Hopefully you’ve paid close attention to our forecasts the past few days. If so, you’ve finished up any project that requires dry weather and are now ready for a week of rain. No, it’s not going to rain for the next 168 hours non-stop. Instead, we’ll see a succession of wet Pacific weather systems moving into the Pacific Northwest.
After a very wet September, the faucet has shut off this first half of October. We’ve seen little/no rain the past 10 days in the Portland metro area
And of course it’s been a very cool 1st half of October; temperatures are running 5 degrees below average at PDX so far… THIS HAS BEEN THE COLDEST 1ST HALF OF OCTOBER IN PORTLAND IN MY LIFETIME! Only two have started colder, October 1968 and October 1949. Those were followed by some interesting winters…just throwing that out there. I highly doubt what happens the first two weeks of October means anything about the upcoming winter. Notice the last few Octobers have been wetter than average
A cool upper-level trough (dip in the jet stream) is sitting in the Eastern Pacific and moves a bit closer tomorrow
Tonight a weather system is sitting offshore; it’ll move inland Wednesday morning. That system will be quickly overtaken by a cold front by tomorrow afternoon. So we get two waves of rain tomorrow. Behind that cold front, Thursday and Friday will feature the usual cold showers mixed with sunbreaks. Friday night and Saturday a quick-moving trough spins up a surface low pressure system offshore. Models are showing quite a slug of rain and gusty southerly wind with this one.
That said, I don’t see any hints that we’re entering a real stormy pattern with multiple areas of deep low pressure tracking along the coastline. We’re just going to see a parade of wet and breezy systems moving overhead. In October, in this pattern, it’s possible to get those waterspouts or weak tornadoes too if the pattern is just right. We’ll be on the lookout for that.
Now that you’ve finished planting your spring bulbs, garlic, or cover crops, you’re probably wondering how much rain is on the way? Quite a bit! The WRF-GFS from UW shows less than 2.50″ in the western valleys ending next Tuesday
ECMWF, GFS, & GEM models all show somewhere between 1.50″ and 3.00″ in the western valleys of Oregon and SW Washington. Maybe 5-10″ wettest parts of Cascades and Coast Range. This isn’t enough to cause flooding when spread out over a week, but it’ll help recharge groundwater I suppose
This is the reason that I’ve been saying to “wrap up all your dry weather projects” by tonight. It’s going to be quite wet over this upcoming week.
What about more dry days? Models are suggesting we get some sort of upper-level ridging over the USA West Coast starting a week from now. All three of the above models show a strong ridge right over us 8-10 days out. Here’s Friday the 25th
It’ll be interesting to see if we get a setup we’ve seen twice this autumn; a trough suddenly comes across the ridge, pushing it back to the west and putting us under cold northerly flow. There are a few hints of that in the 12z ECMWF ensemble chart; some ensemble members take quite a dip in the 2nd week.
To wrap it up…enjoy your inside time this next week. And enjoy the gentle Pacific Northwest rains splashing on your roof.
Chief Meteorologist Mark Nelsen