Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211923
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
223 PM CDT THU JUL 21 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 223 PM CDT Thu Jul 21 2016

The latest Rap analysis and satellite/radar imagery show this
mornings thunderstorm complex continuing to drop southeast over
lower Michigan early this afternoon.  Meanwhile, storms are
redeveloping over western Wisconsin and central Minnesota ahead of a
weak cold front.  ML capes upwards of 2000 j/kg are building again
over western Wisconsin though ML cins remain quite high.  Some
storms may also be elevated, where cins are reduced.  As the
atmosphere recovers with some sunshine over central and eastern
portions of the state this afternoon, potential for these storms to
survive as they move east but think that north-central WI is mostly
out of the woods when it comes to thunderstorm development. Though
unlikely because of the turned-over atmosphere, an isolated severe
storm cannot be ruled out. Precip trends and temps are the main
forecast concerns in the short-term.

Tonight...The cold front will move south across central and
northeast Wisconsin during the evening hours, and clear east-central
WI overnight.  The threat of thunderstorms will continue over mainly
central and east-central WI until the front exits late tonight.
Though the severe threat should be waning during the evening, still
cannot rule out an isolated severe threat for the first half of the
evening.  Drier air will be moving in behind the front, which will
limit fog potential despite the relatively humid airmass in place
and recent rainfall.  Will back off on the fog mention across the
north, but leave a patchy mention over central and east-central WI
where the front will exit late.  Lows ranging from the middle 60s
north to middle 70s south.

Friday...The weak cold front will settle over southern Wisconsin
during the morning hours.  Though the area will be on the north side
of the front, the airmass will not be much colder than todays.  The
difference will be felt in the humidity levels due to lower
dewpoints in place.  Under sunny conditions, temps will rise into
the upper 80s to a few mid 90s.  Heat indices will range from the
mid to upper 90s, which is not quite hot enough for a heat advisory.

.LONG TERM...Friday Night Through Thursday
Issued at 223 PM CDT Thu Jul 21 2016

Zonal flow will prevail across the Great Lakes from this weekend
out through much of next week. Surface high pressure will keep the
weather dry for the first part of the weekend as a mid level
trough and associated shortwave track across the international
border. This system is forecast to track through the western Great
Lakes Saturday night, however showers and thunderstorms cannot be
ruled out Saturday afternoon as the leading edge of the shortwave
taps into a narrow ribbon of around 1000 J/kg of MUCAPE. The best
chance for storms looks to be Saturday night when a cold front
pushes towards the western Great Lakes and the main trough tracks
through the area. Given the instability and shear it appears some
of the storms will be strong, with a few possibly severe. Some
lingering activity is possible with and behind the cold front on
Sunday.

The next best chance for rain will be later in the week on
Wednesday and Thursday as another mid level shortwave tracks
through the Great Lakes region. The timing and strength of this
feature is difficult to pindown given the model differences,
therefore the blanket chance pops are warranted this far out.

Temperatures this weekend ahead of the cold front will be quite
warm, with highs returning to near normal levels by the start of
the work week behind the cold front.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1157 AM CDT Thu Jul 21 2016

A large thunderstorm complex has exited the taf sites at midday, but
additional storms are developing over central Minnesota and western
Wisconsin.  Some of these storms may push across central and east-
central WI later this afternoon or early this evening, if they
survive the trip.  The airmass will be more stable to the east after
this mornings storms, so confidence is low enough on timing and
coverage to leave out of the taf forecast for now.

Then a cold front will drop through the region this evening into
early overnight.  This may be a tad sooner than what was expected
earlier.  Dewpoints will be dropping behind the front, which will
limit fog potential despite the rainfall and muggy airmass in place.
Based on these facts and the recent statistical guidance, have
backed off fog formation over central and north-central WI.  East-
central will still have potential for lower vsbys/cigs in fog late
tonight, since the passage will be later in the night that other taf
sites. Once any fog burns off, vfr conditions to resume on Friday
morning.
&&

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

$$

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



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