Wind roses

Posted on

I love when friends and readers ask me questions I’ve never been asked before, especially when I don’t know the answer. It’s a learning opportunity! On Sunday, a friend asked how she could find out the seasonal wind direction for some property she is purchasing and planning to turn into a farm. Her goal is to be sure the barn isn’t upwind of the bedroom. Smart thinking!

While I doubted the town nearby had weather records, I knew there must be some data out there I could find to give her a good approximation. So, I asked a climatologist friend where I should look. She suggested looking at the North Carolina Climate Office’s wind rose tool.

The climate office’s website defines a wind rose as “a graphical tool used to show wind speed and wind direction for a particular location over a specified period of time.” The tool allows you to choose from a multitude of stations in six states plus Puerto Rico with hourly wind measurements.

I could tell it would prove a useful tool in the future, but not in this case. The farm in question is in southern Michigan – not in one of the six states covered. I looked up that state’s climate office website, and it didn’t prove nearly as user friendly as ours. So, I decided to take a different route and use the information provided by her local National Weather Service office.

Grand Rapids, Michigan, issues a climatological report annually for some of it’s official reporting sites. Battle Creek was the closest to the farm. I looked at the data for 2017 and 2016, and the info was pretty consistent with the average direction between the two years being just six degrees apart. In case you’re wondering, those degrees refer to the 360 degrees of direction on a compass with zero or 360 degrees being north and 180 degrees being south.

Meteorologists usually refer to the direction from which the wind is coming. A wind direction of 241 degrees means that the wind is coming from the west-southwest and blowing toward the east-northeast. In this case, we are considering the average wind direction over the course of the year, and without a wind rose to give more detail, there are some assumptions being made. We’re assuming over the long term, she’ll see the wind coming from that general direction. One thing to keep in mind with averages though, is that sometimes it takes extremes to get that average.

Cape Hatteras is a good case in point for wind extremes while Raleigh-Durham International Airport is an example of the typical direction being closer to average. Cape Hatteras has greater exposure to tropical cyclones and nor’easters and diurnal wind oscillations – meaning sea breezes and land breezes. With the exception of the occasional tropical system reaching inland, RDU’s winds tend to be generated by land-based weather systems and its piedmont geography. You can look at the wind roses for each location to see the similarities and differences.

By sharing this information, I hope to give you the ability to do your own research using recorded observational data and tools your tax dollars are backing. This is publicly-supported science at work!

Cape Hatteras wind rose

Cape Hatteras, NC, wind rose

 

RDU wind rose

RDU International Airport wind rose