More snow and slightly less cold this weekend before next arctic surge on Monday

Friday, December 6, 2013

The very cold temperatures these last few days will moderate a bit later today and into the weekend as another surge of colder air drops into the western part of the large trough over the western US. This forces more southwesterly flow over our area by late tonight which should bring some noticeable warming to the mountain slopes. Valleys will remain cold.

That energy to our west will begin to move over our area by Saturday afternoon and will produce light to moderate snowfall through Sunday. While the absolute moisture in the air is low due to the cold temperatures, we may see some significant accumulations if the temperatures warm enough for the snow crystals called dendrites to form. Dendrites are the easily recognizable pointy star-shaped crystal that leads to very low density fluffy snow. If temperatures are too cold, as they are today, the snow crystals that form are more needle-like and pack together much more efficiently, leading to higher snow densities and denser snow.

Due to the snow continuing Saturday night and most of Sunday, I may expect a fluffly 6-12” on the hill by Sunday afternoon. The flow does finally turn to the northwest during the day Sunday which is constructive for snowfall, but moisture should be decreasing then partly offsetting the favorable wind direction.

A final dry trailing wave looks to cross the area early on Monday bringing another surge of arctic air into the area, but no snow. If skies clear Monday night, Tuesday morning could see the coldest temperatures of this event in the valleys as the fresh snow very efficiently cools the low-lying surfaces. However, mountain slope temperatures will begin to moderate as the week progresses, becoming noticeably warmer by Wednesday.

Another storm approaches the west coast near the end of the work week, though current model trends have this storm splitting and weakening as it enters the US.