Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 130231

Area Forecast Discussion
National Weather Service Green Bay WI
831 PM CST Fri Jan 12 2018

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

Issued at 826 PM CST Fri Jan 12 2018

No changes to the Wind Chill headlines this evening.

As sometimes happens, winds in north-central Wisconsin have
dropped off despite a modest surface pressure gradient across the
area. Temperatures at those sites that lost the wind completely
for a time after sunset have plunged. KD25 and KTKV have already
hit double-digit below zero air temperatures. But the winds have
come back at both in the past hour, and a few lake clouds have
reached KD25, so at least the temps should stabilize for a while.
In any case, the Wind Chill Advisory seems pretty much on track
for the times when the winds will be a little stronger, so no
changes are necessary.

The 00Z dataset is just beginning to arrive, but a quick look at
the new NAM still suggests much of the area is still in line for
several inches of snow Sunday night through Monday. (Though
the onset of the snow may perhaps be a little slower.) The snows
will probably linger into Tuesday over the east, where lake-
effect could push totals even higher.

Updated product suite will be out ASAP.

.SHORT TERM...Tonight and Saturday
Issued at 234 PM CST Fri Jan 12 2018

Lake effect clouds and flurries should diminish across the northwoods
tonight with mostly clear skies elsewhere. Light northwest winds and
subzero temperatures should make for wind chills of 20 to 25 below
in central and northcentral Wisconsin where wind chill advisories
are in effect. Wind chills of 10 to 20 below zero are expected
across the east. Saturday will be sunny and very cold with highs
10 to 15 degrees below normal.

.LONG TERM...Saturday Night Through Friday
Issued at 234 PM CST Fri Jan 12 2018

Forecast concerns mainly center around the potential snowfall late
Sunday into Monday night, with a sprinkle of bitter cold also thrown
into the mix.  The gfs and ecmwf remain in good agreement with this
system, so will continue to use a blend for this part of the

Saturday night through Monday night...Arctic high pressure will be
sliding southeast from the northern Mississippi Valley to the Ohio
Valley on Saturday night. The pressure gradient will be considerably
more relaxed than on Friday night, and many locations will likely
see their winds decouple.  Where this occurs, temps will likely fall
into the teens to low 20s below zero, mainly over central and north-
central WI.  Scattered locations may see their winds remain in the 3-
5 kt range, which combined with the cold, will drop their wind
chills to 20-30 below zero.  So no matter how you slice it, it will
be cold, and a wind chill advisory may be needed for central and
north-central WI.  Clouds will then be on the increase from the
northwest from late Saturday night into Sunday ahead of a digging
upper trough and associated reinforcing cold front.  Enough forcing
and moisture will move into central and north-central WI for light
snow to arrive on Sunday afternoon.

The bulk of the snowfall will occur on Sunday night and Monday as
low pressure swings across southern Wisconsin.  Northern WI is
expected to be positioned in the deformation zone, with inverted
troughing providing a focus for snowfall.  Lake enhancement off Lake
Michigan and Lake Superior could also enhance snowfall.  Though the
snowfall will likely be light (and also fluffy in nature), the long
duration of snowfall and high snow to liquid ratios could bring a
widespread 3 to 5 inches of accumulations, and potentially higher in
the lake enhanced areas.  The light snow will gradually diminish on
Monday night as the low finally moves away.

Rest of the forecast...High pressure will then return to the area on
Tuesday and Wednesday.  Temps will remain below normal, with wind
chills of 10 to 20 below on Tuesday night.  Moderating temps remain
on track to arrive late next week.

.AVIATION...for 06Z TAF Issuance
Issued at 826 PM CST Fri Jan 12 2018

Primarily VFR conditions are expected for the next 24 hours,
though lake-effect clouds will affect north-central Wisconsin at
times. The clouds are expected to remain primarily north of the
TAF sites.

Wind Chill Advisory until 9 AM CST Saturday for WIZ005-010>012-


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