NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 131030
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
530 AM CDT Mon Apr 13 2026

.KEY MESSAGES...

- Multiple windows for thunderstorms this week, with each having
  varying degrees of strong to severe potential, beginning
  tonight then each day and night possibly through Thu.

- Heavy rain and flooding potential will increase through the
  week as rainfall accumulates from rounds of showers and
  storms. Srn WI rivers are expected to rise with some reaching
  minor flood stage, and potentially higher levels of flooding.

&&

.UPDATE...
Issued 530 AM CDT Mon Apr 13 2026

Forecast remains on track this morning with mild and muggy
conditions in place regionally. Look for broken cloud cover to
stick around through the day today with a stout EML based
near/above 850 mb keeping low level moisture trapped in the
lower portions of the column. Can't rule out some light spits of
drizzle from some of the low cloud cover, though confidence in
preferred locations of drizzle development is low. Will be
monitoring trends through today and adjusting the weather grids
where necessary.

Still watching for significant severe weather potential this
evening/tonight toward central and north-central Wisconsin.
Broad set up for storms is clarifying this morning, with low
pressure currently centered over southwest Nebraska forecast to
track northeast toward the Twin Cities vicinity by late
afternoon. Low will drag an attendant dryline northeast with it
into northern Iowa/southern Minnesota in the process. A surface
warm front is expected to extend east-southeastward from the low
into west-central and east-central Wisconsin by late afternoon.
Convective initiation appears probable by late afternoon/early
evening near the triple point intersection of the surface low,
dryline, and warm front. Observational trends will refine
specific initiation corridors through this afternoon, but an
area generally extending from Wautoma-La Crosse north to the
Twin Cities over to Wausau is currently favored for the zone
most likely to see CI. Given this anticipated corridor, current
expectations are for storms to stay north of the area through
the initiation phase of the event (~3 - 7 PM). Any southward
trends in the favored initiation corridor, however, would place
the northwest corner of the CWA in line for discrete supercell
development during late afternoon/early evening, with very large
hail, damaging winds, and a few tornadoes all being possible.
Will be watching trends regarding initiation very closely
through this afternoon.

Barring a last-minute southward shift in initiation corridor,
the most likely scenario for storms & severe impacts in
southern Wisconsin remains centered on the mid-evening to early
overnight timeframe (~ 7 PM - 1 AM), with locations north of
I-94 being at highest risk. Following discrete supercellular
development during late afternoon/early evening, general
expectations are for convection to steadily grow upscale into
one or several clusters as the low level jet increases
regionally. Propagation of these clusters will prove critical
for severe potential in southern Wisconsin, with forward-
propagating Corfidi vectors & Bunkers vectors implying a general
east-northeast movement of storms away from the initiation zone.
This places far northern counties---specifically Marquette,
Green Lake, Fond du Lac, and Sheboygan---at greatest risk for
strong/severe storms this evening. Given the expected linear
mode of storms, damaging straight line winds & QLCS-type
tornadoes would be the greatest severe hazards. Torrential
downpours would also support some potential for flooding
impacts, particularly in any areas of training. Continue to
expect a sharp cutoff in the southern extent of the severe
threat given the aforementioned propagation vectors &
significant capping moving south/away from the warm front. Will
nevertheless need to monitor for some activity trying to make it
as far south as I-94. In the event storms do approach I-94,
straight line winds would be the primary concern.

Quigley

&&

.SHORT TERM...
Issued 1208 AM CDT Sun Apr 12 2026

Tonight through Monday night:

The widespread light to brief moderate rainfall is expected to
end from west to east across ern WI by 07Z, as the shortwave
trough responsible for the rain moves away across Lake MI.
Meanwhile, farther to the north, cyclogenesis over nrn Ontario
and srn Hudson Bay will support a dominant low developing in
said region, while its cold front shifts ewd across nrn WI. The
front will weaken and stall over central or srn WI by 12Z Mon.

