Area Forecast Discussion
Issued by NWS Green Bay, WI
FXUS63 KGRB 210408 AAA
Area Forecast Discussion...UPDATED
National Weather Service Green Bay WI
1008 PM CST Fri Jan 20 2017
Updated aviation portion for 06Z TAF issuance
.SHORT TERM...Tonight and Saturday
Issued at 318 PM CST Fri Jan 20 2017
Fog trends, precipitation trends and type, and temperatures will
be the main forecast concerns.
A band of mixed rain, snow and sleet will continue to lift north
across the region as a short-wave trof pivots through. The mixed
pcpn should end across the far north by around 02z. Overnight,
saturation through about 800 mb suggests the potential for mainly
drizzle, especially as the next short-wave approaches late
tonight. Although air/road temps will be above freezing across
most of the region, parts of north central and far northeast WI
will likely have air/road temperatures slightly below freezing for
a while late tonight into Saturday morning. This will result in
patchy freezing drizzle, but probably not enough to warrant a
headline at this time. Fog conditions are not too bad right now
according to observations/web cams, though there is some dense
fog over Door county and patchy dense fog over the rest of the
lakeshore counties and Fox Valley. Decided to reissue a dense fog
advisory for Door county, and let the evening shift determine if
additional counties need to be added this evening. Meso-model vsby
forecasts suggest that the advisory may need to be expanded over
most of the forecast area this evening.
On Saturday, an upper low/trof will shift northeast across the
state, with the best forcing pushing through our western counties.
Have boosted pops to likely over north central and central WI. Aside
from the previously-mentioned threat of freezing rain in our
northwest counties in the morning, rain will be the primary pcpn
type, as temps slowly climb into the upper 30s and lower 40s.
Areas of fog will continue, and may be dense at times, especially
over the deeper snow pack in central, northeast, and north central
.LONG TERM...Saturday Night Through Friday
Issued at 318 PM CST Fri Jan 20 2017
Lingering light precip chances and continued fog potential are
the first forecast concern Saturday night through Monday.
Continued mention of drizzle through Saturday night. Surface
temperatures at this time look to be at or above freezing, and
METRo road temperature forecasts only show a small dip below
freezing right before sunrise. Due to this, would not be
surprised to see a quick period of freezing rain/drizzle, but the
potential for widespread freezing on roads like the past few
mornings looks minimal. With the snow pack still melting and dew
points above freezing, persistent fog development looks reasonable
through at least Monday morning.
The next concern is the chance for light precip on Monday. As an
area of low pressure passes well south of Wisconsin Sunday and
Monday, some models solutions keep showing light wrap around
precipitation making it into the forecast area, particularly in
eastern Wisconsin. Other models remain dry. Therefore, confidence
of precipitation during this period is relatively low. Continued
with the blended chance pops through Monday night.
Attention turns to the low pressure system expected to affect the
area Tuesday and Wednesday. Growing confidence that there will be
a system to bring precipitation to the area, however uncertainly
remains on system track and precip type. Models show slightly
different storm tracks, with a slightly more southern track
supporting snow everywhere, but a slightly more northern tracking
bringing the boundary for a rain/snow mix into the southern
forecast area. Current forecast shows this trend but will likely
need adjustments as the period gets closer.
Northwest flow behind the system brings a continued chance for
lake effect snow showers through the period, mainly in far northern
Wisconsin. Temperatures also trend cooler late in the week, but
still remain at or slightly above normal for late January.
.AVIATION...for 06Z TAF Issuance
Issued at 1004 PM CST Fri Jan 20 2017
Poor flying conditions will continue into Saturday night due to
low clouds, fog, drizzle or rain. Drizzle is expected to become
more widespread overnight with light rain or drizzle expected
through much of Saturday. There is still some potential for
freezing drizzle across far northern Wisconsin as pavement
temperatures are expected to drop to around 32 degrees. Any
risk of freezing precipitation should end by 9 or 10 am.
Otherwise, the precipitation should diminish to drizzle later
Saturday afternoon or Saturday evening across much of the area.
Dense Fog Advisory until noon CST Saturday for WIZ022.