October 11, 2013 § Leave a comment
Seen first in Spinsheet Magazine.
In my town there is a regular summer sea breeze. It doesn’t set up every day, but it is persistent and predictable enough to have caused the locals to coin the expression “cooler by the lake,” now a de facto advertising slogan for Milwaukee. Sailors have another name for it.
A local 470 sailor who helped organize our community sailing program in the ‘70s passed away recently, and in his honor, his friends deemed these special days “Doug Drake Days.”
On many warm summer days there is very little wind in the morning. Starting at about 10 o’clock a.m., as the sun warms the land, the air over the land heats and rises. The cool air over open water fills in for the rising hot air over land and a breeze builds from the southeast that lasts until dusk. Some days it is countered by a western gradient breeze; that is, the wind tracking with larger systems. This usually results in a battle of the breezes that can frustrate sailors. More often, gradient winds with some easting mix with and augment the thermal air that wants to go east too so as it builds it shifts. On days like this, the 3pm forecast is for 12 to 15 knots of wind and 1 to 3 foot, sparkling, blue-green waves from about 130 degrees. As an added benefit, the lake’s warmer surface water is pushed towards shore by the sea breeze and the swimming is fine. You know it’s going to be a Doug Drake Day when you spot the puffy clouds popping up over the shoreline as vapor forms with the rising and cooling air.
Doug had lucked into enough of these days in his long sailing life to know what to expect of them and he used them to his advantage. He had a storied racing career, in part, because he was a master of the sea breeze. For example, on one end of our bay, a solid southeaster sets up a starboard tack lift that Doug coveted and used to win many races. Sometimes, depending on the strength of the heating effect, the sea breeze can drop in from the outside or the inside. Other times, the sea breeze can be the only movement of air over water bouncing up and down in narrow, fleeting bands. Finding and staying with it is the best chance for successful sailing. Old timers, like Doug, did it best. While sea breeze may seem elusive and fickle, years of observing it gives advantages to the observer.
I’ve developed a shallow habit to try to understand the wind, and for a time, hoped it would speed my sea breeze reckoning. Like many modern sailors I routinely visit a handful of weather and wind forecasting websites many times before going out for a sail. I prefer the sites that show a map of the region, color coded for wind velocity, and with arrows to show wind direction. I print the pages showing what to expect for at least as many hours as we’ll be on the water.
But while wind models do well predicting wind speeds and angles from large, jet-stream-driven high and low pressure systems, they struggle mightily with local thermal conditions. Most models can’t show sea breeze effects for two reasons: (1) they haven’t integrated enough sensors and data sources into the weather computer networks, and (2), the variables that cause local conditions and changes are hard to program into software that thinks regionally. For example, how does a programmer in Texas account for the heating from concrete roads and buildings in a shoreline city in Wisconsin? A couple of thermal degrees over a couple of miles can matter a lot. It’s a simple question of resolution. Weather models are generally low resolution, and local factors that set up local conditions often happen in finer resolution than the models can handle. A local forecaster has the benefit of his/her own observations to be able to override the model’s coarse prediction, but rarely from a position on the water.
In this year’s Race to Mackinac, forecasters attempted to tackle the resolution problem by using a derivative of Nate Silver’s now famously accurate statistical election prediction method, combining many weather models and the voices of many local forecasters into a crowdsourced prediction. The forecast called for small high pressure systems mid-course that would bring light and variable winds on the lake, and that would force the fleet to either the east or western shore where the only decent breeze would be thermal. The models were generally right at a high level, but still lacked local precision. For example, sailors wondered how far from shore was ‘in-shore’ and what would happen the next day, or around the next bend. A quarter mile and fifteen minutes mattered during the race, but couldn’t be seen in the model.
Eventually computers and software may catch up. The day when all sailboat instrument wind readings will be sent to the internet to be integrated with other data may not be far away.
However, call me curmudgeonly, I prefer Doug Drake’s decades-proven, hands-on, environmentally-aware approach. Instead of swiping and pinching my semi-informed iPad hourly to guess where the lift might be, I hope to be there, on the water sailing; feeling and seeing the sea breeze enough times in my life to eventually be able to silently join forces with it.