The front will then move back to central WI as a warm front
during the afternoon as sly winds increase over srn WI. The sly
winds are a result of low pressure tracking ewd along the SD
and NE border. Very steep mid level lapse rates around 8C/KM
will overspread srn WI, capping a very mild and moist airmass.
The return of low level moisture beneath the cap will simply
result in widespread stratus and possibly even patchy drizzle by
later in the day. Have lowered Max temps a bit to account for
this.

A weak shortwave trough will then track from the central Great
Plains to srn MN by 00Z Tue, then across nrn WI Mon nt. This
will shift the low pressure area and the nose of a strong low
level jet across central WI. The warm sector will be strongly
capped but right along and north of the front, convective
initiation and severe convection is likely. There are
differences among the models on the aforementioned features, but
the CAMs and 00Z HREF trended north with the deep, moist
convection. Some CAMS then suggest a MCS will slip esewd into
central WI and possibly se WI from the late evening into the
early morning hours. MUCAPE will range from 1500-2000 J/KG with
mdt effective shear present. Damaging winds would be the main
threat but cannot rule out the possibility of QLCS tornadoes if
the MCS maintains maturity.

Gehring

&&

.LONG TERM...
Issued 1208 AM CDT Sun Apr 12 2026

Tuesday through Sunday:

A stationary front will reside in the vicinity of srn WI on Tue
into Tue evening, while a vorticity maximum approaches in swly
flow aloft. In the lower levels, low pressure will track across
the central Great Plains into ern NE with the nose of a strong
low level jet developing into srn WI. MLCAPE around 2000 J/KG
and mdt deep layer shear is expected, and with the aforementioned
lift, the cap is expected to erode. Scattered to numerous
strong to severe convection will ensue either late afternoon or
early evening and continue to expand. Large hail and damaging
winds will be the primary threat with lesser chances for a few
tornadoes.

A more organized shortwave trough will then approach from the
southwest Wed nt, but not before a vorticity maximums lifts nwd
ahead of it into se WI by late Wed afternoon. Thus additional
rounds of showers and storms are expected from Wed afternoon
through the night. Some showers may linger on Thu as the
shortwave trough passes in the morning.

Yet another larger and stronger upper trough and n-s sfc trough
will move out of the Great Plains and into the wrn Great Lakes
for Fri nt-Sat. In summary, multiple rounds of showers and
storms are forecast from Tue-Sat, with a few inches or more of
rain possible. River rises are expected with some flooding
possible. Some severe storms will likely occur at times.

Gehring

&&

.AVIATION...
Issued 530 AM CDT Mon Apr 13 2026

MVFR and IFR flight categories continue into this morning at all
terminals, with gradual CIG improvements occurring from late
morning into the afternoon hours. Stout layer of warm air aloft
will keep at least SCT-BKN cloud coverage around through the
entirety of the day. Can't rule out some -DZ from some of these
clouds, though confidence in development & location is far too
low to support any mentions at this time. Will be watching
trends through the day. Significant convective development
remains forecast over central and north-central Wisconsin this
evening, with impacts currently most likely at SBM. Have
inserted prevailing -TSRA mentions in the coming 12Z SBM update.
How far south storms make it remain uncertain. Will need to
monitor for some activity trying to make it as far south as
I-94, though confidence in this occurring is much lower compared
to areas further north. Have thus maintained PROB30 groups at
MSN, UES and MKE in the 12Z update, with quiet conditions
expected further south. Will be watching for LLWS potential once
more tonight, with insertions possibly becoming necessary in
coming updates.

Quigley

&&

.MARINE...
Issued 1208 AM CDT Sun Apr 12 2026

A broad area of low pressure around 29.4 inches over Ontario
becoming deeper over southern Hudson Bay early this morning.
This will bring breezy south winds to all of Lake Michigan, but
with gales expected over the north third into early this morning.
A Gale Warning is in effect.

Winds will weaken later this morning as the low quickly moves
away and the trailing cold front stalls over central Lake
Michigan. Then, a couple passing low pressure system along the
stalled front will lead to intermittent showers and
thunderstorms through the middle of the week. Areas of dense fog
will likely occur at times due to a relatively mild and humid
airmass over the cold waters.

Gehring

&&

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

$$

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