FOX 12 Weather Blog

Weather Blog Note

November 7, 2022

This is the “legacy” FOX12 weather blog site.

Nowadays I post to our station website, then when I have time I copy the post to this site.

Since this is a simple copy/paste, you’ll notice occasional formatting errors, or extra large/small text. You also can’t click on most images to take a closer look since it’s a simple copy/paste.

The reason for this is that with a company change we’ve moved to new blog composer. I like the new one much better so I write over there and then copy here for future use/research. I strongly encourage you to bookmark/use this site: https://www.kptv.com/weather/blog/ And I thank you for reading all these posts for the past 17 years!

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Posted by Mark Nelsen

50 below zero in Oregon? It happened once. Plus weekend cold weather update

January 26, 2023

Have you ever wondered how cold it can get in our region? A winter low temperature of 20 degrees is somewhat normal west of the Cascades, 10 only happens every decade or so, but down to zero? Or below? It HAS happened, but it’s rare.

I’ve collected the “all-time” record lows from across Oregon in these graphics. Of course all-time means in the historical record of the station. Some records only go back to 1950, some well back into the 1800s. I don’t think any of the stations below go back before 1870. First the coastline

Then the western valleys and Mt. Hood

You’ll notice lots of those record lows are from the December 1972 cold spell. Here in Portland there is still a 10 day stretch in early December in which every daily record cold high temperature is from 1972.

East of the Cascades, those record lows are MUCH colder. That’s to be expected since in general it’s colder all winter east of the mountains.

The state record of -54 degrees was set at both Ukiah and Seneca during the same cold spell in February 1933. By the way, Washington’s all-time record low is -48 degrees.

WHAT’S THE PLAN FOR THIS WEEKEND?

Not much has changed the past 24 hours except for two items

1) Models have backed off a bit on intensity of the cold airmass moving in Saturday night and Sunday

2) It’s very clear now that showers end Saturday evening before temperatures get down close to freezing = no sticking snow

This graphic summarizes your snow chances well. No sticking snow west of the Cascades at the lowest elevations. It’s possible that only a dusting/trace falls even up at 1,500′. I think there’s a chance of 1″ or so in the central/eastern Gorge, but even that could be a stretch. The issue is that the system is moving very quickly = not much moisture to work with.

Our GRAF model shows the timing well. Around sunset Saturday temperatures will be around 40 degrees with very light/spotty showers. Modified arctic air (cold and dry) is pushing south into northcentral and northeast Oregon. But notice the air isn’t as cold as what we saw in December. I’d estimate about 10 degrees warmer

Then by 9pm, the “arctic front” has passed through the metro area. A gusty northeast wind has arrived, but since the arriving airmass isn’t that cold, temperatures are still well above freezing. Showers are finishing up; remember the upper-level system is moving quickly southward and heading to California.

By midnight, or soon after, the cold/dry air has taken over. Showers are gone and skies are mainly clear. But the gusty east wind is STILL keeping temperatures above freezing. That will allow any wet streets to dry before late night freezing; more good news for Sunday morning. No snow and no ice

A summary…

So instead of highs in the low-mid 20s (cold spell just before Christmas), we’ll see highs 10-15 degrees warmer PLUS sunshine all day Sunday. Sure, windchills will be in the 20s Sunday, but reasonable if you have a good winter jacket ready to go.

I do expect 8-15″ new snow in the Cascades the next two days. So very good ski conditions on the mountain with fresh snow Saturday and then a cold day Sunday. Luckily models have backed off the extreme cold in the Cascades. Temperatures will at least make it to 10 degrees up there; think Rockies or Utah ski conditions. Bluebird day Sunday!

https://e529d18e6892727ae99d61c865cc53ad.safeframe.googlesyndication.com/safeframe/1-0-40/html/container.html

The main message for the upcoming weekend is that we’ll see a dramatic change between Saturday and Sunday, and it’ll be quite chilly Sunday.

23 Comments | Weather | Permalink
Posted by Mark Nelsen

Cold weather arrives Saturday night, but sticking snow tougher to find

January 25, 2023

9pm Wednesday…

Portland’s official snow total so far this season is a HUGE 0.2″. That’s just a skiff of snow twice. We’ve seen more freezing rain than snow so far…

If you are hoping for some “sleddable” snow in the metro area, or anywhere west of the Cascades, that’s looking increasingly unlikely this weekend. But cold air IS on the way.

