497
FXUS63 KGRB 060003
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
603 PM CST Wed Feb 5 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Light snow will impact the area this evening into Thursday
  morning. There is a 60-90% chance for at least 2" of snow north
  of a Merill to Wausaukee line. Lower snowfall amounts are
  expected south of this line. A period of freezing drizzle is
  possible, especially as the snow ends Thursday morning, which
  may create a glaze of ice on untreated roads and surfaces.

- Increasing westerly winds are expected late Thursday morning
  into Thursday evening with gusts of 30-50 mph. There is a 60-80%
  of 45+ mph winds in central and east central WI. A Wind Advisory
  has been post for locations south of a Tomahawk to Wausaukee
  line. There is a small chance (less than 10 percent) that winds
  could gust over 55 mph.

- Another round of accumulating snow is possible this weekend,
  with an area-wide chance of 65-80% for at least 3" of snow and a
  50-60% chance for greater than 6".

&&

.DISCUSSION...
Issued at 231 PM CST Wed Feb 5 2025

Short Term...Tonight and Thursday

A clipper system will move across the region tonight, bringing a
round of light snow which could switch over to freezing drizzle
before ending. The main concern tonight with respect to snowfall
amounts and precipitation types will be saturation at the low
and mid levels. Radar shows a band of echoes moving into southwest
Wisconsin, however none of this is reaching the ground. Bufkit
soundings indicated a large dry layers from 925 mb to 700mb
through early this evening. I have delayed the onset of the snow
by a few hours with the main brunt of the snow from mid evening
into early Thursday morning. Snowfall amounts should be under an
inch south of a Wausau to Marinette line. Snowfall totals across
the far north have been lowered a little bit with amounts around
two and a half inches across Vilas County. Bufkit soundings
indicated the light snow would taper off to freezing drizzle late
tonight into early Thursday. With a light snowfall expected
and expecting road crews to be plowing/treating roads, the impact
of the freezing drizzle is not expected to be significant. Evening
shift may need to monitor if a Winter Weather Advisory may be
needed if the freezing drizzle becomes more impactful.

Any lingering precipitation will end Thursday morning. The main
concern will the strong west winds. Increasing westerly winds are
expected late Thursday morning into Thursday evening with gusts
of 30-50 mph. There is a 60-80% of 45+ mph winds in central and
east central WI. A Wind Advisory has been post for locations south
of a Tomahawk to Wausaukee line. There is a small chance (less
than 10 percent) that winds could gust over 55 mph. If would
mixed to 3,000 feet like the bufkit soundings suggest, some
locations could peak out near High Wind Warning Criteria (58 mph
or greater gusts). Highs should top out in the 20s to lower 30s,
but will likely gradually fall during the afternoon.

Long Term...Thursday Night Through Wednesday

Strong Winds Thursday Evening...Cold advection and mixing into a
strong 35-45kt 925mb jet behind a departing short-wave will continue
to produce strong westerly winds Thursday evening into the early
overnight hours. Wind will begin to diminish first across northern
WI during the evening. However, HREF probs show ~25% chance for
gusts greater than 45 mph in east-central WI through 10pm Thursday.
Winds will have greatly diminished by daybreak Friday with generally
light winds expected the remainder of Friday.

Weekend Snow Chances...The best chance for snowfall through the
extended forecast arrives Saturday as a Pacific waves works across
the northern plains into the upper Midwest. Synoptic scale models
show a LFQ providing upper-level support to this system as
widespread snow beginning to spread west to east across the region.
Forecast soundings show dendritic grow should be very efficient
Saturday with strong lift in a deeply saturated DGZ. SLRs are also
forecast to be 15-20:1 which may help snowfall totals. However, one
potential downfall for this event is dry air entrainment from a
developing high pressure system over the northern Plains and
Canadian prairie. Pinning down snowfall amounts with this remains a
challenge, as the NBM 10-90th percentile range is 3-12" across much of
the region.

As this system comes into range for the CAMs over the next 48 hours
should start to get a better handle on the mesoscale features (i.e.
f-gen banding and lake enhancement). Winter Weather headlines will
likely be needed this weekend, but the exact details will need to be
refined.

Temperatures...Colder air is forecast to arriver behind this weekend
system to start next week. NBM probs shows a 50-80% chance for lows
Monday mornings to fall below zero with wind chills falling into the
-5 to -15 degree range. The colder air will stick around at least
through next Wednesday.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 602 PM CST Wed Feb 5 2025

Lake effect clouds with MVFR ceilings will continue to move inland
and cover most of the area by mid evening.

An upper level disturbance and surface front will produce light
snow and IFR conditions later tonight, especially north of a ISW
to MNM line where an inch or two is possible. The light snow could
end as a couple hours of freezing drizzle 12z to 15z Thursday south
of a CWA to GRB line.

Ceilings will rise and visibility will improve Thursday, but west
surface winds will increase to 20 to 30 knots with gusts up to 45
knots possible in the late morning and afternoon. Airfields with
dry snow cover could have blowing and drifting snow and poor
visibility. The wind will diminish during the evening hours.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 9 AM to 9 PM CST Thursday for WIZ018>022-030-
031-035>040-045-048>050-073-074.
&&

$$

DISCUSSION.....Eckberg/GK
AVIATION.......RDM