Freak 2-3ft Snowfall at Mission & Hurricane Ridges

Thanks Amar, I was thinking more Mission specific, and I do appreciate the unique event, thanks for the fascinating report.

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.

Possibly, rather than look through all the years of mountain data, the more direct route would be get information from the NWS or perhaps local PA newspaper about Fraser outflow events and then cross check with Mission ridge data. It would almost always be associated with lowland snow on the north Olympic Peninsula. I'm guessing this happens about once a year on average, probably less going as far back as records are kept, and for huge snow totals like this more like once every 10 years. If I recall, my study looked back at previous similar events, but unless I find the paper no way I can remember. I can recall a few dates though... November/December 1985,January 1989 or 90, and maybe late December 2006. Note that the current storm created only moderate snowfall at lower elevations, whereas the above storms were significant at sea level ish.

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.

That's a good point. I've expanded my reply #10 above to discuss the set of circumstances and possible correlations, since the discussion seems to fit nicely there.

To explore hypotheses like these it would be nice to be able to compare correlations among the various measurements (e.g. 24 hr snowfall at Mission Ridge and temps in the lower Fraser R valley). If one could find other observables that were correlated with the fabled 'big days' at Mission, it might suggest a physical explanation.

Are Hurricane Ridge snowfall and Mission Ridge snowfall more correlated than generic locations?

Thanks for the very interesting discussion, Amar.

Amar wrote:

"(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."

Just to be clear, my understanding of a strait effect snow by definition includes your points 3-6. The most common set of circumstances is a moist air mass in place as the arctic front sweeps down from central BC. This will often result in a synoptic widespread snow event somewhere in the Puget Sound area followed by dry, clear, and cold. Except on the north Olympic Peninsula where moisture is picked up from the strait and dumped in a narrow band somewhere between Port Townsend and Twin River area, depending on the exact direction of the wind. The wind direction is a function of the track of the departing low, which will be to the south and could as I said produce the wrap around moisture and snow at Mission more frequently than it would seem at first glimpse.

This snow will continue for a day or so after the cold front and the rest of the PNW is only clear and cold. I also have a hunch that the snow falls in a relatively narrow elevation band, so that sometimes Hurricane Ridge may be above the moisture, which would also add to the rarity of the Mission/Hurricane combo that we saw 1/1.

Unlike true lake effect snowfall in the Great Lakes region, which I have also been able to enjoy as a phenomenon, at some point relatively soon in the process the contrast between the cold air and the warm water is no longer sufficient to continue to evaporate and transport moisture and the snow shuts off. So it is rare for the local event to last much more than a day or two in contrast to the Midwest where it can last much longer. In the great lakes the meteorologists have a pretty good handle on the necessary contrast in temperature and can predict the occurrence and severity quite well (even flake size), although it too can be very localized. Also the lakes have a much longer fetch than our set up. (Haha- Just looked at northern Michigan forecast, and it's lake effect snow for the foreseeable future).

The storm that piqued my interest in January 1989 dumped 6" or so of snow in Seattle (enough to close the UW) so I hopped on a bus to get to PA. The day was clear and cold in Seattle, I could start to see the clouds at the Hood Canal Bridge, and very snowy by Sequim. Downtown PA was windy with moderate snow, but at 500' it was dumping hard and stayed that way for at least another day, with total snow 30" while the clear and cold weather held throughout the rest of the PNW. It would be interesting to see if that storm was connected to a Mission Ridge dump as well.

Of course Mission can get upsloping winds and a resulting huge snowfall without the connection to the Fraser outflow, and Hurricane can get large dumps with a normal snow from the southwest pattern also, so your overall point that the combination is rare is absolutely correct. And this one may have been much larger amounts of snow than any previous event.

Looking at archived Seattle weather, the storm I am referring to was the first week of February 1989. Seattle's low was 7*F.