Conditions will trend quieter and cooler in the wake of the departed
cold front Wednesday through Thursday.

Monday: Widespread thunderstorm development is forecast from the
Central Plains into the mid-upper Mississippi Valley during the
afternoon/evening hours as upper troughing & a surface cold front
impinge upon a warm/moist & unstable air mass in place regionally.
An overlap of ample instability with abundant speed & directional
wind shear will be supportive for potentially substantial severe
weather hazards in thunderstorm development. Precipitable water
values in the 1.25-1.50"+ range will also be favorable for heavy
downpours & locally heavy rainfall in any convection. Certainty of
the severe weather forecast picture in the MKX CWA, however, remains
cloudier relative to areas further west, as influences from early
day showers/storms could impact the quality of the afternoon/evening
warm sector over southern Wisconsin. Further, a number of different
solutions regarding the forward progression of the ejecting upper
trough & mirroring surface features remain apparent in available
global/mesoscale forecast guidance. If slower solutions apparent in
some guidance win out, the corridor of peak severe potential would
trend further west/away from southern Wisconsin. Will thus be
monitoring forecast trends very closely through the weekend, as
small changes in expectations for early day storms and/or storm
system progression will have large ramifications on the potential
for severe weather in southern Wisconsin on Monday.

Tuesday: Could see shower/storm potential linger around the region,
particularly in the scenario of a slower storm system
evolution/delayed cold frontal arrival in southern Wisconsin.
Wouldn't be able to rule out a few stronger storms with additional
heavy rainfall in the event the cold front hangs up long enough &
instability can build back into parts of the area. Will be watching
trends over coming forecasts.

Quigley

&&

.AVIATION...
Issued 641 AM CDT Sat May 16 2026

VFR conditions are anticipated today amid light west to
northwest winds. There is a conditional threat for storms
tonight along the WI/IL border. If storms form, a storm or tow
could become severe, capable of hail and gusty winds.

CMiller

&&

.MARINE...
Issued 1140 PM CDT Fri May 15 2026

Low pressure around 29.1 inches exiting into the Hudson Bay will
keep gusty southerly winds across the Lake through early
Saturday morning. Expect winds to shift to become northwesterly
and light into Saturday as a front crosses the lake.
Thunderstorms are expected along this front, with a few
becoming strong with gusty erratic winds possible. Storms will
end shortly after sunrise. Lighter northwest winds continue
through Saturday, with light and variable winds overnight.
Sunday, low pressure around 29.2 inches will develop in the
central High Plains, shifting winds to easterly. Winds remain
easterly through Sunday, shifting to southwesterly and becoming
gusty Sunday night through Monday night as low pressure ejects
into the western Great Lakes region. A few strong thunderstorms
are possible on Monday as low pressure crosses Lake Superior.
Potential for a few strong thunderstorms remains into Tuesday as
low pressure lingers in the region.

MH

&&

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

$$

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