One “Bomb Cyclone” Down, One to Go!

10pm Thursday…

After a very warm day with some lower 70s in the metro area, moderate to heavy rain has arrived with a Pacific weather system. I expect steady rain for a few more hours, then the usual scattered showers behind the front the rest of tonight. Expect more showers Friday but decreasing as the day goes on.


  1. You may hear/see something about a powerful storm (or worst ever?) for the Pacific Northwest this weekend. No, there is not a mega-storm on the way for the region. THERE WILL BE A HUGE STORM OFFSHORE, but it’s far enough away that we get typical wind/rain. No big storm.
  2. Things are moving fast/furious now with a strong Pacific jet stream overhead, so weather will be changing quickly from day to day…make sure you are paying attention to forecasts.

Tonight’s front is the leftovers of a powerful “Bomb Cyclone” that moved through the northeast Pacific ocean well west of the Pacific Northwest. A bomb cyclone is simply an area of low pressure that deepens “explosively” in a short period of time. Anything over a 24 millibar drop in 24 hours is considered a “meteorological bomb cyclone”.  No, it’s not a made-up media phrase.  Meteorologists have been watching these storms develop in the north Pacific/Atlantic for decades and that’s the term we’ve always used.  Somehow national media stumbled upon the term a few winters back and decided it was appropriate for the public to hear.  Generally (for good reason) I have kept the word “bomb” out of my on-air forecasts, but apparently it’s okay now and I sure used it last night! So that first cyclone is now weakening after bottoming out at around 950 millibars well west of the 130W “danger zone”. When deep low pressure centers track through this area we watch very closely!

Our big windstorms west of the Cascades almost always occur when a low pressure center tracks within this area

Now this is amazing; we have a second (and stronger!) bomb cyclone developing Saturday night and Sunday. Yep, that’s two huge storms relatively close to the region in less than 4 days. Highly unusual.

The latest global model forecasts are in remarkable agreement this evening. All are forecasting a surface low pressure center to drop from around 993 millibars Saturday morning to 943, yes 943, millibars. You can see the track of both lows, notice this 2nd one will be a bit closer

That 943 millibar value will probably be an all-time record deep low pressure so close to the region. For comparison, the Columbus Day Storm was “only” around 960 mb, but less than 50 miles off the coastline! Tracks of the last three major regional windstorms…all well inside 130W.

Ryan Maue, a meteorologist with, checked lowest surface pressure in the 1950-2021 record. He tweeted “the minimum central pressure of 944 millibars from next storm off Pacific Northwest coast will likely be the deepest/most intense in this area of ocean at 45°N and 135°W at least since 1950” The graphic he tweeted shows that boxed area. Plus you see the lowest pressure right up against our coastline (the past 70 years) was that 960mb during the Columbus Day Storm.

This is all interesting stuff of course, but what’s the effect along the coastline and interior? A gusty east wind Sunday morning turns breezy from the south Sunday afternoon and Monday. Yet the strong wind field remains offshore through the event.

The ECMWF model shows this well, gusts over 100 mph over the open ocean, but under 70 mph along the Oregon coastline. This shows accumulated gusts (highest gust) from now through 5pm Sunday.

Most likely we’ll see gusts 55-65 mph along the beaches and 30-40 in the valleys. That’s relatively weak of course, not a windstorm, but enough to make for a windy Sunday afternoon!

That’s it for now, I’ll be off tomorrow but back at work Saturday and Sunday tracking our very wet weather pattern.

Chief Meteorologist Mark Nelsen

142 Responses to One “Bomb Cyclone” Down, One to Go!

  1. Hank from Salem says:

    Winter 2021-22 Thoughts
    October 27th, 2021

    About this time each fall people start asking me “What this winter will be like?” or “I’ve heard it’s going to be a bad winter!“. Actually sometimes they start asking in August! For the record, I’ve NEVER had a person say “I’ve heard it’s going to be an easy winter“. Apparently most of us are quite cynical and expect the worst.

    I don’t put out a “winter forecast”. That’s because seasonal/climate forecasting has a long way to go before we say we can “forecast” a winter. So we’ll just call it “my thoughts” for the upcoming winter since we can at least glean a few ideas by looking over some weather tidbits. I’ve been doing this for quite a few years and it seems to work.

