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000
FXUS63 KMKX 112103
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
403 PM CDT Thu Apr 11 2024

.KEY MESSAGES...

- Localized heavy rainfall, small hail, and even an isolated
  land spout tornado remain possible later this afternoon /
  evening along a broken line of thunderstorms near our western
  CWA. These impacts are likely to be confined to southwestern
  and south central WI.

- River flooding will continue through the weekend on isolated
  portions of the Lower Fox and Rock Rivers.

- Gusty northwest winds are expected through most of Friday,
  with a gales expected over the open waters.

- Above normal temps expected for the weekend into early next
  week.

- Keeping an eye on thunderstorm potential next Tuesday.

&&

.SHORT TERM...
Issued 400 PM CDT Thu Apr 11 2024

Tonight through Friday night:

We currently find ourselves on the northwestern quadrant of a
deepening surface low, with a negatively tilted trough axis just
west of us, and the resultant PVA favoring ascent. A north-
south-oriented axis of 925mb Petterssen FGEN (as seen on
Mesoanalysis) exists just west of Mineral Point and Lone Rock
WI, and a line of showers and thunderstorms has strengthened
along it. The descending branch of this frontogenetical
convection and NVA from an exiting 500mb vort max appear to be
responsible for a partial clearing of the clouds on either side
of this line, allowing solar heating to further sharpen low
level lapse rates and instability on either side. Mesoanalysis
and HRRR forecast soundings expect roughly 500 j/kg of SBCAPE to
develop on either side of the surface boundary. Light east
winds east of the boundary coupled with northwest winds on the
west side of the boundary create some surface vorticity along
the line of storms, which may serve as an ingredient in weak
landspout tornadogenesis. Given how slow moving this linear
system is, localized heavy rainfall remains a concern. Small
hail cannot be ruled out.

Though this system appears to be stationary on radar (western
edge of the CWA), note that the progression of the upper air
pattern (and the cloud clearing) further east may lead storms to
build on their eastern flanks, resulting in scattered to broken
shower and storm coverage over our western CWA later today
(just as CAMs expect). Storm coverage and intensity are forecast
to decline around midnight, likely clearing out by sunrise
Friday. Gusty northwest winds (gusts over 35 mph) are expected
on Friday, with clouds gradually clearing out from west to east
and daytime highs in the 50s.

Sheppard

&&

.LONG TERM...
Issued 400 PM CDT Thu Apr 11 2024

Saturday through Thursday:

Synopsis: The low pressure system bringing impacts to the short term
weather will continue to move east into Quebec during the day on
Saturday. Extending from the Dakotas into KS early Saturday morning,
a compact trough axis will quickly pivot into the Lower Great Lakes
Saturday night, bringing slight chances for showers and isolated
thunderstorms. A weak surface low will accompany the upper impulse,
allowing winds to turn out of the southwest as it moves into MN on
Saturday afternoon. This will mark the beginning of an upward trend
in high temperatures through the weekend, with above-normal warmth
continuing into the beginning of next week. Moving across the Great
Basin on Sunday, a more organized upper trough/low will progress
toward the Front Range of the Rockies on Monday, ejecting into the
Central Plains Monday night. Attendant surface cyclogenesis will
occur beneath the encroaching trough along the CO-NE-KS border
vicinity Monday afternoon. The surface low will advance through the
Missouri Valley on Tuesday as its parent upper low becomes
negatively tilted across the Upper Mississippi Valley. A warm front
is forecast to extend east-southeast of the low, and will likely
advance at least partially into southern Wisconsin as the surface
low pushes east on Tuesday. Showers and thunderstorms are possible
Tuesday afternoon/evening as DPVA affiliated with the approaching
upper trough overspreads the warm sector building into the area from
the south. Rain chances will continue into mid-late week with an
upper jet streak lingering across the Western Great Lakes.

Saturday Night - Early Sunday Morning: Isolated showers and
thunderstorms are possible across portions of the area as the upper
impulse discussed above shifts across the region. Probabilistic and
deterministic QPF forecasts depict the greatest signal for rainfall
over northern WI and the Upper Peninsula of MI, where a compact jet
streak accompanying the impulse is forecast to track. Said signals
are reflected in the afternoon update, which places the greatest
(~30-40%) precip probabilities along & northwest of the I-43
Corridor. If rainfall occurs, it will have the potential to be
convective in nature given a plume of steep mid-level lapse
rates/resulting MUCAPE moving in from the west. Apart from some
isolated, sub-severe hail, hazards are not anticipated in the event
that isolated showers/storms move across the area Saturday night
into early Sunday morning.

Monday Night - Tuesday Night: This will be the portion of the period
to watch the closest from a hazards perspective. Anticipate periods
of showers and embedded thunderstorms as a combination of upper
diffluence & mid-level DPVA affiliated with the approaching Plains
trough shift across the area. Of particular interest will be any
development that occurs Tuesday afternoon/evening as the warm front
discussed in the synopsis approaches and pushes into the state. A
multitude of factors -- particularly the arrival time of the most
favorable forcing, as well as the impacts of any antecedent precip &
cool waters of Lake Michigan on northward progress of the warm front
-- will play into storm development, with many uncertainties
remaining as of this forecast. Despite remaining uncertainties,
early forecast soundings depict a warm sector environment with
sufficient instability and overlapping shear to support at least
some potential for more organized storms next Tuesday. The Storm
Prediction Center has highlighted most of southern Wisconsin in a
15% risk for severe weather in its Tuesday convective outlook in
light of this potential. We will continue to closely monitor
forecast trends during this portion of the period.

Quigley

&&

.AVIATION...
Issued 400 PM CDT Thu Apr 11 2024

A broken line of showers and weak thunderstorms (oriented North
to South) currently rests over southwestern WI. It is expected
to gradually build to the east, resulting in scattered shower /
thunderstorm coverage near KMSN and KJVL this evening, but the
exact timing is uncertain. Thunder is much less likely the
further east you go. Light easterly winds are expected to
continue until the surface boundary (where the storms are)
passes over. Afterwards, expect steadier northwest winds
tonight.

Storm coverage and intensity decrease around midnight, with
cloud ceilings dradually descending to MVFR. Clouds then begin
to lift to VFR altitude after sunrise Friday, with skies
clearing out from west to east Friday afternoon. Gusty northwest
winds are expected throughout the day, declining Friday night.

Sheppard

&&

.MARINE...
Issued 400 PM CDT Thu Apr 11 2024

A low pressure system over Ohio will track northeastward, deepening
to around 28.9 inches and passing Toronto Friday morning.
Northwesterly gales develop over the open waters late tonight (all
open waters included in Gale Warning), with gusts to around 40
kts. The strongest winds and waves will be towards the east side
of the lake, as well as the northern third of the lake.

Winds will gradually weaken later Friday night into the weekend
as the low tracks northeast into Quebec. A small ridge of high
pressure traverses Lake Michigan on Saturday, allowing gentle
winds (around 15 kts) to back from northwesterly to southerly. A
weak low pressure around 29.6 inches crosses the lake Sunday
morning, veering winds to the north (roughly 15 kts or less)
Sunday afternoon.

Sheppard

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Gale Warning...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 AM Friday
     to 7 PM Friday.

     Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...1 AM
     Friday to 7 PM Friday.

&&

$$

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