Let's do a quick checkup on January so far:
1. It has been VERY WARM compared to what we usually see in early January. Through the 10th, Portland is running 6 degrees above average, 7 at Redmond, and 9 degrees at Pendleton! Almost the entire USA has been much warmer than normal...who stole Winter 2020-21?
2. It has been WETTER than average across much of the PACNW, more so the farther north and west you go
- Mild to warm conditions continue for the next 8-10 days
- We get soaked Monday-Wednesday this week, then much drier Wednesday through the 18th-20th
- There's no sign of lowland cold/snow/ice west of the Cascades through at least the 20th
The Stormy Weather
I see an "atmospheric river" headed our way tomorrow through Wednesday. That's basically a low level flow of very moist air that hits the Coast and Cascade ranges, squeezing out a lot of precipitation. Of course plenty falls along the beaches and in the valleys too, but not as much. This will be powered by the Pacific jet stream reaching from Japan all the way to the PACNW. Check out the 235 mph maximum wind over the far western Pacific Monday afternoon!
A good way to look at heavy rain events/atmospheric rivers is by using Integrated Vapor Transport (IVT); kind of like checking a river gauge to see how much water is flowing through. That's quite a "river" tomorrow evening...
Then again Tuesday night, this is around 10pm.
Since the flow is not coming directly west-east, it's possible we get a bit more rain into the valleys than we sometimes see. ECMWF and RPM are both pretty reasonable showing maybe 2" in the valleys by the time it dries out Wednesday
I think 3-6" is a good bet in the mountains around us; this is similar to what we saw this last time around. That led to minor flooding on some coastal rivers, but nothing significant inland. That said, anytime we get this much rain in just a couple days it's fair to expect some mudslides and/or landslides in spots.
Wind is something else to watch. The boundary line between cooler air to the north and warm south of us will be sliding north/south through the region a couple times. When it is just to our north, we'll get a gusty southerly wind, especially if a "wave" moves along the front. That should happen tomorrow night and again late Tuesday night. There is some model disagreement on how strong the wind gets based on their disagreement where the waves, or even a surface low track. Right now the ECMWF seems reasonable showing the stronger 2nd "event" late Tuesday night.
Gusts 60-70 on the beaches and 35-50 in the valleys; not a big windstorm by any means.
As of now the NWS does not have a flood watch OR any wind advisories/watches/warnings. I assume that will change in the next 12-24 hours.
- Expect light rain Monday, but it'll turn heavy at times Monday night through early Tuesday. Then a 2nd wave of rain later Tuesday through around sunrise Wednesday. 1.50-2.50" in valleys and 3-6" in mountains. THIS SHOULD BE ENOUGH FOR LOCALIZED PONDING OF WATER OR FLOODING, BUT NOT ENOUGH FOR A WIDESPREAD FLOOD EVENT.
- Expect one surge of southerly wind about this time tomorrow evening or a bit beyond, calm wind Tuesday, then a stronger surge sometime Tuesday night. NEITHER APPEARS TO BE A SIGNIFICANT WINDSTORM, but I'll be keeping a close eye on it of course.
In the Cascades
As mentioned in a previous post, and in our podcast, Cascade snowpack is running below average for early-mid January. Things will get a bit worse over the next week. Check out the snow level forecast
Not good. Only Wednesday and late Friday/Saturday are reasonably cool. ALMOST ALL OF MONDAY-TUESDAY'S PRECIPITATION WILL FALL AS RAIN AT THE SKI RESORTS. If you want to ski, go VERY early Monday, or wait until Wednesday-Friday. Our 7 Day forecast for the Mt. Hood area...
I'm about out of time so I'll make it brief. There are pretty clear signals on all models that some sort of significant pattern change may arrive in the January 20th-24th timeframe. The warm ridging that is giving us mild weather, along with an atmospheric river moving through that ridge, is shifting much farther west in about 10 days. Next Sunday you can see a strong ridge right over us = mainly or all dry MLK Weekend
And here's an example of one week later, quite a change with heights much lower over us = cooler.
Will this finally give snow to elevations down around 2,000' and below like a normal La Niña winter? It's been mostly absent so far! All models at least show cooler systems coming in from the northwest at that time, and a few ensembles bring arctic air down from the north. It's far too early to know what we're going to get out of this. It could be 1) A more typical La Niña pattern with cooler systems but still no valley snow, or 2) Colder arctic air slides south and really cools us off, with the chance of lowland snow. Nobody knows as of now. I'll post again later this week or for sure next Sunday with an update.
Chief Meteorologist Mark Nelsen