926
FXUS63 KGRB 221141
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
541 AM CST Fri Nov 22 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Light rain and snow are possible Sunday night through Monday
  night. Minor snow accumulations look possible over north-central
  Wisconsin where there is a 20-30% chance of greater than 1 inch
  of snowfall.

- A cooling trend is forecast over the next week. Highs in the 30s
  and 40s through the weekend will cool into the 20s and 30s by
  the middle of next week.

&&

.DISCUSSION...
Issued at 152 AM CST Fri Nov 22 2024

Short Term...Today...Tonight...and Saturday

Quieter and low-impact weather through Saturday as high pressure
slowly builds in from the northern Plains. Light rain showers or
drizzle due to upslope moist flow off Lake Superior will continue
this morning mainly north-central, before ending this afternoon.
Otherwise, as primary sfc low focuses over the Mid Atlantic and
high pressure ridge axis remains to the west, north-northwest flow
will keep swath of low-level moisture, mainly cloudy skies in
place into Saturday. A few breaks in the low clouds may develop on
Saturday, but mid clouds in warm air advection will still lead to
mostly cloudy skies.

Northwest winds may gust to 20-25 mph over eastern WI today. Winds
tonight and Saturday will become lighter while staying from the
west/northwest. Temperatures today will be slightly above normal
with around 40 in the north and mid to locally upper 40s east-
central WI. Cooler tonight with readings mainly below freezing,
most so in central and north-central WI. Temperatures near normal
for Saturday, upper 30s north and lower 40s central WI east to
the lakeshore.

Long Term...Saturday Night Through Thursday

Focus of this forecast remains on the low pressure system due to
pass across the region on Sunday night into Monday, then followed by
colder temperatures thereafter.

Sunday night into Monday:  A shortwave impulse will be traversing
the region during the Sunday night and Monday period, with an
associated surface low traveling from southwest to northeast over
the Great Lakes. The GFS has trended slower and deeper with this
surface low and appears to be an outlier compared to other medium
range models and the ensemble means.

Weak isentropic ascent will move into the region in advance of the
surface low on Sunday, but mid-level moisture is lacking and
therefore it continues to look like precip will hold off until
Sunday evening.   Thermal fields look like precipitation will fall
as rain over northeast WI and a mix of rain/snow over north-central
WI on Sunday night.  As colder air wraps into the region behind the
low, thermal fields will be more conducive for snow, but chances of
precip look to become more confined to far northern WI.  As a
result, probabilities of greater than 1 inch of snow only reach 20-
30% over far north-central WI during this time frame.

Rest of the forecast:  Another low amplitude shortwave could move
into the region on Wednesday, which could bring minor snow
accumulations to the region.

Temperatures:  A colder trend will be occurring over the next week.
Highs will mostly be in the 30s and 40s through Monday, followed by
20s and 30s thereafter.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 540 AM CST Fri Nov 22 2024

Spotty drizzle lingers this morning over north-central WI (RHI)
but this ends by afternoon. Otherwise, MVFR to low VFR cigs will
persist through tonight regionwide, though IFR cigs will occur
this morning north-central. Northwest winds prevail through tonight,
with gusts 15-20 kts late this morning into the afternoon.

&&

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

&&

$$

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