NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 130603
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
103 AM CDT Sun Sep 13 2026

.KEY MESSAGES...

 - Active start to next week, with multiple periods of showers and
   thunderstorms expected Monday evening through at least
   Tuesday. Some storms could produce heavy rainfall and some
   gusty winds.

- Gales are possible Monday night into Tuesday morning across
  the Lake Michigan open waters as increasing south winds
  develop. A Gale Watch has been issued for the northern two-
  thirds of the open waters of Lake Michigan. A Small Craft
  Advisory is likely Monday afternoon into Tuesday morning for
  the nearshore waters.

&&

.SHORT TERM...
Issued 1202 AM CDT Sat Sep 12 2026

Current Overnight through Tonight:

Conditions will remain quiet overnight as high pressure remains
overhead. The dry air present and clear skies will allow
temperatures to drop into the low 50s.

After daybreak today, the base of a trough is expected to pivot
over the state, bringing a 300mb jetstreak with it. Strong 700mb
fgen is expected at the base of this trough, and this fgen
should move along and south of the WI/IL border late this
morning and into the afternoon. The fgen will drive lift and
saturation aloft just above the 700mb level, but a moderately
strong 1022mb high pressure will remain at the surface. As such,
a pocket of dry air 1 to 3km deep near the surface from the
high pressure may eat into a lot of the potential rain today.
Still, areas immediately along the WI/IL border may saturate
enough to beat the dry layer and squeak out a couple hundredths
of rain, with areas further north to near I-94 seeing sprinkles.
With the rain evaporating into dry air near the surface and the
presence of cloud cover, today is likely to be cool, with highs
in the mid to upper 60s.

Rain largely ends late this afternoon, with skies quickly
clearing out. The high pressure center is expected to move
overhead tonight. Clear skies and dry Td's will allow
temperatures to dip into the 40s for overnight lows.

CMiller

&&

.LONG TERM...
Issued 1223 AM CDT Sat Sep 12 2026

Monday through Friday:

High pressure should slowly push east Monday morning, keeping
the morning hours mostly dry. By noon warm advection is
expected to surge north between the exiting high pressure
system, and an occluding low pressure system over the central to
northern Great Plains. A swath of rain will ride the WAA wave
into Wisconsin and Monday afternoon looks to feature some steady
light to moderate rain, with some heavier rain tied to
embedded thunderstorms, as a few hundred J/kg of MUCAPE will
arrive with the rain. Some of the downpours with the embedded
thunderstorms could be heavy, as PWATs of 1.7 to 1.8 inches are
expected to arrive Monday afternoon. It does look like earlier
concerns for severe weather have lessened as the warm sector of
the occluding low should stay to our west in Iowa while we see
weak elevated convection through the afternoon and early
evening.

By Monday night, the more defined warm sector from earlier in
the day will give way into an elongated baroclinic zone. This
baroclinic zone will then sink south-southeast as a cold front
from early morning Tuesday to midday. Convection is expected to
light up along the front overnight, and track from southwest to
northeast along the sagging front. With the high PWATs mentioned
before, these storms may cause some heavy rainfall. An aggregate
of the CAMs, deterministic models, and GFS and ECMWF ensembles
generally show 0.5 to 2 inches of accumulation on the lower and
upper ends of the envelopes from Monday Afternoon through
Tuesday morning, but locally higher amounts may occur where
storms track repeatedly. Some gusty winds can't be ruled out
with these storms Monday night into Tuesday morning, given the
water load in the storms and more MUCAPE near 1000 J/kg over the
area.

Lighter, showery rain may then linger through Tuesday afternoon
before the front completely pushes rain south of the WI/IL
border and the front stalls over northern IL. We'll have a
break Wednesday morning, before the stationary front wiggles
north a bit, bringing some rain chances for Wednesday afternoon
into Thursday morning. Details get murky beyond, but it does
appear that some shower chances may linger into Friday, with the
NBM painting broad PoPs over Wisconsin from 35 to 55% through
the day.

CMiller

&&

.AVIATION...
Issued 1153 PM CDT Sat Sep 12 2026

Expect continuing VFR overnight and into this morning amid
continuing light northwest winds. KSBM may see some gusts to
near 20 knots this afternoon. Some light rain may impact
terminals along the WI/IL border briefly this afternoon, with
rain less likely with northern extent away from the
Wisconsin/Illinois border.


CMiller

&&

.MARINE...
Issued 1146 PM CDT Sat Sep 12 2026

Light to moderate northwest winds will prevail through today with
occasional gusts to 25 knots over the lake this afternoon.
Winds ease tonight as high pressure moves across the lake into
Monday morning.

Winds will then increase and veer to south-southwesterly Monday
afternoon into Tuesday as low pressure develops over Manitoba.
Gales appear likely Monday night into the first half of Tuesday.
A Gale Watch has been issued for the northern two thirds of the
open waters of Lake Michigan.

Periods of showers and thunderstorms will accompany the
developing low from as early as Monday evening into Tuesday. Winds
will trend northerly and weaken behind a cold front Tuesday night
into Wednesday.

CMiller

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Gale Watch...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ675-LMZ868-LMZ870-LMZ872-LMZ874-
     LMZ876...7 PM Monday to 1 PM Tuesday.

&&

$$

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