Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 112302
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
502 PM CST Sat Nov 11 2017

.UPDATE...
The afternoon forecast discussion highlights the challenges well
with regard to the system moving in tonight/Sunday morning. The
intermediate runs of the medium range models that have just rolled
in, coupled with the higher res hourly ones suggest a tighter pop
gradient will be needed toward the WI/IL border. There is a
general shift to a more southerly solution to the precip moving
in. Precip type is still a big challenge with temps close to
freezing and plenty of dry air to overcome yet. We`ll make those
adjustments in the next hour or two.

&&

.AVIATION(00Z TAFS)...

Look for MVFR CIGS to overspread southern Wisconsin overnight.
These lower CIGS will reach KMSN toward 06z Sun and the southeast
TAFS by around 12z Sun. This is in response to a low pressure
system mostly passing by to the south of Wisconsin later tonight
and Sunday. Conditions will improve to VFR levels from west to
east late Sunday afternoon and into the evening. A wintry mix of
precipitation is also expected with precip types tricky due to
temperatures hovering close to the freezing mark. The bulk of any
precipitation will arrive after 06z Sunday, diminishing late
Sunday morning and into the afternoon.

&&

.PREV DISCUSSION... (Issued 209 PM CST Sat Nov 11 2017)

SHORT TERM...

Tonight and Sunday...Forecast confidence is medium to high:

A shortwave will approach the area tonight, then move through on
Sunday. It will stay mainly dry until later this evening into
tonight when better forcing/moisture arrives. Models are in
decent agreement in focusing the axis of higher precip amounts
near the WI/IL border, with lighter amounts toward the north. The
northwest forecast area may be dry later tonight into Sunday.

The main concern tonight into Sunday will be precip type.
Temperatures aloft and at the surface will be right near the
freezing/melting point. It looks like the bulk of the precip
should fall as snow, but a mix with or brief changeover to rain is
possible. Given borderline temps, the snow will be wet with
fairly low snow to liquid ratios. So, kept snow accums down to
around an inch.

Temps aloft will continue to warm Sunday, allowing highs to reach
around 40 for the afternoon. This should take care of most or all
of the snow that does fall.

LONG TERM...

Sunday night and Monday - Confidence...high

Northwest flow behind the departing shortwave will dominate the
pattern aloft. High pressure/ridging will establish itself in the
lower levels, resulting in cool and calm conditions. The atmosphere
looks mostly dry through this period, though most guidance does
linger some low level moisture through Sunday night. Therefore skies
will likely gradually clear out through the night, allowing temps to
drop into the mid 20s thanks to the northwesterly flow. Mostly clear
to partly cloudy skies on Monday should allow the temps to rebound
nicely.

Monday night through Wednesday - Confidence...high to medium

By Monday night, all guidance is showing a ripple coming down the
upper level northwest flow. The ridge axis follows shortly
thereafter before giving way to yet another trof on Wednesday. The
best support for ascent occur on Wednesday morning, ahead of the
trof.

Closer to the surface, a low pressure system will track across
southern Canada. By Monday night, we`ll start to see the effects of
the warm front extending to the southeast of the low, with winds
swinging around to the south and moisture moving into the mid
levels. The combo of WAA and moisture aloft could result in some
light precip on Tuesday, but there will quite a bit of dry air to
overcome in the lower levels as this warm front pushes through.

By Tuesday night, the warm front will have completely moved through
and the cold front will make its approach. The cold front, combined
with the finally moist lower levels and the arrival of the upper
level support for ascent, will likely result in precip from Tuesday
night through Wednesday morning. Thanks to the ample WAA ahead of
the cold fropa, all precip is expected to be rain. All guidance
showing a pretty impressive dry slot moving in on Wednesday,
clearing most of the moisture out by the afternoon.

Thursday through Saturday - confidence...medium to low

High pressure and northwesterly winds will result in cool and calm
conditions Thursday. By Thursday night, models begin to diverge
somewhat. The GFS, Euro, and Canadian all show an amplified trough
moving through the Midwest toward the end of the week, with
considerable differences regarding the timing of the trough passage.
The more progressive GFS bring the trough through on Friday, the
Canadian on Friday evening, and the Euro late Friday night.
Unsurprisingly, the surface low and precip comes through with the
same discrepancies.

At this point, the precip looks to be mostly rain. However, if the
quicker GFS verifies, there is a chance temps will be cool enough to
support snow as the precip begins late Thursday night. Additionally,
if the precip does linger into Friday night, as suggested by the
Euro, temperatures would again be cool enough to support a mix of
rain and snow.

By the weekend, all guidance shows another round of clear and
cool temperatures as high pressure moves back in.

AVIATION(21Z TAFS)...

Should be mainly dry for the rest of the afternoon, though a few
snowflakes are possible in the northwest half of the forecast
area.

Much better chance for precip arrives late evening into tonight,
with the bulk of models focusing the best chance in the south.
Precip will wind down Sunday morning.

Model temps suggest a mix of rain/snow, though looks like a
period of just snow for a few hours that might put down a dusting
to up to an inch toward the IL border. Any accumulations would
melt Sunday afternoon with highs getting up to around 40.

MARINE...

Will leave the Small Craft Advisory as is for now, though it will
probably be able to be dropped a little early based on latest
forecast waves.

Lighter winds and lower waves are expected the next couple days.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 9 PM CST this evening for LMZ643>646.

&&

$$

Update...Davis
Tonight/Sunday and Aviation/Marine...DDV
Sunday Night through Saturday...BSH



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