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000 
FXUS63 KGRB 121153
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
553 AM CST Thu Dec 12 2019

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 356 AM CST Thu Dec 12 2019

Winter weather headlines will be the main concern today.

Only minor changes to headline timing, with a later start time
for the southern tier of counties, including the northern Fox
Valley. 

Light snow continued to develop over northern WI, in association
with the RRQ of an upper level jet and strong WAA. This initial
band of snow was lifting northeast, leaving central WI and the 
Fox Valley dry at this early hour. Bands of snow are expected to 
continue to form over northern WI early this morning, though 
lingering dry air in the low-levels may limit the intensity and 
result in some breaks in the steady snow at times, especially 
over the far northeast. The snow is expected to become heavier and
more widespread from west to east during the morning as low 
pressure approaches and the low-level jet cranks up to 40 to 45 
knots. A potent short-wave over the Dakotas will provide 
additional forcing as it moves through the region during the 
afternoon. The heaviest snow is expected from mid-morning through
mid-afternoon. Moisture will shallow out during the mid to late 
afternoon, leading to the potential for freezing drizzle. Do not 
think the freezing drizzle will be very impactful, as it will be 
falling on snow covered or treated roads. Snowfall totals will 
range from 1 to 3 inches south to 5 to 7 inches north. Highs will 
range from the upper teens northwest to the lower 30s southeast.

Lingering light snow or freezing drizzle will taper off in eastern
WI this evening, with mostly cloudy skies persisting through the
night. Lows will be in the teens northwest and lower to middle 20s
southeast.

Weak low pressure/inverted trough will approach the region Friday
afternoon, and bring a small chance of light snow or freezing
drizzle, especially across our western counties. Highs will be in
the 20s and lower 30s.

.LONG TERM...Friday Night Through Wednesday
Issued at 356 AM CST Thu Dec 12 2019

The main highlights for this forecast period are the chances for
accumulating snow Friday night through Saturday and below normal
temperatures for next week.

Friday Night through Saturday...An upper-level shortwave trough 
will move into the Upper Mississippi Valley Friday night.
Questions then arise with the surface low pressure system/cold
front. Model guidance is not in agreement with the track of this 
system or amount of moisture associated with it, and shows some 
phasing problems. However, there is some agreement with weak 
forcing during this time, making for light snow accumulations. Do
to much uncertainty with this system, did not steer much from
model blend.

Rest of the forecast...By Saturday night, the upper-level trough
will shift east leaving behind chances for light lake effect snow
showers over far north-central Wisconsin. A surface high pressure
system will then push into the northern Plains funneling cold 
Canadian air into the forecast area. Therefore, temperatures 
beginning Sunday morning through the rest of the extended will 
remain below normal. A small break in the below normal
temperatures may occur on Monday as model guidance shows a low 
pressure system moving into the Midwest from Oklahoma on Monday.
This system could bring some snow to southeastern Wisconsin, 
however, models are not in agreement with the track of this 
system. Beyond this system, another area of high pressure will
move into the northern Plains bringing more cold Canadian air to 
the region through midweek.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 542 AM CST Thu Dec 12 2019

Light snow over the northern and western parts of the forecast
area will spread southeast across the rest of the region and 
become heavier this morning. As this occurs, flight conditions 
will deteriorate to IFR/LIFR at most locations. The snow will
diminish and mix with freezing drizzle from mid-afternoon through
early evening. Though visibilities will improve significantly as
this occurs, ceilings are likely to remain IFR or lower-end MVFR
through the night. Gusty southerly winds are expected to develop 
along the lakeshore today.

Plowing operations will be needed today, with accumulations
ranging from 1 to 3 inches south to 5 to 7 inches north. The 
heaviest snow is expected to fall from mid-morning through mid- 
afternoon.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 AM this morning to 6 PM CST this 
evening for WIZ037>040.

Winter Weather Advisory until 6 PM CST this evening for WIZ005-
010-018>022-030-031-074.

Winter Weather Advisory until 6 PM CST this evening for WIZ035-
036.

Winter Storm Warning until 6 PM CST this evening for WIZ011>013-
073.
&&

$$

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