Air mass battle gives nasty, messy weather to B.C.
Friday, January 12, 2018, 5:36 PM - La Niña winter seasons in B.C. are often active with the oscillation of mild Pacific air and dense arctic air along coastal sections; consequently, the arctic air is often lurking close to the coast, while plentiful amounts of frigid air remains locked up in the Interior of British Columbia.
This has been the primary culprit for bouts of treacherous travel in the Fraser Valley this winter, paired with strong outflow (northeast winds surging down the Fraser River). This local weather feature provides the refrigeration to allow this wintry mess to unfold.
Mild Pacific air is flowing in aloft from the Pacific Ocean, but at the surface, a relatively thin layer of arctic air is entrenched and is often replenished by high pressure situations over Central B.C. steering this dense, cool air towards coastal sections.
This sets up our battleground and the nasty weather conditions that developed late Thursday.
Over the next 48 hours, all precipitation types are in play for the province.
Coastal British Columbia, you’re off the hook and only have to deal with a single precipitation type at sea level. Rain. There's no chance of mixing, freezing rain, or snow for the coast with this system, with the exception of some of the remote valleys along the north coast of British Columbia.
Rain is expected through Friday evening along coastal sections, but inland remains messy.
As the warm front lifts north, precipitation will ease from south to North through the day on Saturday. Snow will primarily remain relegated to the higher elevations along the coastal mountain range and through much of the Interior, but more local accumulations into the Fraser Valley are possible through Friday.
Whistler, you can expect up to an additional 15 cm of snowfall through Saturday before freezing levels soar on Saturday with the passage of the warm front.
Periods of snow will intensify Friday evening with the approaching warm front, especially above the 1200m alpine, before the addtional snowfall eases early Saturday.
The trickiest of precipitation types
Computer models are very poor at handling the transition from an arctic air mass to a mild Pacific one. Below is an excellent product that highlights the regions that are at risk for additional freezing rain:
As of Friday morning, a thin coat of ice has accreted across much of the Eastern Fraser Valley, and we saw some very impressive winter storm conditions in parts of the Valley, including Chilliwack. Several school closures and delays were reported as of Friday morning.
A lot of uncertainty remains for the Fraser Valley as we flush out the remaining cold air Friday evening. Stubborn locations east of Chilliwack could potentially remain extremely close to the freezing mark through pre-dawn Saturday causing issues for wintry-mix and freezing precipitation to continue over the next 24 hours.
Saturday, freezing levels soar and we await the next system to impact the region next week.
The Gulf of Alaska becomes extremely active with low pressure systems tracking towards Haida Gwaii over the next 7 days bringing locally damaging winds, heavy rain along the coast, and significant amounts of snow for higher elevations.
The time periods to watch for active weather include late Monday through Tuesday and late Wednesday into Thursday for powerful Pacific storms to impact the region.