908
FXUS63 KGRB 220443
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1043 PM CST Sat Dec 21 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Minor lake-effect snow accumulations are possible in Door County
  and along the Lake Michigan shoreline late tonight into Sunday.
  Amounts would be less than 1 inch for most, with localized
  amounts of 1-2 inches possible in Door County if a lake band
  becomes more persistent.

- The potential has increased for a band of 2+ inches of snow
  north of Highway 29 late Sunday night into Monday, which could
  impact travel ahead of the Christmas holiday. Patchy freezing
  drizzle is also possible over mainly north central and central
  Wisconsin Sunday night.

&&

.DISCUSSION...
Issued at 338 PM CST Sat Dec 21 2024

Short Term...Tonight and Sunday

High pressure has kept most of the area dry today, however north
winds had created a few bands of light lake effect snow impacting
mainly the Door peninsula, but some flurries were observed as far
south as Green Bay. Webcams across Door County showed very light
snow this afternoon, but roads looked clear and impacts were
little to none. This snow will come to an end in the next couple
hours as the high moves east and winds gradually shift to the
south.

With the southerly winds, this creates another opportunity for
lake effect snow bands to setup across Lake Michigan late tonight
through early Sunday afternoon. Most of the CAMs show some
development of these lake bands, but it`s less certain whether
they will move onshore in northeast WI. Door County has the
greatest chance to see snow, with the lakeshore areas of Kewaunee
and Manitowoc counties possibly seeing a little snow, too. Amounts
will be less than 1-inch for most, but localized amounts of 1-2
inches are possible where a band may persist longer.

Meanwhile, models have backed down on light snow being generated
ahead of a shortwave in central/north-central Wisconsin on Sunday.
Kept a small mention of flurries here, isolated amounts of a tenth
or so cannot be ruled out, but most places will not see any snow
accumulation.

A colder airmass is still in place tonight, so lows will fall
into the single digits for most, with low teens along Lake
Michigan. With southerly return flow starting to kick in Sunday,
highs will be a little warmer, in the mid 20s to low 30s.

Long Term...Sunday Night Through Saturday

Main concern in this forecast period is the potential for area-
wide wintry precipitation late Sunday night into Monday.

Precipitation...Models have come into much better agreement on a
low pressure system tracking from SE MN/NE IA through east central
WI late Sunday night into Monday. Strong WAA on the nose of a
30-40 kt low-level jet may generate some light precipitation
Sunday evening. Better forcing arrives with a coupled upper jet
structure, mid-level fontogenetic forcing and a potent short-wave
trough, which may lead to a band of more significant snowfall
(2-3 inches) late Sunday night into Monday north of Hwy 29. There
is also potential for some freezing drizzle, particularly over
NC/C WI Sunday night, where mid-level dry air will limit the
presence of ice crystals in the saturated layer at times. Surface
T/Td depressions are initially quite high Sunday evening, so
freezing drizzle is more likely overnight. Confidence is not there
yet, but could see potential for a Winter Weather Advisory if a
more concentrated band of snow evolves or freezing drizzle looks
to be more widespread than currently expected. The snow is
expected to taper off from west to east Monday afternoon, and be
out of the area by evening.

High pressure and ridging aloft should lead to dry conditions
Tuesday and Tuesday night. A short-wave trough and weak inverted
surface trough could bring a small chance of light rain to our
southeast counties Christmas afternoon/evening. A warmer pattern
with a couple periods of precipitation looks to set up over the
latter half of next week, though models are in poor agreement on
any of the details. Rain would appear to be the dominant precip
type during this period.

Above normal temperatures are anticipated through most of the
extended forecast, with much above normal possible later next
week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1043 PM CST Sat Dec 21 2024

Middle clouds will increase across the area overnight, with a few
snow flurries possible. In addition, lake effect clouds and snow
showers are possible later tonight at SBM/MTW/SUE/3D2/2P2.

Middle clouds are expected Sunday through the mid evening hours.
MVFR ceilings and light snow or freezing drizzle is possible by
late evening across central and northcentral Wisconsin. Light snow
and IFR conditions are likely late Sunday night and Monday over
much of the region.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....KLJ/Kieckbusch
AVIATION.......RDM

NWS GRB Office Area Forecast Discussion