    For those of you with a short attention span, just three points:

    Plan on an “active” winter this year. The last 3 winters were quite “boring” (most of the time) for the weather professionals. Which means they were “easy winters” for regular folks (most of the time). Of course we all remember the 4 day stretch of snow/ice around Valentine’s Day right? But most of last winter was quiet weather-wise except for that event plus some flooding in mid January. The odds are tilted toward more changeable weather this winter; I expect it to be busier here at KPTV. A better chance for a windstorm, flooding, and lowland snow. And I doubt we’ll be locked into weather patterns for weeks/months at a time.
    Expect at least once we’ll see some snow or freezing rain in the metro area and lowlands west of the Cascades. I would be surprised if we get through this entire winter without measurable snow in Portland. I’d peg the chance of “sleddable” snow at about 70% some point between November 10th and March 1st. No, we have no idea when that could happen until at least 7-10 days ahead of time
    Expect a good snow year in the Cascades. Good for both water next summer and skiing during the winter. Go ahead and plan on a normal ski season with the usual variable ski conditions from week to week. I’d give this about a 70% chance of happening too. It IS possible to get a low snow year during a La Nina winter. In fact two La Ninas back in time we saw terrible ski conditions through January! Then February/March were incredible.
    Two winters back…2019-2020 So boring…this was our 2nd consecutive “El Nino” winter. There was a real lack of Pacific storms; it was as if the jet stream just didn’t want to perform last winter.

    Last winter…2020-2021 It was a surprising La Nina winter because of the mild temperatures, plus almost nothing interesting happened weather-wise until mid January! Some widespread (light-moderate) flooding showed up at that time, but then all was quiet until a 4 day blast of cold air arrived starting February 11th. That cold air was overrun by plenty of Pacific moisture which produced a snowstorm from Portland north/east and a severe ice storm from south metro down to around Albany in the Willamette Valley. Then temperatures warmed and typical (wet) winter weather resumed. We dried out dramatically in March and April, but with plenty of cool temps.

    You can check out the rest of my winter recap presentation here:

    So much of the past 3 winter seasons have involved a lack of storminess and drier than average weather. About time for some action don’t you think? But that’s what I thought would happen this past winter too…there’s so much we still don’t know about our climate.

    We have entered weak/moderate “La Nina conditions” once again this fall. Models tell us most likely it’ll be a weak to moderate event through the winter. So this will be our 2nd La Nina winter. That can give us a few hints, definitely not a forecast, but what direction our winter might be “weighted” toward. I’ve spent some time looking at past La Nina episodes and what happened here in the Pacific Northwest. I based all my graphics/research on a weak/moderate event. Right now the Oceanic Nino Index (or ONI) is in the WEAK La Nina category.

    Model consensus says we’ll likely be in a WEAK-MODERATE category during this upcoming winter. Here’s the latest plume of ocean/atmosphere models. Anything below the “-0.5” is weak La Nina, below “-1.0” is a moderate event. Strong would be “-1.5” or lower.

    Typically in these winters there are 3 effects observed to varying degrees:

    The north Pacific jet stream tends to be more “wavy” which means there is more of a north & south component to the jet instead of travelling straight west to east
    There is increased tendency for blocking somewhere in the east Pacific
    As a result there is sometimes more interaction of the cold Canadian air to the east and Pacific moisture with the jet stream weakening dramatically at times too.
    Likely effects this winter based on a moderate La Nina event:


    I think it’s unlikely that we’ll have a drought winter; but far more likely precipitation will be above average. La Nina winters in the Pacific Northwest are dominated by a strong jet bringing frequent disturbances across the region, interspersed with sudden ridging or northerly flow. Then it’s back to the westerly flow. For this reason they tend to be wet. It’s likely the #1 most noticeable event in these winters. And the chance for “wet” is much higher in northern Oregon than the southern half of the state. Although the current weather pattern this week suggests otherwise with an incredibly wet northern California very early in the season.

