Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 101008
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
408 AM CST Wed Jan 10 2018

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 408 AM CST Wed Jan 10 2018

There are many forecast concerns to deal with, including
precipitation trends, snow and ice accumulations, and whether or
not to issue winter weather headlines.

South flow has caused dew points to gradually rise overnight,
especially near Lake Michigan, where flow off the lake was
promoting low cloud development. Stratus was also moving into
our southern counties early this morning. Based on a lack of
drizzle development so far, and shallow moisture, decided to
run with a dry forecast for much of the day. However, recent
observations in southern WI have shown some drizzle, so will
watch the trends and see if drizzle/freezing drizzle needs to be
added back into the forecast before my shift ends. Regardless,
there is likely to be slippery spots on the roads due to
increasing dew points and road temperatures in the 20s, leading
to road frost development. Will issue a Special Weather Statement
to address this possibility for the morning commute.

RH timesections show moisture gradually deepening tonight, as
a 35-45 knot low-level jet continues over the region. Will have
a gradual increase in pops overnight, with the highest pops
over our northwest counties late, as a short-wave trof, LFQ
of a jet streak and mid-level frontogenetic forcing arrive. Most
of the region will see drizzle or light rain, as temperatures
are expected to remain in the middle 30s northwest to the lower
to middle 40s southeast. However, it seems likely that road
temperatures will remain a little below freezing in parts of far
northern WI, so have continued a mention of freezing rain and
minor ice accumulations there. As low-level moisture continues
to increase over the snow pack, areas of advection fog should
develop, and may become dense in some locations well into Thursday.

The cold front will move across the region on Thursday, though
the best dynamic forcing will remain focused over north central
WI, where persistent mid-level frontogenetic forcing is expected.
Deeper moisture and ice crystals in the saturated layer will
lead to snow development over north central WI, where 2 to 6
inches of snow is anticipated, heaviest in northwest Vilas county.
Rain will gradually change over to mixed precipitation then snow
from northwest to southeast as the front moves through, though the
changeover may not occur until evening in the far east. By late
in the day temperatures will have crashed to 10 to 15 degrees in
north central WI. Wet roads may also flash freeze over north
central, northeast and central WI in the afternoon, leading to a
hazardous commute, even for some areas that receive little snow.

Based on coordination with surrounding offices, have opted to
leave the winter weather headline decisions to the day shift,
especially since any significant impacts should hold off until
later tonight. Will highlight the impacts in the Hazardous Weather
Outlook and a Special Weather Statement.

.LONG TERM...Thursday Night Through Tuesday
Issued at 408 AM CST Wed Jan 10 2018

Back to the deep freeze will be the main story during the period.
There will be periodic chances of snow showers across the far
north due to the cold flow off the relatively warmer waters of
Lake Superior. There is a chance of light snow across much of the
region Sunday night into Monday.

For Thursday night, the arctic air will be finally settling into
the lakeshore counties while the far north will be firmly entrenched
in the cold air. Some lingering light snow is possible across east
central Wisconsin. Across the north, 850mb winds are almost perfect
for lake effect snow showers to move into northern Vilas county.
Per coordination with Marquette/Duluth, have increased chances for
snow into the likely category and bumped up snow amounts. There
may be another half inch in the snow belt region of northwest
Vilas between midnight and 6 am Friday. Also, did add a small
chance of snow showers Friday morning across northwest Vilas
county. Winds should back later in the morning, bringing an end to
the snow shower activity.

Otherwise, we will be in the deep freeze Friday into the middle
of next week, although it may not be as severe as the last
episode. Anyways, the number of subzero days will be on the
increase as lows through the weekend into the first half of next
week should be below zero on many nights north and west of the Fox
Valley. Low temperatures across the Fox Valley and lakeshore
region should to several degrees either side of zero. High
temperatures will run some 10 to 20 degrees below normal for this
time of year. The next two weeks are the climatic minimums for
our high and low temperatures, then we start the slow climb as we
head into February. There is a chance of light snow Sunday and
Monday with a system moving across the region. Amounts appear to
be light at this time. No significant changes made beyond the
Monday period.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1049 PM CST Tue Jan 9 2018

Conditions varied from VFR out to the west to IFR out to the east
as low level moisture increased from onshore flow from Lake
Michigan. Conditions will continue to deteriorate to MVFR and IFR
at all locations as this moisture spreads over all areas tonight,
with some freezing drizzle possible late tonight into Wednesday
morning. The low level moisture and warm air over cold snow will
keep conditions at these levels through the rest of the TAF period
as some drizzle once again is possible Wednesday evening as
moisture becomes a bit deeper. LLWS is forecast through the
period with strong low level winds as indicated by the KGRB VWP.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Eckberg
AVIATION.......Kurimski



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