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LMZ541 Rock Island Passage To Sturgeon Bay Wi- 433 Pm Cst Thu Dec 7 2023
.small craft advisory in effect from 4 am cst Friday through Friday evening...
Tonight..SE wind 10 to 20 kts. Gusts to around 25 kts after midnight. Partly cloudy in the evening then becoming mostly cloudy. Waves 1 to 3 ft building to 3 to 5 ft after midnight.
Friday..S wind 10 to 20 kts with gusts to around 25 kts. A slight chance of drizzle in the morning. Waves 4 to 7 ft.
Friday night..S wind 10 to 15 kts. Gusts to around 25 kts in the evening. A chance of light rain after midnight. Waves 3 to 5 ft subsiding to 1 to 3 ft.
Saturday..NW wind 5 to 10 kts backing W 10 to 20 kts in the afternoon. Rain likely in the morning, then a chance of light rain in the afternoon. Waves 2 to 4 ft.

LMZ500
No data

FXUS63 KGRB 072115 AFDGRB

Area Forecast Discussion National Weather Service Green Bay WI 315 PM CST Thu Dec 7 2023

Forecast discussion for routine afternoon forecast issuance

KEY MESSAGES
- Small chance of drizzle or freezing drizzle over northern Wisconsin after midnight.

- Warm day expected on Friday with temperatures 10 to 20 degrees above normal.

- Potential for 2 inches of snow or more has decreased for Saturday, and are now around 10 to 30 percent across north- central Wisconsin.

- Precipitation will consist of mainly rain over the Fox Valley and east-central Wisconsin Friday night through Saturday. Minor snow amounts less than half an inch are possible (20 to 40 percent chance).

DISCUSSION
Issued at 313 PM CST Thu Dec 7 2023

SHORT TERM...Tonight and Friday

Main forecast concerns to be on small chance for drizzle or freezing drizzle to develop over northern WI later tonight, followed by extent of clouds and temperatures for Friday.

The 19Z MSAS surface analysis showed an area of low pressure over western ND with a cold front extended southward into the central Plains and a warm front extended east-southeast through southern sections of MN and WI. Visible satellite imagery indicated patches of mid-level clouds over northeast WI with clear skies farther to the west and south.

The warm front is forecast to slowly lift north tonight with eventual south winds beginning to tap gulf moisture. As temperatures slowly drop and dew points rise, expect low clouds to develop along with patchy fog after midnight. The question then becomes whether any precipitation will develop. Forecast soundings still show dry air aloft, thus drizzle/freezing drizzle would be the precipitation type if it does form at all. Most models stay dry, but feel that northern WI may see this mixed precipitation so have added this potential to the forecast. Min temperatures are forecast to bottom out in the lower 30s north, middle to upper 30s south late this evening, then slowly rise overnight as cloud cover develops. As temperatures do moderate toward daybreak, any freezing drizzle would become drizzle.

Any drizzle should end by mid-morning Friday as the warm front lifts farther north through Upper MI. Patchy fog could also linger until mid-morning before mixing out. Southwest winds and warmer air will continue over the area on Friday, however forecast soundings show a pretty stout inversion that be tough to break. If clouds hang tough, it will be hard for temperatures to significantly warm. Even if the low clouds mix out, middle and high clouds are forecast to arrive in the afternoon. For now, have max temperatures ranging from the lower to middle 40s over north- central WI, to around 50 degrees across east-central WI.

LONG TERM...Friday Night Through Thursday

The main focus remains on the system to impact the area Friday night through Saturday night, bringing a mix of rain and snow.

There has been some back and forth on whether there will be one main wave, or two separate waves which generate precip Friday night through Saturday night. Latest runs are on the two wave scenario. Lift generated from the first approaching shortwave Friday night into Saturday morning, along with proximity to the LFQ of the upper jet, will allow precipitation to begin.
Temperatures Friday night will initially be in the middle 30s to lower 40s, resulting in nearly all rain at precip onset as it spreads in from the south. Temperatures cool Saturday morning starting in the north. This will lead to a transition to snow as the second shortwave moves through mid-morning through Saturday night. QPF amounts during the snow portion of the event have lowered, which has resulted in slightly lower snow totals in this most recent forecast update. The potential for 2 inches or more is highest across far north-central Wisconsin, but these percentages are down to 10 to 30 percent. Potential for 4 inches or more is now zero. Across the rest of the area, a trace to 1 inch is the most likely scenario.

Cooler air will filter in behind this system; however, readings will still be near normal for early December. High temps from Sunday through Wednesday will range from the middle 20s to middle 30s, low temps will be in the teens and 20s.

Precipitation chances look low through the rest of the long term forecast. A clipper system moves across Canada Wednesday and Thursday. Right now, any associated precipitation remains north of the Wisconsin border, but will need to monitor in case the track drifts any farther south.

AVIATION
for 18Z TAF Issuance Issued at 1122 AM CST Thu Dec 7 2023

Other than a band of mid-clouds moving through the area early this afternoon, generally clear skies are expected this afternoon into this evening.

Models indicate that gulf moisture will return from south to north after midnight. Sufficiently strong winds in the boundary layer will likely result in this moisture manifesting as low stratus. Have cigs in the IFR/low-end MVFR range for late tonight, then in the MVFR range through Friday morning. There is still some uncertainty as to whether these low clouds will be able to mix out on Friday as a relatively strong low-level inversion would need to be broken.

Finally, winds are marginal for low-level wind shear after midnight across most of northeast Wisconsin. Have mentioned this potential for all TAF sites.

GRB WATCHES/WARNINGS/ADVISORIES
None.

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