January 08, 2017

Freezing Rain Hits Portland with a Threat to WA Passes

Temperatures are rapidly warming aloft as a Pacific weather system approaches.    Sounds good for cold-weary NW residents right?  But those located in or downstream of gaps in the Cascades or in particularly cold areas are experiencing something else:  freezing rain that produces surface icing, a real threat for aircraft and those driving.

As a result, Portland International Airport is essentially closed, with nearly all flights cancelled (see below)

A look at the flightware tracker website shows a lot of overflights but virtually none taking off or landing.

Aircraft are taking off and landing at Seattle Tacoma Airport and the time-height cross section of weather observations from aircraft indicate tremendous warming aloft, with temperatures above 8C in the lower atmosphere (heights in pressure, 850 is around 5000 ft, red is temperature in C)

Right now there is an absolutely HUGE difference in pressure across the Cascades, with high pressure to the east.   The value is nearly 16 hPa (mb).... believe me, that is unusual.  Such a pressure difference drives easterly flow... cold, dry easterly flow... at low levels through gaps and passes.  To show this to you, here is a short forecast (for 10 AM today) of sea level pressure, surface winds, and low-level temperatures (blue is cold).  You can see the tongues of colder temperatures and higher pressure extending into gaps and the large pressure gradient across the Cascades.

With cold, below-freezing air, at low levels and warmer air aloft, one gets a set up for freezing rain.   Precipitation starts as snow higher up and then falls into above-freezing air and melts into rain.  But then the rain falls into a below-freezing layer near the surface and cools below freezing, but remains liquid.  This is called supercooling of water.  Then when the supercooled rain hits the cold surface or an aircraft it freezes into ice....freezing rain.  Portland and the western Gorge is particularly susceptible to such freezing rain events because it is downstream of the Columbia Gorge...a near sea level conduit of cold air from eastern WA.

The latest observations at Portland Airport (KPDX) shows several hours of freezing rain.

My colleagues at the National Weather Service in Portland put out an ice storm warming last night (see below)....a good call.

The ice storm/freezing rain should weaken during the afternoon around Portland as the warm air reaches the surface and pressure differences relax,  Will hold on longer in the Columbia Gorge.

Here is a picture of an iced window looking out from the NWS office in Portland.

Further north, the big freezing rain threats are in the Cascade passes, which also supply a conduit of cold air from the east.  At this point, the NWS is mainly going for heavy snow in the Cascades, but I suspect that there is also a major freezing rain threat.

And did I mention winds?   With a huge pressure difference across the Cascades, winds in the Gorge are gusting to 30-50 mph, even higher in exposed location.   For example, Crown Point in the western Gorge, where gusts are exceeding 70 mph! (see below)

And to make things interesting, the Langley Hill weather radar is broken.  Not good.  Anyway, be careful if you around Portland, the Gorge, or the WA Cascade passes.


  1. Thank you for mentioning us down here in Portland. A lot of us regularly read your blog because much of what happens in Seattle also happens here. On those occasions like this weekend where we're getting slammed but Seattle is having just another winter day, it's nice to get some perspective from such a knowledgeable source about what's happening down here.

  2. These recent storms are also sneaking in from the SW, right through the Oregon 'radar hole' - we need another radar intervention but times could be challenging for Federal spending on science projects..

  3. Hi! I was hoping you could answer. Apart from today, has there been any precipitation this month (apart from what was left over from NYE?) If not, would that not be an extreme aberration 7 days into one of the wettest months? December was also bitterly cold and far below normal precipwise as well.

    I am thinking of last year, when all our rain was completely shut down at the end of March, and did not resume until October. With only two months of rain left, and the current month being persistently bone-dry, are we to expect both a brown winter and a brown summer? Yes,yes I know things can unexpectedly change, but let's work with the current pattern/conditions. Keeping my own opinion out of this, the vast majority of people enjoy PCN/style glowing green grass over brown grass. In your professional judgement, would the former be in short supply this year? We'd have a lot of unhappy folk who have been inordinately traumatized by the events of the past year (and before someone argues and tears me to pieces, as a pacticing psychologist, I can inform everyone that there is an irrefutable corrolotion between the familiar - spectacular green grass in this case - and our ability to recover quickly from being bombarded with incessantly bad news. Any hope for us to enjoy green grass? We need some good news - some comfort - no matter the shape it takes. Thank you!

