Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 221535 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1035 AM CDT Sun Oct 22 2017

.UPDATE...

Showers will continue to affect the area into this afternoon,
driven by low level frontogenesis response from passing cold
front. The front is moving into the eastern part of the forecast
area, and will shift to the east of the area by early this
afternoon.

The showers will linger this afternoon, with differential cyclonic
vorticity advection from approaching 500 mb shortwave trough. They
will then slowly taper off from west to east later this afternoon
into early this evening. Dry air moving into the area, with cold
air advection behind the front, will help end the showers.

Temperatures should remain nearly steady in the lower to middle
50s behind the front this afternoon. Winds will shift to the
northwest as well.

Quiet weather is expected tonight, as skies gradually clear out.
Lows should drop into the lower to middle 40s, with the cooler
airmass in place.

A secondary cold front will push east through the area Monday. A
digging 500 mb trough will slide toward the area from the
northwest as well. Various vorticity maxima rotating around the
trough should help bring more clouds and a few showers during the
afternoon. One more mild day in the upper 50s to lower 60s is
expected.

Wood

&&

.MARINE...

Small Craft Advisory continues until 4 PM CDT across the
nearshore waters of Lake Michigan. The pressure gradient will
relax into early afternoon, as the cold front moves east through
the area. This should allow gusty south to southeast winds to
gradually weaken, as they veer to the west and northwest after the
frontal passage by middle to late afternoon.

Subsequent waves of 4 to 6 feet should also gradually subside
during this period. The waves may linger above 4 feet until 00Z
Monday across areas north of Port Washington. The Small Craft
Advisory may need to be extended there a few hours to account for
these lingering waves.

Gusty northwest winds are expected to develop across the nearshore
waters later Monday night and linger into Tuesday night. This is
in response to a tight pressure gradient developing over the
region. Gusts of 25 to 30 knots are possible during this time.
Waves of 3 to 5 feet are possible toward the open waters of Lake
Michigan, higher over the open waters. A Small Craft Advisory may
be needed for later Monday night into Tuesday night.

Wood

&&

.PREV DISCUSSION... (Issued 634 AM CDT Sun Oct 22 2017)

UPDATE...

The anticipated increase in coverage of the showers is occurring,
and should continue over most of the area this morning.

AVIATION(12Z TAFS)...

A band of showers and isolated thunderstorms will move across
southern Wisconsin near a cold front. Cigs will drop to the low
end of MVFR, and briefly IFR. Much of the high- res guidance is
now indicating that those low cigs will hang around into the
afternoon due to the fact that the cold front responsible for the
precipitation will be slow to move through Wisconsin. A weak wave
riding north along the slow moving cold front was increasing the
showers. Instability is minimal, so no widespread thunderstorms
expected.

PREV DISCUSSION... (Issued 246 AM CDT Sun Oct 22 2017)

DISCUSSION...

Today and Tonight...Forecast Confidence is Medium...

An upper level trough moves across the Upper Mississippi Valley
today, as the main jet max east of the trough axis lifts north
into Canada. Another trough begins to form across the northern
plains late tonight, as the lead 250 mb trough axis never really
moves across the forecast area. The upper divergence driving the
evening convection to the west weakens early this morning, before
increasing again later today. 700 mb upward motion lifts north
early this morning, then increases again later this morning and
afternoon southeast as a weak low/mid level wave rides up the slow
moving cold front. This should bring an increase in showers
again, especially southeast. However CAPE remains minimal or non
existent. therefore thunderstorm chances will be low.

Rain amounts will be on the increase again with the wave on the
front, with most areas receiving moderate amounts.

High temperatures will be warm again east ahead of the cold front.

Mid/low level drying then takes over briefly tonight behind the
cold front.

Monday and Tuesday - Confidence...Medium
500 millibar low evolves across the area Monday and then shifts
into the eastern Lakes on Tuesday. Several spokes of vorticity
will be rotating this circulation. A surface low north of Lake
Superior and one riding northeast from the Ohio Valley on Monday
congeal and strengthen to our east on Tuesday. Low level cold
advection arrives Monday night and lingers into Tuesday. The GFS
is most aggressive with the initial trough passage on Monday with
some light QPF, the models all show an uptick in precip Monday
night into Tuesday as the low strengthens to the east with an
implied def zone component kicking in. Most areas will not see
temps get out of the 40s for Tuesday and with a blustery northwest
wind around the low there will be quite a bite in the air. While
some subzero 850 temps move in appears the lower levels remain
sufficiently warm to keep precip in the form of liquid.

Wednesday - Confidence...Medium
A shortwave rides southeast on the western periphery of the
departed upper low. Colder boundary layer conditions combined with
the cooler 850 temps suggest some flakes mixed with rain be
possible early before becoming all rain as low levels warm.

Thursday - Confidence...Medium
Low pressure is proggd to strengthen to our southwest and pull a
modifying airmass into the area on southeast winds. Precip
expected to remain confined to NW WI/MN or IA with 925 temps
across srn WI modifying to 3-6c.

Thursday night through Saturday - Confidence...Low to Medium
Another large scale trough will be carving out across the Plains
with cyclogenesis evolving. the GFS is faster spreading rain in
on Thursday night while the ECMWF holds off until Friday. Cold
advection stronger on GFS and would suggest some snow mixing in
Friday night and Saturday morning. The ECMWF has a warmer thermal
profile suggesting less mix potential.

AVIATION(09Z TAFS)...A band of showers and isolated
thunderstorms will move across southern Wisconsin early this
morning, reaching the southeast late morning. Cigs will drop to
the low end of MVFR. Much of the high- res guidance is now A band of showers and isolated
thunderstorms will move across southern Wisconsin early this
morning, reaching the southeast late morning. Cigs will drop to
the low end of MVFR. Much of the high- res guidance is now
indicating that those low cigs will hang around into the afternoon
due to the fact that the cold front responsible for the
precipitation will slow down quite a bit as it moves through WI. A
weak wave riding north along the slow moving cold front should
increase the showers again today. Instability is minimal, so no
widespread thunderstorms expected.

indicating that those low cigs will hang around into the afternoon
due to the fact that the cold front responsible for the
precipitation will slow down quite a bit as it moves through WI. A
weak wave riding north along the slow moving cold front should
increase the showers again today. Instability is minimal, so no
widespread thunderstorms expected.

Low level wind shear in the south flow ahead of the cold front
will diminish.

Look for skies to clear from the west tonight.

MARINE...Small Craft Advisory continues until 21Z across the
nearshore waters of Lake Michigan. Brisk south winds with a tight
pressure gradient and good low level mixing are expected during
this period. Gusts of 25 to 30 knots are expected, with the
highest gusts this morning.

Waves of 4 to 6 feet should linger into tonight, highest toward
Sheboygan. These winds and waves should slowly subside this
afternoon behind the cold front, as the pressure gradient
weakens and winds become more northwest.

Other periods of gusty winds and building waves are possible
Tuesday into Tuesday night, and again Thursday night into Friday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 PM CDT this afternoon for
     LMZ643>646.

&&

$$

Update...Wood
Today/Tonight and Aviation/Marine...Hentz
Monday THROUGH Saturday...Collar


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