Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 152341
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
541 PM CST Sun Jan 15 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 246 PM CST Sun Jan 15 2017

Main forecast challenge arrives tomorrow afternoon as the leading
edge of precipitation lifts northward. Exactly what the
precipitation type will be remains the toughest part of the
forecast.

The 20z MSAS surface analysis showed a large area of high pressure
stretched from the Upper Midwest east through the Great Lakes to
the New England states. Skies were mainly sunny over the northern
half of WI with some high clouds over the southern half. The next
weather system of interest is still churning over the southern
Plains...but starting to make a move to the northeast.

Quiet and not as cold conditions to prevail across northeast WI
tonight as the area resides under the western fringes of the
retreating surface high. Central/east-central WI will continue to
see high clouds pass by ahead of approaching weather system. More
wind in the boundary layer should keep the atmosphere more mixed,
thus temperatures will not fall nearly as far as last night. Look
for mins to range from the upper single digits to lower teens over
most of northeast WI, with middle teens for locations closer to
Lake MI.

Models all pretty much take this southern stream system northeast
into the central Plains/Mid-MS Valley on Monday with the surface
low reaching northwest MO by 00z Tuesday. A warm front will extend
east-northeast into northern IL and as gulf moisture surges north,
expect to see a band of precipitation lift north into southern WI
Monday morning and into central/east-central WI Monday afternoon.
Precipitation type continues to be a major headache as
temperatures in the lower part of the atmosphere reach or go
slightly above freezing, but road temperatures remain below
freezing. Most of central/east-central WI should see precipitation
begin as a snow/sleet mix, however our southernmost locations may
see a complete mix of rain/freezing rain/sleet/snow as the warmer
air lifts north. After collaboration with ARX and MKX, have
decided to issue a winter storm watch starting at 21z Monday for
areas along and south of a line roughly from AUW to SUE. This
would allow the next shift to look at one more model run to get a
handle on icing potential and either go with a warning or an
advisory. Max temperatures are forecast to mainly be in the lower
30s which just adds to the difficulty in forecasting precipitation
type.

.LONG TERM...Monday Night Through Sunday
Issued at 246 PM CST Sun Jan 15 2017

A wintry mix is in the forecast for Monday night and Tuesday as a
low pressure system tracks to our south. Recent model runs have
tracked a bit further south this run, keeping a cold layer of air
at the surface longer with a slower intrusion of warm air at mid
levels. This will lengthen the amount of time the area will
experience icy precipitation as snow transitions to sleet,
freezing rain and eventually rain across the far southeast during
this period. The models have also been a bit slower this run,
meaning the bulk of the precipitation is slated to fall on Monday
night, which will exacerbate the ice potential as area roads
remain below freezing even when precipitation changes to all
liquid. Tuesday will bring little relief as area roads remain at
or below freezing for much of the morning despite air temperatures
above freezing as roads take several hours to respond to the
warmer air temperatures. Overall it looks like a wintry mess
across central and east central Wisconsin during this period, with
the potential for a few tenths of an inch of sleet as well as 0.1
to 0.2 inches of freezing rain with the possibility of a quarter
of an inch across some areas. The greatest potential for
significant freezing rain will be across the extreme southern cwa
and the lakeshore counties with the potential for sleet along the
same area and just to the north of these areas. The threat for
significant frozen precipitation falls off precipitously as you
get north and west of Green Bay during this period with a less
pronounced mid level warm layer. Even further north there is some
concern that dry air will keep some if not a good portion of north
central Wisconsin dry per the GFS solution.

Given the current track of the low and the possibility of this
system to alter its track will go ahead with a Winter Storm Watch
for central and east central Wisconsin with the thought that the
northern edge of this Watch could be transitioned into a Winter
Weather Advisory and the southern edge into a Winter Storm Warning
in a subsequent forecast issuance. The confidence is not high
enough to make this determination with this forecast issuance as
the system continues to make transitions with each run.

The precipitation will end from west to east on Tuesday as it
becomes mostly rain given the warming surface and eventually road
temperatures above freezing. Some lingering light precipitation
may linger Tuesday evening across the east, with a small threat
for freezing rain or drizzle after sunset.

After a relatively quiet period Wednesday and Thursday, another
system will impact the area late Thursday night and into the
weekend. This system will initially lack mid level moisture
Thursday night, once again bringing the threat for freezing rain
or drizzle to the area. However warmer temperatures Friday and
into the weekend look to keep the precipitation as mainly rain for
the rest of the extended period as temperatures warm into the 40s.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 539 PM CST Sun Jan 15 2017

VFR conditions are expected for the most part through noon Monday
as an area of high pressure begins to slip farther to the east.
There may be another round of patchy fog across parts of central
WI later tonight which could lead to MVFR vsbys. Otherwise, look
for flying conditions to gradually deteriorate from south to north
late Monday afternoon into Tuesday as a system approaches and moves
through the Great Lakes. A mix of precipitation, including sleet
and freezing rain, can be expected.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday afternoon through Tuesday morning
for WIZ020-022-030-031-035>040-045-048>050-074.
&&

$$

SHORT TERM.....Kallas
LONG TERM......Kurimski
AVIATION.......RDM


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