    1. I can tell you most definitively that all of our rain was not "shut down" at the end of March last year...I coach Little League baseball and we rescheduled a lot of games due to rain in April and early May.

  4. I'm noticing the pressure dropping a decent amount right now, down to 997mb at the moment and still dropping, which is lowest it's been in over a week.

    We've had bouts of gusty winds here, north auburn, mainly from the E or SE, our temps are starting to drop now as well at 2:30pm (down 1 degree) and dew point is quickly approaching the temp.

    Also noticed a LOT MORE RAIN than what was forecast for today, it's been pouring rain all day (I'm super sad it's not snow!).

    I'm curious if this rain continues into the night and the temps drop far enough, are we looking at potential for snow monday morning?

  5. Can anyone explain this super localized snow event that seemed to affect areas of north SeaTac(and west of Tukwila), BURIEN, and Normandy Park(from New Years Day), all of which received more, far more in some cases, than anything close to it? Other nearby areas-to my knowledge- such as Des Moines, Kent, Renton did not see close to the same type of snow accumulations, or lingering ice on the roads. I know this general area because I commute from Auburn to where I work at SeaTac, and could see the spread of snow on roads near the airport everyday since Jan 1. In the short span of about 400 yards or less, there were noticeable differences in some cases.

  6. tracksdc89 said: "I am thinking of last year, when all our rain was completely shut down at the end of March, and did not resume until October. With only two months of rain left, and the current month being persistently bone-dry, are we to expect both a brown winter and a brown summer?"

    Rain was completely shut down? We were less than 2" shy of average in those "selected" months you chose last year, in a water year that finished the year at 49" (vs. an avg. year of 37") We were 130%+ of precip last year, the reservoirs were full and then some. We were not remotely close to a drought last year, ever, and people (including the park dept.) watered their gardens and lawns, and the $ for that water went to SPU, and the city of Seattle.

    For this water year? Currently we are sitting at 125% of normal (21.12" vs. 16.9 avg.). Our snowpack is also above normal - http://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/wa_swepctnormal_update.pdf and the reservoirs are above average and being used more for flood control than anything else.

    You want to talk about an "extreme aberration" in monthly rainfall 8 days into the month? This is like the joke about sunny days: "It was a beautiful day today but you know what that means? We tied the record for driest day in all of history!"

    As those of us remember from the "wet drought" claims of 2015 (one of the more bizarre moments for water supply followers), Cliff has been one of the few willing to tell the truth on the yearly drought campaigns and political games that take place in our region. Thank you Cliff. Our summers are dry. Our falls and winters - and this year is no exception - are wet. It is why we have (big) reservoirs, and have had them since the city was young.

  7. Really amazes and frustrates me how we can have such a good pattern for cold air yet cannot seem to get the moisture for a good lowland snow event in the Seattle metro area. Aside from New Years Day in a very narrow area around Sea-
    Tac, most of us have been shafted! Portland South to Eugene has seen snow and ice, Eastern Wa. looks more like Fairbanks, (my sister lives in Pullman and cannot believe the consistent snowfalls since mid December), yet in Seattle, nada. I know historically we can get some decent snowfalls, but I cannot help but vent that it's been rather disappointing as snow lover thus far this winter. Hoping for some kind of redemption before it's too late. My guess, is I am not alone...

