NWS-Milwaukee/Sullivan Forecast Discussion

						FXUS63 KMKX 221225
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
725 AM CDT Wed Apr 22 2026

.KEY MESSAGES...

- Well above-normal temperatures continue through Thursday. A
  lake breeze keeps eastern WI cool today.

- Periods of showers and storms expected late Thursday night
  into Friday. Widespread severe weather is not expected,
  though some storms could produce heavy downpours.

- Showers and thunderstorms return Sunday night through Tuesday.

&&

.UPDATE...
Issued 700 AM CDT Wed Apr 22 2026

GOES Satellite RGB imagery depicts some low stratus (and fog)
developing over the southern third of Lake Michigan, with a
light northeasterly wind advecting it towards shore. Cameras
along the shoreline in eastern WI confirm that the fog (for the
time being) is not dense in most areas, with the exception of
the shoreline in Racine county. We'll continue to monitor it's
movement on the light NE winds.

The remainder of the forecast remains on track. The latest model
guidance hints that Thursday's southeasterly lake breeze (amidst
the gusty due-southerly synoptic flow) may only extend 1-1.5
counties inland and arrive relatively late in the afternoon,
thus the warmth will spread further east.

Sheppard

&&

.SHORT TERM...
Issued 1125 PM CDT Tue Apr 21 2026

Rest of Tonight through Thursday:

Synopsis/Mesoanalysis: Surface observations place a weak cold front
along an approximate Prairie du Chien - Baraboo - West Bend axis
late this evening. Nudged by a broad area of high pressure centered
over the Lake Superior vicinity, the boundary will continue to drift
south into the region through the remainder of tonight, bringing a
light but steady north wind shift in its wake. The boundary's
progress will slow as it approaches the Wisconsin-Illinois border
during the predawn hours, keeping winds light and variable along and
south of the I-94 and US-18 Corridors through daybreak. The light
winds will combine with clear skies & efficient radiational cooling
to support areas of fog development in locations most proximate to
the slow-moving surface boundary during the predawn hours. Slow down
& use low-beam headlights if encountering areas of fog during the
early morning hours. Upper ridging will glide across the western
Great Lakes during the day Wednesday, allowing for mostly sunny
skies and continued well above-normal temperatures away from the
Lake Michigan shoreline. A pronounced upper trough will eject from
the northern Rocky Mountains on Thursday, encouraging surface
cyclogenesis over the Dakotas. Remaining well east of the low,
increasing southerly winds will allow for even warmer conditions
across southern Wisconsin on Thursday afternoon. Precip impacts from
the Northern Plains trough & surface low will hold off until
Thursday night/the beginning of the long term period.

Rest of Tonight: Will be monitoring for areas of fog development
after midnight. With clear skies and still modest moisture in the
near-surface layer, conditions will be broadly favorable for
visibility reductions with continued cooling. Tend to think the
greatest potential for fog will be along & south of I-94 and US-18,
where proximity to the surface front sagging into the region will
result in light winds & the best chances for decoupling of the
boundary layer. Have maintained fog mentions over the southern part
of the CWA given these expectations. Will be monitoring visibility
trends further north, though higher surface winds should preclude
widespread fog potential over this part of the area. Whether or not
any fog will become dense remains uncertain, and will likely be
contingent on a complete stall of the encroaching surface front such
that winds can remain calm for long enough in any given location(s).
Will be watching trends through the remainder of the overnight.

Thursday: Continued low level warm advection will result another
afternoon of well above-normal temperatures areawide. Trended
forecast temperatures up slightly in the evening update, with
widespread mid-upper 70s & low 80s anticipated across much of the
area. Breezy southerly winds should keep the lake breeze from mixing
too far inland, though the boundary may attempt to work inland
during the mid-late afternoon hours. Could thus see locally cooler
high temps near the immediate Lake Michigan shoreline. Think highs
will remain just below April 23 records (83 in 1960 in Madison & 85
in 1960 in Milwaukee), though trends will continue to be
monitored.

Quigley

&&

.LONG TERM...
Issued 1125 PM CDT Tue Apr 21 2026

Thursday night through Tuesday:

Synopsis: The upper trough moving into the Northern Plains Thursday
will progress from the Upper Mississippi Valley through the western
Great Lakes during the Thursday night - Friday time frame. Attendant
surface low pressure will concurrently occlude over the Canadian
Prairies, with an occluded front moving across southern Wisconsin
during the day on Friday. Thunderstorms will develop along the front
to the west of the area Thursday evening, moving into southern
Wisconsin after midnight as they steadily decay. Additional
shower/storm development is possible during the daytime hours Friday
as the occluded front crosses the area. Widespread severe weather
potential is not expected in any thunderstorms during the Thursday
night-Friday time period, though some storms could produce brief
heavy downpours. Drier and cooler air will work into the region
behind the departed front Friday evening, with passing high pressure
maintaining dry conditions across southern Wisconsin through the
majority of the weekend. A second upper wave will approach from the
southwest Sunday night into Tuesday, bringing additional chances for
showers and embedded thunderstorms to southern Wisconsin.

