Weathercatch: Warmer, drier weather likely to stick around for a while

Cool weather sweeping the region and the season’s first snowfall in the Washington Cascades is a big flip-flop from the month we just left behind. In October, there was no need to wrap ourselves in a comforter – at times we needed a fan. With more than two weeks of unusually warm weather, we couldn’t mourn the passing of summer; instead it felt like June.

During a typical October in Eastern Washington, temperatures dip 4 degrees from one week to the next, making it the month with the biggest temperature drop from start to finish. But this year, we saw something different.

Depending on where in the region you were, temperatures hovered in the 70s or 80s for 14 days throughout the first three weeks. In the Spokane area, the mercury hit 77 on Oct. 1, 10, 16 and 17. Compare 77 degrees on Oct. 17 to the average high of 59 for the same date – a difference of 18 degrees.

Which explains why, in mid-October, tomatoes continued to ripen on vines and residents wore T-shirts as they raked autumn leaves.

In Yakima and the Tri-Cities, it got even hotter, with temperatures reaching the 80s on Oct. 1, 2, 10 and 13. For comparison, the average high temperature for Oct. 13 at both locations is 66, a 14-degree difference. And many of the nighttime lows were high, with temperatures running an average of 9 degrees above normal. Most impressive was Yakima on Oct. 18, when the thermometer dropped to a balmy overnight low of 52 – compared to the average low of 33 for the same date.

But wait, there’s more: With an average high of nearly 70 degrees, the town of Prosser, where Washington State University’s AgWeatherNet is headquartered, experienced the warmest October ever recorded.

What caused our weather to mimic summer as the calendar shouted October?

First is El Nino, a weather system that’s been building strength in the Pacific Ocean since March. By causing the ocean to release huge amounts of stored-up heat into the atmosphere, it sets off a torrent of meteorological impacts around the globe, including warmer and drier weather here in the Pacific Northwest. Another big climatic driver is the Pacific Decadal Oscillation, similar to El Nino but broader, with a 15-to-20-year cycle. Every few decades, a massive arc of water in the Pacific flips between warmer and cooler conditions, bumping atmospheric temperatures up or down. Recent studies indicate that a bump to a warm phase has been underway since summer 2014.

Both PDO and El Nino played prominently in October’s weather, and they’re not expected to fritter away any time soon.

All of which makes it likely that our November and winter will exhibit plenty of above-normal warmth and dryness. Not summer-like, mind you, but not as cold or snowy as usual either.