Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 231939
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
239 PM CDT Sat Mar 23 2024

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- There is a 60 to 90% chance of at least 6 inches of snowfall
   accumulations across parts of central, north-central, and far
   northeast Wisconsin Sunday afternoon through Monday morning.
   Confidence on these percentages is highest across north-
   central WI where there is a 80% chance of at least 8 inches of
   snow. Gusty winds of 30 to 35 mph could also create areas of
   blowing and drifting snow, and make for very difficult driving
   conditions during this time frame. The Monday morning commute
   will likely be severely impacted.

 - Precipitation will likely change over to a wintry mix or rain
   Monday afternoon through Tuesday, before changing over back to
   snow on Tuesday night over north-central Wisconsin. Minor snow
   accumulations are possible. A rumble of thunder may also be
   possible on Monday and Monday night.

&&

.DISCUSSION...
Issued at 238 PM CDT Sat Mar 23 2024

Short Term...Tonight and Sunday

Mostly clear skies this evening will give way to increasing clouds
tonight with increasing mid level moisture. In addition, some
modest mid level frontogenesis will combine with isentropic lift
and warm air advection to bring a swath of light snow or flurries
through the area from around midnight through Sunday morning. The
best chance for light snow and accumulating snow will be across
central and north-central Wisconsin (30-50 percent) where moisture
and lift will be maximized. Snowfall amounts from this round of
snow will be light, generally a few tenths of an inch with a few
locations possibly reaching around an inch.

The more significant snow will arrive Sunday afternoon as more
substantial mid level frontogenesis, warm air advection,
isentropic lift, and deeper moisture arrive to the western Great
Lakes region. Probabilities for 1"/hour snowfall increase
precipitously (40-60 percent) west of the Fox Valley after 21Z on
Sunday. By late Sunday afternoon the probability to already see 3"
of snow will be fairly high (50-80 percent) west of a line from
Florence to Antigo to Wisconsin Rapids. As southeast winds
increase Sunday afternoon, there could be blowing and drifting
snow across the area especially across central Wisconsin.

Headlines:

Given the earlier onset of the heavy snow Sunday afternoon will
pull the current headlines to start at 18Z Sunday instead of 21Z.
In addition, given the fairly high confidence in reaching 6 inches
(80 percent or higher) will upgrade the current Winter Storm Watch
to a Winter Storm Warning for Marathon, Lincoln, Langlade, Oneida,
Vilas, Florence, and Forest counties. Further east where
confidence is still lower (50 to 70 percent) due to the changeover
to rain will keep or expand the Winter Storm Watch for northern
Marinette, northern Oconto, Menominee, Shawano, and Wood counties.

Long Term...Sunday Night Through Saturday

 Main focus of the extended period continues to be the heavy snow
and blowing snow potential Sunday night into Monday on the
leading edge of a strong cyclone ejecting out of the Rockie
Mountains.

Sunday night through Tuesday...Models continue to shows a strong
cyclone lifting northeast out of the central Plains Sunday night
into Monday brining heavy snow and gusty winds, especially for
central and northern WI. The main forcing with this system will
be a strong warm air advection regime setting up out ahead of the
main surface low. There will be additional upper-level support
Sunday night as a divergence zone associated with a right rear
jet quad moves over the area. Models also show a left front jet
quad setting up Monday afternoon as the subtropical jet noses
over the area. In addition to the strong forcing deep layer
moisture should be abundant during this time frame. NAEFS
standardized anomalies show a 0.75-1 PWAT standard deviation
Sunday night through Monday.

The most glaring difference amongst models during this period is
QPF. The GEFS has been the most aggressive with QPF amounts
across central WI when compared to the ENS and GEPS. This
difference is QPF is also notable in the deterministic models. It
is also worth noting that there has been an upward trend in QPF
over the past 36 hours.

The last piece of the puzzle in terms of snowfall amounts is when
a change over from snow to rain occurs. Precipitation is expected
to remain snow from the onset through early Monday morning, but
as warm air surges in from the southeast thermal profiles suggest
a change over to rain rather quickly from south to north Monday
morning into early afternoon. Currently, the threat for any
freezing rain looks minimal as the duration of any warm noise
looks short.

With all of that probabilities of 6-hour precipitation rates of
greater than 0.30" will occur northwest of a Stevens Point to
Marinette line (40-70%) between 7pm Sunday and 1pm Monday. In
turn this gives ares in northern Marathon, Lincoln, Oneida and
Vilas counties a 50-70% for greater than 6" of snow by Monday
afternoon and a 20-50% chance for greater than 8". Probabilities
for these high of snow totals drop off quickly south and east.

A tightening pressure gradient will also create strong
southeasterly winds Sunday night through Monday with gusts 25-
35 mph possible. The strong winds and heavy snowfall may lead to
blowing snow, mainly across central WI with reductions in
visibilities possible.

As the cyclonic flow pushes off to the northeast rain will likely
linger across the region through much of Tuesday. There is a
chance as colder air wraps in on the back side of this system for
a transitions back to snow, mainly across northern WI Tuesday
evening.

Rest of the forecast...As the cyclonic flow pushes off to the
northeast Wednesday expect dry conditions to return for the end
of the work week besides some lake effect snow across far
northern WI. Near to slightly below normal temperatures are
expected Wednesday and Thursday along with breezy westerly winds.
Warmer air is forecast to arrive Friday ahead of a potential
clipper system that may being another round of precipitation to
region next weekend.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1227 PM CDT Sat Mar 23 2024

VFR conditions will prevail through tonight. There will be an
increase in high based stratocu late this afternoon into this
evening. A winter storm will bring snow to the area Sunday as
conditions fall to MVFR and eventually IFR. Several inches of
snow and considerable blowing and drifting snow will occur
northwest of the Fox Valley late Sunday afternoon through Sunday
night. Most severely impacted terminals will include CWA, AUW and
RHI.

Snow will begin to change to rain late Sunday night over the
southern Fox Valley to the lakeshore. Snow will then change to
rain all areas through the day on Monday.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 1 PM Sunday to 1 PM CDT Monday for
WIZ005-010>012-018-019-030.

Winter Storm Watch from Sunday afternoon through Monday
afternoon for WIZ013-020-021-031-035.
&&

$$

DISCUSSION.....Kurimski/GK
AVIATION.......Kurimski


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