Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 181220

Area Forecast Discussion
National Weather Service Green Bay WI
620 AM CST Sat Jan 18 2020

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 355 AM CST Sat Jan 18 2020

Regional radars and surface observations show the first phase of
this winter system ongoing early this morning, with the
steady/heaviest snow associated with the warm air advection
exiting to the east. A mix of lighter snow and freezing drizzle
has replaced the heavier snow as the dry slot brought some mid-
level dry air along with a lull in the stronger lift. Southeast
winds have gusted between 20 and 30 mph at times during the early
morning hours, creating some minor blowing and drifting snow.

For today, look for the mix of light snow and freezing drizzle to
continue early this morning, then as the low pressure system and
trough axis swing across the area, deeper moisture and stronger
lift return to the area changing the precip back to all snow. In
general, an additional 1 to 4 inches of snow is expected across
the area, highest across far northeast WI and lowest across
central WI. Will be watching for several factors to be come
together to produce a burst of moderate to possibly heavy snow in
the mid to late morning, mainly across far northeast WI. They
include the mid-level trough pushing across the area, the surface
low strengthening as it heads into northern Lower Michigan,
strong QG forcing, steep mid-level lapse rates, and a brief period
of strong lift within the DGZ. Luckily, these features will be
progressive and not linger over one area for too long. But a quick
accumulation of 2-3 inches will be possible. Southeast winds will
decrease this morning as the low moves overhead, then winds turn
to the west/northwest this afternoon and evening, with gusts to 35
mph expected, highest across central and east central WI. This
will create areas of blowing and drifting snow. Without knowing
exactly how much snow fell across parts of the area, a little
concerned we could hit warning criteria over far northeast WI, but
prefer to keep the advisory going as QPF has been running on the
high side compared to observation, plus the strongest winds look
to stay farther south. Toward central WI and the southern Fox
Valley, the advisory look to be in good shape with lighter amounts
of new snow but gustier winds and more blowing and drifting snow.
Temps will creep to around or slightly above freezing across
eastern WI, the strong cold air advection kicks in later today
ushering in much colder temps.

For tonight, lake effect snow showers are expected across the
snowbelts of north central WI through the night, with favorable
NNW flow and delta Ts in the teens. Up to 3" of additional snow
possible, highest near the MI border. Flurries and a few snow
showers are expected farther south. The cyclonic flow across Lake
Superior will make it tough to get the clouds to clear, but some
clearing is possible, mainly across central WI. Temps could fall
below zero if the clearing materializes. Gusty winds up to around
30 mph will remain possible through the late evening hours,
highest across central and east central WI. Wind chills will be
bumping up against wind chill advisory criteria early Sunday
morning, but will let the day shift sort out any headlines for the

On Sunday, lake effect snow showers will continue across the
snowbelts, but conditions become less favorable through the day as
moisture slowly decreases. Flurries will be possible farther
south. Winds will be calming down as well. It will be colder with
highs ranging from the teens in central and north central WI to
the lower and middle 20s across eastern WI.

.LONG TERM...Sunday Night Through Friday
Issued at 355 AM CST Sat Jan 18 2020

The main highlights for the extended forecast are the below normal
temperatures through midweek and the next chance for precipitation
to end the work week.

Sunday night through Tuesday...An upper-level northwest flow will
remain over the Upper Mississippi Valley through Tuesday as a
surface high pressure system slides from the Northern Plains to
the Middle Mississippi Valley. It is possible for some light
lake-effect snow showers to linger into Sunday night over far
north-central Wisconsin. Little to no additional snow
accumulations are expected. In addition, the high pressure system
will bring below normal temperatures and sunshine to the region.
High temperatures will range from the upper teens to the lower
20s. Monday night`s low temperatures are expected to be the
coldest of the extended with values ranging from the single digits
above and below zero.

Rest of the extended...As the surface high pressure system tracks
east over the Ohio River Valley Tuesday night, some upper-level
riding will be in place over the Upper Mississippi Valley. The
upper-level pattern will then transition to a mean southwest flow
on Wednesday. This flow supports Gulf moisture to lift north
bringing chances for snow Wednesday and Thursday. Meanwhile, an
upper-level trough will dig over the central Plains. Some model
guidance indicates this trough could bring significant
precipitation to the region on Friday, however, there are
considerable differences with the timing and track of this system.

.AVIATION...for 12Z TAF Issuance
Issued at 620 AM CST Sat Jan 18 2020

Poor flying conditions will continue this morning with periods of
snow continuing. IFR conditions are expected through the morning
hours, with periods of LIFR conditions possible in the heaviest
snow. A slow improvement in CIGs are expected later today into
tonight as the snow comes to an end. Lingering lake effect snow
showers will continue across northern WI, mainly impacting KRHI
tonight into Sunday. Southeast winds will turn to the
west/northwest late this morning and early afternoon and gust up
to around 30 kts. This will create some blowing and drifting snow.

Issued at 355 AM CST Sat Jan 18 2020

Gusty southeast winds will diminish this morning. Then, gusty west
to northwest winds are expected this afternoon and evening. Gale
force gusts are likely south of an Oconto to Algoma line. Winds
will be slightly lower to the north.

Winter Weather Advisory until 6 PM CST this evening for

Lakeshore Flood Advisory until 9 AM CST this morning for WIZ022-

Winter Weather Advisory until noon CST Sunday for WIZ005.


SHORT TERM.....Bersch
LONG TERM......Hykin
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