NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 051645 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1145 AM CDT Wed Aug 5 2026

.KEY MESSAGES...

- Periods of showers with isolated lightning expected through
  this afternoon and early evening. Brief heavy downpours are
  possible.

- Heat & humidity return Saturday-Tuesday, along with periods of
  showers and storms.

&&

.UPDATE...
Issued 1145 AM CDT Wed Aug 5 2026

A surface front is stalled over southern WI today, but the
precipitation coverage is lower than what we had anticipated for
this morning. Currently, the showers tracking through central WI
are right along the 850mb frontal boundary where there is weak
convergence but not much warm air advection. There are a few
widely-scattered, light showers elsewhere in southern WI, but
nothing organized. We are in a moisture-rich environment but
with no organized forcing and some mid level dry air.

The deeper moisture and better forcing is focused
well to our south. The more widespread thunderstorms are along
the nose of the 850mb low level jet in eastern IA, and
coincident with 925-850mb warm air advection and frontogenesis.
That area will slide into north central IL and clip south
central and southeast WI later this afternoon, but the overall
forcing is expected to weaken. With the 850mb front still over
our area, we could see afternoon showers all the way up to Fond
du Lac and Sheboygan so I added low pops there.

Models are showing an increase in the instability over
southeast WI this afternoon, so any showers that can make it
into southern WI will have a chance for lightning. With weak mid
level lapse rates and low shear, storms will not be severe; lightning
and heavy downpours are the threats today. Precipitable water
values are between 1.5 and 2 inches over southeast WI, so any
showers will be efficient rain producers.

Cronce

&&

.SHORT TERM...
Issued 1057 PM CDT Tue Aug 4 2026

Tonight through Wednesday Night:

Upper level divergence and WAA to our west in northern IA is
sustaining rain and thunderstorm development late this evening.
Both the upper level DIV and WAA are expected to slowly move
east with time. This will be a gradual process similar to the
motion of the sfc cold front that is draped across southern
Wisconsin. As these features pivot across southern Wisconsin
tonight into Wednesday morning, more widespread rain is expected
across the area. PWATs are fairly high across the region around
1.5 to 2 inches. This could lead heavy rain/downpours with any
shower. Any training or slow storm motion could result in some
urban and small stream impacts with flooding.

Heading into Wednesday afternoon, the aforementioned cold front
is expected to be around the WI/IL border which will work as a
focus point for additional scattered shower/storm development.
The chances for additional development for areas south of
Interstate 94 is around 30-50%. Areas along and north of
interstate 94 should stay fairly dry Wednesday afternoon and
beyond.

Heading into Wednesday night any lingering rain/storms are
expected to come to an end as the sfc front sags south of the
area and high pressure begins to return to the Great Lakes
Region.

The largest concern with any showers and storms by far will be
the heavy rain and risk for flooding should any training occur.
Small streams and urban areas are the most likely at risk for
flooding. This should leave any impacts fairly minor and
localized. There is a lack of shear in this environment and if
cloud cover persists from tonight into Wednesday afternoon
without any break, instability will also be lacking Wednesday.
Just not a great environment for any stronger to severe storms.
If any stronger storms do develop, gusty winds would become the
main concern. Any storms that becomes tall enough with the high
PWATs will likely be water loaded and could produce some
downburst winds. But with limited instability and shear the
chances are very low for any isolated storm to get tall enough
to do that. A low but non zero chance.

Patterson

&&

.LONG TERM...
Issued 1057 PM CDT Tue Aug 4 2026

Thursday through Monday:

Behind the cold front, high pressure is expected to briefly build
into the Great Lakes Region bringing quiet weather for Thursday.
Light and variable winds, mostly clear skies and highs in the
upper 70s to low 80s Thursday. As the high pressure moves out of
the area heading into Friday, south to southwest winds will return
and so to will the WAA. Hot and humid conditions are expected to
return to the state with highs in the 80s and dewpoints expected
to climb back into the 60s. A weak cold front is expected to move
across the state which will bring a low chance (10-20%) for rain
and a storm or two for Friday night.

Heading into the weekend, zonal flow is expected to set up across
the northern US, including the Great Lakes Region. This puts
Wisconsin in a situation where multiple shortwave troughs could
move through the larger scale flow. This unsettle pattern is
fairly consistent across guidance, however when the shortwaves
move through and the strength of each varies. Rain and storms
chances will be persistent Saturday afternoon through early next
week. Monday looks to have the best chances for rain around
40-70% otherwise the rest of the precip chances are around
20-40%. As we get closer in time to this unsettled period, the
rain chances should become more defined in time, duration and
intensity. Not anticipating any all day rains at this point.
Uncertainty remains for any stronger to severe storms as well.
Some guidance wants to hit at stronger storms, but these same runs
are the ones that want to hit at potential heat indices in the
90s. Stuck to the average among guidance for the forecast given
all the uncertainties.

Patterson

&&

.AVIATION...
Issued 1145 AM CDT Wed Aug 5 2026

The MVFR ceilings and showers are slower to move into southern
WI today, but the isolated showers are helping to lower the
cloud bases. Expect a downward trend this afternoon, especially
in southeast WI where shower coverage should be greater.
Isolated lightning is still possible this afternoon and early
evening.

The lower Cigs may continue into tnt or redevelop late tnt
along with areas of BR and fog.

Cronce

&&

.MARINE...
Issued 1057 PM CDT Tue Aug 4 2026

A cold front is slowly moving across the waters this evening into
Wednesday morning, bringing a brief north-northwest wind shift.
Periods of showers and storms will accompany the slow-moving
front, with severe weather appearing unlikely at this time. Winds
will trend variable Wednesday evening through Thursday, when 30.1
inch high pressure is forecast to build into the western Great
Lakes.

A prolonged period of south-southwest winds will become established
across Lake Michigan Thursday night through Sunday as 30.1 inch
high pressure lingers off the Mid-Atlantic coast and 29.6 inch
low pressure stalls over the Hudson Bay. A slow-moving surface
front will linger across the western Great Lakes Saturday into the
beginning of next week, bringing multiple periods of showers and
thunderstorms. Some of these storms could be stronger, with
additional details clarifying through the end of this week.

Patterson

&&

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

$$

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