Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 170006
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
606 PM CST Fri Feb 16 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 323 PM CST Fri Feb 16 2018

Skies will start out clear this evening as a surface ridge axis
shifts east of the region. Mid and high clouds will increase late
tonight as a short wave approaches from the northern Plains
states. The combination of upper support from the left exit region
of a strong jet lifting northeast from Iowa and broad warm
advection should be enough to produce light snow Saturday despite
an initially dry atmosphere. The best snow should be in central
Wisconsin, where an inch or a bit more are possible. The rest of
the area should get a dusting to half inch. Lows tonight will be
close to normal, while highs tomorrow will be around five degrees
higher than average.

.LONG TERM...Saturday Night Through Friday
Issued at 323 PM CST Fri Feb 16 2018

Chances for snow and mixed precip Sunday into Tuesday and/or
Wednesday are the main forecast concerns. Model differences
continue and no clear trend or favorite to latch onto at this
point. Each model is sticking mainly to its story, making for a
low confidence forecast.

Any lingering light snow will be exiting the area Saturday evening
as a trough/shortwave pushes into Lower Michigan, with no
additional accumulation expected. Otherwise, Saturday night looks
to be dry as the atmosphere briefly dries out. Although some
linger low level moisture will remain, partial clearing is
expected across the area in the evening, then mid/upper level
clouds will quickly spread back into the area Sunday morning.
Enough clearing is expected to allow low temps to drop into the
single digits over north central WI and mainly the teens across
eastern WI.

As the first wave of low pressure approaches, warm air advection
and frontogenetic forcing will allow snow to develop across
locations north of Hwy 29 on Sunday. The Canadian continues to be
the most aggressive and farthest south with the snow, showing
totals over 6 inches possible near the WI/MI border. However,
GFS/NAM/ECMWF favor a farther north solution, keeping the heaviest
snow across the U.P. and Lake Superior. Even though model
uncertainty still exists, think 2-4" seems reasonable for totals
during the day on Sunday over the north, with locations south of
Hwy 29 seeing little to no snow. Some models show mid-level
moisture could be lacking as the snow comes to an end, which would
create a period when freezing drizzle could mix in with the snow.
Highs were the snow is expected will be in the middle and upper
20s, with lower to middle 30s expected south of Hwy 29.

A more widespread precip event is expected Sunday night into
Monday, as a stronger low pressure system tracks into the Great
Lakes and a frontal boundary moves through. Models still disagree
on where the front will set up, which leaves temps at the surface
and aloft in question. Models not as different as yesterday, but
still differ by 4C to 8C. Using a model blend, the transition zone
will set up from central WI into far northeast WI. Portions of
the Fox Valley and lakeshore would see a period of rain on Monday
as 850mb temps climb above 5C then transitioning back to mixed
precip as colder air filters in behind the front. The north still
looks to see mainly snow. Still too early to talk totals, but
northern WI looks to see at least advisory level snow amounts
(3"+). Depending on surface temps, the rest of the area could see
enough of a wintry mix to warrant an advisory as well. But we have
some time before those would be issued and hopefully some of the
uncertainty can be removed from the forecast.

Models disagree slightly on how fast this system will exit the
region as well. GEM bring another wave of low pressure across the
Great Lakes on Wednesday, brushing the area (especially eastern
WI) with another round of light snow, but the other models keep
things dry, so will lean in that direction. Arctic high pressure
then builds into the region for Thursday bring quiet and cold
conditions.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 602 PM CST Fri Feb 16 2018

A period of relatively poor flight conditions is expected Saturday
morning as an area of light snow develops and pushes through the
area. Isentropic lift combined with some QG forcing associated
with a modest mid-level shortwave will generate the lift for the
precipitation. LLWS will also develop from northwest to southeast
across the area overnight, and linger into Saturday morning.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......Bersch
AVIATION.......Skowronski


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