Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 191740
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1140 AM CST Mon Feb 19 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 411 AM CST Mon Feb 19 2018

Precipitation trends and type, snow and ice accumulations and
headlines are the main forecast concerns.

Have attempted to simplify headlines this morning, and just issued
winter weather advisories for the entire forecast area. Snow
accumulations are not expected to be significant due to a lack
of deep saturation, though Vilas county will likely pick up 1 to 3
inches today. Ice accumulations of a quarter to third of an inch
are anticipated across all but far north central WI, though these
accumulations are spread over a 30-36 hour period, which should
reduce the impacts to some degree. If localized heavier amounts
appear likely, an upgrade to a warning can be made.

A cold front was moving through north central WI early this
morning, but the coldest temperatures were observed ahead of it,
where winds have dropped off and skies have partially cleared.
Temperatures were still holding above freezing in the Fox Valley
and lakeshore areas. The front is expected to steadily shift
southeast this morning, and exit the forecast area by around
midday. Used a mix of several blended model data sets for
hourly temperatures, and this kept readings at or above freezing
in the Fox Valley and lakeshore areas until mid to late afternoon.
Precipitation should overspread the region during the late
morning and early afternoon as strong frontogenetic forcing
develops. Precipitation should be a mix of snow and freezing rain
far northwest, freezing rain from central into northeast WI, and
rain changing to freezing rain in the Fox Valley and lakeshore.
For the sake of simplicity, kept the starting time of the advisory
at 9 am for the northwest two-thirds of the CWA, and 3 pm in the
southeast, where temperatures will be slower to fall.

Models agree that precipitation should decrease across much of
the forecast area tonight, so pops and QPF have been reduced
accordingly. Even so, light freezing rain and freezing drizzle
will continue to produce some ice accumulations overnight.
On Tuesday, temperatures are forecast to warm above freezing
over the southeast half of the forecast area during the afternoon,
which could effectively end the icing there. Despite this
expectation, we kept a 00z/Wed expiration time in order to match
up with our neighbors. If the expected warming occurs, the
headlines may need to be canceled around midday southeast of a
line from Wautoma to Shawano to Crivitz.

.LONG TERM...Tuesday Night Through Sunday
Issued at 411 AM CST Mon Feb 19 2018

A persistent upper air pattern will shape up across North America
over the next week, with a deep trough settling over the western
conus, and ridging east of the Mississippi River.  This pattern
would place the western Great Lakes within southwest flow aloft,
which is more conducive for near to above normal temperatures, and
periods of precip.  Due to the upcoming winter storm, will just use
the multi-model blend for the forecast.

Tuesday night through Wednesday night...The cold front will finally
accelerate eastward on Tuesday night. Light precip consisting of
rain or freezing rain will likely be ongoing at the start of the
evening, then gradually come to an end from west to east through mid
evening. Any additional ice accums should be minor. Then Arctic high
pressure will build into the area during the overnight hours into
Wednesday. Skies will slowly clear during the time, which should
result in plenty of sunshine for Wednesday. As the high quickly
departs on late Wednesday night, may see some mid and high clouds
move in late, but no precip is expected at this time. Highs on
Wednesday falling to near normal.

Rest of the forecast...As weak isentropic lift returns, models are
more aggressive in bringing light precip to the area on Thursday
afternoon into Friday morning.  Temps look to be just cold enough
for snow, though wouldnt take much for some mixed precip to push
into central and east-central WI.  Could see an inch or two of snow
if temps remain below freezing.  After a brief period of dry
weather, another system looks to arrive next weekend, with
temperatures playing a critical role again in determining the precip
type.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1107 AM CST Mon Feb 19 2018

A cold front will slowly sag south over the area today
into tonight. Widespread IFR cigs north of the front will spread
over central and east central Wisconsin as the front slides south.
precipitation type will mainly be snow across the north...turning
to light freezing rain or drizzle near the front and rain or
drizzle south of the front. The rain or drizzle will transition to
a freezing rain or freezing drizzle variety later this afternoon
and evening as surface temperatures fall below freezing.

A period of gusty northeast winds to 25 or 30 mph will occur in
the Fox Valley and lakeshore areas as the front slides through,
then subsiding this evening.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 PM this afternoon to 6 PM CST
Tuesday for WIZ038>040-045-048>050.

Winter Weather Advisory until 6 PM CST Tuesday for WIZ005-
010>013-018>022-030-031-035>037-073-074.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......MPC
AVIATION.......TDH



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