NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 122003
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
303 PM CDT Sat Sep 12 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 Small Craft Advisory is likely Monday afternoon
  into Tuesday morning for the nearshore waters.

&&

.SHORT TERM...
Issued 303 PM CDT Sat Sep 12 2026

This afternoon through Tuesday:

A dry cold frontal passage is expected this afternoon. Despite
MLCAPE of 1500 J/KG, weak surface convergence and capping should
prevent convective initiation in se WI. The broken stratocumulus
cloud cover ahead of and along the front is an indication of the
capping. Gradual cold advection on nwly sfc winds will then
prevail tnt-Sun. Aloft, a fairly strong and fast shortwave
trough will track from srn Canada across the nrn Great Lakes on
Sun. The upper wave will help induce a west to east band of mid
level frontogenesis across srn WI that could result in a few
high based, light showers. Rain chances of 20-30 percent are
forecast. A 1025 mb high pressure area will then move across srn
WI Sun nt. Low temps in the lower to middle 40s are expected
inland from the lake. High temps around 70F are forecast Sun-
Mon.

For Mon afternoon into Tue, cyclogenesis is expected from the
nrn high plains to srn Hudson Bay. A sly low level jet of 50 kt
will develop over the Upper MS River Valley Mon afternoon then
veer across WI Mon nt-Tue AM. There are timing differences with
the onset of low to mid level warm, moist moist advection and
frontogenesis. The GEFS and ECMWF are slower and mostly hold off
until Mon eve-nt, while the NAM and most CAMs begin widespread
showers and scattered storms Mon afternoon especially well north
and west of the MKE metro area. Will be following the NBM PoPs
which is similar to the slower GEFS and ECMWF. PWATs of 2 inches
will then overspread srn WI Mon nt as the thermal ridge shifts
ewd and the low level jet veers into central and srn WI. There
is some weakening of the approaching cold front for early Tue
AM, but overall believe widespread showers and storms will
likely occur over srn WI. MUCAPE is expected to remain below
1000 J/KG and elevated with heavy rain the main concern. Flash
flooding would be possible if persistent training of storms
occur, but there is uncertainty on longevity and placement of
the more intense rainfall rates at this time. The antecedent
conditions are also fairly dry with low river levels. Lesser
rainfall amounts would then be expected on Tue as the low level
jet and front weakens and slows as it passes through srn WI.

Gehring

&&

.LONG TERM...
Issued 303 PM CDT Sat Sep 12 2026

Tuesday night through Saturday:

Wswly flow aloft will continue for the week with a stationary
front wavering north to south at times, and likely residing
over IL much of the time. Rounds of warm, moist advection north
of the boundary over srn WI will be possible at times during the
week with additional showers and storms. By the end of the week,
cyclogenesis may accompany a shortwave trough moving ewd across
the Great Plains and bring more showers and storms to the
region. Slightly below normal temps are forecast from Wed-Sat
partly due to the potential for clouds and rain.

Gehring

&&

.AVIATION...
Issued 303 PM CDT Sat Sep 12 2026

Areas of MVFR Cigs this afternoon with widespread VFR conditions
expected tnt-Sun.

Gehring

&&

.MARINE...
Issued 303 PM CDT Sat Sep 12 2026

A cold front will move across Lake Michigan late this afternoon
with modest southwest winds shifting west northwest. Modest
northwest winds will then prevail tonight and Sunday until high
pressure around 30.3 inches moves across the lake late Sunday
night into Monday morning. Winds will increase and veer south
southwest Monday night into Tuesday as low pressure around 29.4
inches develops over Manitoba. Gales appear likely during this
time frame. 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. A Small Craft Advisory will likely
be needed Monday afternoon into Tuesday morning for breezy
south winds and high waves.

Gehring

&&

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

$$

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