Highlights for lowlands west of the Cascades

Mild weather continues through Saturday. Weather likely won’t affect your life much through at least sunset Saturday.
Cold air will arrive on a gusty east wind Saturday evening with temperatures dropping into the 30s, and eventually upper 20s by sunrise Sunday.
As the cold air arrives, will there be enough moisture around for sticking snow Saturday evening? It appears increasingly unlikely the two will match up for a widespread coating of snow. Models are in great agreement that it’ll likely be dry for most of us by 10pm at the latest, especially in the metro area. Temperatures won’t drop below freezing until later in the evening. By the time temperatures are down to freezing or below, we’ll probably be mainly or all dry.
Will it snow at my house Saturday night? West of the Cascades anyone could see snow in the air Saturday evening, or mixed in the rain showers. But for reasons mentioned above, it seems unlikely you get real snow at your home.
Sunday and Monday should be totally sunny days! But high temperatures will only be in the mid-30s…Brrr! Still, that’s 10 degrees warmer than what we saw in December. Plus, a breezy east wind Sunday (not too strong) will go calm Monday = it’ll feel more reasonable that day.
At this point this doesn’t appear to be a historic or record-setting cold airmass. Partly due to extreme cold we’ve seen in the past this time of year, but also the airmass just isn’t historically cold.

This graphic shows what we DON’T expect…yes, I referred to 1″ of snow as a “snowstorm” in Portland. My point is just that anything more than that is unlikely

What’s new this evening

It’s nice that once again, 3-4 days ahead of a cold weather event, models are in surprisingly good agreement. The bitterly cold upper-level polar vortex will remain anchored over Hudson’s Bay the next week, but several cold “waves” of energy will rotate southward down the western side of that low. Notice that greenish trough rotating down through PACNW Saturday night. It’s moving quickly south instead of lingering right off the coastline. THAT is why models are drying things out so quickly; we don’t have any significant time spent with moisture riding over the cold air. These quick-moving shortwaves rarely produce any significant snow for us.

That was the GEM model, but other models look almost exactly the same in the upper levels of the atmosphere. That’s both timing and intensity of the upper trough. Models are still in some disagreement over how cold the airmass will be. 850mb temps on the GFS model only dip to around -8 to -9…barely even “arctic air”. Yet both the GEM and Euro have been forecasting numbers down around -10 to -15…much colder. This is where ensemble forecasts are very helpful. Both GFS and Euro ensemble average bottoms out around -9 to -11. It’s hardly a major arctic blast, but plenty chilly. Under sunshine that would give us a high temperature around 35 in late January. The GEM ensembles are a bit colder, around -12. That’s a bit chillier. Regardless, we will not be seeing a repeat of the low-mid 20s we saw on Thursday the 22nd of December. That day was brutal with cloudy skies, a few afternoon ice pellets, and wind gusts 40-50 mph blowing across the metro area. This should be far more tolerable.

The reason I’m really downplaying the sticking snow chance? As mentioned above this upper-level shortwave is really trucking along heading south Saturday night. Look at the dramatic change from onshore mild flow to offshore cold flow. Timing is slightly different on each model, but they ALL look like this. Euro 5pm Saturday…sunset. Rain showers and temps near 40.

4 hours later? 9pm… Cold east wind has arrived, temperatures have dropped, rain showers change to snow showers…and then…it just stops

5 hours after that? 2am Sunday all precipitation is gone and skies have gone clear. It’s breezy and chilly across the region as we drop below freezing.

Again, because of this no model is showing any real snow west of the Cascades. Possibly some wet spots that freeze for Sunday morning, but with that much dry east wind it’s possible roads just dry out before freezing.

With all this in mind, we come up with a 7 day forecast like this for Portland. Notice no FIRST ALERT WEATHER DAYS in red this time around. That’s because it won’t be crazy cold, wind won’t be extreme, and widespread sticking snow is not in the forecast. Assuming we go calm Sunday night and Monday night (without clouds), I could see as low as 15 in coldest outlying areas and 20 in the city.

Keep in mind, with cold air banked up against the east side of the Cascades Sunday…it’s going to be COLD at the ski resorts. Around 10 degrees those days.

This is the same time of year some of our coldest low temperatures have been set. Check out the late January/early February cold spell in 1950. That was Portland’s coldest month on record; interesting because the rest of that winter was quite mild. Warmer than normal in December, February, and March.

