After a very strange Summer and a very back-and-forth Autumn, what lies ahead for the Winter of 2009-2010? As we all remember, the last two winters have been pretty rough with lots of snow, frequent storms and quite a bit of cold weather. Will this year repeat? While the official Climate Prediction Center forecast won’t be issued for some time yet, the most recent outlook continues to show above normal temperature for the upcoming Winter season. Part of the reason for the warmer forecast is El Nino. El Nino is characterized by warmer than normal ocean water in the Equatorial regions of the Pacific. Even though El Nino is thousands of miles away from us, it does impact our weather. Typically, El Nino brings us milder Winter months with warmer temperature and above normal precipitation. The stronger El Ninos increase the odds of warmer temperatures.
During the strong El Nino episodes from 1950 through 2008, 6 out of 8 winters in Waterloo had above normal temperatures. Those warmer temperatures might also tilt the scale away from snow and toward more rain and ice during the winter. Here’s a link that talks more about El Nino and Iowa Winters.
Don’t put those snow shovels too far way, though! There is another factor in play, and it might override the normal El Nino effects. There’s another Pacific Ocean phenomena called the PDO, or Pacific Decadal Oscillation. The PDO changes from a positive phase (warmer ocean water) to a negative phase (colder water), and this, too has a huge impact on the climate. Looking at the graph below we can see that the PDO flipped
from positive to negative back around 2005. The various PDO phases seem to last for quite some time…somewhere in the neighborhood of ten to thirty years! Having the PDO in the negative phase seems to increase our odds of colder Winter weather.
So, what’s it gonna be? Warmer Winter or colder Winter? El Nino or the PDO? No one seems very sure at this point. One final wild card in all of this is the fact that El Nino is quite variable in strength…and it may increase or decrease over the next couple months. Also, if El Nino occurs farther West than usual, the effects on our weather would tend to be less.
At least for now, the long-range outlook says a milder Winter ahead. Keep in mind, however, that was the forecast for the last two Winters, too…and we all know how they turned out!