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FXUS63 KGRB 082107 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 307 PM CST Fri Dec 8 2023

Forecast discussion for routine afternoon forecast issuance

KEY MESSAGES
- Light snow will cross northern WI tonight, with amounts generally less than an inch.

- Potential for 2 inches of snow or more remains low Saturday morning, around 10 to 20 percent across north- central Wisconsin.

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

- Secondary wave to bring a dusting to 2 inches of snow Saturday evening into Sunday morning. Small chance (10%) of up to 4 inches of snow in extreme north-central Wisconsin with this round of snow.

DISCUSSION
Issued at 304 PM CST Fri Dec 8 2023

SHORT TERM...Tonight and Saturday

Rest of the Day...
Fairly chaotic skies are expected across the region under the warm air advection regime. Sunshine will get through at times for portions of central to east-central WI, but areas in the north will see an area of low stratus cover the area by the evening. Temperatures will continue to run warm through this time period, with highs from this afternoon likely only slowly dropping as we head into the overnight hours.

Tonight...
Expect the continuing warm advection pattern to bring cloud cover back in the evening to early overnight hours. The main shortwave still appears to arrive in the hours after midnight, bringing overspreading precipitation to the region through the morning hours Saturday. General consensus brings the center of the low along eastern WI through the overnight hours, with the strongest forcing crossing along the eastern portions of the state as well. Between fairly strong lapse rates and the LFQ of the upper jet, suspect a rumble of thunder still isn't out of the question, with the most likely area(s) being somewhere in east- central WI or southwards. Snow totals during this time period continue to be one of the more uncertain aspects of the forecast.
On one hand, soundings certainly support snow across north-central WI when precipitation arrives and if any of the forcing previously mentioned works its way there, accumulating snow is not out of the question. A few of the shorter term models still show that very thing, retaining a very narrow swath of around 2-3 inches. On the other hand, temperatures today are already running much warmer than current models initialized with, and dewpoints across the north have pushed into the upper 30s across the north. The incoming low stratus deck will likely inhibit too much cooling overnight as well, which together would melt much of any snow as it falls. Thus together, decided to retain some accumulating snowfall across the northwoods, but left amounts to generally less than an inch, favoring warmer overnight temperatures around 33-34 degrees in the cold spots and accumulations focused towards grassy areas. This will be relatively low impact solution, as the warmer temps would also mostly inhibit icy across the area. That said, this is still an area to watch and details could still change rapidly if a window for cooler temps in the north arrives ahead of the precipitation.

Saturday...
As the main shortwave transitions off to the east, a lull in the precipitation is expected Saturday afternoon, with quieter and even dry conditions returning to much of the forecast area for at least a few hours. The northern stream shortwave then arrives late in the day, with a colder airmass and a bit more snow for the region. Please see the extended discussion for additional details.

LONG TERM...Saturday Night Through Friday

Main focus is on part two of a two-part system expected to bring precipitation to the area Saturday evening into Sunday morning.
After that, precipitation chances will be low through the week.

Saturday evening through Sunday...Upper trough with second embedded mid-level shortwave will be moving across the area, which includes a coinciding surface cold front sweeping across from west to east. By the time this wave moves across, expect snow to be the main precip type as there is no longer any warm nose and soundings indicate a snow profile with saturation into the DGZ.
No shortage of lift with these features, but QPF amounts are still somewhat inconsistent, leading to some variability in model snowfall amounts. Generally looking like up to another tenth of an inch of QPF from 00Z to 18Z Sunday, yielding additional snowfall of 1 to 2 inches in far north-central Wisconsin, and a dusting to a few tenths of snow elsewhere. There is a small chance (up to 10%) of snow amounts in extreme north-central Wisconsin to reach up to 4 inches. Amounts this high would be very localized. Some slippery roads and lower visibilities will be possible as this snow falls.
This will cause some minor travel impacts for those driving around during the night and early Sunday morning. Rising heights and high pressure building at the surface will lead clearing skies Sunday afternoon.

Next week...A system moving across central Canada on Tuesday will drag a cold front across Wisconsin on Tuesday. Right now, the main impact will be increasing winds and cooler temps, with precipitation staying north of the Wisconsin border. Some PoPs may need to be added to the far north with time, but these should be minor. High pressure and warmer westerly flow will bring seasonable and dry weather for the rest of the work week.

AVIATION
for 18Z TAF Issuance Issued at 1238 PM CST Fri Dec 8 2023

For the afternoon and evening, high clouds will pass over the region but will keep VFR in place for most. The only exception will be an area of MVFR clouds that are moving into north-central WI this afternoon and will likely impact RHI starting in the mid afternoon.

Tonight, an active weather system will move in from the south, bringing widespread 5000-6000 foot ceilings followed by rain. As we get into the morning, ceilings will drop to MVFR and possibly lower in portions of central WI. Visibility could also drop briefly in the late morning as rain ends and some fog develops. A few spots in the far north could see snow from this system as it departs the region, so made a mention in RHI. Finally, there should be some improvement in conditions in the afternoon for Saturday, before another round of active weather arrives Saturday evening. Snow will be the more likely precipitation type Saturday evening into Saturday night.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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