Tuesday, January 4, 2011

Mountain sky and new snow over the BC coastal range

2010 December 28

We picked a fantastic day for skiing at Mt Seymour in the British Columbia coastal range after an overnight storm dropped some good winter snows down to a fairly low elevation.

The storm left every tree on the mountain with low freezing levels but also low cloud base led to huge amounts of rime ice that added to the quality of the winter scene.   This entry is my attempt to explain the conditions that led to one of the prettier days on a mountain that I've had.  First, here are some shots.

This scene was taken at 2055 UTC from the top of Mt Seymour's highest lift facing west. 
 The trees were coated with fresh snow and rime from the previous evening.  Meanwhile, low-level moisture persisted behind the storm allowing low clouds to form on thermals helping to give the mountains an appearance of more height.  High clouds added depth to the sky.  In the case of the picture above, a large jet contrail appeared.  I'm typically not a fan of jet contrails but this one was interesting.  In fact a recent overpass from the MODIS Aqua polar orbiting satellite showed the same contrail about 40 minutes earlier.  See it below.

MODIS Aqua satellite full color visible image courtesy of MODIS today. The blue triangle is the location of Mt. Seymour.

The low cloud cover increased just a bit to enhance the depth of the sky.  In some areas they provided a backdrop to further enhance the mountains.
An image facing west from the top of Mt. Seymour at 2255 UTC. 
 The mountain convection in nearly saturated air resulted in this updraft forming with a base below us and then flattening out on a stable layer above us.  This low cloud coverage was the maximum that we saw today.  Imagining what the sounding at our site looks like that would yield these clouds I took the Quillayute, WA, and the Kelowna, BC soundings and took my best guess as to what ours looked like.  See below.

The Quillayute, WA sounding in black is overlaid by teh Kelowna, BC sounding in orange.  My best guess sounding is in red.
I decided that the potential convective layer of the Quillayute sounding was a bit too shallow for us considering that I was already at 1300 m altitude and the cloud updraft ascended well above me.  However, the convective layer depth at Kelowna (100 mi northeast) implied a cold enough cloud tops for snow showers.  We saw no showers around the ski area.  So I believe the inversion where the clouds were flattening out was located higher than Quillayute but not by very much.  This picture below was to the east where similar shallow convection sets the backdrop of a spectacular valley.
The scene east of Mt. Seymour, BC taken 2309 UTC.

When the sun lowered further into the southwestern sky, the low clouds thinned out a little and the light warmed enough to allow me to take some shots across to Vancouver Island such as the one below. 

A view across the Salish sea toward Vancouver Island taken at 2329 UTC.

 Just after this shot, I noticed a peculiar cumulus cloud over over Burnaby well south of the terrain.  At first I didn't think much of it but after three chairlift rides up without seeing it dissipate, I figured there was a heat source that took advantage of the atmosphere that day to allow a semipersistent updraft to continue.  Perhaps there is a power plant underneath it somewhere.

A shot south of Mt. Seymour of a persistent cumulus cloud that may be partially anthropegenic in nature.  This shot was taken at 2353 UTC.

What made this day special was a combination of a relatively cold precipitation event the night before that dumped a fresh layer of new snow with added riming from a low cloud base and cold temperatures.  Then during the day, we had a shallow convective layer that allowed mountain cumulus to form but not so much as to flatten the lighting or obscure us in fog.  The high clouds were there to add depth but not so much to destroy the contrast.  I couldn't ask for a better setup considering the location.

I have more pictures at http://towerofstorms.net/gallery2/main.php?g2_itemId=4655