December 23, 2008

Snow versus Rain

Tomorrow represents a classic problem for local meteorologists in winter...snow versus rain. Many winter events are on the margin around here because warm air from off the ocean is always close. Later tonight and tomorrow AM we will initially see snow.. in fact, take a look at the latest satellite and radar imagery....a disturbance is making landfall and associated snow showers are moving into the western Strait and Forks is reporting light snow. In fact, snow appears to be coming in a few hours early..and that is good. But after that the models suggest that by midday the lowland temperatures will be too warm (into the mid 30s) for snow below 300-500 m and we will see rain as a stronger disturbances (an occluded front) moves in. But before it does so, we could get 1-2 inches of snow. However, my colleagues at the National Weather Service have a different interpretation and their latest discussion suggests they believe it will be all snow tomorrow--with 2-4 inch totals. So it will be interesting to see what is going to happen.

Take a look at the model total snow forecast ending at 4 PM to check out your local area based on the latest model run. And clearly the mountains will be getting plenty of new snow.

Snow 101

Surface temperatures don't tell the entire story about snow...and snow can fall when surface temperatures are above freezing by a few degrees (although wet snow). It takes about 1000 ft of above-freezing temperatures to melt snow completely into rain. Thus, the snow level is about 1000 ft below the freezing level. And whether the temperatures will be cold enough can be difficult to determine. For example, if the air is relatively warm, but dry, then evaporation can cool the air down sufficiently to get least until the air becomes saturated. Another issue is precipitation rate. Precipitation around here almost always starts as snow if you go high enough. When the snow hits warmer air below, it melts and cools the air as it does so. (It takes energy to melt ice!). The heavier the precipitation the more melting and cooling...and if you have heavy precipitation, the snow level can be driven to the surface. So this makes the problem not only need to be able to predict the incoming air temperatures, but you have to get the humidities and precipitation rates right as well.
You can see why meteorologists need a happy hour once in a while.


  1. Cliff, since I have to work I'll go with your forecat for Wednesday over the NWS's.

    Meanwhile, shifting from atmospheric science to geology, wouldn't it be "interesting" if in the middle of all this wintry mix we had a "Big One,", namely, perhaps, a subduction zone quake, say of a magnitude 9.0

    This is just a friendly reminder to be prepared. Our atmospheric weather is nothing compared to the geological monster lurking below!

    Stay war! Be prepared!

  2. I meant "STAY WARM! Be Prepared."

  3. Cliff--

    Love the snow accumulation plots. Two questions:

    Is there a web address we can get these from on-demand, rather than hoping you include one with every subsequent post until this is all over (hint, hint)?

    How often are these models updated? Hourly? 4 times a day? What?

  4. Part of what makes this (respectful, happily) difference of opinion especially interesting to me is the fact that the NWS WAS in the direction that Cliff is still predicting ("There has been a chance the precipitation
    would change to rain in the afternoon in some areas. That chance appears to be fading now."). I didn't really see a reason why they've shifted, unless it's that the dew points are expected to stay below freezing. But I don't really know how all that works . . .

  5. Bellingham is already 23degF with the low tonight forcast at 28, I wonder if this will effect snow amounts?

  6. When I get a certain type of rain on the windshield (not usually when it is this cool, more like our usual) I often refer to it as "s'rain"...after all the Arctic people formerly known as Eskimos had sixteen words for snow.
    Now, I'd settle for pure good ole rain, though over time (my home's downspouts are frozen)

  7. Wow! Just finished reading the most recent update (Snow v. Rain). No wonder it's so hard to predict the weather future around here.

    I love it when there's a difference of opinion re: the forecast. Looking forward to seeing who got it right.

  8. Jason...yes, all the plots are at:


  9. Interesting how the radar apparently picks up precipitation echoes even when it doesn't make it to the ground. Right now it looks like there should be some precip falling on much of King Co., but doesn't seem to be any happening here in Mountlake Terrace.

