Area Forecast Discussion
Issued by NWS Green Bay, WI

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019
FXUS63 KGRB 131725
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1225 PM CDT Sun Aug 13 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 341 AM CDT Sun Aug 13 2017

Some showers tonight and Monday, otherwise seasonable
temperatures with more humid conditions next week.

The high latitude flow over North America will remain blocky
during the forecast period. To the south, a band of westerlies
will gradually becomes established across southern Canada and the
northern CONUS. The development of the relatively low amplitude
flow across the forecast area favors only modest day-to-day
changes in temperature, with readings mainly near or a little
above normal. More humid conditions are also expected by mid-week.
There will be several opportunities for precipitation. The first
one tonight through Monday evening will be modest as dry air
lingers over the area, but subsequent systems will have more
moisture to work with and probably be better precipitation
producers. The best guess is that amounts will end up near or a
little above normal for the period.
&&

.SHORT TERM...Today...Tonight...and Monday
Issued at 341 AM CDT Sun Aug 13 2017

A shortwave currently over the northern Plains will track east
across the area during the short-term portion of the forecast. The
main forecast challenge is configuring PoPs for the precipitation
generated by the shortwave. The trend the past couple days has
been to slow the arrival of the precipitation due to a combination
of a slower eastward progression of the wave and dry air
lingering across the area longer than previously expected.

Today looks dry. Some showers are possible this evening, mainly
near the upper Michigan border and over central Wisconsin. There
should be a more significant eastward push to the precipitation
after midnight. Showers and some thunderstorms are likely across
about the northwest half of the forecast area Monday. Rain chances
in the southeast are more uncertain. A significant percentage of
the guidance keeps the far east dry much of the day, with just
some scattered showers late. The ECMWF is about the most
aggressive with the eastward surge of the precipitation, and about
the only model with substantial precip totals (> 1/4 inch) over
east-central Wisconsin. Am somewhat concerned a continued slowing
of the advance of the precipitation could hold the best chances in
the east off until Monday evening, and the the best forcing will
have already passed through by then. For right now, the chance
PoPs for east-central Wisconsin on Monday supplied by the broad
based blend of guidance seem reasonable, though this is a low-
confidence aspect of the forecast.

Stayed close to a blend of the top performing guidance products
for temperatures.

.LONG TERM...Monday Night Through Saturday
Issued at 341 AM CDT Sun Aug 13 2017

Low amplitude flow aloft should prevail across the northern CONUS
during this part of the forecast.

Monday`s showers and storms will linger into the evening hours,
but things then look dry until late Tuesday night when an
approaching mid level short wave and surface system bring a
chance for showers to the area. Showers and thunderstorms are
expected as a cold front and the mid level trough pass through
Wisconsin. The chance for rain drops off by Thursday as these
features move away from the state. Another mid level trough will
bring chances for showers Friday into Friday night

High temperatures should generally be near or a little above
normal.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1050 AM CDT Sun Aug 13 2017

Lingering dry air at low-levels will probably keep ceilings and
vsbys vfr over the period. But clouds will be on the increase as
a storm system moves in from the west tonight into Monday. Chance
of light rain will slowly ramp up from late tonight through the
end of the taf period.

&&

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

$$

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



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