I almost never use the term “freak” while describing weather events, because media can easily overuse the word. But one week ago we saw a freak mid-April snowstorm in far NW Oregon and SW Washington. I use the term because, just like the heatwave last June, the setup is unlikely to be repeated again in my career (or lifetime?). The reason for this post (a week later) is that I want a good record of the event. I was out of the area. In fact I was on the other side of the planet, somewhere between Greece and Montenegro on a large ship. With little/no internet. Typically April is a “safe month” for a chief meteorologist to take a vacation. I hit the wrong week this year.
April is generally considered a relatively mild month weather-wise in our region. Cold showers mixed with warm sunny spells is normal. Sometimes those cold showers can contain snow pellets, hail, or even snow mixed in. At 1,000′ in the hills it’s not even unusual to get snow in April. I’ve had brief morning snowfalls a few times at my home the past 18 years in that location. There was nothing really unusual about Tuesday and beyond last week – lots of cold showers with thunder and hail. We have had some very mild Aprils lately, in fact April has been turning warmer as our climate warms. Notice how often we used to have sub-50 degree highs in the past compared to now.
But in the past 8 days we have reverted to a chilly pattern similar to what we’ve have seen in the past. We hit 75 the day I flew out of PDX. But then things went downhill around the 10th
That snowstorm one week ago goes WAY beyond a normal chilly April weather setup though. It was the perfect “snow storm” pattern that would have given us 10-15″ snow in the metro area if it would have been December-early February. Maybe most interesting is that it was almost perfectly forecast by models, yet (just like June heat wave) meteorologists were doubtful that such an extreme event could occur so late in the season and downplayed snowfall totals. I would have gone for lighter snow just like local mets did that Sunday ahead of time.
500mb forecast charts show cold air dropping south as a cold upper-level low sweeps across the area Sunday night through Monday night. 1st image is Sunday afternoon, next is Monday 8am. All these charts are from the WRF-GFS model.
By Tuesday another cold trough was swinging through, then the last of the really cold stuff moved by Wednesday
What has happening down below? The approaching trough spun up a very deep surface low. Notice on Sunday it’s about 1014 millibars (mb)
It crosses the coastline Sunday night around Lincoln City, then is east of Madras by 5am Monday. This wasn’t about “cold east wind” like wintertime. It was about very heavy precipitation dragging the snow level down lower than it would typically be during an event like this in April. At this points a breezy northwest wind had picked up across the snow storm area.
So at this point it’s down to around 993 mb. That’s a 20 mb. drop in 24 hours – technically a bomb cyclone passed right across Oregon last Monday! It’s rare to see a low deepening AFTER it crosses the coastline. By 11am Monday it’s way over in NE Oregon and you can see the dynamic cooling is ending over NW Oregon and SW Washington. Most lower elevation spots are changing back to rain at this point.
Those are some serious atmospheric dynamics (lifting and atmospheric cooling) going on around such a quickly deepening low pressure area. And it’s well known that the area just north of a surface low can give some great precipitation and snow totals. Take a look at the precipitation forecast from Sunday evening through Monday evening. 1 to 1.5″ likely, a big April soaker!
Now look at the snowfall forecast from the WRF-GFS from Sunday evening. Just about nothing south of Wilsonville or Chehalem Mtn. A foot is possible in foothill locations (and West Hills), 5-8″ in parts of Clark County and hills of Clackamas/Multomah counties. And 2″ in lowest elevations along Columbia River in middle of metro area.
To make a forecast of 2″ snow in Portland in mid-April, when that hasn’t happened anytime after first few days of March? I think I would have said Trace-1″ and left it at that. Quite a good performance by models!
The final snow totals…
FINAL THOUGHTS
- This was a historic event for our area. I’d say it’s similar to getting a couple of 90 degree days in mid-October. Or maybe similar to a 3″ snowfall in the city for Halloween? A freak snow storm for sure!
- 1.6″ fell at NWS Portland, and 2.0″ downtown, both the latest on record. 0.3″ fell the next day (officially), but that was mainly graupel and temperature didn’t fall to freezing. We will see if that number remains.
- The weight of extremely wet snow (falling at 33-34 degrees) approaches that of an ice storm. Lots of trees either snapped off or fell over under the weight. I lost all or part of two ornamental trees, yet they’ve been fine through several 1″ ice storms. No leaves on those trees either.
