Sunday Morning Surprise


Some of you have inquired more about deformation zones… one of which produced the unexpected rain and snow last night. Here is more information for you:

A deformation zone results when two competing areas of low pressure in the middle and upper levels of the atmosphere "pull the air apart".  In between the two lows, there is a line dividing where the air is sucked towards one low and where the air is sucked towards the other low.  In the area of the line, there is an absence of air created by the diverging winds.  Air rises from below to replace that vacancy of air aloft… and that rising air cools and condenses, resulting in a skinny swath of clouds and precipitation.  Specific to last night’s situation, there was an upper low over Canada and an upper low over the southwest U.S…. and the middle (deformation) zone was right over us.  Deformation zones are notoriously hard to predict and are often slow moving, dropping rain or snow over the same localized area for hours.


Just when I thought it was safe to say "it’s over"… it’s not.

A "deformation zone" of showers is moving east to west right across the Portland metro area as I write this (1:00 am Sunday morning).  Temperatures are too high for the precipitation to fall as snow at the lowest elevations, but above 500 feet I expect snow to be falling through the night in the band.  The sticking snow level should be somewhere between 500 and 1,000 feet.  Portland’s higher West Hills should have a fresh blanket of snow in the morning, as should the northern Oregon Coast Range (Vernonia has already picked up a few inches) and higher elevations of Clark and Multnomah counties.

With the cloud cover, freezing temperatures are unlikely below 1,000 feet tonight… so if you heard a forecast for "clearing sky and below-freezing temperatures" in the Portland area, that forecaster wasn’t paying attention.

If you wake up to snow in the morning, send your photos to

I’ll update things, if necessary, tomorrow morning sometime.

– Drew J

256 Responses to Sunday Morning Surprise

  1. Droppin says:

    I agree with the others. Josh the “Snowman” has never been anything but friendly, mature and professional on this blog. Us diehard bloggers consider him a friend. We appreciate his knowledge and interpretation of weather patterns as he is up north in Everett and often our weather comes down from his area. So PLEASE Mark, or Drew, unban Josh the “Snowman”

  2. Mat says:

    hey Mark, what about Josh “the snowman”, he didn’t do anything. He just e-mailed me and said he was still banned. C’mon, we all love his input. Thanks

  3. Droppin says:

    Ok great. Ty Derek for posting that and ty for whoever did unban me. I agree Kirk this is a forum to discuss the weather and I am a diehard weather fanatic, but when you are banned due to others immaturity and disrespect it is upsetting. I enjoy posting and giving my insight and discussing things with you all immensely and I look forward to continuing to do so. Again tyvm Derek. A quiet weather night for sure, but hey, with this unstable air maybe we can get enough sunbreaks and heating for some hail/t-storms Tuesday 🙂

  4. Droppin says:


  5. kirk says:

    OK I was not going to say anything but stop the crying about people that were baned. Listen I think we are lucky we have been given the chance to hang here and BS about the weather. I do not think this blog was ment to turn into a chat room in the first place. Im sure Mark and Drew don’t come to work wanting to babysit a bunch of immature people. These guys come to work so they can present a professional forecast to the public. This blog is probably the least of thier worries. That is why you should all understand what a treat it is they take the time to interact with us on here. Please grow up and lets not turn this blog into a big joke.

  6. salemphil says:

    OK, Please I just want to say one non-weather related thing and that is PLEASE DO NOT confuse me (SalemPhil) with the other one! I would die if I could not chat on here with all of you wonderful people!!

  7. B Rein says:

    i say we have to sign in with a membership… that would get rid of the imposters and if you slack off have your account deleted.

  8. Justin says:

    I’ll just say that the only posters who I’ve EVER seen abuse the privilege of having this wonderful blog space are Kyle and Phil, who have tried their best to seal the fates of others by posting as them. All I have to do is see the email address, and these are the only two who I’ve seen impose as others. Everyone else is here to talk about their love and passion, the weather. I don’t want to overstep my boundaries, but I agree that its only fair considering that they obviously aren’t here to cause a scene.

