Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 152101

Area Forecast Discussion
National Weather Service Green Bay WI
301 PM CST Thu Feb 15 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 301 PM CST Thu Feb 15 2018

Cold front moving across the region may be followed
by some snow showers of flurries tonight. No accumulation is
expected. Skies should clear late tonight as surface high pressure
moves in. Lows tonight and highs Friday will be near normal.

.LONG TERM...Friday Night Through Thursday
Issued at 301 PM CST Thu Feb 15 2018

Several forecast concerns/questions in the long term as a complex
weather pattern sets up across the region this weekend into early
next week. Models continue to show a pattern change from a zonal
flow this weekend, to a strong southwest flow early-mid next week
as deep trough digs over the western U.S.

As high pressure slides east of the Great Lakes Friday night, a
trough will be quick on its heals. Best dynamics associated with a
departing upper jet will be well southeast of the area, however,
sufficient forcing associated with the trough and approaching
upper jet should get an area of snow to spread across the area
very late Friday night into Saturday. Deep level moisture will be
lacking (precipitable waters only in the 0.20-0.30" range), plus
it might take awhile to saturate the atmosphere with plenty of dry
air overcome at the onset. Accumulations up to around an inch are
expected. As the snow exits from west to east on Saturday, dry
conditions are expected Saturday night as drier air and weak
subsidence pushes over the area.

Attention then turns to a series of low pressure
troughs/shortwaves that will bring a prolonged period of precip
to the area. The first arrives Sunday morning, focused across
northern WI. Increasing moisture, warm air advection, and
frontogenetic forcing looks to set up closer to the MI border. A
band of heavy snow will be possible where these features all come
together. A little too early to pin down exact placement, as ECMWF
shows the heavier snow just north of the area, while the GEM and
GFS have the band near the MI/WI border.

The forecast becomes very complicated as we head into Sunday
night and Monday, with models in poor agreement regarding
specifics on trough/low/shortwave timing/location, location of
baroclinic zone, and temps at the surface and aloft. This creates
a low confidence forecast with lots of details still to pin down.
GFS is the coldest/snowiest, with ECMWF a little warmer, and the
GEM the warmest. Models differ by up to 7C to 10C at the surface
and aloft, which is a major forecast challenge as precip type
could range from all snow, to a mix, to even a period of rain
mixing in near the Fox Valley and lakeshore. Bottom line, a
wintry mess is on the way for the entire area, with heavy snow,
mixed precip, and some icing all possible, but exactly what precip
type combo will occur is still up in the air. To add more
uncertainty into the forecast, the models do not agree on if a
secondary low pressure system will cross the area on Tuesday. This
could bring additional wintry precip into the area. It should be
noted where the precip stays all snow, over a foot of snow will be
possible, likely occurring in up to 3 rounds of snow.

High pressure builds into the western Great Lakes behind this
system for the middle of next week, bringing quiet conditions with
temps near or slightly below normal.

.AVIATION...for 18Z TAF Issuance
Issued at 1135 AM CST Thu Feb 15 2018

A cold front will bring VFR/MVFR clouds as it moves
across the area this afternoon. Some snow flurries are expected
behind the front tonight, with BKN to OVC ceilings between 2500
and 3500 feet. The clouds should exit the area by 12z Friday, with
good flying weather Friday through Friday night.



LONG TERM......Bersch
AVIATION.......RDM is the U.S. government's official web portal to all federal, state and local government web resources and services.