- It’s unlikely this will happen again in our lifetimes, or at least in the next 20 years. Everything had to work out PERFECTLY to get the heavy/wet snow down to sea level. Timing + precipitation intensity. Similar, but not as extreme, events occurred in April 1963 and April 1936.
- If it had occurred 6-10 hours later, it’s likely no snow would have stuck in the lowest elevations. Notice that Portland officially picked up 1.5-2.0″ snow, out of 1.40″ precipitation that day. It just barely worked out in the lowlands. The high later that day was 51 degrees! If we had been 25-30 degrees with this setup, a solid 10-18″ could have fallen in the entire metro area. The track of the low was similar to the January 1998 snow storm.
- Out of all that drama, we didn’t get a freezing temperature in Portland. Latest frost is still March 10th.
ABOUT THAT FORK
Each February, I have people asking me if winter is “over” in February. And each year they ask if it’s okay to turn on outside water spigots, take off the chains, or if we’re done with the chance for an all-day snow event. So about 15 years ago I started “forking winter”. Twice during that time I’ve been burned. In late March 2012 a heavy/wet snowfall of 1-8″ occurred in parts of the Willamette Valley. Then this year we had a real snowstorm 6 weeks after I pulled out the fork. To be clear, March and the first week of April was very mild this year and we are definitely in spring. Yes, it can snow in spring every 10-30 years in the lowlands. Just like it can get hot in fall or spring too, but that doesn’t mean it’s summer. I’m guessing the same people thinking I should drop the fork thing will be asking next February 20th… “Is winter over?” We will see!
Chief Meteorologist Mark Nelsen
FOX 12 Weather Blog 
As you know, thunder appears to be possible tomorrow, with a chance of severe weather. My personal update (includes chances for S. Valley) https://youtu.be/xitc15W5Li0
BTW From the PDX Weather facebook group, Mark Nelsen commented that it probably will be after the front, if we get any at all. In their 7 day forecast for tonight, they said T-storm chance.
Sure is quite a difference in temperatures this April compared to last year’s at this time. April 2021 I had afternoon highs in the 70’s during mid-month. This year I’ve only seen one day above 60F, it was during the first week of the month.
It is the polar opposite of 2021. Pretty crazy to think about.
The models still look really good for May which are showing very warm and dry, what a contrast it will be from April.
I don’t think we’ll see showers/clearing today. Looks like rain just hangs over us most of the day.
Thank you for the update Mark 🤗 I’ve lived in Oregon all my life and haven’t seen it snow that much in April!!
Moving forward, I just looked at the SPC forecast and it looks like we could be having chances of thunderstorms the next 3 days.
This is for today
This is for Wednesday and as you can see, the chances increase
And this is for Thursday
It’s been awhile since I’ve seen 3 days worth of thunderstorms for our area. It could get interesting 🤔⛈️
Foul ball Mark…lol
I will agree it has been a sort of weird spring season and it sure has if nothing else felt cold up here for the Port Orchard area where I have been since October 2nd.
This season I had 12.8 inches of snowfall and it has come over the JAN-FEB-MAR-APR time frame. April was the least amount with only a trace where there was a little accumulation on the day that you mentioned.
I am curious to see how cool it will stay this year with La Nina predicted to be with us until early summer according to the NOAA CPC. Will this be a summer where the REAL summer starts after July 4th and lasts at least until September 21st when the Puyallup Fair ends? I guess as the NWS says it bares watching. 🙂
This validates me too. I wasn’t lying, W7. I’m close to where the 5 and 205 intersect. No white here.
Thanks Mark!
Well that explains why I didn’t really get any snow. I’m sitting right beneath Lake Oswego in that dry portion. Amazing that parts of Lake O got 3 inches of snow and I got zilch.
Pete Parsons latest outlook has us warmer then normal for May so ignore the cpc they are however showing another got summer after June so no surprise there, getting a cool summer around here is impossible anymore.
That was for Lisa.
“Ignore the cpc” buddy, how about in winter when the only word you could say was CPC, but now that they show cool, you ignore it.
There only wrong about may according to Parsons outlook the cpc was right about a cool winter and early spring I’m not saying ignore the cpc completely I’m also not warm or cold bias I try to take in all data either if it’s from cpc or other experts such as Parsons, I guess I should have made myself clearer.
