NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 300837
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
337 AM CDT Wed Apr 30 2025

.KEY MESSAGES...

- Widespread light rain expected late tonight through Thursday.
  A few rumbles of thunder will be possible in far southeast WI.

&&

.SHORT TERM...
Issued 336 AM CDT Wed Apr 30 2025

Today through Thursday:

An area of low clouds developed near Green Bay late last evening
and slowly expanded into east central WI overnight. The
trajectory keeps them confined to Sheboygan and Fond du Lac
counties early this morning, and then mixing will help them
dissipate by mid morning. Temperatures dropped into the upper
30s across much of east central and southeast WI thanks to cool
air from Lake Michigan on slightly enhanced northeast winds.
Winds were probably too high to allow for frost development.

There will be a large difference in temps between the lakeshore
and western Waukesha County (and north-south of there) due to a
steady east wind off Lake Michigan all day. Inland temps should
reach the mid to upper 60s from Madison and westward.

Dewpoints are in the 30s and they are not expected to make much
headway into the 40s today, per the upstream obs in IA and IL.
Therefore, min RH values will be in the 35 to 40 percent range.

The arrival time of the precip today looks slower than
previously forecast due to all the dry air in place over WI.
The convection ongoing over MO will lift into the Upper Midwest
later today. However, the nose of the LLJ (and vorticity
advection with a southern stream upper trough) that are driving
that convection is expected to split around southern WI. This
means that one wing of the precip will track into northeast IL
today and lower Michigan this evening; the other wing of precip
will track northward into southern MN, following the right
entrance region of the upper jet and a mid level shortwave
trough.

Eventually, the southern stream shortwave trough will
push into the mid Mississippi River valley and a more connected
flow from there into southeast WI will develop overnight. Thus,
that is when the more widespread showers will arrive in
southeast and east central WI. However, the disjointed upper
levels between the southern stream upper trough and northern
stream upper trough means that south central WI and central WI
will likely have lower precip amounts from this system. Total
rainfall amounts are forecast to range from around 0.75 inch in
southeast/east central WI to 0.35 inch in south central/central
WI.

A surface low will develop over central IL as the MS River
valley mid level shortwave trough gets closer. That surface low
will slide across southern Lower MI during the day Thursday, and
the steadier showers over southeast WI will taper off from west
to east from Thursday afternoon through Friday evening.

Given that we will be on the northwest periphery of the main
forcing of this system, our chance for thunder is very low. The
steeper mid level lapse rates should be limited to right along
the WI/IL border late tonight through Thursday. Elsewhere, lapse
rates look moist adiabatic and thus quite stable.

Temps Thursday will remain cooler by the lake, especially
toward east central WI due to steady northeast winds. Inland
highs will be in the upper 50s, except lower 60s near the WI/IL
border.

Cronce

&&

.LONG TERM...
Issued 336 AM CDT Wed Apr 30 2025

Thursday night through Tuesday:

Meanwhile, the northern stream upper trough will be slow to make
eastward progress. This will bring additional light showers to
southern WI Thursday night. While shower chances continue
through Friday due to the upper trough passing overhead, the dry
air surging in from the north may win out and keep us dry. Any
precip will not be a steady rain, but instead characterized by
several waves of light to moderate showers, as various
shortwaves rotate through the larger scale upper trough. Highs
Friday will be a touch cooler, with readings in the mid to upper
50s to around 60.

The main upper level trough is expected to pass through the area
Friday night, with high pressure building into the region on
Saturday. Guidance is suggesting that an omega block will set up
across the CONUS, with deep troughs/upper lows over the eastern
and western US, and a strong ridge over the central part of the
country. This suggests a stretch of quiet and warm weather as high
pressure slowly drifts eastward, with highs early next week
approaching the upper 70s and low 80s.

Boxell

&&

.AVIATION...
Issued 336 AM CDT Wed Apr 30 2025

An area of low clouds developed near Green Bay late last evening
and slowly expanded into east central WI overnight. The
trajectory keeps them confined to Sheboygan and Fond du Lac
counties early this morning, and then mixing will help them
dissipate by mid morning. Northeast winds are elevated near Lake
Michigan and lighter for inland areas. High clouds will continue
streaming into southern WI from a storm complex crossing the
MO and IL today.

Light rain chances should hold off for southern WI until
evening, although virga is possible. Then more widespread
showers should develop in southeast and east central WI
overnight tonight. A few rumbles of thunder will be possible
near the IL border.

VFR today. Ceilings will fall tonight as the rain moves in,
with IFR expected after midnight and through at least Thursday
morning.

Cronce

&&

.MARINE...
Issued 336 AM CDT Wed Apr 30 2025

High pressure of 30.3 inches centered over Upper Michigan will
cross Lake Huron today. Steady easterly winds will persist through
Wednesday night, then increase Thursday as low pressure around
29.6 inches tracks from IL to southern Lower Michigan.

Winds will become northerly Thursday afternoon and westerly
Friday afternoon as that low exits the region. High pressure
around 30.2 inches will return to the Upper Great Lakes for the
weekend, bringing quiet weather and light winds to the region.

Cronce

&&

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

$$

Visit us at weather.gov/milwaukee

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSMilwaukee
www.twitter.com/NWSMilwaukee
www.youtube.com/NWSMilwaukee