Marine Weather and Tide Forecast for Green Bay, WI

DISCUSSION
Issued at 237 AM CDT Thu May 22 2025

Short Term
Today
Tonight...and Friday

The latest RAP analysis and satellite/radar imagery show Wisconsin positioned downstream from a blocking ridge over north-central Canada and beneath cyclonic flow aloft. Light rain showers have exited central and east-central WI early this morning as a trough axis shifts south into the southern Great Lakes and low pressure slides over the eastern Great Lakes. Relatively drier air is moving into northern WI from the Lake Superior region, but more low cloud cover over northern Ontario is poised to surge southeast towards the region. As a result, cloud cover and sprinkle chances are the forecast concerns through Friday.

Clouds and Rain Chances: Cyclonic flow will continue across the region as an upper low drops south across Lake Superior today and northern Lake Michigan tonight. Within cold advection, northerly winds will bring moisture off Lake Superior and into northeast WI.
While forecast soundings do not show deep saturation, forecast soundings indicate low level instability up to 100 j/kg developing during peak heating this afternoon. Should therefore see convective clouds build with the heat of the day after partial clearing this morning. Can't rule out a few sprinkles over far north- central Wisconsin and also most of northeast WI this afternoon and will add to the forecast.

After partial clearing this evening, clouds will surge south again overnight into Friday. Don't see as much instability on Friday compared to today, so will keep the area dry.

Winds: Cold advection will steepen low level lapse rates today which will be favorable for breezy conditions. Most areas will see gusts 20-25 mph today. Door County could see gusts up to 30 mph.
Lighter winds are forecast for Friday (up to 20 mph).

Temperatures: Because of the north flow and cloud cover, below normal temperatures are expected through Friday with highs mainly in the 50s each day. Despite lows in the middle 30s over north- central WI tonight, there will be too much cloud cover and winds to make favorable conditions for frost.

Long Term...Friday Night Through Wednesday

A stable blocking pattern remains forecast over central Canada while an upper low spins over the Great Lakes or northeast into early next week. Cooler than normal temperatures and mostly dry conditions will prevail under this upper low. The ensembles show this pattern starts to break down towards the middle of next week when the central Canadian ridge builds towards the Great Lakes and warmer air moves into the region.

Rain chances...Little to no precipitation is forecast over the next week. The medium range models indicate diurnally based showers develop on each afternoon from Saturday through Monday.
Forecast soundings indicate a capped lower atmosphere so think precip chances are overdone. But should see decent coverage of convective clouds develop each afternoon.

Temperatures... Below normal temperatures will persist through the weekend, before moderating back to near or slightly above normal early to middle of next week. With weak high pressure at the surface, light winds will lead to favorable conditions for frost over far northern WI on Friday night and Saturday night. Cloud cover could negatively impact frost potential but it's too early to resolve those details.

AVIATION
for 12Z TAF Issuance Issued at 546 AM CDT Thu May 22 2025

VFR conditions prevail across northern Wisconsin early this morning with patchy 5000 ft ceilings pushing south towards the U.P. border. With daytime heating, expect convective clouds to build around 15-16z but generally remain VFR (3500-4500 ft). These clouds will gradually rise over the course of the day before scattering in the evening. Late tonight, MVFR ceilings are forecast to push south over northern WI and have included in the RHI taf.

Light northerly winds early this morning will become gusty again by 15-16z with gusts up to 20 kts. Winds subside again early this evening.

GRB WATCHES/WARNINGS/ADVISORIES
None.