497
FXUS63 KGRB 211956
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
156 PM CST Fri Feb 21 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- A light wintry mix will be possible at times from Sunday night
  through Wednesday. Best chances for wintry precipitation will be
  on Sunday night, when there is a 40-60% chance of a wintry mix.

- Temperatures warm this weekend through early next week. Highs
  ranging from the middle 30s to the lower 40s will be possible
  from Sunday through Wednesday.

&&

.DISCUSSION...
Issued at 156 PM CST Fri Feb 21 2025

Short Term...Tonight and Saturday

The latest RAP analysis and satellite/radar imagery show high
pressure centered across the central and southern Mississippi
Valley early this afternoon. The leading edge of more mild,
Pacific air is shifting east across the northern Plains, but it
appears that much of this warming is occurring above the boundary
layer as evident by surface obs showing temps in the teens and 20s
over North Dakota. Looking further aloft, several shortwaves are
tracking towards the northern Great Lakes within fast northwest
flow. Cloud bases are generally above 10 kft with these
shortwaves. Forecast concerns generally revolve around cloud cover
and temps.

Shortwave energy will be tracking southeast across the region at
times through Saturday night. Saturation will be more robust
across the Lake Superior region where there will be a chance of
light snow on Saturday.

Mid and high clouds will be passing across northern Wisconsin at
times through Saturday night. The GFS shows more boundary layer
moisture and saturation on Saturday that could lead to the
development of low clouds. Dewpoint depressions look relatively
high upstream and return flow will originate out of a very dry arctic
airmass. So think the probability of low stratus forming is
relatively low.

Temperatures will continue the warming trend with highs on
Saturday ranging from the upper 20s to lower 30s. Low temperatures
will be near normal tonight and Saturday night.

Long Term...Saturday Night Through Friday

The latest ensemble means indicate that split flow will be the
predominate pattern which will remain rather progressive across
North America. Medium range models show fairly good agreement on
the large scale pattern through much of next week, though still
considerable variability in the details of individual systems. The
primary focus of this forecast is to assess the impact potential
for wintry systems from Sunday night through next Wednesday.

Sunday Night and Monday: Shortwave energy will be pushing a
surface low across northern Ontario during this period. Warm
advection aloft will be occurring south of the low track and
across northern Wisconsin. Moisture is rather disjointed, with mid
and high moisture out ahead of the lower moisture. But there
appears to be a short few hour window where there will be
sufficient saturation for light precip. Highest chances will occur
across northern WI where there is a 30-45% chance of measurable
precip.

Thermal profiles will be warming by Sunday night with the critical
thicknesses lifting into northern WI. Time of the day combined
with the cold ground leads to concerns for light icing to take
place, even further south than the critical thickness lines.
Confidence is low enough to exclude from the HWO, so will pass
concerns along to the next shift. This light precip is projected
to exit the area by the start of the Monday morning commute.

Tuesday and Wednesday: Another fast moving shortwave is forecast
to move across the area during the Monday night period. Thermal
profiles will be slightly cooler by this point, but precip type
will continue to be a concern, particularly over central and
east-central WI.

A stronger system could impact the region on Wednesday. Early
indications suggest the boundary layer will be warmer by this
point and could be looking at more of a rain/snow scenario as
opposed to a wintry mix of sleet/freezing rain.

Temperatures: Will range from 5 to 10 degrees above normal from
Sunday through Wednesday before falling back to near normal by
next Thursday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1107 AM CST Fri Feb 21 2025

VFR conditions remain expected across the area through the entire
taf period. Cirrus will move across the area at times this
afternoon. Then cloud bases will lower tonight into Saturday
morning to about 10 kft as mid-level clouds arrive from the
northwest. Some models depict a layer of MVFR stratus developing
on Saturday morning but confidence is too low given the relatively
high dewpoint depressions upstream.

The only significant change to the forecast was to add low level
wind shear at all taf sites tonight.

&&

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

&&

$$

DISCUSSION.....MPC/MPC
AVIATION.......MPC