Freak 2-3ft Snowfall at Mission & Hurricane Ridges

Super interesting, thanks for the write up Amar and additional context everyone. Stormking do you have a link to the paper, I'd like to see it.

Does anyone (Amar?) have access to the historical telemetry data in an easy to analyze form? I think it would be interesting to quantify how frequently this occurs. It should be easy to write a few simple rules to find events like this in the historical data once it is in an easy to analyze form.

Cool stuff. The cliff mass blog has a bit about the mission ridge part, I think he mentioned the Pendleton site showed an update that hinted toward it but was still not expecting quite that much.

Haha. No link for sure. I'm old and this was before the age of computers. My recollection is that I hand wrote it, for sure hand typed. I might still have it laying around somewhere. Not sure I'm brave enough to post a sample of my freshman year writing though, even if I did get an A+ as I recall.

Amar, while it is unprecedented to get the amount of snow we had yesterday, events  like this, all be it much shorter in length happen almost every year. (a non scientific observation of similar conditions)

Jtack, maybe you're looking at this in a way that's too Mission-Ridge-specific. And maybe I wasn't clear enough in the original post, so I'll try to clarify in case others are also thinking that this event is only slightly unusual, and I'm making a big deal over nothing.

The unprecedented thing about this event is not the 3+ ft of snow at Mission, even though that may be a record 24-hour snowfall at that site (does anyone know what their record is?). It's the combination of 3+ ft at Mission, 2+ ft at Hurricane, and ZERO at almost all sites along the line connecting those 2 regions and also north of that line, over a vast mountainous region that typically gets heavy snowfalls throughout whenever it snows at both Hurricane and Mission. That is the total "event" that I'm writing about, and such an event basically never occurs, I wouldn't be surprised if its statistical period-of-return (if that could even be estimated in the most approximate way) were far beyond a 1-in-100 year event, perhaps even 1-in-1000 years or more. It's the zero snowfall between the 2 huge snowfalls that makes it so bizarre, improbable, and unprecedented. Certainly I can't recall seeing anything remotely like this 2ft-ZERO-3ft combination over the 23 winters since I moved to Seattle.

Amar, it seems to be that the only way this (lots of snow at Hurricane and Mission and none elsewhere)happens is with a specific set of weather circumstances, i.e. Fraser outflow events. I don't think it is that uncommon for those to be associated with a low down in Oregon somewhere- that is what sucks the cold air out of Canada. The wrap around moisture falling on the east slopes of the Cascades (Mission)may often be a part of the whole set up.

A very specific set of circumstances was required to allow this event to happen: in addition to needing (1) a strong-enough, wet-enough low-pressure system tracking eastward on a specific path along the Columbia Gorge which is conducive to heavy upslope snowfall near Mission Ridge and (2) then slowing/stalling in just the right place along that path to dump heavy snowfall for many hours at Mission, there needs to be (3) a large mass of cold Arctic air already in place over the interior of BC to allow the very strong Fraser outflow to develop, and (4) that outflow needs to continue for roughly the same period of many hours on the same day in order to simultaneously dump heavy snowfall at Hurricane Ridge. But in order to get zero snowfall over the North and Central Cascades during the same day, (5) the cold Arctic air must also have leaked south on both sides of the Cascades by the time that low comes ashore, at least down past the latitude of Snoqualmie Pass and not just be sitting up in BC, and then (6) that cold Arctic air needs to have arrived in large enough quantity to completely shut off and prevent snowfall over that entire North-Central Cascades region as the storm system slowly tracks eastward just to the south.

The hard part about figuring out how unlikely this event is, is that (as you say) there may be some degree of correlation between some of these 6 circumstances which are required. But it may not be much correlation, as the low-pressure systems that do follow that specific track and do give heavy snowfall to Mission every few years can readily occur irrespective of any Arctic air mass in place over the Northwest or BC. The eastern Cascades are easily cold enough throughout winter to have snowfall at the 4600-6800 ft elevations of Mission Ridge even during normal seasonable temperatures.

My gut feeling (and it's only a guess as of now, since I haven't had time to even try to look through older data) is that any previous time in the historical record that both Mission Ridge and Hurricane Ridge have gotten heavy snowfall on the same day (let's say both got at least a foot in 24 hours), that large areas of the North and Central Cascades would have gotten at least a few inches of snowfall during the same day too. Certainly the same SE upslope winds which dump snow at Mission can easily reach the Snoqualmie Pass region up the Kittitas Valley and simultaneously produce snowfall there, unless enough cold Arctic air is already in place there to prevent that like this time.

Cool stuff. The cliff mass blog has a bit about the mission ridge part, I think he mentioned the Pendleton site showed an update that hinted toward it but was still not expecting quite that much.

Cliff mentions the Pendleton radar data in his blog, but not the NWS Pendleton forecast office, which was probably just as completely blindsided by the extreme snowfall totals at Mission Ridge as the NWS Seattle office was by the extreme snowfall at Hurricane Ridge.

