Area Forecast Discussion
Issued by NWS Green Bay, WI

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341
FXUS63 KGRB 302021
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
321 PM CDT SAT JUL 30 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 321 PM CDT Sat Jul 30 2016

A surface ridge, from high pressure centered over Ontario, is
expected to remain across the forecast area through Sunday and
weak upper level flow is forecast.

A few small, light showers developed in central and western
Wisconsin this afternoon where surface to 1.5 C/km lapse rates
increased into the 9 to 9.5 range. CAPE values there ranged from 100
to 500 j/kg with little or no CIN. Based on these factors it
would seem likely that any showers and/or storms would end with
the loss of daytime heating. So, the tonight period of the
forecast has been kept dry. Light surface winds and the lack of
significant cloud-cover will lead to at least patchy fog
overnight. Cannot rule out areas of dense fog but have not
mentioned included it at this point.

QPF fields looked quite different among the 12Z models, but all
have small areas of QPF in or around the forecast area. Think
keeping the forecast dry rather than going with slight chances for
the entire area would be the best way to go at this point, but do
not have great confidence in this solution.

Used a blend of the best performing guidance, ADJECS, and the
previous forecast for tonight`s lows and Sunday`s highs.

.LONG TERM...Sunday Night Through Saturday
Issued at 321 PM CDT Sat Jul 30 2016

Wisconsin will be on the southern edge of the
westerlies much of next week, which makes the timing of fronts
and precipitation somewhat difficult.

As the upper flow transitions to zonal a shortwave trough
approaches Monday night which produces a southerly low level jet
which should generate some showers and thunderstorms north of a
warm front. A weak cold front is forecast to arrive Tuesday but
models are not in agreement in how quickly it moves through and
where it stalls out. Monday and Tuesday should warmer and more
humid but not nearly as much as Wednesday and Thursday might be.

A strong upper system approaches Thursday with an associated cold
front and potential for thunderstorms. That front looks sufficiently
strong to move through and bring a few dry days behind it. Friday
and Saturday look to be less warm and humid than the middle of the
week, but still several degrees above usual for this time of the
year.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1244 PM CDT Sat Jul 30 2016

VFR conditions should persist for the rest of the day, with SCT-
BKN035-040 clouds this afternoon, mainly in central and northern
Wisconsin. Thunderstorm development cannot be ruled out just
outside, or on the fringes of, the forecast area this afternoon
due to a weak mid level trough over Wisconsin and midday heating.
Most of the clouds should dissipate around sunset, and surface
winds will be light with high pressure over the state. This brings
up the question of fog tonight into early Sunday. Have generally
left the fog forecast alone, keeping it confined to the AUW, CWA
and RHI TAFs since they tend to be the most fog-prone of the TAF
sites. VFR conditions are expected to prevail by late Sunday
morning.
&&

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

$$

SHORT TERM.....MG
LONG TERM......RDM
AVIATION.......MG



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