Why Has February Been So Wet?

The 2016-2017 winter has been an extraordinarily wet winter for California, but Washington and Northern Oregon have actually been drier than normal for most of the winter. But with Seattle on track to break their all-time reocrd for monthly rainfall in February and Portland not too far behind, one wonders what is responsible for the sudden change in our weather. In this blog I’ll explain why we’ve transitioned to a warmer and wetter pattern, and take a look ahead through the rest of the month to see if we have a chance of breaking any monthly rainfall records across the region.

Let’s start out by looking at the observed precipitation and temperature departures from average over the past 90 days. As you can see, there is a clear increase in both precipitation and temperature as we head further south.

The reason for this distribution is because the jet stream has been further south than normal this winter, directing strong storms into California and leaving areas further north on the “cool” side of the jet stream. Instead approaching our area directly from the west like it often does, the jet stream was pushed north into Alaska by a big ridge of high pressure over the Northern Pacific. It then dove southward into California thanks to a large trough off the West Coast, giving us cool northwesterly flow with frequent periods of dry northerly or northeasterly flow as continental arctic air surged into our region.

But for February, the pattern has changed significantly. The ridge has retrograded to the NW and is now closer to Kamchatka, and with this ridge out of the way, the jet stream is traveling straight across the Pacific, giving us our more typical southwesterly flow that we all know and love.

We’ve seen very strong southwesterly flow over the past couple days as a strong “atmospheric river” plows into the area. As a result, several rivers around the region are flooding and numerous landslides around the region have been reported. Follow our forum keeping track of the latest landslides, washouts, sinkholes, and more to get the latest on this front. Yes, pun intended. 🙂

We’ve seen what a shift from NW flow to strong SW flow can do for our rainfall totals, but what does the rest of February look like? Will we be able to beat any monthly rainfall records?

The rest of February looks significantly drier and cooler than the first two weeks as a ridge builds in the NE Pacific and a large trough forms just off our coast, directing (once again) the bulk of precipitation to California. The Climate Prediction Center keeps the West Coast cooler than normal, with below-normal precipitation for Washington and Oregon and closer-to-normal precipitation throughout California.

However, because rainfall totals are already so high, it won’t take much more rainfall to break any records. After 1.54 inches of rainfall today (and counting), Portland is currently sitting at 8.04 inches, and they need two inches to break their February record of 10.03 inches set back in 1996. Seattle is at 7.84 inches after receiving a half inch today, and needs 1.27 inches to match their record of 9.11 inches from February 1961. With 12 more days to go, I’d be surprised if Seattle doesn’t break their February record. It’ll be a little tougher for Portland to beat their record set back in 1996, but they certainly have a decent shot.

One thing is for certain: February 1996 will be far more memorable than February 2017 in the rain department for Portland, as the Willamette River crested ten feet over flood stage and caused massive flooding throughout the Willamette Valley back then. After all the rain today, there are plenty of large puddles around, but I don’t see the Willamette overflowing its banks anytime soon.

Thanks for reading, and don’t forget to comment in the forums with any information you may have regarding landslides, sinkholes, and washouts!
Charlie