A new rainy season started Sunday. What should we expect?

Cars and pedestrians brave the rain in downtown Bellingham in September.
Cars and pedestrians brave the rain in downtown Bellingham in September. pdwyer@bhamherald.com

Western Washington saw an above-normal “water year” close Saturday with a third of an inch of rain in Bellingham, making September the first month since April with near-average rainfall.

“It’s the start of the rainy season,” said National Weather Service meteorologist Johnny Burg in Seattle. A water year isn’t the same as annual rainfall, which is measured by calendar year, he added.

Less than a quarter of an inch of rain fell Sunday to open the 2017-2018 water year, a period that’s measured from October to September in the Northwest. No rain is in the forecast through at least Saturday.

But it was enough to persuade Whatcom County officials on Monday to lift a summer-long ban on outdoor burning in unincorporated areas. A ban on recreational fires was lifted Sept. 20.

Last year’s rainy season opened with a deluge as 19.12 inches of precipitation fell from October through December, according to measurements at Bellingham International Airport. Normal Bellingham rainfall is 13.69 inches for that period, records show.

It might be another rainy autumn this year, as the next three months are looking somewhat wetter than normal, Burg said, adding the NOAA Climate Prediction Center is showing an equal chance of a rainy October in the Northwest and a better than equal chance of a wetter November and December, especially on the Olympic Peninsula and the northern Northwest interior, which could include Bellingham.

“There’s an increasing chance of above-normal rainfall and temperatures,” Burg said, adding climate conditions influencing the Northwest remain in what forecasters call a “neutral phase.”

But that could change as a La Niña weather pattern begins to strengthen in late fall, as it did last year, he said.

“There’s a possibility that a La Niña might develop,” he said. “It usually means for us weather that’s colder and wetter than normal.”

Bellingham recorded its 19th wettest water year since records started being kept in 1948, Burg said.

Burg said 37.79 inches of precipitation was measured at Bellingham International Airport from Oct. 1, 2016, to Sept. 30, 2017. A normal water year in Bellingham is 35.83 inches.

Some 1.76 inches of precipitation was recorded at the airport in September 2017, the first near-normal month month since 2.72 inches fell in April.

Bellingham’s record water year was 1975-1976, when an astonishing 73.44 inches of precipitation was recorded – about double this year’s numbers.

Only a wet period from October 2016 to April 2017 saved Whatcom County from a below-normal water year.

Rainfall in May, June, July and August was all far below normal. During that period, Bellingham went a record 84 days – nearly three months – without a “wetting rain” of a tenth of an inch or more.

Only the extremely wet months of October-November 2016 (15.16 inches) and February-March 2017 (10.22 inches) kept Bellingham’s water year at near-normal levels, Burg said.

Robert Mittendorf: 360-756-2805, @BhamMitty