That’s it for now. Make sure you have your outside faucets covered up again (if you uncovered them) by Saturday afternoon. And turn off any outside water lines, or lines in unheated buildings/garages too!

19 Comments | Weather | Permalink
Posted by Mark Nelsen

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

January 23, 2023

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

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

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).

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!

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

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.

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.

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!

47 Comments | Weather | Permalink
Posted by Mark Nelsen

Saturday morning’s surprise snow; some brief wintry fun

January 23, 2023

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′.

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.

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.

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

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.

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.

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.

3 Comments | Weather | Permalink
Posted by Mark Nelsen

A mild January; but weather pattern change brings much drier weather soon

January 16, 2023

7:30pm Monday…

The weather pattern these past 3 weeks has been somewhat monotonous; lots of clouds, rain at times, and temperatures a bit warmer than average. The Christmas Weekend ice storm was the beginning of a long wet period; lots of (usually) weak weather systems bringing regular rainfall. The only dry day (without measurable rain) in Portland this month was New Year’s Day!

That gives us 15 consecutive “rainy days” in Portland as of this evening. I make the giant leap of faith that incoming showers will deposit at least .01″ rain at PDX before midnight of course. Which brings up the question…

What’s the longest consecutive rainy stretch in Portland weather records?

It’s 29 days; nope, not quite the biblical 40 day stretch, but close! You may be thinking we MUST have gone 40 days or more in the past. Most likely it’s been a situation with 20 days, then a dry day or two, then another 20 days. Here are the numbers; notice total rainfall at mid-month is about normal.

In a typical year, we are wettest from late November through December, then (believe it or not), rain starts to back off a little bit in January and February. One of those 3 years sticks out. January 1950. Any serious local weather geeks knows about January 1950. Who would have thought that THE coldest, and THE snowiest month in Portland’s history would also contain the longest “rainy” stretch! 41″ of snow fell that month on 21 separate days! All the melted snow, freezing rain, and liquid rain added up to 10.10″ precipitation for the month…a soaker. BTW, the 2nd coldest month was the previous January…1949.

DRIER PATTERN AHEAD

Quite a change is in store for the West Coast. The persistent westerly flow that brought flooding to California and consistent (lighter) rain to the Pacific Northwest will dry up later this week. The pattern change is a strong upper-level ridge of high pressure developing over or just west of the West Coast. This graphic shows 500 millibar height from the ECMWF model ensembles. Warm colors represent higher than average heights, cool colors lower than normal. This goes from now through the next 15 days.. Each image of the animation represents a 5 day average.

Higher heights mean more sinking motion in the atmosphere = drying and less cloud cover. The result is drier than normal weather beginning this Thursday and continuing for the following 7-10 days. From the Canadian model ensemble average…well below normal all along the West Coast over the next 10 days

Models are in agreement on this big change. See the ECMWF ensemble forecast for Salem rainfall. Not much happens from this Thursday all the way through Saturday the 28th (both circled below)

As of this moment, there’s no strong signal that the big ridge could back up and allow an arctic blast to flow south into the region. Remember we started with dry ridging in mid-December, then transitioned into the cold pattern for a week or so as that cold air came south. GFS temperatures are very stable for the next 10+ days. This IS the ensemble average, but I’m not seeing many members going REALLY cold next week.

Due to the ridge being slightly west of us, I don’t see a long (or significant) period of strong easterly Gorge wind. That’s good, because it has been a ROUGH season so far. At this moment, Troutdale has seen as many “gusty east wind days” as ALL of last November through February!

November and December combined saw more windy days in the east metro than any other November+December since 2006. Too much wind. We will see how many FOR SALE signs go up in Troutdale, Camas, Gresham, and Corbett this coming spring…Remember the wind peaked on December 23rd with a gust to 88 mph in Corbett, 93 mph beside Women’s Forum SP viewpoint, and who knows how strong at Vista House. Oregon State Parks folks tell me they will be replacing the anemometer that blew away that day, hopefully with something a bit stronger.

