Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 231145
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
645 AM CDT Fri Jun 23 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 400 AM CDT Fri Jun 23 2017

The cold front had just about exited the forecast area at 09z and
the rain should end by daybreak. Cooler and drier air will work
it`s way into Wisconsin today, though there could be scattered
showers in the afternoon hours over central and northcentral
Wisconsin. Highs will be close to normal for this time of year.

SKies should start the evening our clear, but some clouds will
increase overnight as an upper low approaches from North Dakota.
With dewpoints in the upper 40s to low 50s, low temperatures
should be a few degrees below normal.

Saturday will be breezy and cool, with showers and thunderstorms -
especially in the afternoon. The approaching upper low will be
accompanied by 500 mb temperatures of -20 to -25 C by evening
creating an unstable atmosphere that could support thunderstorms
with gusty winds, small hail and perhaps some cold air funnels.

.LONG TERM...Saturday Night Through Thursday
Issued at 400 AM CDT Fri Jun 23 2017

An amplified mean flow to persist into early next week, consisting
of an upper ridge over the western CONUs and an upper trough over
the eastern CONUS. The flow will then flatten toward the middle of
next week as the eastern trough shifts into the Atlantic and the
weakening upper ridge gets shoved eastward across the central
CONUS, being replaced out west by another upper trough. Models are
having issues with the movement/strength of this new upper trough
which places uncertainty into the forecast for next Wednesday/
Thursday. Bottom line is that the unsettled weather/cool
conditions will continue Sunday/Monday, then a warmer/perhaps more
unsettled pattern for mid-week.

A vigorous little shortwave trough is forecast to push across the
eastern half of WI Saturday evening, before shifting into Lower MI
later Saturday night. Even though instability will weaken with the
loss of daytime heating, there is decent mid-level forcing so
anticipate showers/few thunderstorms to carry over through
Saturday evening and mostly come to an end overnight. Despite
plenty of cloud cover, the air mass aloft is quite cool by late
June standards (8H temperatures at +2C to +4C range), so min
temperatures will still get down into the middle 40s north-central
WI, lower 50s east-central WI. The next shortwave trough is
expected to drop southeast into the western Great Lakes region on
Sunday and bring yet another chance for showers/afternoon storms
to northeast WI. While this trough is not as strong as its
predecessor, MUCAPES do approach 300 J/KG over east-central WI so
a few of these storms could briefly become strong with small hail
possible. Temperatures will remain well below normal with readings
only in the lower 60s north-central, upper 60s for eastern WI.

Much like Saturday night, it is going to take a while for these
showers/thunderstorms to dissipate Sunday night. In fact, some of
the models linger the threat of showers through the night as
instability is slow to diminish and mid-level forcing lingers. The
air mass aloft does not change much, therefore look for min
temperatures to again be in the middle 40s north-central, upper
40s central/far northeast and lower 50s east-central WI. The last
in the series of shortwave troughs is progged to move into the
Great Lakes region on Monday. By this time, upper heights are
beginning to rise over WI as the main upper trough shifts
eastward, thus the air mass aloft will start to moderate. Less
instability should keep shower chances on the low side with no
thunder anticipated. Max temperatures to range from the middle 60s
north-central, upper 60s to around 70 degrees elsewhere.

An area of high pressure is forecast to build into WI Monday night
and reside to our east on Tuesday. Northeast WI will finally get a
stretch of dry weather with a return of sunshine Tuesday, along
with an uptick in temperatures. Look for readings to mainly be in
the lower to middle 70s.

The mean flow to have become somewhat zonal from the West Coast to
the Great Lakes by Tuesday night. Under this regime, models
typically struggle with timing of systems and this occurs once
again headed into Tuesday night/Wednesday as the GFS/CMC are
faster than the ECMWF. The faster solution already has
precipitation chances overspreading northeast WI Tuesday night,
while the slower solution holds precipitation off until Wednesday
afternoon. For now, will split the difference and bring small
chance pops to central WI late Tuesday night and go with chance
pops for the entire forecast area on Wednesday (although the
precipitation may hold off until the afternoon hours in the east).
Max temperatures will continue to warm with readings into the
lower 70s north-central/lakeshore, middle to upper 70s elsewhere.
Models continue to struggle headed into Thursday with the GFS
showing a west-southwest flow aloft over WI with a cold front
slowly pushing into WI. Meanwhile, the ECMWF has a west-northwest
flow aloft over WI with no cold front. Just too wide a spread
among the models to have confidence in either one, therefore have
followed the consensus solution which runs a chance of showers and
thunderstorms for both Wednesday night and Thursday.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 645 AM CDT Fri Jun 23 2017

Good flying weather expected today and tonight, though
there could be a brief shower in the afternoon in central and
northern Wisconsin. An upper low pressure system will bring a
better chance of showers and thunderstorms Saturday, especially
during the afternoon and evening hours.
&&

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

$$

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



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