157
FXUS63 KMKX 212036
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
336 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Showers and thunderstorms are likely through late evening. A
  few storms may be strong to severe.

- Most of southern WI will see some beneficial rainfall from the
  cold front passage with amounts generally ranging from 0.1-0.7
  inches with locally higher amounts with any stronger
  thunderstorms.

- Cooler/near normal temps are expected behind the cold front
  Sunday through the start of the week with daily highs in the
  upper 60s and lower 70s.

&&

.SHORT TERM...
Issued 336 PM CDT Sat Sep 21 2024

This Afternoon:

Showers and thunderstorms are developing in a north-south
oriented line that is right along the 1000 j/kg CAPE gradient,
within an area of steady 925-850mb warm air advection. There
was an outflow boundary that developed from the morning
convection over the Twin Cities that is tracking straight down
the instability gradient, and this feature is causing the
intersecting storms to be stronger as the boundary propagates
south-southeast. The area of stronger storms is currently over
Dane County and is producing marginally severe hail and wind.


The next feature of interest is the surface warm front which is
moving into the Mississippi River Valley. There are showers and
a few thunderstorms along this front. The two areas of warm air
advection will slowly track across southern WI through the
evening and therefore, the chance of storms will persist all
evening. Severe storms are not expected, but if there are any
areas of extra forcing such as an outflow boundary of surface
convergence with a lake breeze, then isolated severe is
possible. We will have up to 1500 j/kg of elevated CAPE and
around 30 kt of bulk shear to support a few stronger storms.

Tonight through Sunday night:

The cold front is also going to move through in a couple waves
overnight. There is a surface wind shift to the northwest that
is already in southeast MN and north central IA. This surface
warm front may be enough to kick off a few thunderstorms as it
gets into western WI late this afternoon, but it is also
possible that our environment could be worked over by previous
storms and not amount to much. There is a secondary cold front
back in central MN which has more upper level support with the
mid level vorticity advection. Since the upper wave will be
weakening, its movement toward southern WI will slow down
overnight into Sunday. This means our chance for showers and
storms ahead of an along this secondary cold front will persist
all the way into Sunday afternoon, especially over southeast WI.

Cronce

&&

.LONG TERM...
Issued 336 PM CDT Sat Sep 21 2024

Monday through Saturday:

One more mid level shortwave will track along the WI/IL border
on Monday. This will keep clouds over southern WI. Then an
upper low should develop and stall over the Upper Midwest
Tuesday. This will keep us cloudy and keep our temps down in the
70s. Lots of uncertainty with how that low will move later in
the week, with a trend away from southern WI and retrograding
toward the south central U.S..

Cronce

&&

.AVIATION...
Issued 336 PM CDT Sat Sep 21 2024

Thunderstorms are moving into the Madison area, although the
strongest is expected to remain to the west and south of MSN
airport. Thunderstorm chances will persist through the evening
hours. After a probable lull in showers and storms overnight,
there are renewed chances for showers and storms all Sunday
morning. The showers and storms are most likely just ahead of
and along a cold front that will be slowly crossing southern WI
Sunday morning through afternoon.

MVFR to IFR ceilings and visibility are looking likely Sunday
morning, along with scattered showers and thunderstorms. Gusty
northerly winds are expected Sunday night, especially along Lake
Michigan.

Cronce

&&

.MARINE...
Issued 336 PM CDT Sat Sep 21 2024

Expect southerly winds increase through the evening as low
pressure lifts from MN to Ontario, which will in turn drag a
cold front across WI and Lake Michigan overnight through Sunday.
Showers and thunderstorms will develop ahead of and along the
cold front. Southwesterly winds will become northerly behind
this front Sunday night into Monday. Given the strong cold air
moving over the warmer lake waters, expecting to see gusty
northerly winds during this timeframe. Gusts up to 30 knots and
a few gale force gusts cannot be ruled out, especially for the
southern portions of Lake Michigan. Will see winds weaken a bit
for Monday as high pressure builds in across the Great Lakes
region, but the northerly component will persist through the
start of the week.

Cronce

&&

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

$$

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