Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 212310
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
510 PM CST Wed Feb 21 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 219 PM CST Wed Feb 21 2018

Focus revolves around cloud trends and temperatures over the next
day.

Southwest flow and upper jet continue to dominate the weather
pattern which has lead to scattered high clouds moving across the
area today. Expect this to remain the case overnight which will
not be much of an insulator. With the surface high also passing
across tonight winds will be light to calm. Therefore, kept lows
on the cool side of guidance and a couple degrees cooler than the
previous forecast, especially across north- central Wisconsin.

Warm air advection arrives around daybreak, which will lead to
increasing mid- level clouds through the morning, and afternoon
highs warmer than today, in the upper 20s and lower 30s.

A mid-level shortwave and associated precip approaches Wisconsin
Thursday afternoon, but there will be plenty of dry air to
overcome before anything reaches the ground. May see some light
snow in the far western forecast area (central Wisconsin) prior to
00Z, but the vast majority of this event will be after this time.

.LONG TERM...Thursday Night Through Wednesday
Issued at 219 PM CST Wed Feb 21 2018

The mean flow to generally consist of a Pacific upper ridge, a
western NOAM upper trough and a subtropical upper high that would
stretch from the Gulf of Mexico to the western Atlantic. This
pattern would bring a southwest flow into WI, which should keep
temperatures above normal, but also bring an active weather
scenario to the area. Trying to time each system ejecting out of
the western trough, along with the strength of each system and
precipitation type, all make for a difficult forecast.

A shortwave trough is forecast to lift northeast into the Midwest
Thursday evening and into the western Great Lakes Thursday night.
An initial burst of WAA should saturate the atmosphere enough to
allow for precipitation to overspread central WI in the evening
and eastern WI overnight. The main question remains precipitation
type as warmer air aloft pushes into the region and will lead to a
wintry mix, including sleet and freezing rain. Forecast soundings
indicate light snow initially, however central/east-central WI
would see sleet/freezing rain mix with the snow shortly after
midnight and switch more to freezing rain toward daybreak.
Meanwhile, northern WI should remain mostly all snow through the
night with perhaps a little sleet mixed in late. Snow
accumulations here could be 2-3 inches, while less than one-tenth
of an inch of ice is possible across central/east-central WI. Not
confident enough on amounts yet to go for any headlines, but will
continue to mention potential travel issues for the Friday morning
commute in the HWO. Min temperatures to range from around 20
degrees north-central WI, to the upper 20s east-central WI. Most
of these min temperatures will be reached in the evening before
readings steady out or even rise overnight.

The shortwave trough quickly exits the region Friday morning, but
may still need to carry a small pop over most of the forecast
area. Precipitation type remains a problem as forecast soundings
also show a loss of ice aloft which could bring drizzle/freezing
drizzle into play. Fortunately, the better lift/forcing to have
exited WI by this time, thus precipitation amounts will be
minimal. High pressure is expected to build across the Upper MS
Valley/Midwest Friday afternoon and start to break up some of the
clouds over northeast WI. Max temperatures to range from the
middle 30s north-central, to around 40 degree east-central WI.

This high pressure moves across the Great Lakes Friday night and
will keep quiet weather conditions intact over northeast WI. Skies
will generally be partly cloudy as a southwest flow aloft remains
and at least some high clouds move in ahead of a system organizing
over the central Plains. Min temperatures to range from 10 to 15
degrees north-central, to the middle 20s near Lake MI. A large
piece of the western NOAM upper trough is progged to eject into
the Plains on Saturday and allow for an area of low pressure to
strengthen from the central Plains to the Midwest by 00z Sunday.
Clouds will thicken and lower over northeast WI Saturday morning,
with precipitation overspreading the area Saturday afternoon.
Depending on where temperatures reside when the precipitation
begins, precipitation type could range from snow to a snow/rain
mix to rain. Have raised pops from the previous forecast with
possible minor accumulations over central WI. Max temperatures for
Saturday to be in the middle 30s north-central to around 40
degrees east-central WI.

The surface low tracks northeast into the Great Lakes Saturday
night, although the models disagree exactly how strong this low
pressure will become. Eastern WI could stay either a mix or all
rain into Saturday evening before transitioning back to all snow
later Saturday night. The rest of the forecast area should be all
snow through the night. Too early yet for amounts. Lingering snow
showers or flurries are expected into Sunday morning and perhaps
even into Sunday afternoon across the north as wrap-around
moisture from the departed system clips that part of the state.
Max temperatures for Sunday to range from the lower 30s north-
central, to the upper 30s eastern WI. A weak surface ridge
approaches WI Sunday night, moves across the state Monday morning
and be to our east Monday afternoon. Under mainly partly cloudy
skies, look for max temperatures on Monday to range from the lower
30s north-central, to the middle to upper 30s elsewhere.

A modest cold front is forecast to push into the region late
Monday night or early Tuesday morning. Moisture is lacking
initially, therefore have kept Monday night dry and only mention a
small chance pop for Tuesday. Max temperatures to remain above
normal with middle 30s north-central, upper 30s to around 40
degrees elsewhere. Wednesday`s forecast will depend on exactly how
far this cold front settle south before grinding to a halt as it
encounters the northern edge of the upper high over the southeast
CONUS. Assuming this boundary can sag far enough south, any
precipitation should remain to our south on Wednesday. A decent
amount of cloud cover will limit temperatures a bit with readings
in the lower to middle 30s north-central, around 40 degrees east-
central WI.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 507 PM CST Wed Feb 21 2018

Good flight conditions are expected during the next 24-30 hours
as high and then middle clouds stream up and over the area from
the southwest, while a strong anticyclone remains stretched across
the area at low-levels. Conditions will deteriorate thereafter as
the high moves east, ceilings lower, mixed wintry precipitation
overspreads the area, and LLWS develops.
&&

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

$$

SHORT TERM.....KLB
LONG TERM......Kallas
AVIATION.......Skowronski



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