PORTLAND, Ore. — The autumnal equinox falls just before midnight Pacific Time on Friday, making Saturday the first official day of fall. The way things are looking now, the change of seasons will be accompanied by an appropriate shift in weather across much of the Pacific Northwest.
First, what is the autumnal equinox? It's one of two points each year at which the sun shines directly onto the equator, and when day and night are of equal length — the other day being the vernal equinox at the beginning of spring. Days are longest at the summer solstice, which we saw on June 21, and have been getting shorter since.
From now until the winter solstice on Dec. 21, daylight hours will be shorter than nighttime hours, and getting shorter each day. Sunset will happen at 7:10 p.m. on Friday and at 7:08 p.m. on Saturday.
Technically, due to the way we measure sunrise and sunset, Saturday will not be a day of perfectly equal day and night for us this year — that will happen a few days later. But it's still the astronomical first day of fall.
Fall weather on the way
KGW meteorologist Rod Hill is tracking a "large low center" that will hold offshore as the circulation pattern, accompanied with a strong jet stream, sends in hours of widespread rain stretching from Medford in the south to Seattle in the north, even going east over the Cascades into central and eastern Oregon.
The first of that moisture is expected to arrive during the day on Saturday and again on Sunday, but the bulk of it will fall Sunday night and through the day on Tuesday.
Coastal rain amounts could top 2 inches, while the Willamette Valley and parts of Washington are expected to get over an inch.
The breezy south winds and rain totals aren't expected to produce any weather alerts to worry about, but there will be a beneficial aspect — the rain is expected to soak all of the major wildfires still burning in Oregon and Washington located near the Cascades or further west.
Current weather models suggest that this cool, wet pattern will prevail through the first week of October or slightly beyond.