184
FXUS63 KMKX 221521
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1021 AM CDT Tue Apr 22 2025

.KEY MESSAGES...

- Additional off and on storm chances this afternoon/evening
  into Wednesday with a small potential for strong to severe
  storms.

- Any training storms later tonight into Wednesday may have a
  localized flash flood potential, mainly near the WI/IL
  border.

- Warmer today and Wednesday with a possible temperature drop
  Thursday and keeping temps cooler for Friday.

&&

.UPDATE...
Issued 1020 AM CDT Tue Apr 22 2025

Showers mixed in with a few rumbles of thunder will gradually
dissipate and push to the east through this morning as the warm
front sags south today. Into the afternoon and evening, the
surface warm front is likely to be the focus for any convective
initiation. Most models have focused the warm front to the
south of the CWA keeping the front in northern Illinois with
convection largely remaining south. There remains a chance
(20-30%) that the the warm front does not sag as far south as
expected and if that is the case, convection would likely
initiate further north over at least parts of southern WI.
Regardless of where the front sets up the risks for strong to
severe storms seems fairly limited based on what CAMs are
currently showing however 1000-1500 J/kg of instability and
40ish kts of effective shear is suggestive of some organized
convection with the primary risks being hail and damaging winds.
The winds seem to be the larger threat given some of the
sounding profiles suggestive of a bit of an inverted V with
strong enough DCAPE to bring some damaging wind potential.
Overall chances remain limited for strong to severe storms,
however.

Late overnight into Wednesday expect that warm front to slide
north introducing increased precip/storm chances (40-60%) with
some morning/early afternoon influence from a weak shortwave
with additional influence into the afternoon from increased WAA
and low to midlevel moisture. The level of instability through
the day Wednesday is a bit more uncertain but models are at the
least bring 500-1000J/kg of MUCAPE to the region. The strong to
severe storm potential seems fairly similar to today (in
northern IL), but convection seems likely to be more consistent
through the morning and into the afternoon. This may limit the
upper bounds of our instability throughout the day in addition
to causing cold pools in these areas further limiting the
potential for stronger storms. Outside of some isolated hail
general storms seems most likely with this. Wed evening/night we
will gradually loose our moisture and instability with largely
just showers and weak storms expected (mostly further west) but
gradually dissipating across the region and shifting further
north as the warm front slides further north.

Kuroski

&&

.SHORT TERM...
Issued 356 AM CDT Tue Apr 22 2025

Today through Thursday:

Will begin the active stretch of weather this morning and
continue periodically through the end of the week. Our focus is
on the ongoing and redeveloping showers and storms back across
central IA/south-central MN. The leading edge of this convection
has diminished overnight as it pushed off the modest MUCAPE
gradient which is currently set up around the aforementioned
area. Have seen some redevelopment over the past hour as the
mid-level trough and associated dCVA lifts across the Upper
Mississippi River Valley. These newer storms are firing up where
a band of 700mb frontogenesis and swath of the 850mb WAA align
with the nose of 45kt 850mb LLJ and edge of 500 J/kg of MUCAPE.
Have been seeing some isolated upscale growth with some of this
activity given effective shear greater than 40kt and mid-level
lapse rates of 7-7.5 C/km across IA/MN. Mainly looking at
elevated activity given the lack of surface based support, but
an isolated storm or two will be strong enough to produce some
hail and potentially nearing severe level (1") upstream.
Expecting this activity to follow the elevated instability
gradient and gradually work its way eastward across the
Mississippi River into southern WI a little after daybreak and
linger into the mid-morning hours. While cannot rule out the
stronger storm or two as things push into southwestern WI, this
activity does begin to lose its upper-level support as it moves
further east off the mid- level vort max and as the LLJ
gradually lessens into the mid-morning hours. The 06z HRRR
reflects this trend into southern WI as well. Nevertheless will
monitor upstream trends over the next few hours and see how it
evolves with the better thunderstorm potential being for areas
southwest of I-90 corridor with ares east likely seeing the
scattered shower remnants later this morning.

After the morning showers diminish, a weak low pressure from
the morning shortwave wave trough will meander over the ND/MN
border through the day and lift a warm front across the southern
WI. This looks to advect moisture and warmer temps into the
areas with afternoon temps climbing into the 60s and may even
approach 70F in a few locations out west and along the WI/IL
border. Areas closer to the lake especially where a more
easterly winds persists will remain cooler. The big question
will be where/how far north this warm front will make it before
it stalls out and is pushed southward by a weak cold front and
potentially an afternoon lake breeze. Despite the lack of upper-
level support, any convergence along stalled boundary will be
the focus of additional shower and thunderstorm development
later this evening/tonight into Wednesday. Most of the 00z and
06z CAMs as well a nearly all of the HREF members favor this
boundary being pushed south into IL with scattered storm
development along it. Given this consensus, the trend is to keep
southern WI mostly dry with the evening/overnight activity.
However, still cannot rule out this boundary waffling a bit
northward so will maintain low-end PoPs along the WI/IL border
through tonight. While a stray strong storm or two will be
possible with this activity, will also need to monitor for any
training storms and minor/localized flood potential given this
stagnant setup, especially if things shift northward back into
southern WI.

For Wednesday another shortwave trough is progged to track
across the Upper Midwest and increase southwesterly flow across
WI. This should be enough to lift the stalled frontal boundary
back northward into WI. Again this boundary will be a focus for
surface based showers and thunderstorms development as the
higher moisture (dewpoints in the 50s) and increase instability
(SBCAPE +1000 J/kg) creeps northward. Again with limited upper-
level support, main driver will be the low-level convergence
along the boundary. However, models hint at a modest 30 kt LLJ
to lift into southern WI paired with 850mb WAA and mid-level
lapse rates approaching 7C/km, thus cannot rule out few more
organized storms embedded with this activity for wednesday
afternoon and evening.

Outside of the periodic PoP chances, Wednesday is shaping up to
be even warmer with highs in the upper 60s and low 70s across
southern WI with mild overnight temps in the upper 40s to low
50s.

Going into Thursday, with mainly zonal flow aloft and not much
in the way of any forcing, it appears that the surface front
gathers some steam dropping back to the south. Some signal of it
being a lake/pneumonia front-ish look to given the weak pressure
gradient in place. So, while temperatures will be warm that day,
expect that there will be a mid-late afternoon drop given the
current setup.

Wagner

&&

.LONG TERM...
Issued 356 AM CDT Tue Apr 22 2025

Thursday night through Monday:

Shower and thunderstorm activity is expected to form along weak
warm advection north of a surface low Thursday night. As the
low tracks on a flat west to east path into IL Friday morning,
this area of rain will track over southern WI through the pre
and post- dawn hours. Rain should then move east of the area by
Friday evening with high pressure moving in behind the low.
Temperatures will cool for the weekend, but remain seasonable
with highs in the upper 50s to low 60s Saturday (with cooler
temps along the lakeshore owing to northeast winds) and then low
to mid 60s Sunday. Conditions remain dry until warm advection
driven rain returns Monday morning.

CMiller

&&

.AVIATION...
Issued 1020 AM CDT Tue Apr 22 2025

Some MVFR CIGS will slide across west-central and central WI
this morning into the early afternoon but will for the most part
remain VFR across most of southern WI. Showers have gradually
pushed east and begun to dissipate across the area as well.
Drier conditions are more likely as the day goes on with the
warm front sagging south and bring storms chances this afternoon
and evening to northern IL likely remaining on the drier side in
southern WI. We cannot rule out a few storms/showers pushing
north of the WI/IL border but it appears less likely at this
point. Any storms would carry some VSBY restrictions possible.
Overnight tonight into Wednesday the warm front will kick back
north bring scattered showers and storms to southern WI with the
best chance toward southwest WI. Models indicate some MVFR CIGS
will be possible across parts of southern WI Wednesday but may
be more SCT to BKN. Precip/storm chances will continue through
the day Wednesday before gradually dissipating or at least
becoming more isolated into the evening and overnight hours.
Again, MVFR/IFR VSBYS will be expected with heavier showers or
storms Wednesday.

Otherwise expect light to modest winds today, predominantly from
the south but turning more west as the front sags south. Near
the lake a lake breeze will likely develop bringing more east to
southeast winds behind it into this afternoon. Light southerly
winds will dominate Wednesday.

Kuroski

&&

.MARINE...
Issued 356 AM CDT Tue Apr 22 2025

Lighter westerly winds early this morning from a high pressure
passing south of Lake Michigan will turn more southeasterly
through the day. Expect a low pressure to meander along the
ND/MN border and will see southeasterly winds gradually increase
across Lake Michigan through the late afternoon/evening as the
associated warm front lifts northward. However, expecting this
warm front to stall out across southern third of Lake Michigan
dividing more easterly winds across the northern two-thirds of
the Lake overnight into Wednesday with more southerly winds
across the southern third. Expecting periodic shower and
thunderstorm chances along the stalled frontal boundary during
this time as well. Winds will remain fairly light through
Wednesday as the low pressure to the north weakens as it lifts
northward into central Canada. Expecting to see the stall front
to gradually wash out into Thursday as high pressure builds
across the Upper Great Lakes. Winds look to be variable through
the end of the week before gradually increasing into Friday as
another weak surface low works it way across the Midwest from
the Plains.

Wagner

&&

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

$$

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