Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 171751 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1151 AM CST Fri Jan 17 2020

.UPDATE...

Temperatures across southern WI warmed significantly and quickly
this morning. Milwaukee warmed 11 degrees in an hour, from 18
degrees to 29 degrees. The cloud level is lowering near Lake
Michigan and continuing to spread inland with increasing southeast
winds and enhanced moisture off the lake. This should help
moisten the atmosphere quicker than if we were just depending on
the moisture increasing from the top down, like in upstream areas
of eastern Iowa. In addition, an area of low clouds is also
developing over southwest WI in response to a localized area of
enhanced low level moisture advection.

While snow may begin earlier as some light flakes aided by some
shallow low level moisture, the main impact snow will arrive from
mid afternoon in southwest WI to late afternoon in southeast WI.
As this spreads in, expect visibility to drop to around a half
mile to one mile with accumulating snow and quickly deteriorating
road conditions.

&&

.AVIATION(18Z TAFS)...

MVFR ceilings are spreading inland from the lake due to increasing
moisture from southeast winds off the lake. Meanwhile, another
area of MVFR ceilings is developing over southwest WI and
expanding northeast due to some localized moisture advection.

While snow may begin earlier as some light flakes aided by some
shallow low level moisture, the main impact snow will arrive from
mid afternoon in southwest WI to late afternoon in southeast WI.
As this spreads in, expect visibility to drop to around a half
mile to one mile with accumulating snow and quickly deteriorating
conditions.

&&

.PREV DISCUSSION... (Issued 1044 AM CST Fri Jan 17 2020)

UPDATE...

There are no surprises with the 12z model runs that are coming in
this morning. The air is dry in the low levels, so we are seeing
donuts fill in around the radars as the precip approaches. Once we
can saturate from the top down, precip type will be all snow.
There is still a concern for east central WI, including Sheboygan
area, to pick up a little more snow due to lake enhancement. The
main thing keeping snowfall totals down with this feature is that
there is not a large delta-T (lake temp to 850mb temp difference).

For early Saturday morning, the GFS maintains a better chance for
warming above freezing at the surface for areas south of I-94
which would give us a period of rain. The NAM keeps us colder than
freezing but has a stronger warm layer aloft, thus suggesting a
better potential for sleet.

MARINE...

No change to the forecast at this time. We will upgrade the Gale
Watch for the north third of the lake to a Gale Warning this
afternoon.

Gusty southeast winds will develop this afternoon and linger
overnight, before gradually veering west Saturday morning. The
winds may decrease in magnitude for a time Saturday morning as the
surface low tracks overhead. West to northwest winds will become
gusty again Saturday afternoon and night across the region.

A Small Craft Advisory is in effect from middle afternoon into
middle evening, before a Gale Warning is in effect through
Saturday night, for the nearshore waters of Lake Michigan.

A Gale Warning is in effect for the southern two thirds of the
open waters of Lake Michigan from later this evening through
Saturday night. A Gale Warning is in effect for the northern one
third of the open waters from later this evening through middle
morning Saturday, with a Gale Watch for Saturday night.

Heavy freezing spray is possible later Saturday night into Sunday
morning, with freezing spray at times into early next week.

PREV DISCUSSION... (Issued 542 AM CST Fri Jan 17 2020)

UPDATE...No changes at this time.

AVIATION(12Z TAFS)...Lake effect low clouds beginning to affect
some lakeshore and inland areas. As low level winds become more
east to southeast and increase the next several hours, expect the
stratus to become more widespread and expand over the east. Short
term guidance hinting that low clouds will be transient and move
off to the north later this morning. However with increasing
convergence, potentially the stratus could just expand and persist
over eastern areas. However, for now wl be more optimistic and
keep the low clouds around only for a time in the east this
morning. Widespread snow should develop late this afternoon and
evening, possibly changing to a period of light freezing rain and
drizzle late tonight into early Saturday. Blustery southeast winds
will also develop later today, with gusts of 35 knots tonight.

PREV DISCUSSION... (Issued 506 AM CST Fri Jan 17 2020)

SHORT TERM...

Today Through Saturday...Forecast Confidence Is Medium To High.

No significant changes to earlier thinking, but did add a little
more icing potential. Potent upstream short wave over southern
Nevada will continue on a east to northeast track over the next 36
hours. An increasing low level jet ahead of this wave will
rapidly transport warm and moist air northward today. Still
expecting column precipitable water to increase rapidly this aftn
and evening to 0.50" to 0.75", which is unusually high for this
time of year, about 200% of normal. The peak of this moisture and
warm air advection is late this afternoon through about 08Z or so,
as the short wave amplifies and takes on a slightly negative tilt
across the Upper Midwest.

Short term guidance in good agreement on surface low pressure
developing in western KS later today and taking a northeast track
across IA tonight, passing through southern WI/northern IL
Saturday morning. The nose of the low level jet grazes southern
WI, but remains mostly to the south and east of the state later
tonight into Saturday. So, the highest QPF remains to the south
of the area.

There does remain some differences in the short term guidance
regarding the amount of low level warm air moving into southern WI
later tonight, as well as the amount of drying aloft, above about
8000 feet. The GFS remains the warmest in the low levels later
tonight, but also lacks any significant drying aloft. Meanwhile,
the NAM and ECWMF are in better agreement with the drying aloft,
which reduces the ice falling into the lower cloud layer. This in
turn would result in a better chance for a period of light
freezing rain, while the GFS favors more of snow and sleet.

