Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 121001
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
401 AM CST Thu Jan 12 2017

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 355 AM CST Thu Jan 12 2017

Another round of light snow over the far southeast part of the
area this morning, then a blast of arctic air for tonight and
Friday. Wintry precipitation increasingly likely early next week.

The persistent block over the northeast Pacific will break down
during the period as the positive upper height anomaly from the
block migrates westward into northeast Asia and weakens. The
pattern will then evolve toward having a large, strong negative
anomaly center near Alaska, with a positive center over eastern
Canada. The long wavelength between the features favors splitting
of the flow, which is what is shown by most of the models for next
week.

Another blast of arctic air will take temperatures well below
normal early in the period, then readings will moderate back close
to normal for the weekend, and to significantly above normal for
next week. Disturbances riding along the strong baroclinic zone
currently draped over the area will bring a couple more rounds of
snow the next few days, though amounts will be more modest than
with the last few systems. Some energy ejecting out of the
developing southern stream will probably bring a round of wintry
precipitation early next week, with amounts for the week depending
largely on what falls with this system.
&&

.SHORT TERM...Today...Tonight...and Friday
Issued at 355 AM CST Thu Jan 12 2017

Another disturbance riding northeast within the strong baroclinic
zone across the region will generate a band of snow this morning.
Models were pretty consistent in bringing the snow through east-
central Wisconsin in the 11Z-16Z time frame. The latest radar
mosaic loop suggests the band may track a little farther south
than depicted by the models. Forecast went out with best guess for
PoPs, but that may need refinement based on how the band evolves
during the next few hours. Forcing is higher up in the atmosphere
and not as strong as with yesterdays bands, so amounts will be
more modest (expecting 1-2 inches over the far SE part of the
area).

The next feature of consequence with be intense upper disturbance
forecast to pass by to the north late today. Cold front trailing
from attendant cyclone will probably begin to wash out as it
nears the area, but it will still mark the leading edge of a fresh
arctic air mass that has surged south across Canada from high
latitudes very quickly. Expect some clouds and flurries to
accompany the front. Gusty winds behind the front will likely lead
to some blowing and drifting of the fresh snow across the area,
especially since the top layer is a light fluffy snow.

Wind Chill indices in new forecast reach advisory criteria across
the west late tonight and early Friday. But winds will be
decreasing rapidly during that time, and could fall below the
advisory threshold. Given the uncertainty, opted to hold off
issuing an advisory with this morning`s forecast. This will
provide the day shift the maximum flexibility when making the
final decision on a possible headline.

.LONG TERM...Friday Night Through Wednesday
Issued at 355 AM CST Thu Jan 12 2017

A gradual moderation in temperatures is expected over the weekend
with above normal temperatures expected through much of next week.
A weak disturbance will move across the state Friday night. This
system could bring a band of light snow to portions of central and
east-central Wisconsin Friday evening into early Saturday morning.
Could see up to an inch south of highway 29. Low temperatures
Friday night should fall into the single digits below zero north
and single digits above zero south and lakeshore.

Otherwise, a tranquil weekend is expected as high temperatures
return into the 20s each day. The next weather maker is expected
to move toward the region from the southwest on Sunday. Many
complications to the forecast Monday into Tuesday. First one is
the ECMWF brings the first band of precipitation into the area
late Sunday night and Monday with a lull in the precipitation
later Monday night into Tuesday morning, with the next surge of
precipitation into Tuesday afternoon and evening. Meanwhile, the
gfs brings the main system across the region Monday night into
Tuesday morning with precipitation tapering off Tuesday afternoon.
The Canadian model was similar to the GFS model. This is the first
complication.

Clouds will be on the increase Sunday night with light precipitation
possibly making it into portions of central and east-central
Wisconsin by sunrise. Air and pavements temperatures are the
second complication to the forecast. Precipitation type still an
issue with more snow at the onset, although if precipitation is
light enough could still be in the form of freezing rain or sleet.
The warmer air at 850mb flows northward on Monday with 850mb
several degrees above freezing across central and northeast
Wisconsin. Again, there are some significant differences between
the GFS/ECMWF and Canadian models with respect to how far north
the warm air will make it. At the surface, expecting a cold start
to the morning although temperatures should be slowly rising late
Sunday night into Monday morning. Also, pavement temperatures are
expected to be well below freezing across the entire area Monday
morning. Any liquid precipitation will freeze on untreated roads,
bridges and sidewalks across the entire area.

Across the Fox Valley and lakeshore, easterly winds off the relatively
warmer waters of Lake Michigan should help temperatures rise above
freezing Monday afternoon. Precipitation should be all liquid by
mid morning on Monday. However, there is still concern for slick
spots as pavement temperatures will be slower to respond and may
not rise above freezing until the afternoon or evening hours. Now
for areas just north and west of the Fox Valley, 850mb temperatures
should support liquid precipitation by late Monday morning.
However, surface and road temperatures will be below freezing for
much of Monday. This is the region of most concern for ice
accumulations. Across the far north, some differences in the
models for a mix of rain, sleet, freezing rain or snow.

The differences will linger into Tuesday, especially north and
west of the Fox Valley. Expect mainly rain for the most part
from the Fox Valley and lakeshore region. On Tuesday, temperatures
north and west of the Fox Valley will climb a few degrees above
freezing, however pavement temperatures may still be below
freezing to cause any rain to freeze on untreated surfaces.
Later shifts will be able to fine tune the details.

Only a small chance for rain or snow on Wednesday as highs are
expected to be in the 30s.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 355 AM CST Thu Jan 12 2017

Outside of a relatively short period of MVFR and perhaps some IFR
conditions with the snow band expected to affect east-central
Wisconsin this morning, VFR conditions are expected. Additional
concerns for aviation interests will be gusty surface winds late
tonight into tonight, and the potential for blowing and drifting
snow to affect airports. The blowing snow will probably not
seriously impact the visibility, but snow drifting onto runways
may require removal.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......Skowronski



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