Area Forecast Discussion
Issued by NWS Green Bay, WI

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342
FXUS63 KGRB 192016
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
316 PM CDT Tue Sep 19 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Wednesday
Issued at 316 PM CDT Tue Sep 19 2017

A frontal boundary across the plains, combined with short wave
energy in amplifying mid level flow and the right entrance region
of an upper level jet will bring thunderstorms to the area mainly
Wednesday into the early part of the extended forecast. There
could be some showers and/or storms tonight, toward daybreak,
across central and north central Wisconsin.

The timing of the front will allow the atmosphere to become quite
unstable, with MUCAPE values greater than 2,000 J/kg at some
locations ahead of the front. Looking at the 12Z NAM on Bufkit,
there were 50 kt or stronger winds around 7kft at Wausau at 19Z
when WBZ heights are forecast to be around 10kft. SPC had a
marginal risk of severe storms for much of the area and that
seemed reasonable. Would not be too surprised if they upgrade to
slight risk with subsequent issuances for 12Z Wed - 12Z Thu.

Cooler temperatures are in store for north central Wisconsin
Wednesday due to clouds, rain and the front, but the rest of the
area should be warmer than today. Much of the forecast area will
see highs in the upper 70s and lower 80s.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 316 PM CDT Tue Sep 19 2017

The chance for showers and thunderstorms will continue Wednesday
night as a cold front sweeps through the western Great Lakes.
There is a marginal risk for severe weather during the evening
before instability wanes quickly after sunset. After a brief
period of dry weather on Thursday, a warm front will bring the
chance for additional showers and thunderstorms on Thursday night.

High pressure will then keep most of the region dry and hot to end
the week and into the weekend as 850 mb temperatures soar to
around +20 celsius as a large dome of mid level ridging settles in
across the Great Lakes. Daytime highs on Friday and Saturday will
rise into the middle to upper 80s, with 90 degree readings
possible. These temperatures will be a good 15 to 20 degrees above
normal for this time of year. The main exception to the dry
weather could be across the far north as a low pressure system
stalls over the upper Mississippi Valley.

This slow moving low will eventually be allowed to track east
during the early part of next week as the aforementioned high
slides east. This will bring cooler temperatures and the chance
for showers and thunderstorms to the western Great Lakes Monday
and next Tuesday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1236 PM CDT Tue Sep 19 2017

Most of the area was free of clouds at 17Z but MVFR ceilings
lingered in parts of eastern Wisconsin where light easterly winds
prevailed and dew points were mostly in the lower 60s. Visible
satellite imagery showed a decrease in the clouds over the east
so would expect VFR conditions by late afternoon or early
evening.

Models had IFR ceilings moving into central and north central
Wisconsin tonight in southeast surface flow. The rest of the area
should see some MVFR, and possibly IFR, fog overnight. Showers
will move into central and east central Wisconsin from the west
on Wednesday morning. Did not include thunder at this point, but
by later in the day there is plenty of instability ahead of an
approaching cold front so showers and thunderstorms will spread to
the east later in the afternoon.
&&

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

$$

SHORT TERM.....MG
LONG TERM......Kurimski
AVIATION.......MG



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