Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 171754
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1154 AM CST Sat Feb 17 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 337 AM CST Sat Feb 17 2018

A couple periods of snow can be expected across the region, with
widespread light snow over the entire forecast area today, and a
a more significant snowfall over far northern WI on Sunday.

Patchy light snow was developing over southeast SD and southwest
MN early this morning, ahead of a short-wave trof and a cold
front. This snow is expected to become more widespread as it
shifts into the forecast area this morning. The previous shift
raised pops to likely to categorical over much of the forecast
area, and this looked reasonable. Snowfall amounts should be in
the half inch to an inch range, with the highest amounts in
central WI. The snow is expected to taper off from west to east
in the afternoon. High temperatures should reach the middle to
upper 20s northeast to the lower 30s southeast.

A ridge of high pressure will move through the forecast area
tonight, with clearing skies and light winds allowing
temperatures to drop into the single digits northwest to the
teens southeast.

A warm front is expected to lift into the forecast area on Sunday
as low pressure approaches from central or southern MN. Models
agree that strong dynamics will impact the region, with a 50-60
knot LLJ and associated strong WAA, frontogenetic forcing over
northern WI, and the RRQ of an upper level jet streak. The big
difference in the models revolves around moisture, with the
GFS/GEM models supporting deep saturation over northern WI, while
the NAM/ECMWF have a much drier look. Used a blend of models to
split the difference right now. This results in 1 to 3 inches of
snow across far northern WI, with little or no snow expected
along and south of Hwy 29. High temperatures should range from
the upper 20s north to 35 to 40 south.

.LONG TERM...Sunday Night Through Friday
Issued at 337 AM CST Sat Feb 17 2018

Forecast concerns revolve around precip chances, trends, and impacts
revolving around complex system due to move across the region Sunday
night into Tuesday.  Comparing the various models solutions tonight,
the ecmwf remains the farthest north in terms of frontal positions
and the 850mb thermal gradient than other guidance, with the gfs
positioned between the ensemble mean and the ecmwf.  This slight
difference remains significant when forecasting precip types and
amounts.  Will use a blend of the gfs/ecmwf to try to mitigate these
differences.

Sunday night through Monday night...Low pressure will be moving
northeast from western WI to the Upper Peninsula on Sunday night,
while dragging a cold front across the region.  Warm advection/mid-
level fgen light snow will be ongoing at the start of the night over
northern WI, then will pull out by late in the evening or early
overnight.  Less than an inch of additional accumulations will be
possible near the U.P. border.  After a brief lull in the precip on
late Sunday night, precipitation is expected to redevelop north of a
low pressure system on Monday morning and push northeast across the
region.  Ahead of the low, warm air aloft will surge into central to
northeast WI, which will likely develop a decent setup for a wintry
mix of snow/sleet/freezing rain/and rain, while precip should remain
mainly snow over north-central WI.  Could even see parts of east-
central WI become rain for a time on Monday afternoon.  The main
brunt of the precip will be pulling out by the start of Monday
evening. However, light precip is expected to continue through
Monday night north of the cold front.  Mid-level moisture will be
pulling out early in the night, but saturation depth will remain
supportive for precip in the form of sleet, freezing drizzle and
snow across much of the area. Putting it all together, travel is
likely to be significantly impacted on Monday and Monday night.
Several inches of snow remains possible over north-central WI, with
minor amounts of freezing drizzle. Even with a period of rain
possible over central to northeast WI on Monday, freezing rain and
freezing drizzle could become rather significant, especially looking
into Monday night.

Rest of the forecast...Light precip is expected to continue for much
of Tuesday and possibly extending into Tuesday night as well.  The
temp profile will gradually be cooling during this period, but a
lack of deep saturation will bring a potential for a freezing
drizzle and snow mix for much of central and northeast WI through
the day. Finally, an upper trough will push the troublesome frontal
boundary to the east on late Tuesday night, ending the wintry
precip.  Arctic high pressure will then build into the region for
Wednesday and Thursday, resulting in dry weather and seasonable
temps. The next chance of precip looks to occur on next Friday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1135 AM CST Sat Feb 17 2018

First round of light snow across portions of central and north-
central Wisconsin will move into northeast Wisconsin early this
afternoon. A few hours of light to moderate snow can be expected
with this system. The accumumulating snow will end at KRHI/KAUW/KCWA
by 20z, KGRB/KATW by 22z and KMTW by 23z. Accumulations should be
around an inch or less. Skies will become clear fairly quickly
early this evening, then mid and high clouds will be on the
increase again late tonight into Sunday morning. There are still
some issues regarding snow chances across northern Wisconsin later
Sunday morning into Sunday night. Some models keep the snow north
of KRHI with other models indicating light snow amounts during
this time frame. Have added flurries to the KRHI taf site late
Sunday morning for now.

A heads up to the expected weather Monday into Tuesday. It appears
that a wintry will occur across much of central into northeast
Wisconsin. Precipitation should be mainly snow north of a Merrill
to Wausaukee line. To the south, a mix of rain, freezing rain,
sleet and very little snow is anticipated. A couple tenths of an
inch are possible across central into northeast Wisconsin. Stay
tuned!

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......MPC
AVIATION.......Eckberg



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