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:

 

 

Cold Arctic Blast Potential

Current Snowmometer ranking: see below for more information on numbers

Current Snowmometer ranking: see below for more information on numbers

1010 days can be converted to one of these other measures of times

  • 87,264,000 seconds
  • 1,454,400 minutes
  • 24,240 hours
  • 1010 days
  • 144 weeks and 2 days

Currently downtown Vancouver and more specifically Vancouver International Airport (YVR) has been over 1000 days without a significant snowfall; consequently, one of the greatest stretches in recorded history with this snow drought near sea-level.

We have to look back to February 24th, 2014 the last time Vancouver reported several hours and several centimeters of snow.

But, things are changing. A more significant blast of arctic air is on the move. Here, I'll show you what I mean:

Plentiful amounts of cold air locked up in the northern latitudes, but it will begin its intrepid journey south to British Columbia

Plentiful amounts of cold air locked up in the northern latitudes, but it will begin its intrepid journey south to British Columbia

Now, for a perfect blast of cold air and below seasonal temperatures to reach coastal BC a near-perfect set-up in the upper atmosphere has to take place:

Remember the mega ridge that hampered British Columbia the past several seasons at times, also known as the ridiculous resilient ridge? Well, we need a mega-ridge in Alaska.

When I'm watching for Arctic air and snow potential in Vancouver we need a massive ridge to develop and the pattern to amplify to allow cold air to move south. I'm no expert at paint but this is typically what BC looks like in the winter...a zonal flow:

The main players: the seemingly innocuous high pressure system bubbling up east of Japan and the frigid cold to the north...

The main players: the seemingly innocuous high pressure system bubbling up east of Japan and the frigid cold to the north...

But where's the massive ridge?

Well, its humble beginnings are just east of Japan. Watch what happens to the ridge over the next 72 hours. Our forecast models are excellent for the upper air pattern in this time frame:

Looking more like a traffic jam in the northern Pacific with a variety of blocking patterns. For the weather wizards out there, can you spot the Rex Block? What about an Omega Block? 

Looking more like a traffic jam in the northern Pacific with a variety of blocking patterns. For the weather wizards out there, can you spot the Rex Block? What about an Omega Block? 

I know it's tough to believe, but the blocking pattern over western Alaska is absolutely key to getting cold to migrate towards towards the Pacific Northwest and allow the cold upper trough and arctic front to dig south and west. Ideally, you want this upper region of high pressure to lock in between 150-160W over Alaska and hold for a long duration to allow for multiple reloads of cold arctic air to the coast.

OUR FIRST SNOW THREAT

As the pattern amplifies and cold arctic air begins to filter down the coast cooling begins late Sunday--excuse the horrendous drawing of the arctic front.
 

We know a trough will also be hanging out around the coast at this time, but there is significant uncertainty at how much precipitation will be lingering as cool air spills through the myriad of valleys and inlets in southern BC including the infamous Fraser River gap.

The aforementioned low pressure is a classic 'Inside Slider' where a low hugs the coast. If it tracks too far inland it doesn't pick up enough moisture, too far and west and the precipitation stays off the coast. I see most regions transitioning to wet snow starting early Sunday night at higher terrain and then closer to sea level by Monday

Now, we have high confidence in the atmosphere drying by Tuesday, and then a possible overrunning snow event late next week, where a moist pacific frontal system collides with the shallow layer of arctic air. This type of setup has been known to provide Vancouver's largest snowfalls...but let's get through this first brush with winter first, before I analyse our second potential snow-maker by the weekend.

But, with all of this I have to move the Snowmometer up from it's traditional position of 0. Yes, an aggressive 4 right out of the gate, but I've looked over the model data and determined this is a good initial start. There is some potential for a higher number over the next several days and next week.

For those who are new, here's a quick refresher on Vancouver's snowmometer:

0- sNOw chance. Sorry, not going to happen. (335-340 days/year)

The only place you'll find snow is on one of the beautiful local ski hills.

1-2 Conversational Snow (5-10 times/yr)

  • Typical conversational snow risk, and often local Vancouver blogs will begin to highlight (i.e. build hype and generate revenue) these levels of marginal snowfall risk.
  • This is at its core conversational snow and nothing more, for now...This isn't to say a significant event can come from a 1-2, and a high impact event with very low confidence will likely get a lower score as well.

3-5 Nuisance Snow (4-5 times/year)

  • The level of the snowmometer has long moved past the conversation around the water cooler and is dominating all local news sources.
  • Tire shops have been inundated by the locals rushing who vow never to join the summer tire club.
  • The first stage where you might see your helpless neighbour on bare all-seasons sliding his way along Boundary Rd.
  • Buses to SFU may begin to struggle with the snow with thousands of students praying that classes may be cancelled or delayed.
  • NO snowfall warnings have been issued by Environment Canada with amounts generally less than 5 cm (locally higher).

6-7 Impactful Snow (1-2 times/year)

  • Okay folks, we have medium-to-high confidence of some fairly significant snow for this neck of the woods (locally 10 cm+), but I necessarily wouldn't run to the store to buy milk and bread.
  • School delays are now likely for portions of Metro Vancouver (higher elevations) along with substantial transit delays.
  • Snowfall warnings are likely issued or will be issued by Environment Canada.

8-9 Crippling Snowfall (2-3 times/decade)

  • A once in 5-10 year snow event for the South Coast with significant amounts 30 cm+ forecast. May become especially treacherous with warming temperatures, localized flooding and intense ponding on roadways as storm drains are clogged with slush.
  • Numbers at or above this value will not be used lightly, and may never be used during the life of this blog.

10 - #SNomg #Snowmageddon (2-3 times/Century)

  • Only one or two analog exists, including the blizzard of 1996 in Victoria, BC.
  • Lack of transportation, significant structural damage and accumulations in excess of 50 cm +