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226
FXUS63 KGRB 200406
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1006 PM CST Tue Feb 19 2019

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 901 PM CST Tue Feb 19 2019

Have moved up the start time for the advisory to 6 am in
Marathon, Wood, Portage, Waupaca and Waushara counties, as
several meso-models indicate that accumulating snow will arrive
there during the morning commute. Kept the 9 am start time
elsewhere, as models show a dry wedge hanging tough into mid-
morning.
&&

.SHORT TERM...Tonight and Wednesday
Issued at 255 PM CST Tue Feb 19 2019

Clouds will spread across the forecast area late today/this
evening. Temperatures will be a challenge early as light winds
and little cloud-cover allow readings to fall rather quickly
after sunset, especially in north-central Wisconsin. Think there
will be some lows in the single digits below zero near the Upper
Michigan border, but single digits and teens look okay for the
rest of the forecast area.

Timing of the snow is the next challenge as a developing surface
low approaches the Great Lakes from the Plains. The 12Z NAM was a
bit slower than the GFS or ECWMF, but decided to go with its
timing since the airmass over Wisconsin is quite dry (as seen on
the 12Z KGRB sounding). Expect dry conditions for most of the
overnight hours before snow moves into central Wisconsin toward
morning and continues to spread across the rest of the area
through the early morning hours. Significant snow accumulation
should not start until around 15Z so have used that as a starting
time for a Winter Weather Advisory. Expect about 2 to 5 inches of
snow across the area by 00Z with some additional accumulation
thereafter. Freezing drizzle is possible, mainly across east-
central Wisconsin later Wednesday afternoon due to decreasing mid
level moisture.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 255 PM CST Tue Feb 19 2019

Light snow or freezing drizzle will be ending
Wednesday night as the strong upper system exits the area. Dry and
seasonable weather should follow for Thursday and Friday as upper
flow becomes zonal.

A strong jet streak approaching the Pacific Northwest this evening
is forecast to drop south across the California coast the next
two days, resulting in a closed upper low over Arizona by Friday
night. The movement of this upper low and the degree of phasing
with energy in the Polar jet stream will help determine the
intensity and track of what should be a significant wither storm
for this weekend.

The GFS and ECMWF forecast a track favorable for heavy snow across
the northwest half of Wisconsin, with mixed precipitation across
the southeast half. Analogs of this system to storms of the past
30 years suggest heavy snow from Sioux City Iowa to northcentral
Wisconsin. The analogs are based on the current model forecasts,
so that might change if the models differ with later runs. The
forecast of the system will likely change over the next few days
due to the uncertainty of systems coming ashore from a data
sparse area, and the added problem of phasing jet streams.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 957 PM CST Tue Feb 19 2019

VFR conditions are expected to prevail across the area overnight,
with clouds thickening and gradually lowering. Snow will
overspread the region from southwest to northeast Wednesday
morning, with flight conditions deteriorating to IFR at AUW/CWA
around 12z-13z, and GRB/ATW/MTW/RHI around 14z-15z. There is
potential for a mix of snow and freezing drizzle, mainly at the
southeast TAF sites during the late morning/early afternoon, and
again mid to late evening. A period of moderate snow may occur
across central and north central WI from late morning through
mid-afternoon. Modest improvement in flight conditions can be
expected as the precipitation tapers off and winds become westerly
during the evening.

LLWS is expected to develop from southwest to northeast across
the region during the day, as southeast winds aloft increase
to 35 to 40 knots. The LLWS will taper off by evening.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 AM to 9 PM CST Wednesday for
WIZ005-010>013-018>022-031-038>040-048>050-073-074.

Winter Weather Advisory from 6 AM to 9 PM CST Wednesday for
WIZ030-035>037-045.
&&

$$

UPDATE.........Kieckbusch
SHORT TERM.....MG
LONG TERM......RDM
AVIATION.......Kieckbusch