Wintermission Over? Snow Threats Through 2017

I know winter has just commenced, but after a brief bout of temperatures near seasonal a strong cool signal is anticipated to bring a renewed threat of snow to the South Coast of BC.

I'll break this down by the events:

1) Through Friday December 23rd

trough.png
  • A very robust upper level trough is snaking its way down the coast of BC. let's see where it is forecasted to be tomorrow morning using my favourite level of the atmosphere, the 500 mb level; consequently, you can see where each trough and ridge lies (see right).
  • This is the most marginal snow event chance because it's still not quite cool enough for straight snow in most regions
  • Light, wet flurries for parts of Vancouver overnight into Friday AM
  • Things get more interesting for the LM tomorrow as the atmosphere cools and precipitation pivots into the forecast area
A fairly good representation of what I suspect the atmosphere may look like tomorrow afternoon/evening

A fairly good representation of what I suspect the atmosphere may look like tomorrow afternoon/evening

The common conundrum of the mild west coast will be present. As temperatures are beginning to cool enough for snow, the atmosphere will be in the process of drying, ultimately before outflow conditions take hold through Christmas. so, locally 5-cm of wet snow over higher terrain is possible through pre-dawn Saturday.

2) Boxing Day Impactful Snow?

Classic overrunning (Pacific moisture moves over cold air) snow event with a respectable low moving into Haida Gwaii on Boxing Day below 990 mb.

  • Look for a classic 5-15 cm snow event for parts of Vancouver Island, less near sea level and southern sections, before ultimately changing to rain for most as the onshore flow becomes a little too strong with SE winds near the strait
  • Snow will likely be delayed until later in the afternoon and into the early evening for Metro Van, but also watch for 5-15 cm range across lower mainland with less for SW regions through early on the 27th
  • This has the potential to bring 20 cm to higher terrain including SFU and North Vancouver at this point...but preliminary numbers are a little dangerous to put out this far in advance

3) News Years Snow Threat?

  • Still too far out, but another cooling trend typical of the La Niña pattern looks to take hold during the New year which will bring more marginal snow treats and below seasonal temperatures to most of British Columbia

So there you have it. Lots of fun weather to track for the holiday season.

 

Snow Thoughts...

Hi,

Looking at snowfall for the South Coast and it's once again shaping up to be an extremely tricky forecast–likely one of the trickiest in the series of storms we've seen the past couple of weeks. 

A moist warm front is approaching coastal sections this evening and expect light snow to spread over all regions by pre-dawn Sunday. I'm going to lean on the product below, because I think it best represents the complexities at hand. The map below indicates the threshold where snowfall totals may exceed 10 cm:

Regions south of Nanaimo and southwest sections of the LM will struggle with significant accumulations because of a warm southerly component that pushes into these regions, changing precip over to rain by early Sunday PM

Regions south of Nanaimo and southwest sections of the LM will struggle with significant accumulations because of a warm southerly component that pushes into these regions, changing precip over to rain by early Sunday PM

Below is a snapshot of Sunday late morning, early afternoon where typical southeast winds are picking up in Georgia Strait causing precipitation along the coast to mix with (or change to) rain for East Vancouver Island. Lower Mainland still predominantly snow as a light outflow continues for that region, especially higher terrain even into early evening:

Snow lovers, the southerly wind is not your friend, I assure you. But, you won't have to get much elevation on eastern sections of Vancouver Island to get some significant accumulations...

Snow lovers, the southerly wind is not your friend, I assure you. But, you won't have to get much elevation on eastern sections of Vancouver Island to get some significant accumulations...

To even further complicate things, looking at short range ensemble forecast for YVR... it shows two distinct camps when it comes to accumulation. It all depends on when the precipitation turns over to rain and when the dominant, mild southerly flow takes over:

SREF forecast solutions for YVR...quite an array of possibilities. Likely a quick changeover or a prolonged snow for YVR. Like the lower totals for now close to sea level

SREF forecast solutions for YVR...quite an array of possibilities. Likely a quick changeover or a prolonged snow for YVR. Like the lower totals for now close to sea level

This model is clearly struggling with something. We have high confidence for snow early. In fact, anything above 80% in this particular model is a very strong indication for snow:

Other American model guidance is equally spread out and somewhat useless. An absolute forecasting nightmare showing YVR having somewhere between 1-15cm of snow. Completely unacceptable and a poor forecast indeed. This is what forecasters are up against:

Bottom Line. The higher you are, the better chance you are at evading the warm southerly winds scouring out the remnant cold air at the surface. 

ROUGH SNOW TOTAL FORECAST

  • Campbell River: 10-15 cm (5-8 cm by water)
  • Comox: 2+ cm (locally 5+ cm higher terrain--Cumberland) 
  • Nanaimo: 2-4 cm (5-10 cm higher terrain)
  • Victoria: 1-3 cm (5+ cm higher terrain)
  • YVR Airport: 2-5 cm
  • Surrey: 5-10 cm
  • Burnaby: 5-15 cm
  • Abbotsford: 10+ cm

* I think someone has the potential to see locally 20 cm inland Vancouver Island and highest terrain in the Lower Mainland

Northern sections of east Vancouver Island can once again over-perform in this set-up especially away from the Georgia Strait. Burnaby and higher terrain of Surrey and North Vancouver has the best potential to see in excess of 10-15 cm as well before all the precipitation is predominantly rain by early Monday.  

Enjoy the Snow!