Thanks for the new post. Ended up with 4″ at my place, but was transitioning by 10am. Glad to see all the mountain snow for the region. Bummer this setup didn’t occur in January. Would have been a big snow storm and probably kept us around freezing for the remainder of the week. Not only do we need the perfect setup, we need it in a 3 month window or so for an epic storm.
Weird weather events are actually the norm, in the sense that each year sees one or more “never before” or “once in 100 years” events somewhere in the world. Portland was “lucky” enough to get two of them in a 10-month period.
Don’t forget the February 2021 ice storm and the September 2020 hot, dry wind storm that caused all the wildfires. We’ve actually had four once-in-a-lifetime weather events in the past year and a half.
I don’t think the ice storm belongs on that list.
Interesting. I would have thought I’d get an objection to the wind storm before the ice storm. Do you live outside Clackamas County? Because we were hit way worse than a lot of the metro area by that ice, so I can see how you might not think it was severe if you just got a glazing, or some snow. Extensive tree damage that I hadn’t seen at least since I was a kid living in the Gorge in the ’70s. Ice 1 1/4 – 1 1/2″ thick is pretty extreme.
If Mark were to tell me it wasn’t a once-in-a-lifetime event, I’d believe him, but I seem to remember him being pretty impressed by it in this blog.
The fork creates a lot of fun banter and should remain but I loved suggestion (i believe from tanis) of forking summer too. Prob too much nuance to fork other seasons.
You just might want to add in some language to effect of, “barring a once in a generation anomaly, you won’t see…”
I agree with Andrew. Keep the fork and add a little legalese at the end just as a CYA. I would love a summer fork too. Summer being forked is one of life’s greatest joys for me personally.
Indeed. Fork summer!
Definitely keep the fork!!
As a kid 20 years ago they said Portland would rarely to never see snow and mt hood would get half the snow and here we are In April breaking record and think it’s safe to say they changed it from global warming to climate change because global warming is fake news climate change is a normal occurrence and more appropriate term.
It’s not “fake news”. The globe is warming. What happens in your neighborhood/city/county/state is unlikely to be indicative of global warming. It doesn’t matter if we get 100 degree temps in December or snow in July here in Oregon. The term is GLOBAL warming. That means the cumulative sum of temperature increases around the globe; and it’s 100% accurate.
Even Cliff Mass – who loathes the term and is quick to criticize those that use it – acknowledges its existence and predicted outcome later in the century: https://cliffmass.blogspot.com/2022/04/my-views-on-climate-changeglobal.html
Just to emphasize:
I said something that was technically incorrect earlier and I feel like it needs to be pointed out: it’s not “cumulative sum” in the literal sense, but it is an average of globe-wide temperatures. You can read more about how the increasing temps are measured here: https://www.carbonbrief.org/explainer-how-do-scientists-measure-global-temperature
Also this part is referring to the fact that global temperatures are increasing. It’s not referring to any particular instrumentation value. Just to be clear.
Human emissions have caused 2.5% of 1/2500th of the carbon in our atmosphere. We have been coming out of an ice for more than 14,000 years. Explain how scientists can figure out sun cycles from thousands of years ago. Out of our control.
It’s true that there are natural climate change cycles (known as Milankovitch Cycles) that effect the heating and cooling of the planet over time. However, by those parameters, we should currently be moving into a cooler period. The reason we aren’t is the amount of carbon in the atmosphere. In every period when the earth has been cool, there was less carbon in the atmosphere. In every period it’s been warm, there was more. The amount of carbon currently in the atmosphere far, far exceeds what’s been present at any previous time.
This video explains the Milankovitch Cycles. https://www.youtube.com/watch?v=iA788usYNWA
It’s not a pro-climate change production, but a science video about why ice ages come and go. In fact, the creator had to make a second video when climate change deniers considered it proof that humans aren’t responsible. It shows a carbon graph that instantly makes it clear how different our current situation is from past times. If you want to blame that carbon on cows farting, or whatever, that’s up to you.
That’s all well and good, but I’d like some indication of when this chilly, wet pattern is going to end. The CPC is saying it’ll be cooler and wetter than average through the end of June. Please tell me it isn’t so.