winter 2011/2012

NOAA versus Farmers Almanac -- which one do you believe?

NOAA has published its forecast for winter 2011/2012.  NOAA's #1 criteria for winter weather forecasts for 2011/2012 (temperature and precipitation) is the presence or absence of La Nina.  La Nina is the term used to refer to below average sea surface temperatures in the south Pacific.  Sea surface temperatures routinely oscillate between average or "normal", above average (El Nino) and below average (La Nina).  La Nina conditions are correlated with mild winters and below average precipitation for some areas of North America.  To hedge its bets, NOAA also cites the possible "wild card' of the Atlantic Oscillation.

In almost diametrical opposition, Farmers Almanac forecasts a very cold winter for the northern Rocky Moutains, northern Plains, and western Great Lakes.  Winter temperatures for the eastern two thirds of the U.S. (excluding New England) will be above average but very wet -- mostly cold rain.  Farmers Alamanc does not discuss La Nina effects in its forecast.  FA had to go to press a few months ago and La Nina had gone into hibernation but has since resurfaced.  Maybe FA forecasts would similar to NOAA if they were real time.

I have listened carefully to many meteorologists discuss forecasts for winter weather for many years.  Here is what I know for sure.

• December and January will be colder than September and October -- everywhere exccept maybe southern California and south Florida.
• Cold fronts will be followed by warming trends -- a few days or a week of cold followed by a few days or a week of slightly warmer weather
• Other big picture variable like the Atlantic Oscillaion may or may not override the La Nina effects
• El Nino and La Nina conditions in the Pacific both tend to give North America a warmer than average winter.
• Weather forecasters have difficulty knowing why North America has colder than average winters but sometimes it does.
• Most weather forecasters rely heavily on correlation analysis and probability.  No one seems to understand the true fundamentals other than in a very broad sense.
• We seem to care more about how cold the winter will be when natural gas inventory is below average.  Since natural gas inventory now looks set to reach an all time record high by mid-November, most likely, most of us don't care how cold the coming winter will be except as it affects our plans for ski trips. 

Maybe we ask for too much certainty in what is inherently very dynamic and uncertain.   My personal favorite global climate variable is the Pacific Decadal Oscillation.