We have gone several years since the last big windstorm from off the Pacific.
This year may be different. This blog will tell you why.
The Chanukah Eve Storm of December 14, 2016
Major Northwest windstorms are associated with intense low-pressure centers reaching our coast and then moving to the northeast. As illustrated below, these storms possess intense pressure differences around them, which produces strong winds.
Big Pacific cyclones hitting the Pacific Northwest are rare during strong El Nino and strong La Nina winters.
To illustrate this fact, the figure below shows you the sea surface temperature difference from normal in the central tropical Pacific, the key indicator of El Nino and La Nina, from 1860 through 2000. Normal (or neutral years) are found from -0.5 to 0.5 C. Moderate to strong El Ninos occur when temperatures are more than 1°C above normal. Moderate to strong La Nina's when temperature is more than 1°C cooler than normal.
And now the key point. The latest forecasts suggest we will be in neutral conditions or a weak La Nina this year, a situation in which many big windstorms have occurred in our region.
Below is a graph showing a collection of predictions using different methods, some statistical, some using physical models. Most are predicting neutral or weak La Nina conditions. Good windstorm potential.
Why are neutral years better for strong low centers approaching our coast?
Major Pacific low centers/cyclones are closely associated with the jet stream.
During strong El Nino years, the jet tends to go south into California (see figure)
In contrast, for La Nina years, the jet stream tends to swing north of us, leaving our region in a northwesterly flow not favorable for strong windstorm development. The last few winters have been dominated by El Nino conditions.
No guarantees, but I suspect we have a decent chance at a major blow this winter.
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