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!

Snow Mayhem

A well advertised snow event is on our doorstep for Vancouver Island and the Lower Mainland, but I can't quite tell you how much snow will fall. I'll show you why:

We look to three main computer models to look for clues on certainty and confidence when it comes to a specific forecast. 

Snow forecasts are tricky in general. On the South Coast, the moist Pacific jet stream always wins out, but it's been suppressed and our flow is offshore. Look:

 Image: Courtesy EarthNull, showing pronounced streamlines (wind patterns) racing towards the coast Tuesday evening.

Image: Courtesy EarthNull, showing pronounced streamlines (wind patterns) racing towards the coast Tuesday evening.

Model confidence is low on timing & track and temperature of the air aloft the Lower Mainland and Vancouver Island

1) GFS

  • Puts a single 990 mb low west of Tofino late Thursday. By Friday night it's located close to Tofino before filling (weakening) near the NW tip of Washington State
  • Keeps a dry outflow (keeping the atmosphere dry with winds blowing from the Interior) limiting the heaviest precipitation for parts of the LM. Also, warms the temperatures aloft the most so r/s mix and plain rain near the coastal sections for Friday with snow inland. This would still be a nasty snow event for parts of Vancouver Island
  • Timing late Thursday, but the concern with this model remains the amount of warm air advection (WAA) from the southerly flow brought in by this system

GEM

  • Much stronger low pressure system, but also eventually weakens (fills) near Forks, Washington
  • Faster timing. By Thursday evening snow could begin for the Lower mainland, but this model is colder and continues snow through Friday and Saturday. Regions near the water could still mix with rain though. This is a true snow lovers solution for the LM and Vancouver Island. Potential for up to 30 cm for some in an solution like this

EURO Model

 A special product used to look at forcing in the atmosphere (vorticity or spin) + spin shaded regions used to indicate lift in the atmosphere

A special product used to look at forcing in the atmosphere (vorticity or spin) + spin shaded regions used to indicate lift in the atmosphere

  • Notice the three separate regions of circulations; much different than the other two models
  • Therefore it creates the weakest low, but not the least amount of snow. We really don't want a strong low, snow lovers. This signature shows the system is not phasing the energy properly and takes on a double barrel (two center of lows)...
  • Latest call time for snow (snow would start early Friday) with straight snow throughout the day. IN particular, this low and solution shows very heavy snow for the Victoria BC region that needs to be watched closely. I won't post those snowfall maps yet..

 

In closing, the GFS is too dry and warm at this moment and remains what is called an outlier. I favour the cooler and snowier models at this point. 5-15 cm feels good for the LM at this point through Saturday, but we can't rule out a little less or a little more at this point. Southern Vancouver Island is looking intriguing at this point. Confidence is still low-to-medium for specific snow amounts.

For those that asked: