Marine Weather and Tide Forecast for Green Bay, WI

DISCUSSION
Issued at 153 PM CST Mon Jan 20 2025

Short Term...Tonight and Tuesday

The latest RAP analysis and satellite/radar imagery show arctic high pressure centered from the northwest Great Plains to the central Gulf Coast early this afternoon. The coldest air during this arctic air outbreak so far lies from northern Minnesota to the Dakotas where 32 below to 36 below temps at 850mb are analyzed by 12z raobs at International Falls and Bismarck. Across northern Wisconsin, surface temperatures have warmed to around 0 degrees over the Fox Valley and from 5 below to 9 below zero over north- central Wisconsin at 1 pm. Wind chills generally range from 15 below to 30 below zero.

The core of the coldest air will swing across the region tonight into Tuesday morning. While there are scattered clouds upstream, don't think this will have a significant impact on temps if they move into northern WI tonight.

Snow cover is playing a significant role with temp/wind chill forecasting. Snow depths are analyzed to be greater than 2 inches generally north and west of a Wausau to Iron Mountain line. Where this minor snowpack exists, winds decoupled last night at times which mitigated the impacts of the extremely cold wind chills. MOS forecast guidance indicates similar wind speeds tonight, and think will see winds drop off at times. This means that while low temps will likely be colder than the NationalBlend guidance, wind chills may not always fall into warning criteria. But of course when there is even a slight wind, wind chills from 35 below to 45 below zero can be expected. Have therefore lowered min temps over north- central WI closer to ECMWF statistical guidance.

Elsewhere, wind chills remain on track to fall into the 30 below to 40 below range late tonight through Tuesday morning. No changes to the extreme cold headlines appear warranted.

Highs on Tuesday afternoon will likely remain below at or below zero away from Lake Michigan with wind chills ranging from 20 below to 25 below zero. A Cold Weather Advisory after the Extreme Cold Warning expires will likely be needed through late in the afternoon or late in the evening. Quite a bit of uncertainty how long to run the subsequent advisory as wind chills hover right near or just below criteria. So after coordinating with surrounding offices, have refrained from an Advisory issuance.

This will likely be the coldest stretch of weather since the last two days of January 2019. NWS La Crosse has a nice write up of that event at weather.gov/arx/jan2019.

Long Term...Tuesday Night Through Monday

Focus in this part of the forecast remains on the tail end of the arctic outbreak on Tuesday night followed by light snow chances at times.

Temperatures/wind chills: Arctic high pressure will slide from the Ohio Valley to the mid-Atlantic states as a warm front moves into the northern Mississippi Valley on Tuesday night. As the surface high departs, both warm advection and cloud cover will increase through the night. Both these trends should lead to a warming trend after low temps occur in the evening. As a result, it looks like a Cold Weather Advisory will only be required through the end of the evening.

Temperatures will moderate from Wednesday (middle teens to lower 20s) through the weekend (middle to upper 20s). Temps appear to have trended colder this weekend, so the probability of reaching 30 degrees has decreased.

Light snow chances: Forecast soundings indicate sufficient saturation will occur prior to 6 am Wed for a chance of light snow, but think some of the upward motion will get lost to creating saturation of a very dry arctic airmass. It also appears that moisture profiles are disjointed. Therefore snow chances will remain low on late Tue night into Wednesday night. Isolated accumulations up to 1 inch appear possible but most locations will see a dusting to a half inch.

Additional shortwave energy and a cold front will arrive this weekend in a similar fashion (unfocused/disjointed). The chance of light snow will be the highest during the late Friday night into Saturday timeframe, but accumulation potential looks minor.

AVIATION
for 06Z TAF Issuance Issued at 1026 PM CST Mon Jan 20 2025

Light to moderate west winds and mostly clear skies are expected through Tuesday morning, along with continued frigid temperatures and wind chills. High and mid-level clouds will increase during the late afternoon and evening, and flurries or very light snow will be possible in NC/C WI toward the end of the TAF period.

Surface winds will back SW to S late Tuesday afternoon into Tuesday evening, but will generally be 10 kts or less. However, strong southwest winds aloft will overspread the region from west to east Tuesday evening, leading to widespread LLWS.

GRB WATCHES/WARNINGS/ADVISORIES
Extreme Cold Warning until noon CST Tuesday for WIZ005-010>012- 018-019.

Cold Weather Advisory until midnight CST tonight for WIZ013- 020>022-030-031-035>040-045-048>050-073-074.

Extreme Cold Warning until noon CST Tuesday for WIZ013-020>022- 030-031-035>040-045-048>050-073-074.