The Most Significant March Snow Event in Years

Latest HRRR radar simulation shows precipitation moving into YVR at around 8 or 9 PM. Possibly beginning as wet snow/sleet/rain

Latest HRRR radar simulation shows precipitation moving into YVR at around 8 or 9 PM. Possibly beginning as wet snow/sleet/rain

A repeat of last weekend is becoming much more likely, with scattered flurries developing around metro Vancouver. If you have to drive, now would be the time to do the odd chores etc. before road conditions quickly deteriorate. 

Cold air advection flowing through the Fraser River gap will once again provide enough cold air paired with a low pressure system to provide snow tonight for Metro Vancouver and parts of Vancouver Island. The snow tonight won't be fighting the March sun (solar radiation still penetrates clouds), so snow will be able to accumulate on roads a little better. 

Speaking of pavement and snow accumulation, a couple followers have expressed concern over the West Van Run tomorrow morning...

Now, runners, I don't want you to have nightmares like this tonight. Please watch this right until the end.

Thankfully, the runner in the white was okay, probably just a little embarrassed.  

A large gradient exists by Georgia Strait and Burrard Inlet, but these warmer bodies of waters will help limit the accumulation on pavement. But, if precipitation rates are high enough...the warmer road surface temperatures will be quickly overwhelmed with the heavier snow fall. 

A large gradient exists by Georgia Strait and Burrard Inlet, but these warmer bodies of waters will help limit the accumulation on pavement. But, if precipitation rates are high enough...the warmer road surface temperatures will be quickly overwhelmed with the heavier snow fall. 

I'm going to start by looking at a highly experimental model showing the chances of snow accumulation on roads.

A value of less than 1 indicates that road surface temperatures may be a limiting factor for accumulation on roads (I'm assuming that's what would be preferred by runners tomorrow...

Another round of snow with an approaching warm front Sunday afternoon/evening will also be tricky to predict precipitation type (shown below), with mixing probable along the immediate coast, but if you're inland even a few km's...watch out.

Vertical line represents our current place in time. Look what's coming:

Note how wildly uncertain some of the SREF models are for 3 hourly snowfall accumulation. Sunday has the potential to be more of a high impact event than tonight

Note how wildly uncertain some of the SREF models are for 3 hourly snowfall accumulation. Sunday has the potential to be more of a high impact event than tonight

If you check the current conditions right now at YVR, you see 5C with a very low dew point of -8C. Dew points in Abbotsford are nearly -12C.

Courtesy of Environment Canada

Courtesy of Environment Canada

But it can't snow at 5C right?

I expect a process called evaporational cooling to occur later this afternoon/evening that will drastically drop temperatures in the lower levels of the atmosphere. So if the precipitation begins as rain, know that a change over is imminent as the temperatures fall toward the wet bulb temperature ( somewhere between the current temperature and the dew point, middle is a rough estimate). 

To say this forecast is tricky is an understatement. We're not very confident in how strong the offshore pressure gradients will maintain cold Fraser River outflow and the upper level low...and for how long..

Go easy on your local forecaster this weekend.

This uncertainty can be shown using the SREF plume diagrams. Don't forget to subtract 8 hours to get to PST (Ex: 12Z = 4am PST). The good news for runners is the snow is scheduled to ease up by morning!

Blue line: Probability of precipitation for snow Green: Probability of Precipitation for rain Red Line: Probability of Precipitation for freezing rain

Blue line: Probability of precipitation for snow

Green: Probability of Precipitation for rain

Red Line: Probability of Precipitation for freezing rain

The Heritage Classic is scheduled to take place tomorrow afternoon at BC Place, but as of now NHL management must be pretty smug about the expected weather conditions: 

I don't always plan an "outdoor' NHL game in Vancouver, but when I do I look like a genius

I don't always plan an "outdoor' NHL game in Vancouver, but when I do I look like a genius

Model Talk:

First, lets start with the main global models, and what kind of accumulations they're showing for this event:

GFS (American)        vs.          GEM (Canadian)

Looks reasonable, lower accumulations by the warmer ocean. Enhancement around southern Vancouver Island by the Fraser River Gap. I can get behind this.

Looks reasonable, lower accumulations by the warmer ocean. Enhancement around southern Vancouver Island by the Fraser River Gap. I can get behind this.

Just a note, in this model also includes any frozen precipitation (freezing rain, ice pellets, and sleet).

Just a note, in this model also includes any frozen precipitation (freezing rain, ice pellets, and sleet).

GFS: shows about 15 cm for YVR, more away from the water

GEM: Shows A LOT more: Anyway between 15 and 30 cm throughout the Lower Mainland

EURO: Although I can't publicly share a map due to license restrictions, I can tell you this. It's on the order of 2-5 cm (but with the European ensembles still showing large snowfall totals)

Regional/High Resolution Models

RGEM:

Similar to the CDN global model with accumulations, with a modest amount more. Snow lovers would love for this possibility to verify.

Similar to the CDN global model with accumulations, with a modest amount more. Snow lovers would love for this possibility to verify.

WRF-GFS

Last weekend, this mesoscale model had VERY serious problems predicting snowfall accumulations over the Lower Mainland, and it seems to be the case as well. Not sure why such a discrepancy between the Global GFS and the WRF, but it's likely Vancouver will see more snow than what's being shown here.

Vancouver Island amounts look reasonable though (10-20cm over higher terrain in Nanaimo likely)

48 hour snowfall map for the South Coast (units in inches). The big donut whole is back right over the Lower Mainland..

48 hour snowfall map for the South Coast (units in inches). The big donut whole is back right over the Lower Mainland..

That's all for now. I'll probably start up a live blog later tonight when the flakes fly.

Who's ready for some snow?

#50ShadesofVan