Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 170353
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1053 PM CDT Fri Jun 16 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 324 PM CDT Fri Jun 16 2017

Scattered severe storms possible across eastern counties through
the rest of the late afternoon hours with CAPE of 1100 to 1500
J/kg, inverted V soundings and some decent mid level winds. Other
storms further west are not as likely to be severe as instability
is not as strong.

Additional showers and thunderstorms likely later tonight as
upper jet energy arrives from the west. The activity should
generally end by daybreak. Locally heavy rain is possible, but
probably not enough areal coverage to add to high flowing rivers.
Lows tonight will be about 10 degrees above normal.

More thunderstorms possible Saturday, especially late in the day
as a short wave trof approaches from the northern and central
Plains. Severe threat may be limited by the late arrival of the
best upper support to Saturday night. Highs should be 5 to 7
degrees above normal.

.LONG TERM...Saturday Night Through Friday
Issued at 324 PM CDT Fri Jun 16 2017

Mean flow looks to be locked into place through the middle of next
week consisting of:  a broad upper ridge from the eastern Pacific
into the southwest CONUS, an upper ridge over the western Atlantic
and an upper trough situated roughly over the eastern third of
North America. This pattern would bring an active west-northwest
flow into WI with several systems to move through this flow to
bring precipitation chances to the area on a regular basis.
Temperatures are expected to go below normal early next week, then
rise closer to normal mid/late week.

Timing still looks good for a band of showers and thunderstorms to
sweep across northeast WI Saturday night as a surface cold front
(lift) interacts with a shortwave trough (forcing) and sufficient
moisture (dew points in the 50s and 60s). The stronger
instability, deep-layered shear and a mid-level jet max are
expected to be focused to our south, thus the severe risk now
looks marginal at best for central/east-central WI. We will still
need to watch these storms, as well as locally heavy rainfall
since several rivers/streams are still running high. Min
temperatures to be in the middle 50s north-central WI, upper 50s
central WI and lower 60s for eastern WI.

This trough to be situated over the Great Lakes region on Sunday
with northeast WI on the cool, cyclonic side of the trough. This
cooler air aloft, coupled with daytime heating, will steepen low
and mid-level lapse rates and bring at least a chance for showers
and perhaps a few afternoon thunderstorms to the area. Sunday will
see temperatures fall below normal under a blustery west-northwest
wind (sustained at 10-20 mph with higher gusts). Look for readings
to only reach the lower to middle 60s far north-central, to the
lower to middle 70s eastern WI.

Any instability shower activity will fade away Sunday evening upon
sunset, leaving partly to mostly cloudy skies for the rest of
Sunday night. Min temperatures will be more seasonal with readings
in the upper 40s to around 50 degrees north, lower 50s central/far
northeast WI and middle 50s east-central WI. Northeast WI remains
on the cyclonic side of the east-central North American trough on
Monday, however temperatures aloft are not quite as cool.
Therefore, with lapse rates not as steep, there should be less
coverage of showers across the forecast area. Max temperatures for
Monday to range from the middle 60s north-central, to the lower
70s eastern WI (away from Lake MI).

Diurnally driven showers will once again dissipate Monday evening,
however models show the next shortwave trough moving southeastward
toward WI late Monday night into Tuesday. There are some timing
discrepancies among the models favoring Monday night or Tuesday.
Prefer to focus the higher pops on Tuesday due to better
instability and the aid of a 110+ knot upper jet overhead. Max
temperatures for Tuesday are expected to be mainly in the 70-75
degree range.

This system quickly exits the region Tuesday evening, allowing for
a weak area of high pressure to move into the western Great Lakes
for Tuesday night into Wednesday morning. Expect skies to clear
and winds to diminish, thus Tuesday night appears to be the
coldest night of the extended period with lower to middle 40s
north-central, lower to middle 50s east-central WI. There is
another timing issue with the next upstream system as the GFS
already trying to send showers/thunderstorms into WI Wednesday
afternoon. Have sided with the slower ECMWF/CMC models and keep
northeast WI dry through Wednesday. Max temperatures by Wednesday
should be closer to normal as winds back to the southwest.

This next system does move across the region Wednesday night into
Thursday with the help of some WAA, so more showers/thunderstorms
will be needed in the forecast. The forecast gets more uncertain
headed into next Friday as timing of these systems becomes more
difficult. Have followed the model consensus and will continue the
trend of needing a small pop in the forecast until the mean flow
changes. Temperatures should remain close to normal through the
end of the work week.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1053 PM CDT Fri Jun 16 2017

Thunderstorms should be east of the TAF sites by issuances, with
just showers expected during the overnight hours. Mainly VFR
conditions are expected for the rest of tonight. Additional
showers and thunderstorms are possible Saturday and Saturday night
as a cold front pushes through the region.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......Kallas
AVIATION.......Kurimski



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