January 17, 2009

Fog in the pass

Several of you have asked about the fog in the pass...they thought the mountains should be clear due to their higher elevations...and in fact they have been clear for several days. The cams in Snoqualmie Pass (see attached) do show fog. In fact, the fog has been freezing on trees and other objects. Yet on top of tiger mountain and at Paradise it is sunny...what's up?

The explanation is that eastern Washington is full of low clouds and fog (as it frequently is under high pressure in the winter). They have an inversion overhead. The pressure is higher in eastern Washington than western and this difference is increasing as large scale high pressure is moving eastward. The six hour forecast valid at 10 AM this morning shows the story..cold air in eastern Washington and high pressure there, with a big pressure difference across the Cascades (roughly 10 mb..which is a lot). This difference in pressure is producing strong easterly winds in the Columbia Gorge. It is also pushing the cold air and fog up the eastern slopes of the Cascades and into the passes. You can see this in the visible satellite picture this morning (see picture).

Today, was a good example of a weakness in our current computer models...they failed to produce the low clouds of last night and this morning. We believe that an important reason for this failure is that the models mix the atmosphere too much under stable conditions (like when cold dense air is under warmer, less dense air). The simulation for today at 10 AM is a good example (see below--no clouds over PS).
Today, a good portion of Puget Sound lost the low clouds and we finally saw some sun. One reason is the inversion became so shallow that limited solar radiation could mix it out. Also the strong descending easterlies aloft (forced by the large difference in pressure) might have contributed. WIth solar energy reaching the surface, temps warmed into the mid-forties to 50F. The inversion weakened a bit...but is still there...and will restrengthen tonight as temps cool near the surface. Tomorrow morning I will try tiger mountain..with a thermometer, and see what I find.

PS: Just a reminder...I will be talking about NW snowstorms on Wednesday at 7 PM at Third Place Books in Lake Forest Park.
Will review big historical lowland storms, including the last event, and the rare conditions that produce them.


  1. I did the Tiger Mountain hike today. Most interesting is that the transition out of freezing temps was very quick. Then a gradual warming toward the top. Hit the wall of cold air in about the same place (about 70% percent of the way down). Didn't have a good thermometer, but my little backpack one registered high 50s on top (in the shade).

  2. Just returned from a glorious day at Stevens Pass. It was sunny and just below freezing so the snow didn't turn into a soupy mess. It was fantastic!! Very glad I decided on this weekend to be my very first at Stevens Pass.

  3. We bailed from Olympia and went to Ocean Shores. It was great. The temps were in the upper 40's with a light breeze. It was more pleasant there today than the last time we went in the summer. Go figure.

  4. Up at Snoqualmie Summit today. About 20F all day long and very windy out of the east. Skied in the fog bank all day with the wind and high humidity, it was very cold. Short sun break around 2p, but then socked in again.

    Oh, well, that is the same pattern that gets us snow at times when it is raining just over the ridge. Have to take the good with the bad.

  5. View of inversion from Anti-Aircraft Peak on Cougar Mountain looking northeast. Lake Sammamish in the foreground and Mount Baker in the background. Saturday 1/17/09 about 1:30PM.


  6. Not a bad day here in Woodinville. Has some early morning fog/low clouds, but then by early afternoon, skies became all sunny and pretty much stayed that way. However was still cool though as my high reached 42 with low of 30. Nice to see the sun again.

    With it being clear, you sure could see the haze/ inversion layer just below the Olympics this evening.

    Here`s the link to my pic I took that shows the haze/ inversion layer just below the Olympics.

  7. I just have to share this, the funniest thing (funny in a neat way) I've ever read from a NWS bulletin.

    Here's the original link:


    And here's the part that's very fun to read:

    "Issued by The National Weather Service
    Seattle/Tacoma, WA
    1:58 pm PST, Sat., Jan. 17, 2009



    The upper ridge is big, bigger than most Stretching from LA to the Canadian coast. It brought change from rain, a welcome diversion Along with much warmth above a strong inversion.

    Proceeding down to the pass, you hit the temp wall An almost solid feeling, as if you might fall. Warm and melt above, moist and cold below Make challenging conditions in near surface snow.

    Crusts of fear in places, breakable nearby Turns may be tough, making equipment fly. Hoar frost at night mostly dies during the day Except shaded north faces where it lingers to play.

    At least some slopes have corn, that feels quite nice Just avoid steeper terrain that transition to ice. Only minor changes ahead from this most stable flow With snow stability varying from moderate to low. "

    There's more info after that, but it appears the poem ends there.

    Good stuff!

  8. South Hill Puyallup:
    Still in the soup, it hasn't been above 36 degrees all week. It's really thick now with a 100foot ceiling according to the KPLU metar, and a 300 foot ceiling at the KTCM metar. I can't remember the last day we say sun or blue sky.

  9. Stayed home today. Thought it was going to be the nicest weather that way here just east of Lake Washington. It started gorgeous, just like it had been all week long. But something changed, and the clouds left us in a murky soup of sun by afternoon. I hope the clouds come back tomorrow and Monday so that I can enjoy at least part of my weekend.

  10. Up on Sumas mtn today near the Canadian border showed some great views and the fog moving into the Frasier valley

    Fog from the mtn...

