Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 102335

Area Forecast Discussion
National Weather Service Green Bay WI
535 PM CST Sun Dec 10 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 310 PM CST Sun Dec 10 2017

Precipitation chances and amounts associated with an approaching
clipper system are the main concerns in the short term.

Lake effect snow showers and flurries should come to an end this
evening as winds back and direction becomes unfavorable for lake
effect in the forecast area.

A surface low pressure system and mid level trough in the
Canadian Plains will approach Wisconsin tonight and move through
the state during the day on Monday. Warm advection ahead of the
low will bring snow into the area late tonight and during the day
on Monday, with the majority of the snow falling between midnight
and noon. Looks like most locations will pick up between 1 and 3
inches of snow from this system. Green Bay and the Fox Valley are
likely to see the heaviest snowfall as many head to work or
school. Will forgo an advisory for now, but the evening shift may
want to issue pending analysis of data from 00Z model runs. Snow
should wind down Monday afternoon, but lake effect is expected to
continue in the Lake Superior snowbelt.

Lows tonight will range from around 10 degrees to near 20. Highs
on Monday should be in the lower 20s to lower 30s.

.LONG TERM...Monday Night Through Sunday
Issued at 310 PM CST Sun Dec 10 2017

High amplitude flow with a strong ridge over the western Conus
and deep cold trough over the eastern states will keep the forecast
area in the cold northwest flow regime this week, resulting in a
series of clipper type systems passing over. Track and timing of
these clippers will be the primary challenge.

An early week clipper system will be departing Monday night,
leaving the area in a cold air advection pattern, and increasing lake
effect snow potential across the far north. Northwest trajectory
indicates lake effect snow showers will persist into much of
Tuesday before a ridge of high pressure approaches from the west
toward Tuesday night.

What clearing occurs Tuesday night with surface ridge may be
brief as another clipper system drops in toward mid week. The GFS
prog is looking similar to the early week system, but the ECMWF is
a bit further southwest. More cold air pours into the area behind
this system for the lake effect snows to start up again across
the far north.

Upper pattern begins to change late in the week and into the
weekend toward a more zonal flow with moderating temperatures.
Another northern stream system or clipper type system is progged
to drop into the area next weekend. The warmer boundary layer temps
suggests the potential of a mix variety.

.AVIATION...for 00Z TAF Issuance
Issued at 531 PM CST Sun Dec 10 2017

Another fast moving storm system dropping southeast from Canada
will sweep through the area late tonight and Monday. Lake-effect
snow showers and flurries over the north should end this evening
as low-level flow backs. Snow from the incoming storm system
should spread across the area after midnight, reaching the
lakeshore by about 10-11Z. Anticipate IFR conditions due to
reduced visibilities as the snow moves through. Low ceilings in
the wake of the main snow band will maintain IFR or low-end VFR



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