969
FXUS63 KMKX 280008
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
708 PM CDT Sat Apr 27 2024

.KEY MESSAGES...

- A tornado watch has been issued for Green, Iowa, and Lafayette
  Counties until midnight tonight.

- A severe thunderstorm watch is in effect for most of south-
  central and southeastern Wisconsin until midnight tonight.

- Scattered storms are still expected to develop along a weak
  cold front late this afternoon and evening. A few of these
  storms may become severe with large hail and damaging winds,
  but cannot rule out a tornado or two.

- Rounds of showers and storms are expected from this evening
  through late Sun nt. The flash flood threat will remain low
  but local urban and small stream flooding is more probable.

&&

.NEW MESOSCALE UPDATE...
Issued 655 PM CDT Sat Apr 27 2024

...SEVERE THUNDERSTORM WATCH 151 IN EFFECT FOR MOST OF SOUTH
CENTRAL AND SOUTHEAST WISCONSIN UNTIL MIDNIGHT...

In coordination with the Storm Prediction Center, a severe
thunderstorm watch has been issued for the majority of south-
central and southeastern Wisconsin not included in tornado watch
150 until midnight. The Madison and Milwaukee metro areas are
included in this watch. Scattered storms continue to develop
this evening as low level lift increases along a southeast-
sagging cold front. The lift from said boundary has allowed
updrafts to grow and maintain despite dry air in the 700-500 mb
layer & subsidence beneath a short wave ridge. Effective bulk
shear values ranging between 40-45+ knots along/southeast of the
front will support organization in additional convection that
develops, with large hail and damaging straight line wind gusts
being the main concerns. While not expected to be the primary
hazard, an isolated spin-up tornado can`t be ruled out either.
Have multiple ways to receive warning information this evening,
particularly if planning to be outdoors. Be ready to move to
shelter if a warning is issued for your area.

Quigley

&&

.SHORT TERM...
Issued 345 PM CDT Sat Apr 27 2024

Tonight through Monday:

A Wind Advisory remains in effect until 4 PM CDT for east
central and far ern WI as the LLJ has been slow to exit. A
weakening trend in the pressure and wind fields is expected by
late this afternoon into the early evening.

Cumulus to cumulus congestus are lined up along and east of a
weak cold front over ern IA to sw WI and the Madison area. Brief
convection has been occurring over ern IA into nw IL early this
afternoon. Despite shortwave ridging aloft and weakening
pressure and wind fields into this evening, the CAMs and current
activity suggest convective initiation will occur along the
front from mid to late afternoon and evening. MLCAPE will range
from 1500-2000 J/kg with effective shear of 30-40 kts during
this time. The 0-3 KM hodographs remain fairly straight for any
cells on the front but some 0-1 KM clockwise turning is observed
east of the front. Thus a small tornado threat remains with
better probs for large hail and strong wind gusts. Since the
deep layer shear is parallel to the front, a broken line of
storms may seed each other resulting in greater pcpn efficiency
and a more solid line of storms. However, at this time the QLCS
threat is low as 0-3 km shear is parallel to the front and
weakening into the evening. For late evening into the overnight
it is possible an area of convection currently moving into srn
IA could clip srn WI. There would at least be a small SVR threat
with this activity as well.

The cold front will stall over far nrn IL on Sunday while low
pressure over the central Great Plains tracks to wrn IA. A broad
area of 850-700 MB warm, moist advection is expected on Sunday
with soundings closer to moist adiabatic and very minor elevated
CAPE. Most areas over srn WI will likely see some rainfall.

For Sun nt the occluded low will move toward sw MN while its
warm front will lift nwd through srn WI. Meanwhile, a shortwave
trough rotating around the large upper low will swing newd from
the srn Great Plains into the srn Great Lakes. There will be a
heavy round of convection with this feature but it may only clip
se WI. Overall the heavy rain threat and any flooding will
remain localized tnt-Sun nt.

The occluded front will then pass Mon AM while the low pressure
area tracks from se MN to wrn Lake Superior. Mild temps are
still expected with a few lingering showers possible. Another
cold front will pass in the afternoon but still just a few
showers.

Gehring

&&

.LONG TERM...
Issued 345 PM CDT Sat Apr 27 2024

Monday night through Saturday:

Westerly winds diminish Monday night as low pressure finally
departs the region. Winds then shift to become southerly and gusty
on Tuesday as a low pressure system develops in Alberta and the
northern Plains and progresses southeastward into the Upper
Midwest overnight Tuesday into Wednesday. A cold frontal feature
will sink through the region on Wednesday, leading to shower and
thunderstorm potential and westerly winds. An additional low
pressure system may develop in the central Plains and follow along
the remaining frontal boundary on Thursday, leading to additional
shower and thunderstorm chances. Generally expecting to be within
the warm sector, but a change in low pressure intensity is still
possible at this time frame and may result in cooler conditions
and less thunderstorm chances.

Model discrepancy increases going into Saturday, with GFS and
Canadian indicating low pressure progressing into Canada Saturday
morning, while the Euro keeps the system lingering and stalling
over the Great Lakes.

MH

Gehring

&&

.AVIATION...
Issued 345 PM CDT Sat Apr 27 2024

Sct-bkn035-045 cumulus and cumulus congestus this afternoon and
evening with scattered to numerous storms developing over srn
WI. The passage of a cold front late tonight will then result in
a moist enely flow and low stratus development. MVFR Cigs will
develop by early morning Sunday then fall below 1 kft for the
remainder of the day. Some fog development will also occur
during this time. Rounds of showers and storms will also
continue on Sunday.

Gehring

&&

.MARINE...
Issued 345 PM CDT Sat Apr 27 2024

Low pressure around 29.5 inches over Lake Superior will continue
to gradually weaken as it moves into Ontario this evening. Gusty
south winds are expected across Lake Michigan this afternoon,
with a few gusts approaching or reaching gale force, especially in
the northeast portion of the lake. Areas of dense fog may
redevelop this evening over the northern portion of the lake as
the winds become lighter, while dense fog may form over the
southern portion of the lake late tonight into Sunday.

Winds will then gradually shift from southwest to northerly
tonight as a cold front tracks south, but southerly winds will
continue over far southern Lake Michigan as the front stalls.
Brisk northeast winds will then prevail over central Lake Michigan
on Sunday with lighter winds in the north, and variable winds in
the south where the stalled front remains. Modest east to
southeast winds will then develop over all of the lake Sunday
night as the stalled front moves north as a warm front. Brisk east
winds, possibly reaching gale force, are expected over the
northern tip of the lake late Sunday night into Monday morning.
Breezy south winds will develop over the remainder of the lake on
Monday.

Rounds of showers and thunderstorms are expected tonight into
Monday morning. A few of these storms could produce locally gusty
winds and hail.

Gehring

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 7 PM
     Monday.

     Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ868 until 1 AM Sunday.

&&

$$

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