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FXUS63 KGRB 081102 AFDGRB

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

Updated aviation portion for 12Z TAF issuance

KEY MESSAGES
- 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 Wisconsin.

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

DISCUSSION
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.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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