389
FXUS63 KGRB 250819
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
219 AM CST Mon Nov 25 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Rain and snow will continue to impact the area today. Rain will
  change to snow across central WI this morning, but stay mainly
  rain over northeast and east-central Wisconsin.

- An additional 1-3 inches of snow accumulations remain possible
  north of a Merrill to Iron Mountain line through the end of the
  afternoon. A Winter Weather Advisory is in effect for Florance,
  Forest, Oneida, and Vilas Counties until 3 pm today.

- A cooling trend takes hold this week. Highs in the 30s and 40s
  today will cool into the 20s to 30s by the middle of the week,
  and into the 20s across the entire area by next weekend. Subzero
  wind chills possible Friday night and Saturday night.

&&

.DISCUSSION...
Issued at 219 AM CST Mon Nov 25 2024

Short Term...Today...Tonight...and Tuesday

The latest RAP analysis and satellite/radar imagery show shortwave
energy moving across the northern Plains early this morning. This
shortwave is supporting a surface low which is centered over
west-central Illinois and is tracking northeast. Upper divergence
in the left front quad of a jetstreak combined with deep layer
isentropic ascent and 800-700mb frontogenesis is supporting light
to moderate snowfall generally north of the elevated wet bulb zero
line which runs from just north of Wausau to about Marinette.
Drizzle and light rain has been observed south of this line. This
weather type transition line is farther south that projected last
night and is expected to hold relatively steady for the rest of
the night into early Monday morning.

Radar evolution and higher resolution models indicate a lull in
the snowfall is likely to occur early this morning through about 8
am after the current swath of snowfall shifts northeast into the
Upper Peninsula. As the shortwave energy and low pressure track
over the western and central Great Lakes, snowfall accumulations
and impacts are the focus of this forecast.

Today...After the relatively lull in precip early this morning,
HREF members indicate a swath of precip orientated north-south
along the shortwave trough will move from west to east from about
8-10 am to mid-afternoon. This swath will bring a period of
heavier precip rates to the area. Colder air filtering in from the
northwest will bring the rain-snow line further south across
central WI which could lead to minor accumulations on grassy
surface as temps will be around 34-35 degrees. But further north,
temperatures will be colder in the lower 30s which will be more
conducive for snow accumulations. The latest data suggests 1-3
additional inches of snow will be possible in the Winter Weather
Advisory area before the snow diminishes after about mid-
afternoon. As a result, extended the Winter Weather Advisory 3
hours through 21z.

Further east, a cold rain will be observed at times over the Fox
Valley and lakeshore. Northwest winds will be increasing from 20
to 25 mph by mid to late afternoon.

Tonight and Tuesday...The light precip will be exiting northeast
WI in the evening. Light lake effect snow will likely hang on a
little longer over northern Vilas county, but lake effect
streamers should retreat north of the U.P. border overnight.
Little to no additional accumulations are expected.

Otherwise, an influx of much colder air via gusty northwest winds
will have greater impacts than precip. Lows in the teens and 20s
tonight will only rise from the mid 20s to low 30s on Tuesday.
Wind chills will fall into the single digits to low teens above
zero by early Tuesday morning across most area (except the
Lakeshore).

Long Term...Tuesday Night Through Sunday

Colder conditions will be the primary theme for the long term.
After experiencing weeks upon weeks of above normal temps so far
this fall, a pattern shift is on our doorstep. Appears this cold
will have some staying power, at least into the beginning of
December.

Temperatures: Blended NBM guidance looks to be running too warm
starting Wednesday and lasting into this weekend. This is likely
due to bias corrected data still being ingested into it from
this falls warmer weather. Used blend of raw models to bring down
temperatures, most notably high temps, Wednesday through the
weekend. Result is highs in the upper 20s to mid 30s on Wednesday,
mid 20s north to around freezing for Thanksgiving, then falling
into the 20s even to the Lake Michigan shoreline Friday through
Sunday. Lows drop into the teens and 20s Wednesday and Thursday,
then tumble into the single digits central/north-central to the
lower teens Thursday night through Sunday night. Subzero wind
chills are possible for some areas Friday night, Saturday night
and Sunday night. However, there does not appear to be any risk
of coming close to advisory levels for cold.

Lake effect snow (LES): Northwest flow lake effect will be
present across north-central WI throughout the period into next
weekend. Mostly light intensity lake effect snow (LES) with low
inversions forecast, but there does seems to be some potential
for a flare up of the LES Thursday night into Friday in wake of
re-enforcing cold front. Though boundary layer wind direction
does not change much, staying NW, increasing RH flowing across
Lake Superior and colder air allows the forecast soundings to
point to increasing inversion heights/lake equilibrium levels and
better chance low-level lift will be within the DGZ, helping to
increase SLRs. There is also a hint of stronger wind gusts up to
25 mph in tight pressure gradient behind the front, so some
blowing snow could occur. Coordinated with DLH and MQT and
increased pops for Vilas County Thu night into Fri. Elsewhere it
looks quiet with partly cloudy skies north with some flurries away
from Vilas as far south as RHI to IMT, but mostly clear farther
south and east. Suppose that cold front may produce some light
snow or flurries later on Thanksgiving into Thursday night, but
any snow looks light and brief.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1134 PM CST Sun Nov 24 2024

A surface low will track along the WI/IL border overnight, with
precipitation across the region becoming more widespread. Mainly
rain showers are expected south of a Merrill to Marinette line
and snow north of this this line. The heaviest periods of snow are
expected between 06Z-12Z Monday morning across far northern WI.
Conditions will generally be IFR/LIFR, with some MVFR possible.

As winds turn to the north Monday morning and cold air starts to
advance further south snow may start to mix in with the rain
across central WI. Greatest snowfall amounts of around 1-4 inches
are expected north of Rhinelander to Iron Mountain line. The low
will pull away from the region Monday afternoon, allowing CIGs to
improve to MVFR/IFR Monday afternoon/evening as precipitation
starts to end from southwest to northeast.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 3 PM CST this afternoon for WIZ005-
010>012.
&&

$$

DISCUSSION.....MPC/JLA
AVIATION.......Kurimski