December 22, 2022

The Potential for a Major Freezing Rain Event

 It is looking increasingly probable that a significant freezing rain event will occur during the next day.

Freezing rain can make driving dangerous and result in extensive power outages.

As described in my previous blog, freezing rain occurs when temperatures warm above freezing aloft but sub-freezing air remains near the surface.   Raindrops fall into the sub-freezing air and can supercool to below-freezing, yet remain liquid.  Such droplets can freeze on contact on a cold surface.

The Current Situation

Temperatures are well below freezing throughout the region, as shown by the map below of 2 PM temperatures.


A warm front is approaching the coast, accompanied by precipitation, as picked up by the Langley Hill Radar near the coast (see radar image).  Clouds from the approaching system have already started to spread over the western side of the region and precipitation has now reached the WA southwest coast.


Precipitation will start as snow, then sleet, then freezing rain, and finally rain.   

Let me show you some forecast graphics of the event (just produced by meteorologist Dave Ovens) from the UW high-resolution modeling system.

First, western Washington.

At 10 PM tonight, much of the inland area will see snow (blue), but freezing rain (yellow) will be moving into the coast.


By 4 AM, freezing rain will cover much of the western Washington lowlands, while snow will be occurring over the Cascades and eastern Washington.


And by 7 AM tomorrow, the freezing rain will be ending, with rain moving into the region.


Even greater potential for freezing rain exists in the Columbia Gorge and to ots west over the northern Willamette Valley.  Why?  Because there will be a bountiful supply of subfreezing air moving westward in the Gorge.

Below is the forecast of accumulated freezing rain by the NOAA HRRR modeling system through 8 AM tomorrow.  Lots of freezing rain in Seattle south and in the Willamette Valley.


But while the freezing rain is over for western WA by tomorrow morning, it continues in the Columbia Gorge and Willamette Valley, with huge amounts of icing.   And freezing rain will continue in the WA Cascades. Not good.

By Saturday warm, moist air will flood the region, and this cold/icy/snowy episode will be over the western side of the region.


15 comments:

  1. Thank you Professor! This event has been an especially confusing one for us laity to decipher from the sources which aren't your helpful self. (NWS: "You're all about to die!" weather.com: "meh. it's cold and then it will stop being cold") Off the wall request for future consideration: favorite links to find some basic local information, like wind profiles (long gone: https://atmos.uw.edu/cgi-bin/latest.cgi?profiler ) and forecast ensembles. Thank you and happy tranquil holidays!

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  2. It's really hard to identify geography in the last figure. What's the predicted freezing rain accumulation for Seattle?

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    1. Appears to be less than .05 inches south of the Ship Canal and close to zero north of that line.

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  3. Glad we aren't traveling. Stay safe out there, everyone!

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  4. 'another top notch article about climate and "supercharged snow storms"...what a joke...
    seattle times...via the rag..aka..ny times

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  5. Some incredible stats from this cold weather event. Denver had a 37 degree drop from 42 degrees down to 5 degrees yesterday from 4:00 to 5:00 pm. Yesterday's high there was 51 and the overnight low was -24. Just amazing!

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  6. Generator tested, fueled (don't tell the guv ;-), ready and ... 1992+/- Whatcom County Silver Thaw is a vivid memory. No repeat of that required.

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  7. This is still a bit difficult to parse. Probably because the only thing trickier to predict than a snow storm in this area is an ice storm. Plus the nuances of ice storms with less than a quarter inch being mostly a driving hazard, .25-.5 being more profound with disruption and .5+ getting into the doom territory, we are not talking about much variation. Any one of them is a bad day on the roads, though. Seems like it might be best to count on staying home and a fair chance of a power outage.

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  8. We live between the Willapa Hills bulls-eye and Longview. NWS expects 1/3" thru midnight 23/24th. Hope it's that low! We're locked down with firewood by the door, as ready as can be. Utilities are underground.. but they must come out at some point!

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  9. How is this possible? It is -20c here in Kelowna bc (Okanagan) right now. Yet it is raining! It's hitting the ground and pure ice! How are the raindrops staying liquid?

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  10. Freezing rain happens when the air above trapped cold air is much warmer so any rain that comes down goes through the cold layer and turns to ice when it hits the cold surfaces. There are some nifty graphics out there you can search

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  11. The rain ends up "supercooled".

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  12. would love comments on the ever changing time-frame. Bellevue was dry until about Fri 3am, despite predictions of far earlier on Thur night.

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  13. So far no appreciable freezing rain in SE Portland. Got about 1/2 inch of sleet/snow overnight, and it's still on the ground. Nothing stuck to the trees so far. No problems walking, and the cars seem to be moving fine on local streets

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