    1a. Flooding

    This goes with the rainfall. For obvious reasons we tend to have more flooding events in La Nina winters due to the wetter weather. Keep in mind we haven’t seen a major regional flood in 24 years. That was 1996. Previous big flood was 1964. I wouldn’t say we are “overdue”, but one of these winters it’s going to happen again.

    Mountain Snow

    Lots of precipitation and cool weather systems = plenty of mountain snow. This is probably the #2 most likely event. 7 out of the last 10 La Nina winters have brought above normal snow to ALL elevations in the Cascades. Note that there CAN be a bad year; it just happened during winter 2017-18. Ouch! Check out the mid January snowpack during 2001 & 2018…

    Foothill Snow

    This happens in some La Nina winters…significant snow to lower elevations (1,000′-2000′). This MAY happen again if we get a succession of cold and wet systems coming in from the west and northwest. It didn’t happen last winter, but colder than normal ocean water is poised to the west/northwest of the PACNW.

    Wind Storm

    We are overdue for a regionwide major windstorm here in the Pacific Northwest. The last BIG one was December 1995. That’s 26 years ago! 14 years before that we had the major November 1981 storm. It’s interesting that all the La Ninas from 1950 to the mid 70s had a wind gust of 60+ mph at PDX each time! Not as frequent since that time though.

    Portland Snow/Ice

    This one is tough. Anyone who says a La Nina winter means lots of snow in Portland is mistaken. Average snowfall in weak-moderate La Ninas DOES go up a bit, but not a dramatic increase. Three La Ninas in the last 20 years have produced a major snowfall here in Portland…December 2008, January 2017, & February 2021. I should point out that the “cool/wet” La Nina winters sometimes produce little freezing rain because we don’t get as many inversion episodes to our east, which means less east wind in the Gorge. We need that for a good ice storm either in the Gorge OR in Portland.


    The elephant in the living room I suppose is the fact that our winters are gradually warming, and snow in Portland is more rare than it used to be when we look back more than 70+ years. Although the past couple of decades total winter snowfall seems to have stopped it’s downward plunge. Take a look at total snow each decade since the airport observations started about 1940. Divide by 10 to get average per winter.

    And downtown records that go back to the late 1800s. The low spot in the 80s is missing some data…it should be a bit higher…

    We have always been in a marginal snow climate, but now warming temps are cutting off even more of the winter snow. Every few winters we get a good snowstorm. We all remember that event and that pops up the long-term average. It is interesting that the last 3 decades seem to have leveled out a bit at around 4″ per winter at both downtown and PDX locations.

    Cooler Water In Eastern Pacific There is no blob of warm water in the northeast Pacific like last fall/winter. In fact much cooler than normal now.

    Pacific Decadal Oscillation (PDO) This is directly related to the sea surface temps. Typically during a La Nina we get a negative or “cool phase” of the PDO at the same time. Last year that was not the case. But this year we seem to be in the cool phase (right side figure below). Could that make this La Nina winter behave significantly different (cooler/wetter) compared to last year? You can read up on the PDO here:

    This gives the general picture

    Anthropogenic Global Warming (Climate Change) A warming globe doesn’t necessarily mean we don’t get cold air outbreaks or snow. It can also mean the usual circulations get disrupted. For example it seems to me we just aren’t getting as much storminess over the eastern Pacific the last 3-4 years. That’s just anecdotal of course. But has something shifted the past 20 years? We don’t know, although 30 years from now, we might look back and notice something did change during this period. There is still a LOT we don’t know about climate.

    That wraps it up…as always we’ll see how the winter turns out…my money (again) is on “wet”, “good Cascade snow”, and at least one “snow/ice event” in the lowlands. Maybe several, but hopefully I won’t be spending too much time at the hotel right near the TV station…

    Each autumn the Oregon chapter of the American Meteorological Society puts on a “Winter Weather Conference”. It’s my favorite meeting of the year! I have been a part of this chapter my entire career. Speakers present their thoughts/outlook/forecast for the upcoming winter. The public is always invited. Last year and just this past week we gathered virtually due to the pandemic. Interested in watching? Check out my recap, plus 5 different outlooks on our Oregon AMS web page. I was especially impressed by the passion/talent the younger folks are bringing to our chapter! There is some really good information in each of these presentations. Enjoy!

