Saturday, February 16, 2019

The Potential for More Lowland Snow

Weather update at noon Monday....
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Don't run out to the supermarket yet.  But don't put away your snow shovels or snow boots.  We are about to go into a cooler period, with the potential for snow reaching sea level, and near certainty of the snow level dropping down to 500-1000 ft.

Cooler air, capable of supporting lowland snow is going to move in this weekend--not as cold as last week, but cold enough.  To illustrate this, here is the sea-level pressure and low-level temperature analysis for 4 AM this morning.   Blue is cold, purple is colder, and you don't even want to think about white.  Light blue is cold enough for lowland snow.  Western WA is now too warm for snow, and in fact it is raining.


But here is the same chart, but for the forecast valid at 4 AM Monday.  Blue and purple has moved in.  Much colder, and the cold air has pushed south to northern CA and Nevada.  Cold air that will give us a real shot of Sea-Tac experiencing the coldest February on record.


This movement of cold air at low levels is associated with the building of high pressure aloft over the eastern Pacific, as illustrated by the upper level (500-hPa pressure level) chart for 10 AM Sunday.  Such a configuration is generally dry, since east of upper level ridges there is generally descending motion and lack of clouds/precipitation.   This is not like a typical El Nino situation, more more representative of La Nina years.  We currently have a very weak and dying El Nino--too weak to have much impact.


But this upper level pattern can bring snow if an upper level disturbance moves southward along the eastern flanks of the ridge.  And the latest model runs suggest the potential for this to happen, first Wednesday and then next weekend.

Let us start with the best global modeling system in the world (the European Center model) and the output of its 51-member ensemble system.   I love to use this....since each forecast starts slightly different and we can examine how sensitive the forecasts are to small differences in initialization.

This graphic shows accumulated snow at Sea-Tac for the 51 members (top panel) and the average of the ensemble (green lines below).    Most members show light snow starting around February 20th at 0000 UTC (4 PM on Tuesday).  Around an inch.

And a majority of the runs shows even more snow starting on Friday...bringing the snow total to around 3 inches.  But much more uncertainty with the timing and magnitude of the second pulse.


So, let's examine the Tuesday/Wednesday snow situation in more depth.   Here is the 24-h total snowfall ending 4 PM Wednesday.  Lots of snow in the mountains (our ski areas will brag about the powder available here!), and light snow extending over NW Washington and down to Puget Sound.  Temperatures are marginal for snow near sea level...that is why there is so little around the south Sound, the coast, and the Strait.


What about the ECMWF model for the same period? A nearly identical solution.  Gives us confidence in the prediction.

But what about the potentially bigger event later in the week?  At this point, the uncertainty is simply too large.

Looking at the ensemble snow forecasts at Seattle from the US system (GEFS), we note that nearly all the models are going for snow on Tuesday afternoon (about an inch, with the solid black line being the ensemble mean, which is often the most skillful prediction).  You can see the Friday/Saturday event, but the forecasts are all over the place.   A lot of uncertainty.  We have to wait to have any confidence in the prediction.

Finally, there is a lot of talk about landslides in the media and some weather information sites.  I believe this is highly unlikely.   Even with all the snow, precipitation has been nearly normal during the past 30 days and much of the water is locked up in snow.   With the cold temperatures, the snow will not melt rapidly.  And there is no hint of any weather feature that will cause rapid melt down (like a strong atmospheric river).   I worry about the exaggeration of risks, both regarding weather prediction and in the climate arena.   It may promote more clicks and attention, but in the end it lessens credibility.







16 comments:

nutso fasst said...

Interesting: While 1989 had the 2nd coldest February on record at Sea-Tac, it had the record warmest (9.3F) at Barrow, Alaska (2018 is 2nd at 4F but 2019 may exceed that).

Dennis Lapchis said...

And its all about "clicks and attention", so thank you for keeping it real.

Sharon said...

Unbelievable! I just proclaimed that I don't want to live in a place that snowed frequently--mostly because everyday activity slows or stops. Now, we may have more and my opinion may be tested further.

In truth, I will probably be very happy for more snow for the same reasons I was getting tired of it. Snow can be like a license for embracing play, free time, seeing the natural world differently (of course, assuming conditions allow for safety).

I'm pretty sure I will be drawn back into the dreamy invitation of white snowy memories, current fun activities, building new memories and for a while feeling timelessly care-free. It gets me every time.

Cliff your explanations of your process continue to fascinate. Keep up the good work!

Rabbits' Guy said...

So all the things we have to do this week because we couldn't do them last week will maybe have to become more "do them later" things again?

Well anyway, the Bow WA. reporting station with rock on a string is fully functional again so we are ready.

Also the propane truck got up our hill and filled the tank so OK there too for now.

Todd Hopfner said...

Thanks for keeping it real Cliff

Chris Woods said...

Enough already! Up here in the Canadian Okanagan, we are ready for spring. Give me a charcuterie board and a bottle of wine under the ponderosas.

Trevinski said...

Thanks for the updated forecast, Cliff. It's a bit too early to gauge on whether this event is anomalous or not but it seems highly suggestive of Solar Cycle 25 and the Modern Eddy Minimum we are entering, particularly when paired with the record lows across the states and the slightly warmer temperatures near the poles. Professor Valentina Zharkova gave a great lecture on the forthcoming solar cycles and their cosmic implications.

brian swanson said...

Cliff, we seem to always focus on the tropospheric wind and pressure system, but what is the sea surface temperature off the coast doing this year? Anything unusual that would contribute to all
the cold weather we're experiencing?

Stephanie Rudat said...

You are so helpful. Thank you.

Gpacharlie said...

I was in Barrow mid Winter working for two weeks in (1991?) and remember Seattle being colder than Barrow. I’ve noticed thus Seattle cold Alaska warm on a few occasions.

MAC in Bellingham said...

Trevinski said...

"Thanks for the updated forecast, Cliff. It's a bit too early to gauge on whether this event is anomalous or not but it seems highly suggestive of Solar Cycle 25 and the Modern Eddy Minimum we are entering, particularly when paired with the record lows across the states and the slightly warmer temperatures near the poles. Professor Valentina Zharkova gave a great lecture on the forthcoming solar cycles and their cosmic implications"

Since the climate science community first began publishing the facts about global warming, there have been sporadic "mini ice age" and "cold sun" claims. It has been argued that a prolonged cold spell is just around the corner and that it will cancel out human-caused warming due to changes in the sun's output. And even though this mini ice age has been stated by its proponents to be just around the corner, all the while the earth has continued to warm at record rates. These claims have not been accepted in the scientific community but have been a favorite of the alternative press. According to the World Meteorological Organization:

"2018 is on course to be the 4th warmest year on record. This would mean that the past four years – 2015, 2016, 2017 and 2018 – are also the four warmest years in the series. 2018 is the coolest of the four. In contrast to the two warmest years, 2018 began with weak La NiƱa conditions, typically associated with lower global temperatures. The 20 warmest years have all occurred in the past 22 years."

http://ane4bf-datap1.s3-eu-west-1.amazonaws.com/wmocms/s3fs-public/ckeditor/files/Draft_Statement_7_February.pdf?5.6rzIGwBm5lwDSTPbgprB2_EgrjzRVY

Alexbo said...

Why is it that "all the models are going for snow Tuesday afternoon", yet even now, Weather.com is showing 42 degrees and rain?

Unknown said...

Thank you, Cliff. I wanted to say that your last comment on landslides is spot on as well. I’m a geotechnical engineer and have the opportunity to work on landslides all across the country. The slow melt is saving us from landslides for the most part. This would change if tomorrow it warmed up into the high 40’s and started to rain. Most of the slides would be shallow surface slides, even if that warm up and rain were to happen.

Shorty said...

It’s easy to be lovey dovey with snow if you’re not juggling 40 employees with half of them snowlocked at their residence and 5 clinics bogged down with a patient rescheduling nightmare

Eric Blair said...

"It's a bit too early to gauge on whether this event is anomalous or not but it seems highly suggestive of Solar Cycle 25 and the Modern Eddy Minimum..."

Thank you for bringing this issue up again, it's a dynamic that all too often is ignored in climate discussions.

Trevinski said...

Mac: Thanks for the reply. I meant no dismissal of credibility on any given issue, nor do I think any climate stance should supersede our need to be intelligent stewards here. I was just pointing at changes in the sun that even NASA has reported on- these changes could have significant ramifications if history serves us. Being interested in solar science, the topic fascinates me. I do find it odd that it is rarely brought up as Eric noted. All things considered, we do live in fascinating times.