Weathercatch: The season’s first big storm system to be followed by a harvest moon

The first big storm system of the season rolled through much of the Pacific Northwest this week, bringing rain, winds and lingering clouds that should thin out in time for this year’s harvest moon Friday night.

Depending on where you live in Washington, the change in weather pattern occurred within 48 hours or so of the autumn equinox Saturday.

“The rain has arrived!” the National Weather Service in Seattle posted on Facebook early Sunday evening. “It will be a soggy start to the week.”

Rain, rain and more rain fell in the western part of the state, with some coastal areas getting 2-3 inches on Tuesday .

The storm system slowly moved east, arriving in the Inland Northwest early Tuesday morning. Although the region didn’t get the soaking rains that hit the western side of the state, we’ve experienced consistently unsettled conditions not seen since late spring.

What’s more, as raindrops began to fall, so did the temperatures. Before the storm system arrived, Monday’s high temperature in Spokane reached a summerlike 79 degrees. By Tuesday, however, it barely broke 60 – a drop of almost 20 degrees. Wednesday was even cooler, with a high in the upper 50s, along with more rain and breeziness. Additional shots of moisture pushing inland from the Pacific are expected to bring more rounds of rain Thursday and into Friday afternoon.

Also on Friday, overnight temperatures are forecast to dip to in the mid-to-upper 30s across much of the Inland Northwest, including a low of 38 degrees in Spokane. The last time we saw overnight temperatures that chilly was on April 22.

What triggered this cool, wet and breezy start to astronomical fall? A low-pressure system off the Gulf of Alaska tapped into a potent corridor of moisture known as an atmospheric river that originated in the tropical Pacific Ocean. The two meteorological patterns converged over the northeast Pacific, spinning off a series of storms that took aim at coastal Washington, Oregon and northern California before moving inland.

All of this leads to the harvest moon, an annual spectacle that will be at its peak on Friday night.

Compared to most full moons, this one typically appears bigger, brighter and with a tint of orange, especially shortly after it rises around 7 p.m. Although residual clouds are expected that evening, occasional breaks may reveal the shining moon named after the fall harvest.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek.