FXUS63 KGRB 081102

Area Forecast Discussion
National Weather Service Green Bay WI
502 AM CST Fri Dec 8 2023

Updated aviation portion for 12Z TAF issuance

- Seasonably warm temperatures remain forecast today with
  afternoon highs ranging from 10 to 20 degrees above normal.

- Potential for 2 inches of snow or more has decreased for
  Saturday and now around 10 to 20 percent across north- central

- Precipitation will consist of rain over east-central Wisconsin
  late tonight through Saturday afternoon.


Issued at 313 AM CST Fri Dec 8 2023

SHORT TERM...Today...Tonight...and Saturday

The latest RAP analysis and satellite/radar imagery show low
pressure over North Dakota and high pressure over the far
southeast United States. Strong warm advection above the boundary
layer is occurring between these features and over the western
Great Lakes. Low stratus (300-600 ft agl) is expanding across far
northeast WI and into north-central WI early this morning, while
other 4000-5000 ft stratus is moving northeast into central WI.

Rather large 0-2km dewpoint depressions exist upstream in this
warm advection pattern, and dry conditions prevail over the
central Plains. But then attention turns to potent shortwave
energy moving into the Colorado Plateau and its impacts on the
sensible weather tonight into Saturday across northeast Wisconsin.

Today...Forecast soundings indicate that low clouds will be
difficult to erode across northern Wisconsin thanks to a strong
inversion and additional low level moisture (currently over South
Dakota) pushing in from the west during the afternoon. Parts of
central and east-central WI should see more in the way of
sunshine, and warmer temps. Adjusted high temps slightly lower
across the north to account for more cloud cover. Dont't think
will see drizzle/showers out of these clouds as saturation depth
looks relatively shallow. Highs will range from the lower 40s to
lower 50s.

Tonight into Saturday...Where low stratus doesn't prevail, clouds
will spread northeast across the region after midnight as strong
shortwave energy and low pressure system rapidly move from the
southern Plains to the central Great Lakes. Compared to 24 hours
ago, models have trended weaker and further east with the
strength and track of the cyclone. Significant differences remain
with the precipitation fields, particularly between the convective
allowing models versus the medium range models. Confidence remain
below normal for this time period of the forecast.

Strong lift will arrive between 3 am to 9 am Saturday across
northeast Wisconsin with passage of the shortwave/surface wave.
Negative thetae lapse rates in the 850-500mb layer suggest reduce
stability that could lead to a few lightning strikes over
northeast WI.

With the eastward track, forecast precipitation has trended down
significantly across northeast WI while the heaviest showers
should fall from southeast WI to northern Lower Michigan. In fact,
most of the convective allowing models generate little to no
precip over north-central WI through Saturday morning. Given
relatively warm airmass and lack of high precip rates, the
probability of significant snowfall has dropped significantly
compared to 24 hours ago.

That said, there remain a few models that produce a few inches snowfall
over north-central WI. The 06z HRRR is most aggressive (06z NamNest
not far behind), and produces a narrow band of 6 inches from
Langlade to western Florence county! Therefore think that details
could still change rather abruptly.

After a break in the precip from late morning through early
afternoon, northern stream shortwave will bring light snow to the
north- central WI in the afternoon. Temperatures will be colder
by this time, which should allow for minor accumulations perhaps
around a half inch to an inch by 6 pm Saturday.

LONG TERM...Saturday Night Through Thursday
Precipitation will taper off early Sunday morning as low pressure
departs to the northeast out of the Great Lakes region. Surface-
based high pressure ridging will then expand east and north into
our area. The tail end of a Canadian cold front appears to sweep
through Wisconsin on Tuesday morning and bring some colder
temperatures and gusty winds, but little or no precipitation is
expected with the front as it whips through. The strong high
pressure ridge is then expected to reassert itself again and bring
high temperatures in the 40s later in the week.


.AVIATION...for 12Z TAF Issuance
Issued at 502 AM CST Fri Dec 8 2023

Low stratus developed as expected after midnight across far
northern Wisconsin. This stratus will be slow to erode, and
continue to think it will rise to MVFR by late morning. At least
partial clearing is expected this afternoon, but forecast
soundings don't indicate that clearing takes place at RHI until
this evening.

Meanwhile, a band of 5000-6000 ft ceilings are moving northeast
across central and east-central Wisconsin. These clouds should
depart by mid-morning. Then only mid and high clouds will pass
across this area until late tonight, when low pressure brings
MVFR ceilings and rain to the area.