Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 210329
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1029 PM CDT Fri Apr 20 2018

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 302 PM CDT Fri Apr 20 2018

Will be leaning heavily on persistence for the forecast through
Saturday, as little change in air mass is anticipated.

An increase in high clouds should keep low temperatures 3 to 5
degrees warmer than last night. Have opted to leave any mention of
fog out of the forecast, despite the surface high residing over
the region. Just like yesterday, dew points crashed into the
single digits and teens over most of the area this afternoon,
despite significant snow melt. Given the degree of dryness, and
the presence of high clouds overhead, fog development appears
unlikely overnight.

High clouds should thin out during the mid to late morning
Saturday, followed by plenty of sunshine. Mixing through 850-800
mb will support high temperatures in the middle 50s to around 60,
except upper 40s and lower 50s near Lake Michigan. These readings
should be very similar to today.

.LONG TERM...Saturday Night Through Friday
Issued at 302 PM CDT Fri Apr 20 2018

Warmer temperatures causing the snowpack to continue melting will
be the main concern for the long term. The next chance for
precipitation arrives Tuesday evening with a shortwave trough and
its associated cold front.

For the start of the period through Sunday night, a split upper
level flow occurs across the Central Plains with the Upper
Mississippi Valley remaining in the ridge of high pressure, while
a more aggressive low pressure system travel across the Lower
Mississippi Valley. While the ridge of high pressure remains
dominate over Wisconsin on Sunday, expect slightly warmer
temperatures with mostly sunny skies.

By Monday morning, the ridge almost completely exits Wisconsin
due to the zonal flow strengthening to the north. Temperatures for
Monday could reach to the lower 60s for almost the entire CWA,
excluding the lakeshore counties, impacting the snow melt even
more. The zonal flow continues to the north of Wisconsin Monday
through Tuesday morning before the shortwave trough makes its
appearance Tuesday night. There is much uncertainty amongst model
guidance with the shortwave trough. The 12z ECMWF shows a phasing
problem with the shortwave as a disturbance splits off staying to
the southwest of Wisconsin and a wave of energy advancing faster
to the north dropping some precipitation over the region Tuesday
night. GFS is a bit more aggressive with the shortwave trough
allowing a closed low to form across southwest Wisconsin. It also
appears to be overestimating liquid precipitation values compared
to the other models. A blend of the models was chosen with chance
pops through Wednesday afternoon as the shortwave trough exits
the region.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1029 PM CDT Fri Apr 20 2018

High level clouds will pass over the region through Saturday
morning, with skies clearing out later in the morning into the
afternoon hours. Otherwise VFR conditions should prevail at most
locations through the TAF period. Given the dry air and low dew
points currently in place will continue to leave fog out of the
TAFs during the overnight hours.
&&

.HYDROLOGY...
Issued at 302 PM CDT Fri Apr 20 2018

Warming temperatures are expected to produce significant melting
of the current snowpack over northeast WI. This will lead to
runoff and a gradual rise of area rivers and streams. Several
rivers are expected to surpass bankfull this weekend and possibly
flood stage as early as Monday evening for the Wolf River basin.
People living near rivers and streams should keep a close eye on
the anticipated river rises and keep up to date on the latest
river forecasts.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Hykin
AVIATION.......Kurimski
HYDROLOGY......Hykin



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