Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 200252
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
852 PM CST Mon Feb 19 2018

Updated aviation portion for 06Z TAF issuance
and new information added to update section

.UPDATE...
Issued at 845 PM CST Mon Feb 19 2018

No changes to headlines this evening. Going forecast is pretty
much on track. Light freezing precipitation will continue
overnight and into Tuesday morning. The precipitation will end
from the west during the day, while the front edges north enough
to allow temperatures to rise above freezing from Green Bay south
and eastward by mid-late morning.

A surge of convection heading northeast from south-central
Wisconsin may clip Manitowoc county later this evening.
Fortunately, that is the one area that should be able to handle it
as temperatures are probably 32-34F over the county. In fact,
temperatures from Kewaunee to Chilton have also probably edged up
a degree or two from early evening, limiting the icing potential
in that corridor. The surge forecast by many of the models for
tomorrow morning looks a little less robust than earlier. Have
increasing confidence that the total amount of icing will remain
low enough so that the main impact remains icing of roads,
sidewalks, and parking lots. It seems unlikely enough ice will
accrue to lead to much trouble with tree branches and power lines
breaking.

One additional concern is the potential for dense fog over the
southern/southeast part of the forecast area late tonight into
mid-late morning Tuesday. Outside of the heavier precipitation, a
band of fog with visibilities AOB 1SM was along and just south of
the frontal boundary in the Wisconsin/Illinois border area and
extreme northern Illinois. Surface dew point temperatures were in
the mid 40s to low 50s in that area. Suspect the fog will follow
the front north, especially once the high moisture air begins to
flow over ground that is now ice covered. Will begin to highlight
the fog more in the next round of product updates.

Updated product suite will be out in the next 30-45 minutes.

UPDATE
Issued at 607 PM CST Mon Feb 19 2018

Strong isentropic lift will continue this evening as a wave rides
northeast along the baroclinic zone stretched out across the area.
The strongest lift will be focused south of the area, but pockets
of heavier precipitation are likely to continue to clip east-
central Wisconsin at times.

A pronounced lull in the precipitation is likely from late evening
overnight as the LLJ veers and gets focused off to the east. That
will leave mainly FZDZ across the area, which will continue to
result in some icing and hazardous travel conditions.

The primary concern is what happens late tonight and Tuesday
morning as a mid-level shortwave ejecting out of the Plains heads
toward the western Great Lakes region. That will likely result in
increased lift, and another surge of heavier precipitation toward
the area. But it`s not clear whether/how far it will push into
the forecast area, as it could pass through mainly to the
southeast. Temperatures will also be an issue, as some of the
models show the surface front lifting back north toward the area,
or at least a decrease in depth of the cold air. That may allow
enough warming for temperatures to creep above freezing,
especially to the south and east of the city of Green Bay.

Current expectations are that the amount of icing will remain
light enough to cause mainly travel problems (though admittedly
those could be significant at locations where mainly FZRA/FZDZ
occur). However, if the surge tomorrow morning makes it into
east-central Wisconsin and temperatures cannot recover, then a
more substantial build-up of ice is possible and we might begin to
see some damage to tree limbs.
&&

.SHORT TERM...Tonight
Issued at 244 PM CST Mon Feb 19 2018

A mix of snow, sleet and freezing rain was noted across much of
the region. The only exception was across portions of Waushara,
Winnebago, Calumet and Manitowoc counties where air temperatures
were still several degrees above freezing. Road temperatures well
above freezing from Wautoma to Green Bay/Fox Cites east to the
lake. This should change quickly tonight once the sun goes down.
Latest road temperature forecast have road temperatures dropping
below freezing early this evening, thus motorist should anticipate
slick conditions. To the north and west of the Fox Valley, a mix
of snow, sleet and freezing rain was occurring.

For tonight, the steadier precipitation should taper off by mid
evening to freezing drizzle, except across the far north where
some light snow is possible. Some of the latest model guidance
would suggest there could be a few hours where they may be no
precipitation. However, think freezing drizzle will be back on
the increase again late tonight as the next system approaches from
the southwest. Did make some adjustments downward to minimum
temperatures since we were already close to the forecast values.

.LONG TERM...Tuesday Through Monday
Issued at 244 PM CST Mon Feb 19 2018

Starting with the Tuesday period, progs indicate another wave of
mixed precipitation will slide over the area mainly tuesday
morning. Precipitation will be along and ahead of the 850 frontal
boundary sliding over the area. Forecast soundings, another round
of ice accumulation up to 0.10 inches. Trends has been a bit
quicker and its possible later shifts will be able to cancel the
winter weather advisory a bit quicker Tuesday afternoon. Roads may
be a mess from the morning pcpn for another reason to linger the
advisory.

High pressure to settle into the area Wednesday into Thursday for
a period of quiet weather. Models in better agreement with the
timing of the next chance of mainly snow towards Thursday night
into Friday morning as a weak trough slides over the area. Some
trend with a southwest flow aloft developing with upper heights
increasing late next weekend, for a turn to a milder trend.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 845 PM CST Mon Feb 19 2018

Mainly IFR conditions are expected during the next 9-15 hours as
lift continues over the strong frontal zone stretched out south of
the area. Visibilities may drop to LIFR/VLIFR over the southern
part of the area toward morning as the frontal boundary shifts
back north. Light freezing rain and drizzle will continue into
Tuesday morning. It will end from the west during the day, while
the southeast should warm enough to change it to just rain and
drizzle.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM CST Tuesday for WIZ005-
010>013-018>022-030-031-035>040-045-048>050-073-074.
&&

$$

UPDATE.........Skowronski
SHORT TERM.....Eckberg
LONG TERM......TDH
AVIATION.......Skowronski



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