Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 221810

Area Forecast Discussion
National Weather Service Green Bay WI
1210 PM CST Sun Jan 22 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Monday
Issued at 220 AM CST Sun Jan 22 2017

Light winds and a moist boundary layer producing widespread dense
fog across the region this morning. Mid level low pressure system
centered over northwest Wisconsin will drift over Lake Superior
today before lifting north of Lake Superior tonight. Radars show
weak returns rotating around this low for a few light showers,
otherwise expect mainly drizzle in this moist air mass. Will
continue the dense fog advisory through noon. Anticipate weak
northwest winds in the wake of A weak cold front will provide
some mixing to lesson the widespread fog by noon. Its possible
eastern Wisconsin may hang onto the dense fog longer this
afternoon in an area of weak troughing. Light winds and continued
moist surface dewpoints may open the door for more fog tonight,
but likely not as widespread.

Another upper low system lifting into the Ohio Valley region and
parts of Lower Michigan may produce some light precipitation across
far eastern Wisconsin on Monday. Will keep small precipitation
chances going over the east due to persistent weak troughing over
Lake Michigan extending to the Ohio Valley system. But latest
trends suggest a decrease in this precipitation chance.

.LONG TERM...Monday Night Through Saturday
Issued at 220 AM CST Sun Jan 22 2017

Focus on this forecast revolves around the cyclone projected to move
across the region during the Tue-Wed time period.  Still plenty of
spread in the medium range models in regards to the track and timing
of the surface low.  A middle of the road approach suggests a blend
of the ecmwf and gfs, or not too far off from the sref, for this

Monday night and Tuesday...Though a surface trough now looks to only
approach the Door Peninsula, forecast soundings generally look
saturated below around 900mb through the night across the region. So
think most areas will remain dry except for the Door Peninsula,
which could see some showers/drizzle, but will need a stronger push
of dry air to erode the low clouds.  May get some help in this
regard on Tuesday morning, when a surface ridge axis moves northeast
across the state. Partial clearing will only be brief though, as mid
and high clouds rapidly spread across the forecast area during the
day. Light precip may start to move into central WI by late in the
afternoon, and could start out as rain and snow until surface temps

Tuesday night and Wednesday...Low pressure will be quickly moving
northeast from the central Plains towards Chicago/Milwaukee by 12z
Wed before heading across Lower Michigan on Wed.  If this track or
something close to it pans out (confidence is low to medium), then
there is some potential for a rain snow mix over at least parts of
east-central WI.  Thermal profiles suggest mainly snow elsewhere,
with the highest amounts falling during Tuesday night.  Awfully
difficult to get a handle potential snow amounts, with the
uncertainty in the track/timing and resultant thermal profile. Last
night, mentioned early indications showed a potential 3-6 snowfall.
This looks a little on the high side tonight.  But still think a
lower end advisory type snow is possible for parts of the forecast
area, most likely over central and east-central WI. The heaviest
snow will mostly likely be pulling out on Wednesday morning, with
some snow showers continuing through the afternoon beneath cyclonic

Rest of the forecast...Occasional snow showers and flurries will
likely continue through Friday as the region will reside in deep
cyclonic flow.  Colder air will be filtering into the region during
this time, so should see a temperature trend towards normal for this
time of the year.  Focus may shift towards the lake effect snow
belts for next weekend.

.AVIATION...for 18Z TAF Issuance
Issued at 1205 PM CST Sun Jan 22 2017

A weak boundary is pushing across northeast Wisconsin this
afternoon. Ahead of the boundary, pockets of dense fog lingered
across the Fox Valley into Door County. This boundary will move
across the KGRB/KATW/KMTW taf sites this afternoon, thus some
improvement is expected by 20z/21z. The real question is what
happens tonight with weak cold advection at 850mb and weak
northwest winds. Temp/dewpoint spreads this afternoon would
suggest more fog tonight, possibly dense at times. Have all taf
sites dropping to a quarter of a mile tonight into early Monday
morning. A gradual improvement is expected later Monday morning.
Some drizzle is possible tonight and Monday. Some of the drizzle
could create icy conditions on pavement surfaces across far
northern Wisconsin.


Dense Fog Advisory until 3 PM CST this afternoon for WIZ022.


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