166
FXUS63 KMKX 160258 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
958 PM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Very warm and humid conditions through Wednesday with maximum
  heat indices in the lower 90s.

- Increased shower and thunderstorm chances through the day
  Wednesday (50-80%) with lower chances (20%) lingering into
  Thursday morning.

- Slight Risk (2 out of 5) to see strong to severe
  thunderstorms Wednesday afternoon/evening capable of gusty
  winds, hail, and heavy rainfall.

- Looking cooler and drier later Thursday into Friday with high
  temps in the 70s and lows in the 50s to around 60F.

- Unsettled weather returns for the weekend with 30-50% shower
  and storm chances Saturday and Sunday night.

&&

.UPDATE...
Issued 958 PM CDT Tue Jul 15 2025

Weak, elevated warm air advection and subtle upper divergence
are supporting the development of a few showers over northeast IL
and far southeast WI this evening. This is occurring a little
earlier than anticipated but the forcing should continue
through late tonight. No lightning is anticipated.

Otherwise, expect mostly clear skies, light/calm winds and mild
temps due to dewpoints around 70. Patchy fog is expected in the
Wisconsin River Valley and may also develop in marshes and
other low lying areas.

The storm complex developed as expected over eastern SD and
central NE, and it will weaken overnight as it rolls into IA and
srn MN. The remnants of this complex are expected to interact
with unstable conditions that will build over southern WI and
produce discrete and clusters of thunderstorms over northern IL
and southern WI during the afternoon and evening. There is a
risk (2 out of 5) for severe storms, primarily damaging winds.
Heavy rain is also a threat.

Cronce

&&

.SHORT TERM...
Issued 340 PM CDT Tue Jul 15 2025

Tonight through Wednesday night:

High pressure is expected to retreat eastward through the rest of
the afternoon and into tonight. Skies will stay mostly clear to
partly cloudy overnight with a bit of fog in the Wisconsin River
Valley, but some CAMS depict a bit of elevated instability
lifting north as warm, moist advection occurs around the western
edge of the departing high pressure. A few weak, scattered
showers may form on the leading edge of the WAA, mainly along
the Wisconsin/Illinois border and southeast Wisconsin (15 to 25%
PoPs). This should mainly occur between midnight and 6am before
dissipating.

Meanwhile to our northwest overnight, outflow from convection over
Minnesota and the upper peninsula of Michigan will wash out over the
northern half of Wisconsin pushing a nebulous boundary into central
WI and portions of central Iowa. Other dying convection will then
leave a weak area of low pressure and compact MCV aloft over central
Iowa by daybreak on Wednesday. Through the remainder of the morning,
and into the early afternoon, this area of low pressure is expected
to deepen and track east, advecting a very humid sfc airmass
northward during the late morning and passing over Wisconsin during
the afternoon into the evening. Sfc pressure falls, the
MCV/shortwave aloft, and a few surface boundaries will all work to
kick off shower and storm activity near the Mississippi Valley
shortly after noon. These storms will then move over southern
Wisconsin from west to east between 2pm and 8pm.

CAMs depict an environment with moderate SBCAPE around 2500
J/kg, with mid level lapse rates ranging from 6.5 to 7 C/km.
Effective shear will be around 35 knots and boundary
perpendicular over most of the area, promoting storm
organization and a semi-discrete mode. Hodographs do show some
low level curvature from 0-2km, but flow will be lacking aloft,
likely lending an HP/linear mode to any storms that form. With
some dryness in the low levels, a damaging wind threat may
develop, especially with any linear/bowing storms tomorrow. More
discrete storms, on the other hand may have a short lived hail
threat.

Additionally, PWATS will be between 1.75 and 2 inches, meaning
any storms tomorrow will produce heavy downpours. Urban and
small stream flooding may occur over central to east central WI,
where a larger area of precip is expected to form near the
surface low center and more training of convection is
anticipated to happen.

CMiller

&&

.LONG TERM...
Issued 343 PM CDT Tue Jul 15 2025

Thursday through Tuesday:

The sfc low is expected to drag a cold front over the region and
wrap in dry air from the northwest Wednesday night into
Thursday. Some showers may linger Thursday morning, but a very
welcome reprieve is then expected Thursday afternoon into Friday
as dry, cool air moves over the Upper Midwest with relatively
strong high pressure. Highs are expected to be around 70 on
Thursday, and in the mid 70s Friday.

Temperatures slightly rebound this weekend as weak WAA returns
over the Upper Great Lakes region. Shower and thunderstorm
chances return on Saturday as a sfc trough moves over the
region. This trough should largely pass Saturday night, keeping
most of Sunday dry, but more shower and thunderstorm chances may
return Sunday night as a wave of warm advection returns from the
Plains.

Warmer and more humid conditions then return by the end of the
extended period.

CMiller

&&

.AVIATION...
Issued 958 PM CDT Tue Jul 15 2025

VFR conditions will continue into tonight over most of southern
WI. Areas of fog possible around and in the Wisconsin River
Valley overnight, as well as other low lying areas. A few light
showers are expected over far southeast WI through the
overnight hours.

Tomorrow, scattered thunderstorms capable of damaging winds
appear possible over all of southern WI between 19Z and 01Z
Thurs.

Cronce

&&

.MARINE...
Issued 322 PM CDT Tue Jul 15 2025

A slow moving front will approach Lake Michigan from the
northwest tonight as high pressure retreats east toward the
east coast. Low pressure will then approach lake Michigan from
the Iowa/Minnesota border by Wednesday evening, bringing
chances for thunderstorms over most of the lake.

Winds will remain southerly and light to moderate over most of the
lake through tonight, until the front sinks south over the lake
during the post dawn hours tomorrow. The front will then stay
stationary over the lake with north winds over the northern half
and south winds over the southern half of the Lake into Wednesday
night. Winds will then come around to northwesterly following the
passage of the surface low Wednesday night into Thursday morning.
Gusty winds are then expected Thursday as the pressure gradient
gets squeezed between the departing low pressure, and strong high
pressure over the northern plains.

CMiller

&&

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

$$

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