At this juncture, prefer the higher resolution of the NAM and
ECMWF guidance so wl bump up the mention of a period of light
freezing rain and drizzle later tonight into early Saturday. Never
the less, all areas will see a period of accumulating snow late
this afternoon and evening, with the wintry mix setting in after
midnight.

The wintry mix and potential sleet cuts back a little on snowfall
amounts. With the best chance for the mix in the southwest,
snowfall amounts will range from 3 to 4 inches in this area to 5
to 8 inches in the northeast. Lake enhancement and terrain should
result in higher snowfall totals in the Sheboygan, West Bend and
Port Washington areas, and with potential gusts to 35 mph, was
very close to upgrading this area to a Winter Storm Warning. But,
with the lingering uncertainty regarding the potential mix and
ultimate snowfall totals, held off on upgrading at this point. So,
no changes to Winter Weather Advisory timing or length at this
time.

Blustery west winds will carry the colder air back into the
region Saturday afternoon. The colder air will dry out the
overnight snowfall and should result in areas of blowing and
drifting snow into Saturday evening. Temperatures will be steady
or falling Saturday afternoon.

Saturday Night Through Monday...Forecast Confidence Is High.

Cold air advection continues Saturday night across the region,
with brisk west northwest winds. This will bring cold temperatures
into the area, with lows around zero to 5 above zero over most of
the area. These lows may be a little lower, given the expected 925
mb temperatures. There will be some clouds lingering Saturday
night into Sunday, with 500 mb vorticity maxima lingering nearby,
so this may hold up lows a bit.

Wind chills will be in the 15 below to 20 below zero range later
Saturday night into Sunday morning, close to Wind Chill Advisory
levels. Lower minimum temperatures would lower these wind chills,
so this potential will need to be watched.

Northwest flow at 500 mb lingers into Sunday night and Monday,
with a 500 mb shortwave trough slowly moving southeast through the
region. This may keep some clouds over the region. Cold
temperatures should linger during this time, with wind chills of 5
below to 10 below zero Sunday night into Monday morning.

LONG TERM...

Monday Night Through Thursday...Forecast Confidence Is Medium.

Models generally show high pressure moving southeast from the
northern Plains into the middle Mississippi River Valley Monday
night into Tuesday. This should keep the area dry. Cold
temperatures should remain during this time, with wind chills in
the 5 below to 13 below zero range likely Monday night into
Tuesday morning.

South to southwest winds then try to develop with some steady warm
air advection For Tuesday night into Wednesday night/Thursday.
More moisture may be pulled into the region from the south, ahead
of low pressure in the southern or central Plains. More
uncertainty exists this far out with features and timing, so will
leave blended model PoPs and temperatures for now. Wednesday night
into Thursday would be the next chance for precipitation across
the area.

AVIATION(09Z TAF UPDATES)...

Low level winds will be shifting to the east to southeast as high
pressure ridge over Lake Michigan continues to move off to the
east. This winds should pull the large area of low lake clouds
currently over the southern open waters of Lake Michigan west and
into eastern areas early this morning, with MVFR ceilings.
Possible a few flurries may get shaken out of the low clouds.

Otherwise, widespread mid-high level clouds will continue to
thicken across southern WI this morning ahead of approaching low
pressure. Widespread snow and low ceilings expected tonight with a
chance for some light freezing rain or drizzle later tonight into
early Saturday. Blustery southeast winds will develop later this
afternoon and evening, switching to the west on Saturday.

MARINE...

Gusty southeast winds are expected to develop this evening and
linger overnight, before gradually veering west Saturday morning.
The winds may decrease in magnitude for a time Saturday morning.
West to northwest winds will become gusty again Saturday
afternoon and night across the region.

A Small Craft Advisory is in effect from middle afternoon into
middle evening, before a Gale Warning is in effect through
Saturday night, for the nearshore waters of Lake Michigan.

A Gale Warning is in effect for the southern two thirds of the
open waters of Lake Michigan from later this evening through
Saturday night. A Gale Warning is in effect for the northern one
third of the open waters from later this evening through middle
morning Saturday, with a Gale Watch for Saturday night.

Heavy freezing spray is possible later Saturday night into Sunday
morning, with freezing spray at times into early next week.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST Saturday for WIZ046-047-
     056-057-062-063-067>069.

     Winter Weather Advisory from 5 PM this afternoon to 6 PM CST
     Saturday for WIZ051-052-058>060-064>066-070>072.

     Lakeshore Flood Advisory from 6 PM this evening to 6 AM CST
     Saturday for WIZ052-060.

LM...Gale Warning from 8 PM this evening to 6 AM CST Sunday for
     LMZ080-366-565-567-669-671-673-675-777-779-868-870-872-874-
     876-878.

     Gale Watch from Saturday evening through late Saturday night for
     LMZ261-362-364-563.

     Gale Warning from midnight tonight to 9 AM CST Saturday for
     LMZ261-362-364-563.

     Small Craft Advisory until 8 PM CST this evening for LMZ643>646.

     Gale Warning from 8 PM this evening to 3 AM CST Sunday for
     LMZ643>646.

&&

$$

Update...Cronce
Today/Tonight and Aviation/Marine...MBK
Saturday THROUGH Thursday...Wood


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