Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211938
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
238 PM CDT Fri Apr 21 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Saturday
Issued at 235 PM CDT Fri Apr 21 2017

Main forecast concern to be on temperatures over the next 24 hours
as precipitation chances have finally disappeared from the
forecast. There are minor concerns regarding fog potential late
tonight and depth of dry air for low relative humidities on
Saturday.

The 19z MSAS surface analysis indicated an area of low pressure
responsible for yesterday`s rainfall, now over southwest Quebec.
An area of high pressure was centered over North Dakota. The
pressure gradient was still somewhat tight across WI this
afternoon with gusts in the 20 to 30 mph range. Visible satellite
imagery showed more sunshine over central WI, while a scattered
cu field remained over eastern WI.

The high pressure is forecast to stretch from the northern Plains
to the western Great Lakes tonight and bring mainly clear skies
with light winds to northeast WI. There is some concern with fog
later tonight due to saturated grounds from earlier heavy rainfall
on Wednesday night. However, there appears to be enough dry air
advecting into the region to prevent fog from becoming a problem.
Another concern will be the temperatures as good radiational
cooling conditions to exist and allow readings to drop into the
20s north/parts of central WI, lower to middle 30s south. Even
though the growing season has not officially started yet, anyone
with new plants or vegetation may want to either move or protect
them tonight.

This broad area of high pressure is forecast to extend from the
central Plains northeast into the Great Lakes and remain the main
weather feature across northeast WI. The air mass is progged to be
dry on Saturday and with deep mixing expected, afternoon relative
humidities are forecast to drop into the 20 to 35 percent range
(away from the lake and bay). Fortunately, winds should be under
10 mph with the surface high overhead, thus fire weather
conditions will not be critical. Plenty of sunshine, coupled with
the dry air mass, will allow temperatures to quickly recover with
readings in the middle 50s lakeside, generally lower to middle 60s
elsewhere.

.LONG TERM...Saturday Night Through Friday
Issued at 235 PM CDT Fri Apr 21 2017

Confidence is good that the long term forecast will start out dry,
with a couple stray chances for light pcpn in the north this
weekend. Models also in decent agreement with a system that tracks
north of Wisconsin on Tuesday. Difference arise late in the week
(Thursday/Friday) when another system is progged to move into the
region.

Surface high pressure will still be in control Saturday evening,
with an area of low pressure far to the north over the Hudson Bay.
A frontal boundary extending southwest from this low will become
quasi- stationary near the northern Wisconsin border on Sunday.
This may lead to a few stray showers or drizzle across far
northern Wisconsin from Sunday morning through Monday morning
before the front moves north again. Any pcpn would be light with
little accumulation. Mainly expecting rain, but a rain/snow mix
near the Michigan border is possible as temperatures cool late in
the night. More clouds are expected Sunday, especially in the
north near the frontal boundary. This will also mean a cooler day
with highs in the upper 40s in far northern Wisconsin. Highs will
still be in the low to middle 60s in central Wisconsin and the
Fox Valley.

A better chance of rain moves across the entire area beginning
Monday night. Models in good agreement that a sfc and
corresponding 850mb low will move from eastern South Dakota
towards central Lake Superior on Tuesday. This would bring the
sfc cold front through the area around midday Tuesday.
Some weaker WAA and frontogenesis ahead of this system would
suggest the chance for showers throughout Tuesday morning, with a
second opportunity for showers Tuesday afternoon through Wednesday
morning as a mid-level shortwave and upper level jet streak
follow behind the sfc low. Rain will be the main pcpn type, with
a few snow showers or a rain/snow mix possible in northern
Wisconsin as temperatures cool late Tuesday night.

Models are now in decent agreement that an upper level ridge will
be in place Wednesday afternoon through Thursday morning. This
will keep conditions dry. Models diverge from this point, but GFS,
ECMWF, and Canadian all indicate a stronger system will track
across the Upper Midwest during the Thursday night/Friday time
frame with a deep trough forming to the west. It`s still early,
but may need to add a thunder chance to this period as well. Kept
with a blended model solution for now which features rain showers
through this period.

Temperatures are trending within normal for the next week and
will vary slightly based on the rainy/cloudy times and the clear
times.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1218 PM CDT Fri Apr 21 2017

Low-end VFR cumulus field over eastern WI should gradually
scatter out this afternoon as drier air from the west advects into
that part of the state. Otherwise, VFR conditions to prevail for
tonight into Saturday as a broad area of high pressure moves
across the Great Lakes region. As the high pressure slides to our
east Saturday afternoon, light/variable winds will become more
west-southwest, but remain under 10 knots. Saturday looks to be
a great day for flying!.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......KLB
AVIATION.......AK



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