  10. Now we're talking! Snowfall number 5 in just over a week!!! Our you kidding me? And now snow for Christmas day??? I am a HUGE snow lover and have lived through, and put up with, many lame snow years here in the PNW. (Only in Seattle do you get excited about a slushly inch.) However, this one will be one to remember and it's only December! This may not be Jan. 1950 or even Jan. 1969, but as I look out my window at the flocked evergreens lit up in Christmas lights, I am reminded that it can and does snow in Seattle. Enjoy it before the mild pacific air has the final say. ;)

  11. Lindsey,
    The radar beam is not has angle with the surface and thus is seeing farther and farther above the surface as you proceed outwards. Precip often evaporates before it hits the ground...particularly during the initial stages of an

  12. My own very non-scientific opinion is that we'll have snow all day in Sammamish.

    When the forecast sits on the cusp between rain and snow, we almost invariably get snow.

  13. I'm rooting for your interpretation, but am resigned to the idea of never-ending snow.

    I had to laugh when my sister-in-law in Ouzinkie, Alaska said that they had no snow at all! Something seems a bit skewed here.

    Thanks for the great blog, I've really been enjoying (and learning from) it in this last week.

  14. Somebody please get Cliff a drink!

    PS. It would be really great if everybody so concerned about the plowing would also shovel their sidewalks.

  15. Wow, Cliff... thanks for sharing the motherlode of online data with us... now can you tell us where we can sign up for your course, "How to Interpret Raw Weather Data"? Fascinating!! I seriously would at least audit such a class. :-)

    Thanks for keeping it so interesting. The first flakes are touching down in Bellevue now and I'm dying to see what happens here tomorrow afternoon. I am guessing we'll have a spell of rain that eother switches back over to snow or peters out, allowing a good freeze tomorrow night and then maybe more snow Christmas day. But what do I know?

  16. Walter seems convinced that it's going to snow both W & Th in the lowlands. Us folks who live further east away from the water usually take the brunt of that.

    It looks like we're getting another couple lows coming in from the northwest, and unless they don't break up, that high is moving southwest, so I dunno... he may be right.

    Oh yeah, and do watch out for the earthquake. :) My emergency water is all frozen...

    Merry xmas!

  17. Thanks, Cliff, on the radar info! That's exactly the kind of stuff I want to know.

  18. C'mon rain! I've been shut in here in Shelton for a week. We just shoveled half an acre of driveway (maybe not THAT much, but my back feels like it). Need to get over the river and through the woods to Grandmother's house. At 11:30 PM it is 34 degrees on my back porch, and no precip.
    Weatherfreak, I admire your enthusiasm. But if I said the thought that crossed my mind when I read your blog, Cliff would have to delete this.

  19. The comment on "needing a happy hour every once in awhile" is completely inappropriate. There's no need to mention poison and what should be illegal drinking on a blog about the weather, which has NOTHING to do with the stupid stuff. Plus, you don't want to be telling future meteorologists that it's okay to poison themselves if you work in the meteorology field. Thanks.

  20. Boy, this person needs a drink...

  21. It's feeling quite "wet" here on Capitol hill. RH is heading towards 100 while DP and temp converge on 32+: a big damp sponge that sucks it all down as rain. I'm hoping for a snow dump but this is Seattle and ultimately the ocean always wins.

  22. re: Anonymous who posted about drinking being inappropriate.

    Alcohol in moderation has been proven over and over again, by science, to have health benefits (though the tenor of your comment leads me to believe you may not believe in science) and fermented beverages have been used ceremonially (re: happy hour) for over 9,000 years, spanning almost every culture and religion.

    Please keep your uneducated and nonsensical beliefs where they belong - your self righteous church group.

    The comment on "needing a happy hour every once in awhile" is completely inappropriate.

  23. Eli said: "PS. It would be really great if everybody so concerned about the plowing would also shovel their sidewalks."

