Recently, someone asked about predicting waves on Lake Superior, “How exactly would a person know what the waves are like up there? I am in the Cities and have been dying to see big waves.”
Predicting waves on Lake Superior
Predicting waves on Lake Superior is the black art of weather prediction. Briefly, on the north shore, the waves get best for us on northeast and southwest blows. Although a really strong wind from directly east, west or south can also give us good waves. North and northwest winds do nothing for us. The shore will be calm on those winds.
Wind creates waves on Lake Superior
Wind creates waves and their size results from the combination of wind speed, wind duration and the fetch (distance that wind blows over the water). To get bigger waves you need a long fetch (NE & SW), strong winds and the wind blowing for a long time.
With 15 to 20 mph wind from the right directions we’re likely to see between 2 and 6 foot of waves depending on the time the wind is blowing. With winds between 20 and 30, we’ll often see 6 to 8. When winds get above 30 mph is when the big waves hit.
Where to photograph waves on Lake Superior
In Grand Marais, the Grand Marais lighthouse works best on 20+mph days with SW winds. It can also go with south and really big NE winds. The East Bay explodes with NE winds. If it’s raining and the NE winds are blowing often the downtown parking lot in front of the Co-Op will flood, because the water level of the East Bay rises with a storm surge and seiche which prevents the water from draining out of the parking lot.
On a strong NE blow, it’s best to head to Sugarloaf Cove, Tettegouche State Park, Stoney Point or Duluth. With a SW blow, 121 works great. That’s mile marker 121 on Highway 61.
Prediction tools
There are a few tools you can use to help your search for waves. The first is the NOAA Marine Forecast and the second is NOAA’s Great Lake Forecasting System. Both have flaws, they often predict waves bigger than we actually get, but they give you good info to start your predictions.
I use the tools and combine that with NOAA’s weather forecast for Grand Marais (or wherever I’m at). I look back at the weather history for the last few hours, look at the forecast and then make that black art prediction about whether we’re going to have the right weather to make big waves.
But the quick and dirty answer is there will be waves if the wind blows from the northeast or southwest at 15+ knots for longer that a couple of hours. For big waves, the wind needs to blow at 20+ knots for four or more hours.