SUMMARY

After a bit more rain later Tuesday and Wednesday, we’ll see far more dry than rainy days for at least a week or so.
Temperatures cool to near normal or slightly below the next 7-10 days, but nights will cool and frost becomes more common
There’s no sign of a long east wind period for at least the next week
There’s no sign of cold arctic air or lowland snow through early-mid next week…at least through the 25th
I don’t see windstorms or flooding in this weather pattern
Your life should remain relatively unaffected by weather for another 7-10 days

57 Comments | Weather | Permalink
Posted by Mark Nelsen

What’s up with that “bomb cyclone”? Plus a very mild first half of January

January 5, 2023

10pm Thursday…

The last two days you’ve probably been hearing about the “bomb cyclone” off the California and Oregon coastline. So what’s the deal with it? Well, for one, it’s already dead. These storms come and go very quickly. But what is a bomb cyclone? This graphic explains it quite well.

The Pacific weather systems that regularly move across the region during the cool season typically contain an area of low surface pressure. These low pressure centers are also sometimes called “cyclones”. In this case, the low pressure center is over the mid-latitudes so we call those “extra-tropical lows” since they are “outside” of the tropics. As you know, these systems typically give us a round of rain and at least some wind.

A bomb cyclone is a surface low pressure center that deepens much more rapidly than a typical low. Specifically, the definition is generally agreed to be a 24 millibar pressure drop within 24 hours. For example a low pressure center that’s 995 millibars right now would need to drop to 971 mb. or lower within the next 24 hours to be classified a bomb cyclone. Since the pressure drops so quickly and (usually) quite low, the wind circling in towards these storms can get VERY strong. If the storm is moving rapidly eastward, northeast, or north, the damage can be extreme if they move near a coastline. Most of our major windstorms are bomb cyclones. This satellite image is from November 2019 showing one such storm. It followed an unusual path ESE toward the Oregon/California border, producing strong wind in that area.

One question I’ve heard…

Are bomb cyclones a new thing? Definitely not

No, they’ve always been around. Meteorologists have been regularly using this naming for at least 40 years. Other similar/related names: bombogenesis, a “bombing out” storm, meteorological bomb, etc… I remember in the 1990s saying a low was “bombing out” when talking with other meteorologists.

I can tell you I NEVER used the term “bomb” in any way in public forecasts until maybe 10 years ago!

It always seemed reasonable to me that I shouldn’t refer to a “bomb” in any sense on-air or in public. I figured it would be like yelling FIRE during a weathercast! But, somewhere between 2010-2015, someone in the media along the East Coast decided it would be okay to slip some meteorological lingo into their weather story. Some journalist somehow ran across the term, maybe in a NWS technical discussion? Why not throw in some “geopotential height” or a “tropopause fold”? That’s why I’m rolling my eyes as I write this. Somehow it just became acceptable, and possibly part of weather hype. I remember the good old days (10 years ago), when we just called it a “powerful storm”.

THAT is how the term came into common use. Some strange stuff…

Yesterday’s storm

The storm offshore bottomed out at around 955 millibars yesterday, but it died as it moved up the coastline today. We only saw a brief surge of southerly wind this afternoon in the valley. The big story was the strong easterly wind yesterday and last night. This was a “downslope” wind, not just a gap wind through the Gorge. Peak gusts made it to 50 mph in a few Cascade foothill communities like Yacolt, Hockinson, Estacada, & Sandy. Models did pretty well showing wind a bit outside of the “usual” east wind areas.

The 51 mph peak gust was the strongest there since the Labor Day windstorm in 2020. Of course that’s the event that blew up those fires on the west slopes of the Cascades, destroying hundreds of homes in one day. The wind gusted to 52 mph at PDX that day.

WHAT’S AHEAD

January is here and the we are now in a mild and wet weather pattern until further notice. The cold systems coming down from the Gulf of Alaska 2-3 weeks ago are history. Now we have a series of mild/wet systems approaching from the west and southwest for at least another week. Take a look at the next 10 days (rain and surface pressure) from the ECMWF model. Most of the time the main energy and jet stream will be aimed at southern Oregon and California. That leaves NW Oregon and SW Washington with regular periods of rain, but generally not heavy. Low pressure systems will generally be weakening as they move up the coastline too, so at this point I don’t see anything that screams STORMY. But in this pattern each system needs to be watched closely.

In a mild pattern like this, persistent cloud cover and breezy conditions typically mean our temperature doesn’t move much from day to day. High temperatures for at least another week will generally be around 50 degrees and lows around 40…plus or minus 5 degrees. Note the ECMWF ensemble forecast of high/low temps over the next two weeks is VERY stable.

