Snowave's East Slope Cascades Weather Blog

Storm damage and the PSCZ
Posted by: snowave, 7:00 PM GMT on December 19, 2012 +0
Well... after complaining about the rain and not enough snow, I got what was coming to me I guess... and more.

After a nice tolerable snowstorm last week that dumped 9", we headed off to Socal for a long weekend, and when we tried to come back home to Plain Monday night, there was 3 ft on the ground.. with the added bonus of thousands of downed trees knocking out power, blocking roads and extremely heavy snowfall.

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Interestingly, 15 miles south in Leavenworth, the moon was out and there was maybe a foot of new snow from the night before.

What happened, was a fairly frequent phenomenon called the Puget Sound Convergence Zone (PSCZ) had set up and was aimed from near Everett on the Seattle side, up towards Stevens Pass, and then down the east slopes right at the Lake Wenatchee/Plain area... before it fizzled out just to the east.

 During the 6-8 hours this band of heavy snow trained over the area, it dumped about 10-15" of new snow other areas a few miles away never saw.

What is the the PSCZ, and how does it form?  Basically, it's mostly about wind flow around the Olympic Mountains and/or Vancouver Island.  It is formed when the large-scale air flow splits around the Olympic Mountains/Vancouver Is., and then converges over Puget Sound.





This convergence zone (there are other smaller ones in the area) generally occurs between north Seattle and Everett, and can cause convection (moist upward flowing air current causing clouds to form), which leads to a narrow band of precipitation, which can sometimes be very persistent and often heavy. 


While the PSCZ is fairly common, what was unusual about this event is that:

1.  it's duration over the same area... often the zone shifts back and forth with wind direction and often fizzles out after an hour or so.

2. The intensity of the band of precip all the way over on the other side of the Cascade Crest. Often times, the zone sets up and and stretches up to the crest, and peters out, or is lighter on this side of the crest. This was not the case this time, as the intensity held strongly all the way over to Plain. The snow was relatively heavy, but I've seen much heavier. Long time residents have not seen this type of tree damage before, even in larger storms... so it's a little puzzling to everyone why so many trees came down.

This accumulative precip map shows the persistance of a PSCZ band over Stevens Pass..




(Thanks to meteorologist blogger Cliff Mass for those pics).

Interestingly, a strong PSCZ set up last week over Stevens Pass.. dumping a record 39" of snow OVERNIGHT! Check out Cliff Mass' weather blog on this event.

Link


Lastly, I sit here looking outside my office window at more snow coming down. A predicted 15-30" more in the mountains. I hope the trees can handle it!




Here are some more picts of the snow and resulting tree damage from around the area yesterday

Link
Updated: 11:23 PM GMT on December 19, 2012   Permalink | A A A
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Goodbye River....
Posted by: snowave, 11:32 PM GMT on December 05, 2012 +0
After a month of relentless paddling in the middle of the (subtropical) Atmospheric River, slightly more "normal" December weather looks to arrive this week.

The last low pressure system associated with this persistent storm track- and it's relatively 'warm'  SW flow- has moved out of the region, being replaced by a cooler and less moist NW flow (and airmass).   Good riddance, I say!

What this means.... a progressive pattern, with periods of sun, clouds, and bouts of mostly light snow... although, heavier snowfall is likely in those orographically favored upslope areas of the Cascades (like Stevens Pass)...  so that is great news for the ski areas. This pattern looks to persist into at least early next week. Temps may warm up a bit through the weekend and give us a little wintry mix, at times.

My new weather station is up and running! I hope to have it online by the weekend. My next update I'll share some pics and info about it!
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About snowave
Snowave, his wife and 3 pups live along the East Slope of the Cascade Mtns of Central Washington, just outside the town of Plain, at 2000ft elevation.

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Plain, WA
Elevation: 1952 ft
Temperature: 43.3 °F
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Wind: Calm
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Updated: 7:22 AM PDT on May 10, 2013
Plain, WA
Elevation: 1952 ft
Temperature: 43.3 °F
Dew Point: 38.2 °F
Humidity: 82%
Wind: Calm
Wind Gust: 0.0 mph
Updated: 7:22 AM PDT on May 10, 2013
Plain, WA
Elevation: 1952 ft
Temperature: 43.3 °F
Dew Point: 38.2 °F
Humidity: 82%
Wind: Calm
Wind Gust: 0.0 mph
Updated: 7:22 AM PDT on May 10, 2013
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