Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 202240
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
540 PM CDT Thu Jul 20 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 250 PM CDT Thu Jul 20 2017

Drier air moving into the area from the west will
keep dry weather in the forecast through at least midday Friday.
Some ground fog possible later tonight with clear skies and light
winds. Lows will be around five degrees above normal in most
places.

Upper jet energy and a surface front will be approaching Friday
afternoon. Drier air in the northeast part of the forecast area
may hold off precipitation until late afternoon or early evening.
While severe potential is not zero, the best upper support and low
level moisture and convergence arrives a little later in the day,
so thunderstorms with strong winds and heavy rain appear more
likely during the evening hours.

.LONG TERM...Friday Night Through Thursday
Issued at 250 PM CDT Thu Jul 20 2017

Focus on this forecast revolves around thunderstorm chances and
potential for severe weather on Friday night into Saturday.

Friday night through Sunday...Ahead of low pressure over the Plains,
a strengthening low level jet and upper divergence in the right rear
quad of a jet streak are expected to produce another thunderstorm
complex somewhere over southern Minnesota to western Wisconsin on
Friday evening. This thunderstorm complex is then expected to track
southeast across central and southern parts of the state.  Models
appear more aggressive in surging the elevated instability into
northern WI than yesterdays runs, but wonder if they remain too
aggressive based on the convective trends from yesterday. As a
result, think SPC`s focus for severe weather south of the area
summarizes the severe weather threat well.  Being on the northern
fringes, isolated severe thunderstorms and heavy rainfall appear
possible, mainly for central to east-central WI.  Some showers are
expected to stick around for Saturday morning, mostly for eastern
WI.  Then focus will shift towards northern WI for late in the
afternoon and evening when a potent shortwave trough approaches from
the northwest.  If morning clouds do not hold back the heating
curve, scattered thunderstorms are expected to redevelop during peak
heating.  Some storms could turn severe given the 0-6km bulk shear
values greater than 40 kts. The severe threat should diminish by
late in the evening as instability wanes.  Then scattered showers
and isolated storms could linger through the rest of Saturday night
into Sunday with the upper troughing overhead.  No significant
changes to temps.

Rest of the forecast...Quiet conditions will then move into the
region on Sunday night through Tuesday night as high pressure moves
across the area.  As the high departs and southwest flow returns,
will see thunderstorm chances ramp up on Wednesday through Thursday
of next week.  Temperatures will be going on a warming trend from
the low to mid 70s on Monday into the 80s by Wednesday and Thursday.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 540 PM CDT Thu Jul 20 2017

Good flying weather through the evening hours, with
scattered clouds between 3000 and 5000 feet and some mid clouds
above. Some ground fog is possible after 08z tonight, especially
where it has rained recently, and near lakes. A few places could
have IFR conditions for a few hours before sunrise. Good flying
weather for awhile Friday, but showers and thunderstorms are
possible later in the afternoon, especially over the western TAF
sites. Therefore went with higher chances for thunderstorms out to
the west as a tempo group, with prob30 groups farther east and
north where arrival is less certain.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......MPC
AVIATION.......Kurimski



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