  11. "Crusts of fear in places"

    That is so funny! Though that does sound like some of my experiences skiing.

  12. There are some pretty strong gap winds coming down the Snoqualmie Valley now. The temperature has jumped in 4 hours from 34 to 50 degrees with 10 knot east winds gusting to 30 knots in Fall City. (Had been seeing light west winds prior.) From the looks of wunderground's stations it hasn't made it further west than here though. Lots of low-mid 30s in Carnation and up Happy Valley towards Redmond.

    I wonder if this will keep the fog at bay?

  13. Pretty much stayed clear over night here in Woodinville with my low dropping down to 30. Which is also my current temp here at 7:47am. Perhaps a high around 50 today, but we`ll see.

  14. We went skiing at West Summit on Saturday afternoon. According to the thermometer in the minivan, it was 41F in Seattle, 32F in Fall City (still in the fog), 50F in North Bend (crystal-clear skies), and 27F in the West Summit lot.

    It was sunny for a while down at the base but the top of the Pacific Crest lift was socked-in all afternoon (and it was cold),

  15. Bright sun in Stanwood yesterday as barometric pressure dropped and temperatures rose. Stayed home since, even though gas is cheap, the cost of carbon emissions (to both the atmosphere and environment) remains high.

  16. Yep, it was sunny at 3000' above Lake Chelan on Fri. We went snowshoeing, where there was 2' of snow a week or so earlier, it was mostly gone, washed away by the rains. The Col River Gorge was gusty, I mean really windy Saturday out by Troutdale. It looked like an ocean. The freight train traffic on the radio were restricting them to 30 mph

  17. Washington Coast 52F, East wind 7-10mpm. Clear blue sky day as it has been the last 3 days. The humidity is the lowest I've seen in a long time (usually 95%+) but today its a low 50%. Barometer is 30.29 and rising. I really don't want to go back to Lakewood today.

  18. Can anybody tell me what that bright, orange, glowing orb in the sky is

  19. Can anybody tell me what that bright, orange, glowing orb in the sky is?

    I also see the orb and am baffled. Warning: don't look at it directly for an extended period of time.

    On a serious note, it was about 50F this morning in Sammamish at about 10am. Right now (3:30pm) the temp has dropped a bit, but it actually got up to about 63F a couple of hours ago. It's about 59F right now and I'm sitting out on my deck.

    Yesterday at this time I was kicking frozen fir cones off the deck that had welded themselves on there due to the freezing fog.

    What a difference a day makes...

  20. Can anybody tell me what that bright, orange, glowing orb in the sky is?

    Yes, it is called the sun. We see it A LOT here in western Washington.

  21. The 18z GFS brings 850mb temperatures of -9 C back to Seattle by next weekend. But I'd like to see it happen more often before we get our hopes up too much... :)

  22. The last few days in Winthrop, elevation 1800 feet, it's been foggy most or all day. But going to Mazama, 15 miles west and 400 feet higher, sunny all day. Yet Mazama is still 800 lower than Snoqualmie where it was foggy. Must be the wind pushing thru the pass while maybe it can't get over the North Cascades.

  23. Nice, sunny day here in Woodinville with my high getting up to 62 with low of 30. So a pretty nice mild day.

    However, I checked the Snoqulamie pass DOT cams shortly after 2pm this afternoon and it appeared that low clouds/fog was in place. So guess it was more of that fog from Eastern Wa moving west into the mountain passes.

  24. Skiing today at Snoqualmie - same as reported by Mike yesterday. We left Shoreline at 35F at 7:30, North Bend was extremely gusty, 55F and sunny, and the summit was 30. Very very windy, cold and foggy at the top of Pacific Crest run. So much so that the chair lifts were coated in horizonally crystalized ice.

    The localized fog that we drove in and out of throughout the Seattle area was interesting. We were pretty clear in Shoreline. Then we hit thick fog near the U district which seemed to come in from the sound between Phinney ridge and Queen Ann/Magnolia - creeping through the canal gap and onto Lake Union, but then a littl further and downtown was clear. I'd love to understand that better.

  25. Cliff, or maybe someone else, can you explain this? It was 60 in Everett today. 62 in Woodinville according to Andy posting a couple hours ago. But it was only 51 at SeaTac, and only 46 here in Renton (at the airport), where I live. My thermometer, higher around 400 feet, registered only 44. But the sun was out all day here. Why the difference?

  26. Good question for the one asking about the temp spread today. Perhaps that high of 46 down in Renton was due being further away from the Cascades and not getting in on the strong or light easterly winds from today. Also, did see that a small portion of the south sound didn`t clear up from the fog untill about 1, 2pm-ish this afternoon per the visible satellite imagery loop. So not nearly as much solar heating as up here where it was sunny the entire day.

    Perhaps Cliff can explain better. :o)

    41 here with clear skies here at 830pm.

  27. The answer is this: Those locations that were exposed to the subsiding easterlies (eastern king county lowland, Paine Field) were warm. The inversion was completely scoured out there. Locations that did not get the easterlies stayed relatively cool. I could see SEATAC yesterday from the top of Tiger Mt...they were in the clear with low clouds below them. But they didn't get the easterlies at the surface.


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