    BOY would I LOVE to do that, Eli. I've got about 8 inches of snow in my backyard that is threatening to flood my basement if I don't shovel it out of the way. But after calling every hardware store in Seattle today to find a snow shovel, I'm afraid I'm SOL. Seems that everyone is sold out. Any other bright ideas??

  24. Go Rain! Go Rain!


  25. To the 12:46am anonymous poster: Guess what? I'm a meteorologist, so I do believe in science. Oh, and also guess what? I don't attend church. It amazes me how people who attend church are the same people who do a bunch of crazy things. I guess they attend church because they figure they have to somehow make up for all the other things they do?

    By the way, please snow!! Isn't snow beautiful? :)

  26. Patty - if you live in eastlake, i'll lend you my shovels. And isn't the rough calculation that 10" of snow equals 1" of water? So - maybe no flooding?

    I am in weather nerd heaven w/ your blog Cliff! Thanks so much for it .... and no offense meant by the use of nerd.

  27. I know this might turn political ;-) but even though I'm a non-drinker, I'm all in favor of meteorologists relieving stress once in a while by using and/or abusing the legal substance of their choice. Just please don't drive afterwards! It does seem like a job with potential for high stress; get it wrong, and the whole world notices and gripes about you and what an idiot you must be; get it right, and nobody notices, and they still complain about the weather, whatever it is. In between times, insert ten really tired weather jokes here, a broken computer, a model that doesn't deliver consistent results, and a missing coastal radar, and I can see the recipe for insanity on the job.

    3:25 insomnia-a.m. here in Bellevue, and it's 31.3F and not doing anything outside. Barometer is 29.32 and the Oregon Scientific folks don't believe in snow... the rain icon is doing its dance. I'd rather have more snow since we're not likely to get enough rain to get rid of all we've got.

    Patty, walk around and ask your neighbors. Someone will loan you a snow shovel, I'm sure of it. But any old garden shovel will do, too... though a square-bladed one will work best.

  28. Got some nice medium flakes that have dusted the railing of my deck. I got up at 3 and it's now about 4 and has snowed continuously. Down here at Alki we figure if it's snowing here it's snowing everywhere.

  29. Just drove into work. The snow is sticking on bare pavement in some areas but not sticking in others.
    I'm talking about near the UW. I have just a normal passenger car and the worst problem I had was bouncing around in the front end where the snow was chunkified. My tire tracks seemed to cut through to the bare pavement where the road had been previously clear so I think more traffic will make driving better this morning as long as traffic doesn't get too thick and someone does something stupid. In newsspeak: treacherous.

  30. Alki (20 foot elevation) its snowing hard big wet flakes and is having a tough time sticking on anything bare except by sheer volume. I figure it is sticking up on top of Admiral (350 feet approximately).

  31. Good morning from the Sammamish Plateau - 32.7 degrees with snow falling and a dusting of new. Kind of get the feeling it will be rain soon. I'm getting kind of tired of it all but would like to see it actually snow on Christmas Day for a change.

    Yesterday I was at the UW bookstore - no Cliff books in sight so I asked. "We are putting names on a reserve list, never expected a weather related book to be a top seller" I thought that was great! Having all the snow just before Christmas and then add a great blog was a perfect marketing scheme:)

    To JewelyaZ.... I have been noticing your late night early morning entries - this morning you answered it - insomnia. I'm sorry!

    I bought a snow shovel years ago and it has been a neighborhood favorite this last week. I have an East Indian neighbor who until Sunday had never driven in the snow or shoveled it. Now he can tell his family back home about his new accomplishments. He knew he owned a Subaru for a reason he just hadn't realized how really great it was until a first time snow driving experience.

    Merry Christmas to you Cliff and all fellow bloggers.