    Chief Meteorologist Mark Nelsen

    Share this:

    Winter 2020-21; What’s Ahead?
    October 21, 2020
    In “Weather”
    Winter 2019-20: What Are We Seeing?
    October 31, 2019
    In “Weather”
    Ski Season 2013-2014; Will it Be A Good One?
    November 5, 2013
    In “Weather”
    This entry was posted on Wednesday, October 27th, 2021 at 9:08 pm and is filed under Weather. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

    Post navigation« Previous Post
    20 Responses to Winter 2021-22 Thoughts
    Andrew says:
    October 28, 2021 at 8:15 pm
    Such an excellent write up. A real master class in how to address a seasonal weather discussion. I think the cooler ocean temps off our coast will definitely equate to more foothill snow and probably lead to several bouts of “soupy” rain at sea level, with at least a few sticking events above 500-1000 feet. That would also lead me to think our flooding risk is amplified, since it’s the rapid melting of that lower level snow that always seems to portend flooding concerns. I don’t put much stock in NW Wind Portland snow events. I know the ocean conditions favor cooler air but it’s still such an uphill battle to generate meaningful snow from any onshore flow pattern. We had a very borderline one last January – the definition of a “conversational” snow event. things turned momentarily white but surface temperature just couldn’t drop low enough even with a very chilly onshore flow. It’s just not something i’ll ever take seriously. As a snow lover, i’ve been burned too many times seeing snow in air and temperature plummet only to see conditions come up just short. The types of patterns that DO produce real snow seem fairly unconnected to the ocean temp fluctuations, at least between neutral and la niña winters which is supported by mark’s data. we shall see.

    Anonymous says:
    October 28, 2021 at 10:09 pm
    That’s the most reasonable stance to take on the subject, I agree. Winter in Portland kind of just does what it wants.

    Important to note that Mark’s data only applies to some areas in Portland, not all. Last year for example is misleading when you factor in all the areas that got mostly ice instead of snow. That’s just Portland too, if you factor in the metro area in general, it’s even more misleading.

    Paul D says:
    October 28, 2021 at 2:06 pm
    Stock up on toilet paper NOW!!!

    Anonymous says:
    October 28, 2021 at 6:24 pm
    These kinds of comments are how we run out of toilet paper.

    Hank from Salem says:
    October 28, 2021 at 6:51 pm
    Exactly! Although I think he’s kidding, but if he isn’t, what in the actual heck.

    Weatherdan says:
    October 28, 2021 at 2:05 pm
    70 in Salem at 1:00PM. Some sunshine too. Peace.

    Weatherdan says:
    October 28, 2021 at 3:23 pm
    So far we have reached at least 72 today. Peace.

    Roland Derksen says:
    October 28, 2021 at 10:48 am
    The winter forecast seems promising- but I won’t be impressed if I see another dull, mild January.

    OC550 says:
    October 28, 2021 at 8:56 am
    Great post Mark! Hopefully a good ski season is coming.

    Oliver Watson says:
    October 28, 2021 at 8:31 am
    Man Mark! That is exactly how a winter forecast should be presented. You gave us real data and let us know there are many things we don’t know and understand about the weather which is so true. You also didn’t sensationalize the forecast either. All meteorologists should take a lesson from your responsible reporting.

    JERAT416 says:
    October 28, 2021 at 8:04 am
    January 2017 wasn’t an official arctic blast , but I guess with a bunch of snow that didn’t melt for nearly a week, I keep feeling like it counts.

    Carrie says:
    October 28, 2021 at 12:33 am
    Quote:Wind Storm: We are overdue for a regionwide major windstorm here in the Pacific Northwest. The last BIG one was December 1995.

    Here in Clatsop County we were hit by a pretty significant wind storm lasting three days and gusting up to 145/mph or 165/mph, depending on who was reporting it. All of us lost power for at least fourdays, most of us for a week, and many for three weks or better. Whole hillsides slid blocking us from HWYs 26, 30, 101, and 202. We were completely isolated. National Guard came in to help rescue people from homes buried under trees and sliding downhill. It was called The Great Gale and it happened in December, 2007. It was followed by heavy snow. People in Jewell and Vernonia were burning furniture to keep warm.

