Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 252007

Area Forecast Discussion
National Weather Service Green Bay WI
307 PM CDT Fri May 25 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Saturday
Issued at 307 PM CDT Fri May 25 2018

Threat of severe thunderstorms through early this evening and
again tomorrow afternoon, and fog potential overnight, are the
main forecast concerns.

A cold front extended from near Duluth into south central MN. In
addition, the ill-defined remnants of an old outflow boundary was
situated over parts of central and north central WI. In between
these boundaries, daytime heating was resulting in strong
instability, with SBCAPE of 2000-3000 j/kg. Deep layer shear was
fairly weak, only about 20 knots. Scattered thunderstorms were
developing in eastern MN and western WI, and heading east toward
the forecast area. SPC has issued a severe thunderstorm watch for
Lincoln, Marathon, Wood and Portage counties through 8 pm.

Given the weak deep layer shear, storms are not likely to become
very organized late this afternoon and early evening, with
clusters of multi-cells the expected convective mode. The
strongest instability will reside over our southwest counties
through sunset, so the placement and timing of the watch looks
good. Lingering convection should drift east and dissipate during
the mid to late evening, and exit the region by midnight. Partly
cloudy skies, decreasing surface and boundary layer winds and
low-level moisture from the afternoon/evening rains should lead
to fog development overnight into early Saturday. Locally dense
fog is possible in parts of north central and central WI, where a
weak surface ridge will reside late tonight. Lows will be in the
upper 50s to mid 60s.

After a fairly quiet morning on Saturday, a short-wave trof will
generate scattered thunderstorms across northeast WI during the
afternoon. The storms will be most prevalent near a boundary over
far northeast WI, where CAPE may be as high as 1500-2000 j/kg.
Deep layer shear will be a bit stronger than today, around 25 to
35 knots, so there is potential for a few strong to severe
thunderstorms. SPC has upgraded northeast WI to a Marginal risk,
which seems like a good move. High temperatures will be toasty, in
the mid 80s to lower 90s.

.LONG TERM...Saturday Night Through Friday
Issued at 307 PM CDT Fri May 25 2018

Chances for storms are the main concern during this part of the
forecast. Temperatures will be much warmer than normal through the
end of the period as an upper ridge moves into and across
Wisconsin. Highs in the 90s are expected for at least part of the
area through Monday, with mainly lower to middle 80s Tuesday
through Friday. Temperatures will be cooler near Lake Michigan.

Some showers and storms may linger into Saturday evening as an
upper trough departs. There is a chance for more showers and
storms Monday evening, mostly in the north near an approaching
front. Other than that, mainly slight chance PoPs into Wednesday
morning. Chances for showers and storms return Wednesday afternoon
and continue through Thursday ahead of a cold front and upper
trough. Drier and a bit cooler conditions are in store for Friday.

.AVIATION...for 18Z TAF Issuance
Issued at 1234 PM CDT Fri May 25 2018

Isolated/scattered thunderstorms were developing over western WI
early this afternoon, and should become more numerous as
instability increases and an upper disturbance approaches later
in the day. Though a few storms may impact the RHI/AUW/CWA TAF
sites early in the TAF period, the main bulk of the convective
activity should occur from 21z/Fri-02z/Sat. After the storms move
through, attention turns to fog potential overnight. Partial
clearing, decreasing surface and boundary layer winds, and
abundant low-level moisture from earlier rains should allow areas
of fog to develop. The fog should be most extensive over north
central and central WI, where a weak ridge of high pressure will
reside late tonight.

The fog should dissipate by 13z-14z/Sat, followed by partly cloudy
skies. Additional thunderstorm activity is anticipated Saturday
afternoon, especially over northeast WI.



SHORT TERM.....Kieckbusch
AVIATION.......Kieckbusch is the U.S. government's official web portal to all federal, state and local government web resources and services.