Marine Weather and Tide Forecast for Green Bay, WI

DISCUSSION
Issued at 222 PM CDT Mon Apr 21 2025

Short Term...Tonight and Tuesday

Scattered light rain and light snow showers continued across the far north early this afternoon. Under cloudy skies, temperatures ranged from the middle 30s far north to the middle 40s over central and east-central Wisconsin.

For the rest of the afternoon into early this evening, winds will diminish and skies will clear around sunset. The combination of light winds and mostly clear skies will allow for some fog development overnight. Mid clouds are expected to move into much of the area towards 12z, thus keeping the potential for widespread dense fog at bay. For now, will have patchy/areas of fog. Lows tonight should drop into the middle to upper 20s far north with lower to middle 30s elsewhere.

The mid clouds are in response to 850mb warm advection ahead of a weak low pressure system. Rain is expected to develop west of the state and then should move into portions of central Wisconsin around 12z. The rain will spread eastward into northeast Wisconsin during the day. However, weakening 850mb jet, lack of 850mb warm advection and dry air should resulting in the precipitation drying up during the afternoon, thus chances for rain will be on the decrease during the afternoon. High temperatures should climb into the 50s to around 60.

Long Term...Tuesday Night Through Monday

Despite a warm front lifting north across the region Tuesday night and a low pressure system organizing across the region, rain chances will be meager as lift across the region will be de minimis through Wednesday morning. Isentropic surfaces show winds are basically parallel to the isentropic gradient, which means little to no lift across northern Wisconsin. By Wednesday afternoon, isentropic winds turn more southerly, allowing for a more orthogonal component of the wind with respect to the isentropic surface.

The region will be in an on and off active pattern Wednesday night through Friday as a strong 110+ upper level jet across the international border combines with several mid level shortwaves as a slow moving surface low tracks through the central Plains and southern Great Lakes region. There will likely be dry periods in between the wet periods, as the models indicate. However pinpointing these periods is difficult as there is little consensus between the models on what these specific periods will be.

High pressure will eventually sink south and win out this upcoming weekend as the low tracks towards the middle Atlantic states. As the high moves off to the east, the active pattern continues as another low emerging over the central Plains brings rain chances back to the area Sunday night into Monday.

AVIATION
for 06Z TAF Issuance Issued at 1058 PM CDT Mon Apr 21 2025

The combination of mostly clear skies and light winds along with recent rainfall makes fog develop likely overnight, mainly across central and northern WI. Framed out the best timing for fog and MVFR/IFR vsbys with TEMPO groups at RHI, AUW, and CWA

On Tuesday, clouds will return to the region ahead of a low pressure system that is forecast to lift across northern MN. Cigs should remain VFR through the morning hours, but will gradually lower and become MVFR by early to mid afternoon and as low as IFR central to north-central WI by Tuesday evening. There is also a chance for rain showers at all terminals Tuesday mid morning through the afternoon which is covered by PROB30 groups. Was not confident enough to include thunder in any of the TAFs but a few rumbles are possible during the early afternoon Tuesday, mainly at GRB, ATW, and MTW.

GRB WATCHES/WARNINGS/ADVISORIES
None.