Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 120321
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1021 PM CDT Wed Oct 11 2017

Updated aviation portion for 06Z TAF issuance

.SYNOPSIS...
Issued at 202 PM CDT Wed Oct 11 2017

Relatively mild and quiet mid-autumn weather for the next few
days, then some rain this weekend.

A seasonable upper pattern is in place across North America, with
a trough near the West Coast and downstream ridging mid-continent.
The flow will amplify a bit more the next couple days, then
flatten by late in the weekend as a significant short wave
ejects out of the western trough. Reamplification will likely
begin late in the period.

Though day to day variations are likely due to the passage of
frontal systems and changes in cloud cover, temperatures are
likely to average modestly above normal for the period as a whole.
The main chance for precipitation will occur during the weekend
as the energy ejecting out of the western trough generates a
significant cyclone in the mid-section of the country.
Precipitation amounts will probably be AOA normal for the period.
&&

.SHORT TERM...Tonight and Thursday
Issued at 202 PM CDT Wed Oct 11 2017

The low clouds from last night that shifted into mainly the
southern portion of the forecast area today are likely to expand
back north again overnight as boundary layer flow turns southeast.
Some of the models generated light precipitation late tonight.
Forecast soundings suggest that the precipitation--if it
occurs--will probably be drizzle. While that`s certainly
possible, the depth of the moisture looks marginal and ascent
within the cloud layer looks rather weak. Will make issuance time
decision on to what extent (if any) to include the mention of
drizzle for tonight. Otherwise, clouds will limit the diurnal
temperature range the next 24 hours. Stuck close to a blend of top
performing guidance products, though lowered mins across the
north a little tonight with the expectation of a period of clear
skies and light winds prior to the arrival of the clouds.

.LONG TERM...Thursday Night Through Wednesday
Issued at 202 PM CDT Wed Oct 11 2017

Focus of this forecast centers around the impacts from a storm
system arriving this weekend.  Looking at the latest model runs,
prefer a solution closer to the ecmwf.

Thursday night through Friday night...A cold front will be moving
over the northern Mississippi Valley and into western Wisconsin on
Thursday night.  Mid-level warm advection will be occurring ahead of
the front, but should be of little consequence since moisture will
be in short supply.  Models spit out light precip, however, possibly
indicating drizzle with shallow saturation below 850mb.  Think this
saturated layer is probably too shallow for precip, and most areas
should remain dry. Scattered showers appear possible as the front
moves across the area on Friday.  Mid-level and low level moisture
fields look disjointed, so think precip will remain rather light.
Rain should linger over northeast WI on Friday night, while north-
central WI clears out late.

Rest of the forecast...The front will settle over northern Illinois
on Saturday. Precip will continue to occur north of the front, with
the northern edge approximately south of Wood to Kewaunee counties
during the morning.  Though precip should remain light through
midday, precip is expected to increase in coverage and intensity in
the afternoon as southerly flow increases ahead of a low pressure
system. This surface low will track from Iowa to east-central WI on
Saturday night.  Elevated instability upwards of 500 j/kg, pwats
above 1.5 inches and relatively high moisture transport support
widespread rain, with scattered thunderstorms over northeast WI,
mainly during the evening.  Some rainfall amounts could reach over
an inch across east-central WI, where the heaviest rain should fall.
Do not think that a severe weather threat exists, due to relatively
low levels of instability.

Precip will gradually diminish from late Saturday night into Sunday
morning for most locations.  Though some sunshine is possible in the
afternoon, colder air arriving behind the system should lead to a
cool day.  Precip chances look relatively low through the rest of
the forecast.  A few showers appear possible on Sunday night when a
fast moving clipper moves across the region.  If precip does occur,
a few wet flakes will be possible. After a cool start, temps should
slowly warm up by mid-week.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1015 PM CDT Wed Oct 11 2017

Low clouds will be the main issue for later tonight through
Thursday night and possibly Friday as well. MVFR cigs already
noted just south and east of the area late Wednesday evening.
As winds turn to the east or southeast through the night, MVFR
cigs and some IFR cigs will develop or spread into the area.
MVFR CIGS (possibly some IFR CIGS across north-central WI) will
continue through Thursday afternoon, then IFR CIGS and some fog
are expected Thursday night into Friday morning. It is anticipated
that the drizzle may need to be added to the forecast at some
point Thursday afternoon or Thursday night. At this point, leaning
towards Thursday night but will let mid shift take a look at all
the models and can add it to the 12z tafs.

&&

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

$$

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



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