Thursday night: Expect strong to severe thunderstorms to erupt over
the Missouri Valley during the late afternoon hours, with activity
organizing into clusters and lines as it moves into Iowa and
Minnesota during the evening hours. Expect that activity will work
into southern Wisconsin near or after midnight, though it will be
battling a waning instability pool & weakening wind shear as it
attempts to migrate east. Thus not currently expecting a widespread
or organized severe weather threat in Thursday night's
thunderstorms. Will nevertheless need to monitor areas west of
Madison, where a few storms with gusty winds could be possible if
instability and/or wind shear trend higher in coming forecasts. A
likely progressive & weakening nature to storms should limit the
residence time of higher rainfall rates in any one given location,
which should act to keep flash flooding potential low in Thursday
night's storms. Could nevertheless see some hydro responses in
rivers, streams and urban areas, where conditions remain full &
saturated from last week's rainfall. Will continue to watch trends &
provide more information as additional forecast guidance becomes
available over the next 12-24 hours.

Friday: Given the slow progression of the upper wave & surface
occluded front currently progged in global guidance, expecting some
rejuvenation of early morning showers/storms and/or redevelopment of
showers/storms from late morning into the afternoon hours.
Persistent cloud cover should help to limit instability, though
values could climb to sufficient levels to combine with overlapping
wind shear to support an isolated stronger storm capable of hail and
gusty winds. Will be monitoring trends regarding this potential over
coming forecasts. Additional heavy downpours would be possible in
any thunderstorm redevelopment.

Sunday night into Tuesday: Showers and scattered storms return to
the region ahead of the next upper disturbance. Precip will be
focused by an abundance of synoptic ascent ranging from positive
vorticity advection in the mid-levels to warm advection &
frontogenesis in the lower levels. While there is little uncertainty
regarding the aforementioned abundance of forcing, there remains
considerable uncertainty regarding the precise timing of its passage
amongst global guidance. This is contributing to the wide temporal
range of mentionable precip probabilities in the evening update,
with the expectation for mentionable probabilities to contract a
tighter window(s) as this portion of the period draws closer & the
timing of best forcing clarifies. Passage of the upper wave near or
just south of the region will place the best overlap of instability
and wind shear in the Ohio and mid-Mississippi River Valleys, which
is where machine learning-based forecast guidance is placing the
highest potential for severe thunderstorms. Thus initially thinking
that the primary impact from any storms during the Sunday night -
Tuesday time frame would be heavy downpours, but will nevertheless
be monitoring trends.

Quigley

&&

.AVIATION...
Issued 715 AM CDT Wed Apr 22 2026

Some patches of IFR/LIFR low-stratus cloud ceilings have managed
to form over the southern third of Lake Michigan, including
some fog observed at KRAC (advecting onshore with light NE
winds). These winds will continue to advect some of this fog /
low stratus onshore (perhaps for the next hour or two), but the
abundant sunshine should begin to erode it shortly.

Dry weather and VFR through the rest of the TAF period. Light
winds veer from northeast to due east and eventually southeast.
Breezy due-south winds arrive Thursday.

Sheppard

&&

.MARINE...
Issued 1125 PM CDT Tue Apr 21 2026

A weak surface boundary will continue to work south into the
southern third of Lake Michigan tonight, leading to light and
variable winds with breezier winds further north. The light winds
could lead to areas of fog over the southern third of the open
waters through the overnight hours, with trends being monitored for
possible dense fog advisories through this evening. Light north-
northeast winds will become established over all of Lake Michigan
after sunrise on Wednesday, trending east-southeasterly during the
second half of the afternoon hours.

Southerly winds will increase over the open waters Wednesday night
through Friday morning as 990 mb low pressure develops over the
northern Great Plains. While winds will be breezy, gales are not
anticipated at this time. The low will pull a cold front across Lake
Michigan Friday afternoon and evening, resulting in a breezy north-
northwest wind shift. Periods of showers and embedded thunderstorms
will accompany the approaching/passing surface low & front Thursday
night through Friday. Severe weather is not anticipated at this time.

North to northeast winds will continue through the weekend across
Lake Michigan. 1000 mb low pressure will approach the open waters
from the Great Plains during the day on Monday, resulting in a
breezy east wind shift. The low will cross Lake Michigan Monday
night into Tuesday, bringing a northwest wind shift by Tuesday
evening. Don't anticipate widespread gale potential as of this
forecast, though trends will continue to be monitored over coming
updates.

Areas of fog are possible in nearshore zones tonight. Some fog could
become dense, with trends being monitored for potential headlines
through this evening. Southerly winds will increase in nearshore
zones ahead of low pressure in the northern Great Plains Thursday
evening through Friday, resulting in elevated wave heights. Some
waves could approach Small Craft Advisory thresholds, particularly
from North Point to Sheboygan. Periods of showers and thunderstorms
are expected Thursday night into Friday, with severe weather not
anticipated at this time. Trends will be monitored for possible
headlines in coming forecast updates. Additional Small Craft
Advisory wind gusts and wave heights are possible over all nearshore
zones Sunday night into Tuesday.

Quigley

&&

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

$$

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