  9. Derek Hodges says:

    I was asked by droppin to post this, he says he was banned, so it would be nice if he were unbanned because he didn’t actually say anything there was just the imposter but here it is…
    – I agree with the others. Josh the “Snowman” has never been anything but friendly, mature and professional on this blog. Us diehard bloggers consider him a friend. We appreciate his knowledge and interpretation of weather patterns as he is up north in Everett and often our weather comes down from his area. So PLEASE Mark, or Drew, unban Josh the “Snowman”

  10. Mat says:

    Yeah, its like 43 here as well at 33rd and Alberta

  11. Derek Hodges says:

    Its still like 43 or 44 here but maybe some of you 1000ft people will see a good mix tonight. Maybe even some snow, but I doubt it would stick unless you get a pretty heavy shower.

  12. kirk says:

    38.8 deg here

  13. Andrew says:

    ok, this is interesting…i am sure it was just a moderate shower, but my buddy who lives up near skyline and around 1200-1300 feet just reported seeing some large flakes mixing in with the rain for about 5 min as a shower moved through. Although, then again he does seem to be in a bit of a cold pocket.

  14. Mat says:

    Josh the snowman, Josh the snowman, josh the snowman!!!!!!!!!!

  15. Andrew says:

    While i will not say if we are going to get snow from this system or not, i will say that for this time of year we still have some pretty damn low snow levels. TO be sitting steady at around 2000 feet for this time of year is pretty cold.

  16. Derek Hodges says:

    yeah, I need more than one model to get me to consider it.

  17. Justin says:

    Tomorrow is my ‘due date’. If its saying this tomorrow night then I’ll include the chance, and assume its a good possibility. Right now it looks like we could support a few stronger showers that die off into early Friday morning from this one, especially depending on how the low stations itself and how strong it will be at that point.
    I agree with Andrew though, despite the fact that we’ve had a lot of surprise March snows in the past, and its certainly possible, I still think we need to be within a 48 hour time period at the earliest to call it. The model could easily jump its tracks sometime Thursday and just go back to mid 40’s and rain, so making a big deal out of this is rather silly at this point. I’d like to think that if it does happen that we’ll be one of the first to nail it, but as of now I’m not convinced of anything.

  18. Derek Hodges says:

    MRF is the only model that gives us cold enough air to reasonably hope for snow, GFS would have to cool several degrees.

  19. Andrew says:

    Maybe we could get mark or drew to make a comment on this tonight.

  20. Andrew says:

    Don’t start believing the models when it comes to snow this time of year….unless you are 1-2 days from the “event.”

  21. -100F says:

    MRF shows about 1-2 inches of snow at one point, so its not that bad.

  22. -100F says:

    Same, thats why I think its unlikly.

  23. Derek Hodges says:

    One thing to remember is IF the MRF is correct we won’t need much moisture. Its a more straight northerly flow. Meaning IF it were to occur likely we would be much colder and only a couple measly showers could coat everything in white.

  24. Derek Hodges says:

    less moisture, more northerly flow. It all balances out Lol. I got a feeling it won’t happen.

  25. -100F says:

    Less moisture though

  26. Jerry says:

    I think we have the same shot as we did last week at this time. lol B/C its looks like almost the same set-up

  27. Jerry says:

    Well I will say this. They have been almost consistant with bringing it in since yesterday. Now with that said the temps have been a bit up and down, but they are mostly supporting the cold we need for snow.

  28. -100F says:

    Well yes, it is possible. But dont get exited or anything, I still think this is unlikely.

  29. kirk says:

    I did not have time to look at all the models (not that it would matter). I did peek at the NAM on KATU’s weather page after I saw you guys talking. Wow I see what you all were saying about Saturdy, the flow is coming straight down from the north. No talking weather heads are saying anything though. Mark and Drew are not talking heads, they have 2 real forecasters at FOX12. Seattle NWS hinted at a low droping out of the Yukon earlier today but said only half way down the BC coast. Who knows???

  30. Derek Hodges says:

    ok thanks. I hope so

  31. -100F says:

    So both -6 and -10 will both give snow to all of us, -6 is more borderline.

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