Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 210921
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
321 AM CST Tue Nov 21 2017

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 318 AM CST Tue Nov 21 2017

Windy at times during the next week, with fairly substantial
variations in temperature from day to day. No big storms in the
offing.

The main large-scale features during the next week will be a
trough off the West Coast, downstream ridging just inland, and a
trough over eastern North America. The exact positions of the
features as well as their amplitude will vary throughout the
period. The pattern will support some fairly strong synoptic
systems, but with moisture expected to remain limited, they mainly
will result in wind and changes in temperature.

Temperatures will oscillate from below to above normal, with
departures from normal of over 10F degrees possible on a day or
two. Precipitation will be limited, with below normal amounts
expected for the period as a whole.
&&

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 318 AM CST Tue Nov 21 2017

A strong cold front will sweep off to the east of the area early
today, ushering in a much colder air mass. A strong pressure
gradient on the south side of a cyclone tracking east across
Ontario will combine with CAA and low-level subsidence to produce
gusty winds today. High temperatures will occur early, followed
by falling temperatures. An extensive low cloud deck to the
northwest of the area will shift southeast, and will result in
some flurries over at least the northwest half of the forecast
area. Winds will eventually back northerly enough (especially
above the surface) to bring snow showers off Lake Superior into
north-central Wisconsin. Upped PoPs to likely in the snowbelt.
Anticipate an inch or two of accumulation by the time the snow
showers diminish overnight.

High pressure will pass south of the area Wednesday. Winds will
gradually back southwest, and weak isentropic lift will develop.
But the atmosphere appears to be too dry for any precipitation to
occur on Wednesday.

Used a blend of the short-term guidance products to generate the
hourly temperature grids for today, then derived the high
temperature grid from that. Used a blend of top performing
guidance products for lows tonight, then stuck close to the broad
based blend of guidance products for highs on Wednesday.

.LONG TERM...Wednesday Night Through Monday
Issued at 318 AM CST Tue Nov 21 2017

The latest GFS ensemble mean indicates that upper ridging will be
present over western North America, while troughing will be present
over the east for the next week.  This will lead to northwest flow
aloft over the western Great Lakes.  Moisture will therefore be in
short supply over the period, but will have one significant clipper
impacting the region, during the Fri-Sat time period.  Potential
impacts from this system, to go along with temps, will be the focus
of this forecast.

Wednesday night through Thursday night...A fast moving clipper will
be passing over the region on Wednesday night.  Clouds will continue
to thicken ahead of the system across the region, with enough
saturation probably for a few hours of light snow and flurries
during the late evening and overnight hours.  Due to a lack of
moisture, not expecting much more than a dusting or half inch of
accumulations.  Any lingering light snow is expected to exit by the
start of Thursday morning, with a clearing trend already underway
from west to east.  Will then see a period of mostly clear
conditions until another round of warm advection ramps up by early
Thursday evening. Should see increasing clouds to go along with a
mild and breezy night, but saturation does not look deep enough at
this time for a chance of precip.  No significant changes to temps.

Rest of the forecast...Dry weather will continue until Friday
afternoon and night when a potent shortwave pushes a cold front
across the region.  This front is projected to have better moisture
and upper forcing to work with, which should lead to a decent chance
of rain showers for most locations.  As colder air advects into the
region behind the system, could see light snow move into northern WI
on late Friday night into Saturday morning.  Potential accums should
be generally less than an inch, but the system should also bring
gusty northwest winds during this time as well.  Then continued cold
and breezy through the rest of the weekend, with scattered light
snow showers in the lake effect snow belts.  Warmer weather looks to
make a come back early next week.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 318 AM CST Tue Nov 21 2017

Ceilings with the stratocumulus deck northwest of the area were
generally low-end VFR or high-end MVFR. That cloud mass should
shift southeast into the area today. Expect ceilings to settle
into the MVFR category over the northwest part of the area,
especially after trajectories become more favorable for lake-
effect late morning.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MPC
AVIATION.......Skowronski



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