Driest November in decades not a worry just yet, but could point to shift toward El Niño | KNKX

Driest November in decades not a worry just yet, but could point to shift toward El Niño

Dec 6, 2019

The dry, cool and sunny conditions that brought extraordinary fall color to the Northwest also have toppled a major record. Seattle charted its driest November in 43 years, with just 1.71 inches of rain – about 26 percent of normal. (Spokane was at 30 percent of normal, with .68).

That’s the driest November since 1976 — a “startlingly dry” year that saw about half of last month’s precipitation, says KNKX weather expert Cliff Mass.

But the latest dry weather isn’t cause for concern just yet, he stresses.

“Never call a winter in mid-December,” Mass says. “I wouldn’t be concerned unless these conditions continue into February.”

One key feature is common among the dryness then and now: high pressure over the eastern Pacific. Mass says that was in place 43 years ago, and it has been parked over us this year since November. The pressure forms a ridge aloft that keeps precipitation sparse and weakens weather systems as they come in.

“We don’t tend to get the low-pressure systems that bring our big weather,” Mass says.

And, he says, the state-of-the-art European Center ensemble forecast model points to this high pressure sticking around and keeping us mostly dry through the rest of December, at least.

So, why is the pressure there in the first place? Mass says that’s harder to figure out. But it looks like a weak El Niño winter may be emerging. The sea surface temperatures in the tropical Pacific have warmed substantially, and the configuration of thunderstorms in that area is pointing in that direction, as well.

El Niño years are associated with higher pressure over us, as well as warmer- and drier-than-normal conditions.

Currently, we are officially expecting an ENSO-neutral year, based on observations compiled by the National Weather Service Climate Prediction Center. But Mass sees that changing.

“I think there’s a significant chance that we are getting into a weak El Niño,” Mass says. “And that may be driving these anomalous weather conditions.”