Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 242353
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
653 PM CDT Sun Mar 24 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Snowfall will intensify this afternoon before becoming heavy at
   times across central, north-central, and far northeast
   Wisconsin this evening when snow band lifts northeast across
   the region. There is a 60-80% chance of 1 inch per hour
   snowfall rates from late afternoon through midnight within this
   snow band. Very difficult travel is expected between about 5
   pm to 3 am as this snow band lifts north across the area.

 - 6 to 10 inches of snow are forecast across parts of central,
   far northeast, and all of north-central Wisconsin. Most of this
   snow will fall prior to midnight over central Wisconsin. The
   snow will likely end late tonight over north-central and far
   northeast Wisconsin, and the Monday morning commute will likely
   be severely impacted in these areas. Winter Storm Warnings and
   Winter Weather Advisories have been issued.

 - Precipitation will likely change over to a wintry mix or rain
   Monday morning through Tuesday, before changing over back to
   snow on Tuesday night over north-central Wisconsin. Minor snow
   accumulations are possible, but with little to no impacts.

&&

.DISCUSSION...
Issued at 225 PM CDT Sun Mar 24 2024

Short Term...Tonight and Monday

The initial band of fgen has lifted north across the area early
this afternoon. This initial band over performed a bit across
portions of central Wisconsin, where 1 to 2 inches fell this
morning. The main event is currently lifting north from Iowa and
southwest Wisconsin, as seen on doppler radar imagery, which will
affect the area late this afternoon into this evening.

This band of snow will have much stronger dynamics and more
moisture to work with than this mornings event with strong mid
level frontogenesis, warm air advection, isentropic lift, and
moisture. NWP models indicate mid level mixing ratios will
increase a full 1 g/kg from this morning, going from 2.5 to 3.5
g/kg along with stronger winds almost perpendicular to the
275-285K isentropic layers. This intense lift with better moisture
is expected to yield snowfall rates of 1 to 2 inches per hour at
times late this afternoon into this evening. The main concerns are
the dry air in place in low levels, as evidenced by the low dew
points in the low to mid 20s, along with a dry slot that is slated
to end the snow from southeast to northwest later this evening and
into the early overnight hours.

Headlines:

Despite the concerns, it appears the region will get 1 to 2 inch
per hour snowfall rates for up to 6 hours as this band lifts
north. This should be enough snow to yield warning criteria snow
across the current Winter Storm Warning area as evidenced by the
high confidence (80-99 percent) of reaching 6 inches as well as
high confidence (70-90 percent) in reaching 8 inches. There is
also a small chance (20-40 percent) of reaching a foot of snow
across this area, although this is at the high end of the snowfall
distribution. Overall there are no changes anticipated with the
current headlines given the current forecast and snowfall
probabilities. The only concern at this point is extreme western
Shawano County where they could get close to Winter Storm Warning
criteria, with the bulk of the county staying well below criteria,
especially east of Shawano. At this point will leave the current
headlines in place and continue to monitor snowfall trends this
evening.

Another band of precipitation is slated to lift north through the
area Monday morning and continue into the afternoon. The
precipitation will mainly be in the form of rain across central
and east-central Wisconsin for all of Monday, with some freezing
rain or sleet possible across north-central Wisconsin Monday
morning. Despite the mixed precipitation, impacts Monday morning
should be low given the relatively high sun angle as the
precipitation is expected to fall when the sun is up as well as
the freezing rain falling on snow and likely treated roads.
Therefore, extending the headlines into Monday morning is not
anticipated.

Long Term...Monday Night Through Sunday

As an upper-level trough becomes negatively tilted as pulls a
surface low out of the central Plains toward the western Great Lakes
Monday night through Tuesday rain will continues across the region.
Strong moisture advection will bring PWAT anomalies of 0.75 to 1
standard deviations during this period, which along with upper-level
support from a right rear jet quad could produce waves of heavier
rain at times. A few rumbles of thunder may also be possible
overnight Monday into Tuesday as mid-level lapse rates approach 7
C/km and MUCAPE values approach 100-200 J/kg, mainly across east-
central WI. Models are in decent agreement with a dry slot working
in from the south Tuesday afternoon which will start to diminish
precipitation intensity.

As the surface cyclone pushes north across Upper MI and over Lake
Superior late Tuesday into Wednesday colder air wrapping in behind
may allow for a transition back to snow, mainly across northern WI.
However, this window looks short with global ensembles showing less
than 1" of snow accumulations. Winds veering northwesterly will
remain breezy through Wednesday as the departing low creates a tight
pressure gradient across the region.

As the cyclones pushes further northeast dry conditions will return
for the remainder of the work week with only light lake effect snow
possible in far northern Vilas Co. Ensemble guidances shows the
upper-level flow becoming zonal late this week with a weak surface
low across the central Plains. Weak warm air advection and low level
convergences with this system could be enough to yield a round of
light precipitation Friday night into Saturday, however, there is
uncertainty as to how far north any precipitation would make it, as
the best forcing currently looks to be around the WI/IL boarder. If
precip does materialize thermal profiles would favor mostly rain,
however, snow may mix in across the north.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 653 PM CDT Sun Mar 24 2024

moderate to heavy snow and poor flying conditions will
continue this evening west of a Escanaba to Shawano to Wisconsin
Dells line, and then diminish from south to north after midnight.
East of this line there will be periods of light snow ending this
evening.

Moisture streaming north ahead of a storm system over the central
Plains will bring showers and IFR conditions Monday and Monday
night. Low level wind shear is expected with east southeast winds
around 15 knots at the surface and southeast winds around 40 knots
at 2000 feet.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 7 AM CDT Monday for WIZ005-010>012-
018-019-030.

Winter Storm Warning until 4 AM CDT Monday for WIZ013-020-021.

Winter Weather Advisory until 1 AM CDT Monday for WIZ031-035>037.

Winter Weather Advisory until 4 AM CDT Monday for WIZ073-074.
&&

$$

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


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