And since we’ll be a bit warmer than normal, the mountain passes will only occasionally see snow. Most of the time the snow level will be up around 5,000′ or so over the next week

For those of you wanting snow this January? Very unlikely through at least the 18th or so. We’ve had quite a January “snow drought” the past few years. The last significant January snow was 6 years ago! So far it’s looking like another mild January.

77 Comments | Weather | Permalink
Posted by Mark Nelsen

December 27th wind storm recap

December 29, 2022

11pm Thursday…

I was off on holiday/vacation the past 4 days. After a quick Christmas morning post on social media, I pretty much checked out through yesterday. During that time the thaw finished, downpours commenced, and we had a windstorm. This post is mainly just a recap. That way in the future when I look back this event I’ll see what happened meteorologically.

It was VERY tough to get rid of that cold air. Sure enough, models pushed the cold easterly flow out too quickly last Friday/Saturday and we warmed very slowly on Christmas Eve. That easterly flow continued, although above freezing, through Sunday and Monday. Some spots in the valley hit 60 or higher on Christmas Day in the southerly flow!

By the way, at this point we’re experiencing the coolest December since 2016. That’s a combination of consistently cooler temps and the 3 days of REALLY cold stuff! Still, Portland did not make it down into the teens this time. I think it’s been about 6 years since Portland has dipped below 20! There’s still a chance for another 6-7 weeks or so of course.

As for rain, what a soaker! Between 4-5″ rain in Portland during the 4 day period ending Tuesday the 27th

This rain played a large part in the destructive windstorm on Tuesday. I’ve always noticed our windstorms are more “productive” when we have soaked/saturated soil at the same time. On Tuesday morning, a well-forecast “bent back occlusion” moved inland across southern Washington and northern Oregon. Here’s the WRF-GFS surface forecast for 10am Tuesday, just 6 hours after model initialization time. A main 973mb low moving toward the northern tip of Washington, while a secondary trough or possibly closed surface low moving toward Astoria. Both were beginning to “fill” or weaken.

This is a sort of “double-barrel” low. Radar confirmed this DID occur, in fact the surface “trough” moving onto the coastline sure appeared to be a closed area of low pressure.

That low was weakening while moving inland. Here’s the 1pm forecast

Peak wind for many of us occurred around this time (Noon-2pm). as the weakening low passed by to the north of Portland, tightening pressure gradients. Then by 4pm, the dying low had passed over and east of the Cascades

At this point wind was peaking over the central/eastern Gorge, valleys around Mt. Hood, and north-central Oregon. This DID finally wipe out the last of the cold air as temperatures finally jumped into the 40s in Hood River and The Dalles.

The peak gust of 48 mph at PDX was the strongest southerly wind there in almost two years. We really didn’t have any windstorms (from the south) last winter. Just about all official gusts were in the 45-55 mph range in the lowlands. Here are metro gusts, note Troutdale’s gust is from the east as the storm approached.

Valley wind gusts

And then those strong west/southwest gusts in the Gorge and Hood River Valley

70-80 mph on the river? Must have been quite a sight to see the spray blowing across the water like a hurricane!

Unfortunately there were at least 3 incidents in which trees fell on highways, hitting vehicles and/or causing collisions which led to deaths. East of Seaside on US26, east of Government Camp on US26, and I-84 near Bonneville Dam.

One part of the storm that’s most surprising is the amount of damage and power outages; both seem to be well beyond what we would expect with 45-55 mph gusts (for most of lowlands). To me it appears the damage is more like what we’d see with gusts 55-65 mph. This has happened in the past, and will happen again. Extremely wet weather saturated soils, allowing trees to uproot more easily. Portland alone picked up over 4″ rain in 4 days

You can see the effect on outages. LOTS of us lost power; I was lucky and only out 14 hours. At this moment (10:30pm Thursday), 1,500 of you are still out of power according to PGE’s website. This storm was similar in scope to January 2021, but not as bad as the April 2017 windstorm.

So, lots of rain, then strong wind = plenty of falling trees. We were fortunate that surface low was weakening instead of strengthening as it moved onshore and through SW Washington. Some of Portland’s strong storms (much stronger than this one) have come from that setup.

That’s it for now, I see uneventful weather this weekend as 2022 rolls into 2023. No storms, cold, or snow over the next week as the jet stream aims mainly at California.