Area Forecast Discussion
Issued by NWS Green Bay, WI

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027
FXUS63 KGRB 162032
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
232 PM CST Sat Dec 16 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 230 PM CST Sat Dec 16 2017

Typical winter weather regime over northeast WI with plenty of
clouds around, cold temperatures and small chances for
precipitation due to a lack of a strong system. The main forecast
issues will be trying to determine whether any weak weather
phenomena could generate any precipitation and if lake effect
potential from Lake MI is worth mentioning in the forecast.

The 19z MSAS surface analysis showed an area of high pressure
centered over central Ontario and a nearly stationary front
stretched from eastern IA eastward to the MI/IN state line. A weak
area of low pressure was located along this boundary over central
IA. Visible satellite imagery indicated much of northern and
central WI covered in clouds, however western and southern WI were
mostly sunny, thus parts of central WI may see some late day sun.

Northeast WI to remain locked between the high pressure to our
northeast and the quasi-stationary front draped to our south. Weak
mid-level forcing to remain over the region tonight, thus plenty
of clouds to persist (or fill back in over central WI). Any
precipitation potential may be tied to either any mid-level
shortwaves moving east through the mean flow or lake enhancement
over eastern WI due to an east-northeast wind off of Lake MI. The
timing/location of these shortwaves are difficult at best and may
not have enough lift to create any precipitation. Therefore, have
focused small pops in the east for lake effect. Have mentioned
both flurries and freezing drizzle since forecast soundings do
show a dry layer in the mid-levels. All in all, any precipitation
that does fall would be very light and should not create any
travel issues. The anticipated cloud cover will prevent
temperatures from falling too much with readings ranging from 10
to 15 above zero far northeast WI, lower to middle 20s east-
central WI.

Weak ripples of low pressure are forecast to move along the
quasi-stationary front on Sunday, but with lift/forcing so weak,
it may be hard to generate any precipitation. Thus, have kept the
mention of flurries or freezing drizzle in the east due to
continued lake effect until around midday before boundary layer
winds turn to the south and lake effect ends. Otherwise, expect
mainly cloudy skies across the region on Sunday with max
temperatures in the upper 20s far north, lower to middle 30s
south.

.LONG TERM...Sunday Night Through Saturday
Issued at 230 PM CST Sat Dec 16 2017

Temperature trends and the potential for a winter storm over the
latter half of the next work week, are the primary forecast
concerns.

Zonal flow, generally dry weather, and mild temperatures are
expected for the beginning of the work week, with above normal
high temperatures in the lower to middle 30s on Monday.

A cold frontal passage will occur Monday night, with CAA,
subsidence and 925-850 mb winds of 35 to 45 kts resulting in
strong west winds into Tuesday. Will mention the potential for
gale force gusts in the Hazardous Weather Outlook.

Attention turns to a potential winter storm, which will impact
the region from Wednesday afternoon into Friday morning. The
initial bands of snow Wednesday afternoon and night are expected
to develop in the RRQ of an upper jet, aided by WAA and mid-level
frontogenetic forcing. The best forcing may eventually become
focused over the southeast half of the forecast area as a coupled
upper jet develops late Thursday into Thursday night, and low
pressure approaches from the OK Panhandle. This would seem to be
the preferred time frame for the heaviest snow accumulations to
occur. This will be a difficult storm to forecast, as there is no
potent short-wave trof to focus on, and accumulations will likely
depend on the location and persistence of multiple frontogenetic
bands that will form and weaken with time. Models generally
support the lowest accumulations over our northwest counties,
though it is too early to put much stock in that. This has the
appearance of a potential headline event, but whether it will end
up being a prolonged advisory event or a warning event is in
question.

Colder air will arrive in the wake of the winter storm for the
weekend, but the really bitter arctic blast is expected to hold
off until Sunday night.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1134 AM CST Sat Dec 16 2017

Cigs through this afternoon to range from low-end MVFR across
parts of central/east-central WI, to low-end VFR across far
northeast WI. There could be a passing snow shower or some
flurries mainly over northern WI and near Lake MI due to weak
lake effect. The region to remain between high pressure to our
northeast and a nearly stationary front to our south through
Sunday. Expect plenty of clouds to prevail tonight and Sunday with
cigs in the MVFR range tonight, possibly dropping into the IFR
range toward daybreak. The high-end IFR/low-end MVFR cigs to
persist into Sunday along with spotty flurries/freezing drizzle
north or spotty drizzle south as temperatures warm.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......Kieckbusch
AVIATION.......AK



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