Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 251108
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
608 AM CDT Sun Jun 25 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Monday
Issued at 340 AM CDT Sun Jun 25 2017

Some interesting features today. We have showers across northeast
Wisconsin partly due to the departing upper low, but also due to
warm advection from the northeast. The activity should diminish by
sunrise as the upper low moves further away and low level
convergence and warm advection weakens.

Showers and some thunderstorms will return from northwest to
southeast during the midday and afternoon hours as another upper
trough approaches. Cold temperatures aloft and dry air near the
surface could make for some thunderstorms with gusty winds and
small hail. Highs today will be around ten degrees below normal.

Showers would diminish overnight, with some low clouds or fog if
there is any clearing. Monday should be mostly cloudy and very
cool, with showers and thunderstorms in cyclonic flow with an upper
trough moving by. 850 mb temperatures close to zero will make for
highs in the upper 50s to 60s across the region.

.LONG TERM...Monday Night Through Saturday
Issued at 340 AM CDT Sun Jun 25 2017

At the onset, the mean flow to be in the process of de-amplifying
as an eastern CONUS upper trough moves into the Atlantic and a
weakening upper ridge moves across the central CONUS. Toward late
week, a new upper trough is forecast to slowly move from southwest
Canada (Wednesday) to the Great Lakes (Saturday). Pieces of
shortwave energy are expected to move through this new upper
trough and combine with a frontal boundary hanging around the
Great Lakes, to introduce another stretch of unsettled weather
Wednesday and again Friday/Saturday. Temperatures for the most
part will remain at or below normal into next weekend.

A ridge of high pressure is forecast to move into the Upper MS
Valley Monday night and send a drier/more stable air mass into WI.
Look for skies to clear and winds to diminish, which will
eventually lead to a cool night over northeast WI. Min
temperatures should dip into the lower to middle 40s north-central
WI, middle to upper 40s central/far northeast and around 50
degrees east-central WI. This surface ridge pushes across WI and
will bring a sunny, pleasant day to the region. As winds gradually
back to the southwest, warmer air will start to overspread WI with
max temperatures in the lower to middle 70s north-central/
lakeshore, middle to upper 70s elsewhere.

As the surface ridge slips farther to the east Tuesday night, this
will allow for a return flow to begin in earnest and WAA to
increase into WI. Meanwhile, a shortwave trough/cold front
combination are forecast to move from the northern Plains toward
the Upper MS Valley by 12z Wednesday. For the most part, expect to
see a gradual increase in clouds with a slight chance of showers
reaching central WI toward daybreak. A more mild night on tap with
min temperatures only falling into the lower to middle 50s north,
middle to upper 50s south. Showers are likely, along with a chance
of thunderstorms on Wednesday as the shortwave trough moves into
the western Great Lakes and the trailing cold front reaches the
WI/MN border by late in the day. Both instability and shear values
appear marginal across northeast WI, thus the risk of severe
storms seems low at the moment. Thick clouds/precipitation will
limit the diurnal rise in temperatures with readings in the lower
70s north-central/near Lake MI, middle 70s elsewhere.

Showers/chance of thunderstorms will continue through at least
Wednesday evening as the cold front sweeps across WI. Once the
front pushes east/south through the forecast area, anticipate
precipitation trends to diminish during the overnight hours. The
cold front is progged to gradually pull-up stationary either over
southern WI or the WI/IL border on Thursday. Models indicate
little in the way of focusing mechanisms over northeast WI on
Thursday, thus have kept a dry forecast intact under partly sunny
skies. Not much in the way of cooler air behind the front, so any
sunshine at all will provide a slight boost to temperatures. Look
for readings to range from 75-80 degrees over most locations.

The forecast for Thursday night will be dependent on where the
location of the stalled boundary to reside. If the front is in WI,
central/east-central WI would be vulnerable to showers/storms,
especially if a wave of low pressure rides along the front (which
some models hint at). If this front sags into northern IL, all of
northeast WI would stay dry. Prefer to at least mention a chance
pop over our southern counties due to the uncertainty of the
boundary location. This uncertainty will linger into Friday, with
the additional questions of the timing of the next broad upper
trough forecast to move into the Upper MS Valley by Friday
afternoon. Higher pops should be to our south and west, but cannot
rule out small chance pops over northeast WI on Friday. Max
temperatures on Friday will cool a bit with lower 70s north-
central/lakeshore, mainly middle 70s elsewhere.

This latest upper trough will be more progressive in nature due to
the mean flow becoming less amplified. Look for this trough to
sweep across WI Friday night and already be headed toward the
eastern Great Lakes on Saturday. A chance of showers/few storms
possible over the forecast area Friday night, followed by a chance
of showers/slight chance of afternoon thunderstorms on Saturday as
cooler air interacts with daytime heating. Max temperatures on
Saturday to range from around 70 degrees north-central, to the
middle 70s south.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 608 AM CDT Sun Jun 25 2017

MVFR cigs are expected across the region today with showers
and a few thunderstorms moving in from the northwest ahead of an
upper level trough. The showers will diminish later tonight, with
low clouds or fog possible in north central Wisconsin. Additional
showers and thunderstorms are likely Monday.

&&

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

$$

SHORT TERM.....RDM
LONG TERM......Kallas
AVIATION.......RDM



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