Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 251558
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1058 AM CDT Sat Mar 25 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 420 AM CDT Sat Mar 25 2017

Cloudy, chilly, and wet weather for the weekend, then a little
warmer next week.

The large scale pattern across North America will be dominated by
split flow during the period. A series of southern stream upper
level cyclones will slowly cross the country. The first will
continue to bring wet weather to the area for the rest of the
weekend. A second will pass south of the area early next week. A
third appears likely to bring precipitation to the area late in
the week and into next weekend. Clouds, precipitation, and
northeast winds will keep temperatures cool the next couple days.
Readings should warm to near or a little above normal for the
upcoming work week. Precipitation amounts are likely to end up
above normal, especially across the southern part of the forecast
area which will be closer to the southern stream storm track.
&&

.SHORT TERM...Today...Tonight...and Sunday
Issued at 420 AM CDT Sat Mar 25 2017

Aligning PoPs and determining precipitation type tonight were the
main forecast challenges this morning. The main rain band has now
shifted south, even more so than expected yesterday. It will
shift back north as the upper low from the Plains edges closer,
but models differed on how quickly that would happen. Trended
forecast strongly toward the ECMWF which usually verifies well
with this type of system.

The toughest part of the forecast was determining precipitation
type tonight. On one hand, dry air was just to the northeast of
the area. Surface dew points northeast of Lake Superior were in
the single digits early this morning, and the low clouds in that
area were being scoured out. A continuous feed of that air into
northeast Wisconsin today and tonight favors evaporational
cooling once the precipitation returns, which could easily take
temperatures below freezing over the northeast part of the
forecast area. On the other hand, there will be thick overcast
and temperatures have not been falling as much as expected at
night. Readings barely dropped to freezing last night (though
roads over the north did ice-up from the precipitation that fell
then). Raised mins for tonight a little above the broad-based
blend of guidance products to account for the recent cool bias.
But precipitation type will still come down to a degree or two one
way or the other in temperatures, so opted to go with a mention
of both R/ZR in the forecast. Confidence was just not high enough
to post an advisory with the morning issuance, but will issue an
SPS detailing the threat of getting some icing of roads over the
northeast tonight. It will be up to the day shift will need to
make a final decision on an advisory. They will also have the
benefit of seeing just how much dew points drop as the drier air
starts to filter in from the northeast.

The upper system will pass just southeast of the area Sunday.
But with the system weakening, expect precipitation to gradually
become more scattered with time.

.LONG TERM...Sunday Night Through Friday
Issued at 420 AM CDT Sat Mar 25 2017

00Z models were not as consistent as one would like during this
part of the forecast. Finer details are different but the general
consensus is that PoPs decrease Sunday night through Monday as an
upper system and surface low depart. Precipitation type is a
concern in north central Wisconsin again on Sunday night as
temperatures there fall into the 29 to 32 degree range. Freezing
rain was included Sunday night for this reason.

There were significant differences in the forecast strength
and track of a system that is expected to pass to the south of
Wisconsin Monday/Monday night but its associated QPF should
remain south of the forecast area.

A surface ridge and building upper ridge should help to keep the
area dry from Monday night into Wednesday evening. After that, a
system developing over the southwest CONUS approaches the Great
Lakes, but models showed large differences in the track of the
system. The model blend had a chance for precipitation in the
area from late Wednesday night through Friday, with snow and/or
rain at night and rain during the day.

Near or above normal temperatures are expected through the end of
the forecast.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1054 AM CDT Sat Mar 25 2017

Ceilings are rising to mvfr at most location at midday, where they
should remain through the end of the afternoon. But ceilings and
visibilities will trend down again tonight as the rain shifts
back north over the area. Some icing possible over far northern
WI, including RHI, late tonight.

&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MG
AVIATION.......MPC


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