    W7ENK says:
    October 28, 2021 at 12:16 am
    Oooh, it’s rare when Mark gives some insight into the UPCOMING Winter…

    … This means something… 🧐🤔

    tim says:
    October 27, 2021 at 11:28 pm
    The blob is still there just pushed further west also the cfs model does line up with the current negative pdo then slowly warms again going into winter but remains weakly negative.

    Hank from Salem says:
    October 28, 2021 at 10:26 am
    Beleive it or not I’m not blind.

    Hank from Salem says:
    October 27, 2021 at 10:38 pm
    I commented this 2 blog posts ago, then for his last blog post I copy and pasted it so more people could see, than he dropped another blog post, so I’m commenting this a 3rd time!


    There is some big news for our winter….

    We are no longer affected by the blob for the first time in years, over the last 4 days, the cool gulf of Alaska has dramatically gone south, so much so we aren’t affected by the blob!

    And for our la nina, I’ve done a lot of research the last couple of days (ocean temp archives are surprisingly hard to find!) Over our last 5 extreme la nina’s, None of them were this cool in October! To make this clear, I do not think that guarantees a extreme La Ninã, but it’s looking really good!

    Would like to hear people’s thoughts on this





    Anonymous says:
    October 27, 2021 at 10:30 pm
    I’m more interested in what the shift of the blob westward means for the following seasons. I’m hoping it means no heatwaves next summer. A 2019 repeat would be nice during Spring and Summer. Rain in July perhaps? Yes please!

    Hank from Salem says:
    October 27, 2021 at 10:01 pm
    Thanks for the winter forecast like every year mark! I’ve been looking forward to this since September, Seems like we could all use some lowland snow! I live at a the bottom of a decently popular sledding hill, but it hasn’t had snow on it since February 2019! Hopefully this year kids can sled down it.

    I also noticed the picture of the Ocean temp anomalies, I did some comparing to the 30 day loop, Seems like that picture was Oct 17th,
    Which seems out of date compared to the dramatic change the last 4 days, here’s the difference between now and then

    Ellen in Oregon City says:
    October 27, 2021 at 9:56 pm
    Time to gather up road kill and read the entrails!

    But, seriously . . .I am so impressed with your weather forecasting ability! I never believe it will snow unless you say it will snow!

    Thanks for all you do!

    Lurkyloo says:
    October 27, 2021 at 10:05 pm
    What Ellen said, except for the road kill part … 🙂

    Leave a Comment
    Enter your comment here…


  2. Hank from Salem says:

    There is some big news for our winter….

    We are no longer affected by the blob for the first time in years, over the last 4 days, the cool gulf of Alaska has dramatically gone south, so much so we aren’t affected by the blob!

    And for our la nina, I’ve done a lot of research the last couple of days (ocean temp archives are surprisingly hard to find!) Over our last 5 extreme la nina’s, None of them were this cool in October! To make this clear, I do not think that guarantees a extreme La Ninã, but it’s looking really good!

    Would like to hear people’s thoughts on this





    • Anonymous says:

      Thoughts: Bummer. I despise long, cold, wet, dreary winters.

    • K700 says:

      Watching the warm blob dissipate in that animation was really cool. I’m hoping for a more front loaded winter with some decent snow in December and earlier January as opposed to the late January and February like we’ve had the past 3 or 4 winters.

    • Opie says:

      Here’s a similar, but historical version:;b=coraltemp5km_ssta

      Shows SST’s for every August 1st and December 20th, going back to 1985. You can click on the image to scroll or pause. August 1st, 2010 looks a lot like today’s map.

    • Andrew says:

      Great post, Hank. The dissipation of the blob is definitely noteworthy. However, I recall reading comments last year that it temporarily went away as well after a stormy pattern only to reestablish itself. Is this latest change different?

      • Hank from Salem says:

        Most falls it slightly cools, but not like this year, so the recent changes are definitely different. Most far west the blob has been during its existence, since there’s no years to compare this to, there is no way to tell if it’s temporary or permanent, but it will atleast last through the active season.

