Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 170948
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
348 AM CST Mon Dec 17 2018

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 344 AM CST Mon Dec 17 2018

Cooler today, then a few more days of mild weather before
temperatures trend back closer to seasonal normals.

The large scale pattern will be in flux during the period. A
ridge will temporarily amplify over western North America, forcing
the development of a deep trough over the Mississippi valley by
the middle to latter part of the week. The increased amplitude
won`t last long however, as a trend back toward a more zonal
regime (though with much lower upper heights over the forecast
area than at present) is likely next weekend.

After a cooler day today, temperatures will warm to very mild
levels (~10-18 F degrees above normal) mid-week, then settle back
to within a few degrees of normal by the end of the period. The
pattern still does not look favorable for widespread significant
precipitation, as the primary cyclone with the developing upper
trough will pass south and east of the area. The best chance for
precipitation will be during the middle to latter part of the week
as disturbances digging southeast into the developing upper
trough affect the area, likely generating periods of light
precipitation. But amounts will be modest at best, so below
normal precipitation is expected for the period as a whole.
&&

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 344 AM CST Mon Dec 17 2018

A quiet period. The forecast area will be on the southwest flank
of a polar air mass advecting southeast from southern Canada. The
anticyclone associated with the air mass will shift across the
area tonight, then off to the east Tuesday.

Some clouds and possibly a few flurries are expected across the
north/northeast today in the north-northwest flow across Lake
Superior. Just some passing high clouds are likely once the lake
clouds dissipate/move out of the area this afternoon.

High temperatures today will be about 10-15 F degrees colder than
yesterday--but still above normal. Having the anticyclone directly
overhead and mainly clear skies over a lingering snow cover should
allow temperatures to drop significantly tonight. Started with a
blend of top performing guidance products and then lowered
temperatures a little more--especially in the climatological cold
spots. Sunshine and an increasing surface pressure gradient on
Tuesday should allow for mixing into warmer air aloft and result
in a mild day despite the anticipated cold start, so trended
toward the warmer guidance products.

.LONG TERM...Tuesday Night Through Sunday
Issued at 344 AM CST Mon Dec 17 2018

Precipitation chances and types are the main concerns during this
part of the forecast.

Dry conditions are expected to persist Tuesday night and
throughout much of the day at most locations on Wednesday as
surface high pressure and a mid level ridge move farther from the
area. Precipitation chances return for Wednesday as a mid level
trough and a cold front approach Wisconsin. At this point it
looks like nothing more than a slight chance for drizzle on
Wednesday, mainly south of a line from Merrill to Oconto.
Wednesday night and Thursday will see the best chances for any
precipitation as the cold front passes east of Wisconsin. Chances
for precipitation drop off late Thursday night/early Friday as
the mid level trough finally passes to our east. Surface high
pressure and a mid level ridge will bring drier weather for the
end of the week and into the weekend. Surface and mid level
systems passing north of Wisconsin could bring some snow showers
to far north-central Wisconsin Saturday night or Sunday.
Confidence in timing and location are low for that late in the
forecast period.

There should be mainly snow for Thursday night into Friday, but
warmer air in advance of the cold front will complicate matters
for Wednesday night and Thursday. Warm air aloft and temperatures
falling below 0C at some locations Wednesday night into early
Thursday, and again later in the day on Thursday, will bring the
potential for freezing drizzle or freezing rain. Precipitation amounts
are currently forecast to be pretty low so there should be no
concerns about ice on trees and power lines, but even a little
ice can make untreated roads hazardous. Stay tuned for more
detailed information on this precipitation event as it approaches.

High temperatures should remain much warmer than normal for
Wednesday and Thursday ahead of the cold front. Highs will be
above normal for Friday through Sunday, but not by nearly as much.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 344 AM CST Mon Dec 17 2018

Other than some MVFR ceilings across the north today, generally
good flying conditions are expected as high pressure settles into
the area. Surface winds will be a little gusty today as CAA occurs
in advance of the high.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MG
AVIATION.......Skowronski



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