Earthquakes & Rainy Weather


In the 10pm show tonight I’m talking about what might we see in the city of Portland with a great Cascadia Subduction Zone earthquake.  But did you realize that we know when the last huge earthquake occurred?  In the evening, January 26th, 1700.  Probably around a 9.0 magnitude quake just offshore.  How do geologists know?  If you have some time take a look at this info on the Orphan Tsunami of 1700 .  I think it’s fascinating reading, but of course I find almost anything scientific to be fascinating.  It’s a paper written by Brian Atwater  and others about the clues to a massive West Coast Earthquake.  And since I produced WAY too much content for a 2 minute story, here are two more graphics.  I could have spent a minute just on the Bonneville Landslide , pictured above.
Now, on to the weather…WET Need more info than that?  It was a nice break this afternoon and evening as showers quickly died down and the sun came out.  Most noticeable was the humidity, or more specifically the lack of high humidity this afternoon.  Dewpoints were way down in the lower 50’s this afternoon…all is back to normal in the Northwest.  That doesn’t include the bizarre late July rainy pattern of course.  A big slug of tropical moisture is approaching from the west this evening.  It’ll be here by daybreak and give us a very gray day tomorrow.  We actually have 2 of these systems on the way that include a significant low pressure center swinging northward along the coastline.  The first is tomorrow morning and the 2nd is Saturday night and Sunday morning.  Generally in the summer we have a large surface high pressure area offshore, so this IS unusual.  It messes up the windsurfers in the Gorge (no west wind), campers on the coast (too wet), and marine areas (no cold coastal upwelling without the northwest wind).
Because of these 2 systems, the weekend forecast does look off/on wet, but what about next week?  As I mentioned last night, I’m tired of pushing rain forward one day at a time.  So now that I see the 12z/18z GFS and to a lesser extent the 12z ECMWF show another upper-level trough nudging us the middle of next week, it looks safe to put a few showers in the forecast then.  Basically I don’t see anything in the next 7 days that shows the warm ridge to our east taking over again…Mark

62 Responses to Earthquakes & Rainy Weather

  1. Derek-West Gresham says:

    Hey heat, what is your user name on TWS?

  2. Justin says:

    1. Surface pressure is just the mean atmospheric pressure over the earth’s surface at any given time. It basically is used to show what kind of airmass is over a particular region. Therefore asurface pressure anomaly is just the deviation from the average atmospheric pressure (1013.25mb). The anomlies are directly related to the pressure gradients over the ocean, which determine the strength of the prevailing winds and trade winds over the Pacific.
    2. The Aleutian Islands are a huge chain that make up the SW point of Alaska. They do indeed exist.
    3. I really doubt it. If there even was a correlation, it’d be pretty small and hard to define.
    4. Though I don’t think we’re in immediate danger of seeing one, I’d guess Mark’s forecast would say “Extreme cold. Will make the 1800’s look like a baby” and his highs would be in the low teens and lows around 0.

  3. heat blizzard says:

    Thanks guys. 1.I just don’t know what a surface pressure anamoly is
    2.where is the aleutian islands I looked it up in google earth but it doesn’t exist according to them.
    3. Does anyone think thunderstorms in the NW could be related to PDO phaes since warmer oceans would mean more convection?
    4. If we were to have a super cold blast what would Marks forcast look like if it happened now? I’ve always been curious from what you guys say it probley wouldn’t be much in portland.

  4. Derek-West Gresham says:

    He should mention that rain streak that I searched through the utah climate center for.

  5. offroadjosh says:

    yes he did. Thank you Mark!!!

  6. Derek-West Gresham says:

    Did he mention your name, should have given me an honorable mention. ;O

  7. offroadjosh says:

    hey does anyone know an offroadjosh on the blog lol

  8. Justin says:


  9. Justin says:

    It stands for Pacific Decadal Oscillation. Its like ENSO, it goes through cold phases and warm phases, and is tabulated as a monthly index. Unlike ENSO though, it is a long term index and goes through multi year phases as opposed to 6-12 month ones.
    Its not known how the PDO works exactly or how it completely correlates with ENSO, but like ENSO it revolves mostly around sea temperature (surface and subsurface) and surface pressure anomalies in the North Pacific. You can get a fairly good idea of where the PDO is numberwise by looking at SSTA maps.
    This is the best page on the web for it, at the Washington state climate site
    Right now the PDO is still thought to be in a warm phase, which is less beneficial for snow and cold in the NW. The warm, or positive [hase of the PDO has been ongoing since 1976. What affect on the national temp average this has had is pretty unclear, but its probably partially to blame for some of our mild recent winters/years.
    The cold, or negative phase of the PDO, is generally more supportive of a longterm cool and wet period for the Pacific Northwest, such as the 1950’s..

  10. offroadjosh says:

    haha yup just looked it up
    Dictionary definition…
    A long-term El Niño-like pattern of North Pacific climate variability, with phases that persist from 20-30 years. The positive (warm) phase of the PDO is characterized by cooler than average SSTs and air pressure near the Aleutian Islands and warmer than average SSTs near the California coast; these conditions tend to enhance El Niño teleconnections. ..

  11. offroadjosh says:

    i am not 100% sure but isn’t it a long term el Nino pattern?

  12. heatblizzard says:

    Does anyone know what PDO stands for or what It does?
    I heard it talked about constantly on the weatherservice forums and have heard it’s significant for a good cold winter or not also this is the first time I’ve seen Mark posted WOO HOO! (cameras flash and weathergeeks go nuts,server goes on overload,nobody post’s for a couple days till they get it back online)

  13. Justin says:

    I was asleep for the 2005 event, but I remember the amazing nocturnal lightnign display we had July 21-22, 2000. I must of seen a good 200+ lightning strikes that night.
    For 2005, don’t know how I missed it. PDX reported thunderstorms for about 5 consecutive hours.

  14. Derek-West Gresham says:

    Checked back to 1970, 1990 is on top with 7. I used Utah Climate Center. Assuming wunderground is correct for THIS year than we are at 5 right now. And if we get 8 its probably the all-time record.

  15. Derek-West Gresham says:

    Ok now I have checked back to 1982. The most I have found is 7 in 1990. And like I said we will probably end up at 8. I will keep going.

  16. salemphil says:

    Yeah, work for that shoutout Derek LOL.

  17. Derek-West Gresham says:

    How is this for interesting. Going back to 1993 so far I have found that there have been no more than 5 days with precip in a row. Right now we are at 5 and will probably tack on 3 more to make it 8. I will see how far back we have to go to beat that.

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