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000
FXUS63 KGRB 201113
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
613 AM CDT Tue Aug 20 2019

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 303 AM CDT Tue Aug 20 2019

Satellite imagery this morning, shows a couple of MCSs, one across
North Dakota into northern Minnesota and another across southern
Minnesota into Iowa. Radar, of course, shows a similar trend with
the North Dakota convection shifting to the east to east-southeast
this morning. Surface observations show that the storms over North
Dakota are developing along and ahead of the surface low and
associated cold front.

Today and tonight: A dry surface ridge will remain in place this
morning, keeping mainly dry conditions in place. During the
afternoon hours, a cold front will approach from the west as a
shortwave also slides through the area. Actually, it looks like the
cold front will approach central/north-central WI between 21Z/20 and
00Z/21. MU CAPE values ahead of the approaching front are progged to
be in the 1000-2000 J/kg range, while shear values along and ahead
of the front are expected to be in the 25 to 35 kt range. The
combination of the two could lead to a couple strong to isolated
severe thunderstorms. In fact, SPC has central into northwest WI
under a marginal risk for severe thunderstorms this afternoon, with
the main threats being hail and isolated strong wind gusts. This
area just brushes against the western portion of the CWA. The main
limiting factor in any severe potential will be the lack of overall
moisture and low-end conditionally stable low to mid-level lapse
rates. Additionally, convective cloud debris could lead to lower
instability values later this morning into the afternoon hours.
The combination of the aforementioned issues, will largely limit
overall coverage of any afternoon thunderstorms across the area.
Most of the HI- RES models continue to show very anemic convection
late this afternoon along and ahead of the front. As the front
shifts farther east during the evening hours, instability is
expected to steadily diminish with loss of daytime heating. This
will further limit shower and thunderstorm coverage and intensity
as the system passes through eastern/far northeastern WI.
Otherwise, daytime highs will be mainly in the 80s with overnight
lows in the 50s to low 60s.

Wednesday: A dry surface ridge and deep upper-level troughing will
slide across the area throughout the day. This will allow any
precipitation to end and temperatures to cool into the 70s across
much of the area. These temperatures will feel much more comfortable
as well, with afternoon dewpoints dropping into the 40s to low 50s
across the area.

.LONG TERM...Wednesday Night Through Monday
Issued at 303 AM CDT Tue Aug 20 2019

Dry and cooler than normal conditions are in store for the rest
of the work week, followed by a warming trend and chances for
showers and thunderstorms late in the weekend into early next
week.

Expect northerly flow at the surface and aloft as a surface low
and closed 500 mb move away from the region. This will bring
cooler temperatures to the forecast area. Friday night looks to be
the coldest period during this part of the forecast as a mid
level ridge and surface high pressure pass across Wisconsin. Lows
will be around 40 degrees at some locations near the Upper
Michigan border.

Return flow on the west side of the departing high, and a
transition to southwest flow aloft, will bring warmer temperatures
and increasing chances for rain to the area over the weekend.
There is a chance for thunderstorms across northern and parts of
central Wisconsin Sunday afternoon. Chances for storms will spread
across the rest of the area Sunday night and continue on Monday as
a surface system and a mid level short wave trough approach.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 613 AM CDT Tue Aug 20 2019

Some shallow ground fog will quickly dissipate at each of the TAF
sites this morning. A cold front will approach and then slide
through the area from northwest to southeast this afternoon into
this evening. Along and ahead of the front, there could be some
scattered showers and thunderstorms. This may briefly reduce
visibility at times and lower ceiling close to MVFR. RHI/CWA/AUW
may see some showers work into the area by mid to late morning as
an area of thunderstorms slowly diminish as they shift eastward.
&&

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

$$

SHORT TERM.....Cooley
LONG TERM......MG
AVIATION.......Cooley