  8. Roads and windshields in Bellingham/Whatcom County were glazed with black ice this morning. It seemed that everyone was caught quite by surprise and there were many traffic accidents in the area during the morning rush to work. My commute takes me from near the airport in northwest Bellingham south to Fairhaven in the southwest portion of the city and roadway/parking lot icing was present both at the origin and destination of my journey. According the Whatcom Scanner Report, icy conditions seemed to have become an issue over most of the western county by 7AM and continued to be for about 2 hours. The odd thing, and likely what caught so many (myself included) by surprise, was that temperatures at the time were 37/38 degrees or so under cloudy skies. The overnight minimum temperature was 34 at midnight and I measured .34 inches of rain all of which fell between 1AM and 5AM. The maximum and minimum temperatures on Sunday were 41 and 33. I find that I am struck with bemusement. How did we end up with icy asphalt this morning under cloudy skies and with temperatures having been above freezing for a solid 48 continuous hours? Dr. Mass, if you find the time, perhaps you could elucidate.

  9. The California Reservoir report shows levels over 100% of average for the first time in a long time. Current report is here http://cdec.water.ca.gov/cgi-progs/reservoirs/RES
    Three reservoirs did not report today (Jan 9th) but they are usually net over 100%.

  10. Get used to disappointment. It's not easy to get snow in Seattle, but (what is less often said) is that it's not this hard either. Look at snowfall averages at SeaTac, cut them in 1/2 and you'll still get more snow than we have had for what...5 Winters now? No sign of it ending either.

  11. Kristin Ridl... check the soil temperature and the air temp right at ground level. Official measurements are made a couple of meters up (IIRC) and there can be several degree gradient to ground level.

    My neighbor in Sequim checked soil temps today... 31 degrees F. Pavement (especially asphalt) radiates quickly and will likely be cooler than that.

    The reduced ground temperature may also drop the air temp to the dew point right at the pavement, resulting in ice build-up without precipitation.

    Perfect recipe for black ice. Invisible and deadly.

  12. To Kristen: I am guessing that the heat loss from so called black body radiation cooling (sunday nite/monday morning were clear) is greater than convention heat transfer from air to the road surface.

    I am now seeing (this is about 7 PM Monday night) the same thing happening. The concrete patio at my house is staring to freeze. The air is not yet freezing. It is crystal clear (bright, crisp moon).

    Perhaps if there is a physicsist in the group, they could explain the relationships between black body radiation heat transfer and convection heat transfer. Surely there have got to be computer modeling available that can provide some of the answers.

    I am guessing if you put a piece of black painted metal outside during a dead still crystal clear night and the temperature is at 33 degrees, would the metal be the same temperature or would it be clearer because of radiation?

    To folks here in Bellingham, I am curious, is there an atmospheric sciences group at WWU

  13. Langley Radar is broken? I want names! I want heads to roll! :-)

    Sorry. The cabin fever is getting to me. I make two little local trips, per week, and it looks like the snow / freezing temps are going to screw my piddly little trips up. Between the cold snap and a frozen pipe (no water for 4 days), one gets a tad cranky. Lew

  14. Sulla said - "Look at snowfall averages at SeaTac, cut them in 1/2 and you'll still get more snow than we have had for what...5 Winters now? No sign of it ending either."

    The NWS average snowfall is 5.9" at seatac. (Link - http://www.seattleweatherblog.com/snow-stats/) And btw, this is the correct NWS number, not some of the inflated numbers floating around out there.

    So cut that in half and you get 2.95". We are currently at 4.0" for this year alone at seatac, and the winter isn't half over. We had 4" in 2014 as well.

    I don't get statements like this. Cliff has explained it a number of times and yes, based on our geography and location it is that "hard" to get snow here. Has been for a long time - with a few years (49-50 and 68-69) huge exceptions. But those are the exceptions. Not the years when we get 4", and this one isn't over.

  15. Went Snowboarding at Snoqualmie Central last night. Very clear evening with clam winds. Lots of fog moving in and out of the base of the ski area. When passing through the fog, it felt noticeably colder on the face. Later realized the fog was creating a thin layer of ice on my snowboard. Later, on our way home through Issaquah, we noticed a thin layer of ice on many roadways.

    1. Clam winds can no doubt be attributed to the late, great Ivar Haglund!!!😉

  16. Thanks, John. I will look into acquiring a soil temperature sensor for my weather station.


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