  32. Wakey wakey, eggs and flakies here in West Seattle at 250ft and right at 32 degrees. Hearing a fairly low jet going over-so something is happening at the airports. Sure enjoy this forum for Cliff's expertise and the real time observations. Merry and Happy everyone, and can't say enough about Yak Trax for shoes/boots, have not slipped once. Just stepped on to the west deck and it almost sounds like rain out there. Remember rain?

  33. Cliff, thank you so much for your thorough explanations, and for taking the time to let us know what we should, or could, expect. Your blog has been an invaluable news source for me these last few days and I'm so glad I discovered it. I've often stood (on my way into the shower) listening to your appearances on KUOW in nothing but a towel so as not to miss anything you had to say! You are a local treasure. Many thanks.

  34. Big, fat flakes at Maple Leaf, abourt 500'. Looks like 1.5 - 2 new inches, although it's hard to tell for sure from inside my warm house.

  35. Cliff,

    When you say almost all precipitation here starts at snow, do you mean in the winter or all year round?

    And for the person who said this:
    "But after calling every hardware store in Seattle today to find a snow shovel, I'm afraid I'm SOL. Seems that everyone is sold out. Any other bright ideas??"

    You might do what we did, which was to borrow our neighbor's snow shovel. This is a good time to get out and make some community, instead of staying inside and complaining, which seems to be Seattle's new winter sport.

  36. Tiny flakes here a mile west of Kingston. No apparent accumulation overnight. Apparently just above freezing as my porch is wet.

    The steep hill on our road was hard to walk and the other day I took a couple of spills. Yesterday I found a spare pare of rubber boots in my closet that I decided to alter. Using sheetrock screws I made some "studs" by clipping off the tips, driving them in 1/4", and then clipping all 3/16" protruding. We walked down the hill last night to catch a ride over to some friends. My inexpensive solution to traction worked like a charm!

    Casey Burns

  37. Olalla: about 33 and snowing hard at 7:25 am. An inch or so new. Whoopee ding.

    - Pete

    PS: I appreciate the amount of useful information that's available on this blog!

  38. Yesterday I saw a letter carrier pull up to a row of mailboxes and have to clambor through a pile of plowed snow to get the letters to the mailboxes - poor thing! This morning I am going to shovel a path to our mailboxes - maybe even I can get enough out of the way so he can actually drive the mailtruck up to the mailboxes without having to get out. Then I'm going to put some kind of incredible treat inside. Anyone out there want to join me in this?

  39. Totally dry skies here in Tacoma. We got a light dusting overnight.

  40. 7:30--Steady snow on Capitol Hill.

    Has anyone driven from Port Townsend to Seattle yet this morning? My 8+ month pregnant sister and her husband hope to make that trek this morning and I'd love to hear about road conditions.

    My addiction to the blog and comments continues. Many thanks to all.

  41. Vaughn Bay, Case Inlet, (Pierce County) 34 deg. F
    One inch fresh overnight; snowing but seems quickly turning to rain. Brisk wind out of the south blowing big wet chunks of snow/ice from trees. I'm looking for my hard hat before I go out!

    Not really looking forward to the drive to Seattle later this AM. Downtown, Madison Park, Hunts Point are my stops today. This is the worst time in the typical Pugetopolis snow event: monster slush piles, deep puddles that won;t drain, trucks slinging big waves of slush into oncoming traffic and sidewalk pedestrians. You know the scene =-(

    Be careful out there if you have to go!

  42. Sammamish Plateau - snowing hard - 32.7 degrees - no wind - 2" since it began about 5am.

  43. Ferndale, snowing moderately, 6" of new snow overnight (on top of about 6" that was already on the ground) and still building. 31 degrees.

  44. Sunset Hill elev.80ft
    Current temp is 34 - it has been same temp since at least 4a.m. Big fat flakes at 4a.m. Currently we can see across the sound and have light rain mixed with snow. Light winds out of the east.

  45. Cliff - When was the last time Seattle had 10 or more days in a row with below-freezing low temps? This aspect of the current weather seems unprecidented in my memory (the last 20 years here) for local weather.


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