    • MasterNate says:

      I think the much cooler ocean temps will play a dramatic role for our borderline rain/snow events here in the valley. The flop from +2 to +3 degrees ocean water to a -2 to -3 degree ocean water should translate to colder temps and lower snow levels dramatically increasing valley chances of significant snow. IMO.

      • Hank from Salem says:

        For the NW wind Snow events it will be extremely helpful by cooling us down around 2 Degrees! If it’s ever snowing at 32 31 or 30 degrees with NW wind, we should probably be thankful for that region of water being much cooler, because if we still had the blob, that snow would be rain.

    • MasterNate says:

      I hope it sticks around through the summer. That will translate into cooler nights for sure with onshore flow

    • Michael says:

      I am extremely thankful for this fall weather. It’s high time we all become truely thankful for what we are seeing so far. Keep the faith everyone and thank you all too.

  3. Roland Derksen says:

    Looks like the Halloween weekend is going to be pretty sunny and dry. Great for activities!

  4. tim says:

    I’m looking forward to our yearly December death ridge and pollution after a very active fall, it will give us a chance to clean up for spring.

  5. Patrick b says:

    I think we are going into a more stable pattern, where the wind dies down and the skies clear up, for a most spectacular Saturday and Sunday, for viewing the fall foliage!

  6. Anonymous says:

    Models were showing another 18-24 hours of wind gusts. It’s amazing how yesterday afternoon’s storm was so short lived and mostly uneventful for a lot of us, but then later in the evening hours up to now it’s been consistently gusty.

    Beyond Saturday through 10 days out is looking bone dry at the moment. That’s great news for my leaf-raking activities. The streets are a mess

    • Anonymous says:

      Aaaaaand that didn’t take long. Euro already reversing course on the dry weather. I should’ve known better. From now on I’m just going to assume that if there’s any moisture in the gulf of Alaska, then there’s some chance it’ll find its way here regardless of what the models say. They desperately need to update these models.

  7. Jake says:

    A level 5 atmospheric river if I’ve ever seen one; some insane stats coming out of this storm.

    Both San Francisco and Sacramento had their wettest October days on record:

  8. W7ENK says:

    I almost think today has been more windy than yesterday. Certainly more consistently, and the gusts seem about the same (except for the burst of strong winds associated with that squall line that came through about 1:30pm). Aside from a bit of a lull last evening just before sunset, this wind really hasn’t died off yet in Milwaukie.

    My peak wind gust yesterday actually came at 11:19pm, SE at 35mph. So far today, had a pair of gusts from the SE at 33mph around 9:30 this morning, and one to 32mph about half an hour ago. Still occasionally gusting into the mid to high 20s right now.

  9. Roland Derksen says:

    While I’m not exactly disappointed, (i don’t like power outages and downed trees), this system fell well short of my expectations. Looks like it impacted mostly the outer coastal areas here (like Vancouver Island). Not a lot of rain either, with about a quarter of an inch. The storms of late August 2015 and December 2006 were far more destructive in my opinion.

  10. Andrew says:

    Windier this morning than I was expecting. final hours of these events always seem to exceed expectations. Pretty impressive rain forecast through late week, before things definitely settle down. wouldn’t be late fall/early winter without a couple strong inversion patterns….

    • Joshua Lake Oswego says:

      Pretty impressive rainfall… for Washington. The atmospheric river will set up shop north of us. We will likely end up with slightly above normal rainfall in October and a dry start to November.

    • Michael says:

      The old days of Oregon, back in the 80’s fall often started like this but, with each storm they often came in with more strength than the previous one. It made for interesting weather. Often getting short breaks between storms the strongest one seemed to come in like the turning of the tide, would turn cold and snow. After the snow storm we usually saw nice weather for a somwhat longer break. Not a consitent pattern but many fall/ winters were like that. Keep the faith.

  11. Anonymous says:

    Massive ridging next week across the northern hemisphere looks interesting along with a deep freeze leaking out of the pole down into the central US. Storm-killer.

%d bloggers like this: