Winter isn’t finished yet; colder days return in final days of January

3pm Monday…

We all know January as been very mild. Temperatures are running several degrees above average; the official climate station at PDX hasn’t even dropped below 32 degrees! That mild weather continues through Friday and probably Saturday too, but then we see a change in the last 4 days of the month.

For those with short attention spans…also known as TL;DR (too long, didn’t read):

Quick Summary

• Mild weather continues through Saturday (the 28th). Weather likely won’t affect your life much the next 5 days. Continue with your normal daily lives
• Cold air will likely arrive in the Portland metro area, and all parts of the region, Saturday night or Sunday.
• That means high temperatures fall into the 30s in Portland for Sunday and probably stay that way next Monday. At this point we don’t see the REALLY cold stuff that appeared in December. Remember the afternoon high of 23 just 3 days before Christmas??? 35-39 would be much more reasonable, but still cold.
• As the cold air arrives, will there be enough moisture around for snowfall? That IS a possibility Saturday night or Sunday morning and several of our models are producing that right over the metro area and points north (not so much south of Portland). Others say it’ll be too dry.
• So the question “Will it snow at my house Saturday night?” is answered at this point by “that’s possible”.
• NEXT week could be a busy weather week with cold air interacting with moisture to possibly produce snow. But models are all over the place that far out in time.
• We will be in a cool period Sunday through at least the first few days of February, keep a close eye on the forecast. It’s time to pay attention again!

The Change Ahead

The pattern setting up is a classic one for cold & snow fanatics (yes, there really are people like that!). It doesn’t always produce snow, nor does it always send a really cold modified arctic airmass into the region. But when Pacific Northwest meteorologists see this setup, we watch closely!

A strong upper-level ridge is sitting over the far Eastern Pacific, just off the west coast of North America. It’ll be there through Thursday, blocking storms and keeping us dry; a nice change after almost 3 weeks of continuous rain. Here’s the view Wednesday; uneventful weather

(KPTV)

But then a strong upper-level “shortwave” trough crosses over the top of the ridge and digs down the eastern side. By Friday, that first trough is over us. Showers, cloudy, but mild since flow is onshore

(KPTV)

See #2 up above? That’s a 2nd and much colder trough digging down the back side of the ridge. So the ridge “retrogrades” or backs up to the west. And THAT opens up the door to the north. Cold air comes pouring south. By Sunday morning, that system is directly overhead (and heading south).

(KPTV)

What you don’t see at the surface (this is up at 18,000 ft.) is cold/dry arctic air has surged south as well. It’s banked up against the east side of the Cascades at this point and pouring through the Columbia River Gorge. All models look about like this at 5,000′ Sunday morning; temperatures are in Celsius. BTW, everything is in Celsius on most weather maps. This means it’s about 10 degrees Fahrenheit up at Government Camp Sunday morning…brrr!

(KPTV)

This setup is THE SETUP you want to get cold/snow into the region. Some moisture gets picked up by the cold air heading out over the ocean. Then a little extra lifting as that surface wedge of cold air pushes into the region. Sometimes we get NOTHING snow-wise out of this pattern as cold air arrives, other times maybe up to 2″. It depends on how that upper level trough digs south too. If it just moves by quickly and slightly east of where the Euro model shows it (above), we are typically just dry and a chilly east wind begins to blow. Since we’re still 5+ days out, it’s a real guess exactly how this turns out.

Models are in very good agreement on at least a short period of cold weather. GFS ensemble temperatures seem reasonable

(KPTV)

The WRF-GFS meteogram shows enough moisture for snow sticking late Saturday evening and cold days Sunday through Tuesday. Saturday 4pm is highlighted with the yellow line. This model has been notoriously cold in the extended time range the past 2-3 winters. Maybe some sort of feedback from snow-covered ground. So let’s just assume it’ll be 5+ degrees warmer than what it shows.

(KPTV)

And then notice about 1/2 of GFS ensemble members produce noticeable snow in Portland on the chart below. That’s a decent indicator that SOMETHING is up for this weekend. But what we aren’t seeing yet? MOST of those members producing snow; this situation is very much still evolving.

(KPTV)

My final point is that we’ve probably got some sort of weather action on the way sometime between Saturday night and next week and it could involve more than one chance for snow. The two extreme possibilities I see right now:

1) We pick up 1-3″ of snow Saturday night, Portland is frozen all day Sunday and Monday, then a little more snow falls around Tuesday or Wednesday next week. 3-4 days of icy/cold stuff.

2) A chilly east wind arrives Saturday night, a few flurries fall, but doesn’t affect any of us. Temperatures only reach around 38-42 for a few days, then it’s back to milder/wetter the middle of next week and beyond. No real snow falls in Portland and it’s just a bit cold for a few days. Your life continues the same Sunday and into next week.

My gut feeling is it’ll be somewhere in between. But I’ll be at work all week; no scheduled time off until the end of February!

Saturday morning’s surprise snow; some brief wintry fun

12:30pm Saturday…

Well that was exciting! A bit of snow and ice pellets in the air this morning in the Portland/Vancouver metro area, and even sticking for a short time up in the West Hills.

11am view at Sylvan exit on U.S. 26 shows snow sticking to roads up at 800′.

(KPTV)

Seems surprising (and it was) since our forecast called for “cold showers” at mid-morning. But there WERE strong hints some sort of frozen mix could briefly fall this morning. We mentioned it in the forecast for the Gorge because we knew it would be a little colder out there. And this morning our meteorologist Drew Reeves mentioned it as a possibility on-air from 6-9am and online.

First, temperatures will continue to warm today as milder southwesterly wind pushes in. There won’t be any more snowy fun in the lowlands today.

What happened?

What worked correctly is that a cold front moved onshore with precipitation after a chilly night; some spots were down below freezing last night. That’s always a tricky situation and it looked like a close call. Several models were holding off precipitation until closer to noon; at that time it would be too warm to get snow to stick. There were hints that precipitation might be mixed to start. Take a look at our GRAF model output, note temperature just above freezing as it was warming just about the time precipitation starts. Notice the southerly wind too = mild + warming. There wasn’t going to be a snowstorm this morning.

(KPTV)

Our two best models, the WRF-GFS from UW, and IBM’s GRAF showed no sticking snow in the lowlands this morning, but at the same time they were sure implying it could be in the air.

(KPTV)

(KPTV)

Check out the Euro sounding from last night’s run. It comes out about the time I’m in the 10pm newscast. It was forecasting DRY at 10am today (it was a little slow with precip arrival). Red line is temperature, green is dewpoint. Most important, the blue line. That’s “wet bulb temp”. Precipitation falling into the airmass at that time would cool the air temperature to the blue line. This sounding says IF precipitation starts at this time, it should be all snow. That’s what happened

(KPTV)

The same model forecast at 1pm says milder southwesterly wind has saturated the low level airmass (that’s what IS occurring now), and snow level should up around 2,000′ by that time.

(KPTV)

Our 1am GRAF model had really picked up on things, forecasting snow in the air in most of the metro area but slightly (by 1-3 degrees!) too warm for sticking. This screamed “conversational snow” for Saturday morning coffee time. And that’s mainly what happened.

(KPTV)

Basically models were “catching up” a bit during the night. But just 2-3 degrees up or down can make a big difference!

So yes, definitely a surprise for most of us to look out the window and see snow this morning. But no, meteorologically it wasn’t as if I woke up and said “how the hell did that happen?”.

A simple “rain might be mixed with snow in the morning” would have covered it while I was on during the late newscasts last night. That way you could have looked forward to enjoying your Saturday morning coffee while enjoying the wintry flakes fall. Well, some of you. Many of us just saw rain showers this morning anyway and have no idea what this blog post is about.

By the way, here’s your FIRST ALERT that we see a pattern change coming up NEXT weekend and beyond. We’re talking at least 7-9 days out. The last few days of January will feature cooler air coming in either from the north, or northwest off the Pacific. I’m not saying we see anything like December’s cold/ice, but the warm and wet pattern is going away for awhile and colder Canadian air will be lurking to the north. I’ll write a nice long blog post about that on Monday. We’ve got a week of uneventful weather ahead first.