Does anyone (Amar?) have access to the historical telemetry data in an easy to analyze form?  I think it would be interesting to quantify how frequently this occurs.  It should be easy to write a few simple rules to find events like this in the historical data once it is in an easy to analyze form.

I do have the complete archive of NWAC telemetry data extending back to the 1980s, which Garth was kind enough to send to me on CD-ROM way back in 2005 (what's a CD-ROM? the kids will soon say). However, it's not exactly in an easy to use format, it's just raw CSV files for each site and year, and looks nothing like the current 10 days of telemetry data posted on the NWAC website. But it wouldn't be hard to write a script to analyze it for the simple purposes of looking at snowfall at Mission and Hurricane. Since my version is 12 years old, it would be best to get the full data set from Garth or other forecasters at NWAC.

The real issue (as always with snow sensor data) is getting rid of the data spikes which go up to the maximum snowdepth or some other high value, which are always going to occur with an ultrasonic distance sensor in a snow-stormy environment, and especially tend to occur most often during heavy snowfall accompanied by high winds. There is no way other than manually going through and looking at the data to mask those out, or at least I can't think of a 100% robust way to program such spike removal without some chance of accidentally excluding valid high-snowfall data.

Since October 2004, I have manually saved the current 10 days of NWAC telemetry data ( data.nwac.us/ files ALL.x) at least once every 10 days. This was eventually supplemented by a script which saves the NWAC data.nwac.us/ALL data file every hour, which helps me to manually fill in missing hours of data from the daily ALL.x files caused by the all-too-frequent NWAC data computer crashes. In 2011, I wrote a script which concatenates the data for any single NWAC site for an entire snow year (Oct-Sept), and extracts hours with maximum winds above a chosen value, for use in various TAY threads about high winds at Mission and Camp Muir. Although not intended for public use, my script does provide an easy way to get the data for a full year for any site in a very easy to use format, same as the daily NWAC data, but only back to the 2004-5 season:
www.skimountaineer.com/NWAC/NWAC-SeasonData.php

I've been planning to add several other capabilities to this script at some point (precip totals and max, snowfall totals and max), but haven't gotten around to that yet. Happy to hear any suggestions for improvements to my various telemetry scripts such as this one, or my NWAC 10-day script , or my SNOTEL script .

For the SNOTEL sites near Hurricane and Mission, my SNOTEL script can spit out up to 3 years of hourly data at a time, which was a limitation in the NRCS Report Generator which provides the actual data. Daily snowfall would have to be calculated/estimated from the change in snowdepth.

The Dungeness SNOTEL site was installed in 1998, and Waterhole SNOTEL in 1999, and both included a snowdepth sensor from the start, quite unusually for SNOTEL sites of that era. Most SNOTEL sites did not get snowdepth sensors until the mid-2000s, prior to that there was only a SWE (snow water equivalent) pillow sensor at most sites, which is totally useless for figuring out snowfall. The Trough SNOTEL site was installed way back in 1978, but the snowdepth sensor was not installed until 2001. Similarly the Upper Wheeler SNOTEL and Grouse Camp SNOTEL were both installed in 1980, and got snowdepth sensors in 2002 and 2003. So snowfall data and any information about large snowfall events extends back only 15-20 years for the SNOTEL sites in the northern Olympics and eastern Wenatchee Mountains.

The unprecedented thing about this event is not the 3+ ft of snow at Mission, even though that may be a record 24-hour snowfall at that site (does anyone know what their record is?).

I'm not about official snowfall records, but two events like this happened back in the early '90's. In both of them, an Alaska Low had brushed the coast, not turning inland until in Cali, iirc. In each case, the storm tracked north all the way to the Mission area. I'm not sure, but I don't think Bachelor got a similar dump either time. I was there for one day, doing a photo shoot. 44" of snow had fallen overnight.... and it rivaled the 3-4% that I've skied once or twice at Crystal.
I had a couple shots published of Paul Jones, who, many years ago, was on the PSIA Demo Team for 12 years..... In one, he is almost submerged.  I also saw an image from the previous storm, which was just as deep, which mission used in an ad,  and the snow might have been even lighter.   I saw those SWE totals yesterday and figured they were way low, but. But 1" SWE is possible for 39" of snow.   The snow that day was certainly among the lightest I've ever skied.

I was In my Valley Hi cabin about 15 miles nort of Blewitt Pass and got 2". Drove to Blewitt and didn't really notice much extra snow except at the pass so that was pretty much the northern limit. When we get big snows at my cabin, they usually seem to come in late November - December. The big dumps for us usually just creep out of the Enchantments and get stuck over us. I just snowblew for the first one this year and was able to clear out 3' without any of the usual frozen layers from warm ups. No crusts at all. This weekend could be some memorable skiing in places that don't often have lots of snow. Maybe every snow year is odd and unpredictable.

Thanks for the write up Amar.