30 August 2010

You do know they just make it up, right??

Posted by Dan Satterfield

I enjoy the stories but the day to day forecast is worthless.

I always enjoy reading the stories in the Farmers Almanac. It’s been around for a LONG time and they have good basic astronomical info in it. Although you can get much more precise info from free programs like Stellarium.

About this time every year they release their forecast for the upcoming winter. TV stations everywhere gobble it up and do news stories on what the coming winter will be like.

Great free publicity!

Just to be clear here, the day to day forecasts are made up. They will not have any accuracy over that of a pure guess.

Some real science: An average of all moderate to strong La Nina's shows a milder than normal winter for much of the U.S. and Eastern Canada.

If you want to know what the winter will be like, the only think I can tell you is that with a moderate to strong La Nina brewing, the Southeast will likely have a drier and slightly milder than  normal winter. The odds of this are about 65%. That means there is a 35% chance it will be colder than normal here!

Other parts of the country will vary. See the graphics.

This kind of long range forecast is only possible because the La Nina pattern of colder than normal water in the Equatorial Pacific will cause a fairly predictable shift in the storm track over North America. The affects will actually be felt world wide.

Temperature anomalies for January during La Nina events. Images from NOAA. Click for full size image.

However, not every La Nina winter is the same. Each one is slightly different. Sometimes the La Nina pattern will hardly show up at all in some areas. Sometimes the expected warm areas are super warm.

The temperature anomalies in January for La Nina years shows that it’s quite warm in the Southeast U.S. most of the time but not always. The La Nina winters of 1971 and 1976 were slightly below normal over the Eastern U.S.

A scientific forecast would be for a good chance of having a mild winter in the Southeast. For those of you in Western Canada, a colder than normal winter seems like a good bet. Sometimes it is a super cold winter as well.

Just what you folks in Edmonton wanted to hear, isn’t it!