Beyond the Forecast: The unpredictability of NW weather


by RICH MARRIOTT / KING 5 Meteorologist

Posted on November 12, 2009 at 8:30 PM

Updated Thursday, Nov 12 at 8:50 PM

After last winter's rugged weather, most of us are understandably on edge about this winter's prospects. Although there are no guarantees, the odds seem to be tipping toward a drier and warmer winter.

When it comes to Northwest winters, it's always something. Last year we were battered by snow that didn't want to end. And in 2004 and 2005, we couldn't buy a snowflake, even in the mountains. Why do we see such differences?

Part of it is just what meteorologists call "the variability of the system." Basically, any type of weather that can happen, will happen.
But we know some kinds of weather happen more often than others. Each winter is like a roll of the dice.

We know which numbers are most likely to come up, but on any given roll, we just can't say for sure which one it will be.

But we have learned that predictable variations in the atmosphere can load the dice and make certain outcomes more likely.  In our case, it's El Niño and La Nina that seem to shift the odds the most.

Last winter a La Nina developed and the dice roll definitely came up cold and damp, especially for about three weeks in December and January. 

Dr. Nate Mantua is a UW research professor who studies the shifts in the climate odds.

"What El Nino does to our winter climate is it's shaving the climate odds towards outcomes that would lead to a warmer and drier winter, once you add up all of the days," he said.

But if we win this bet, what are the chances of more lowland snow?

"The shift in the odds is that the low elevation snow fall is quite unlikely during an El Nino winter for places like Seattle or anywhere in the Puget Sound Lowlands, so it can happen but it is much less likely to happen," said Mantua.

But you shouldn't store you skis and snowboards yet.

"The best bet, there will be plenty of snow for skiing, but maybe not a great early start, probably not a lot of great powder days, but enough to get people out there to have a good year," said Mantua.