Now, I know there's been ample and incessant chatter on the recent Vancouver rains, but did you know snowfall is possible as early as late October for portions of Coastal B.C?
Vancouver's latest recorded 20°C day occurred on October 20th, with the earliest snowfall being recorded on October 28th.
Growing up on Vancouver Island, I often heard tales from my elementary school teachers of snow falling around Halloween along the Inner South Coast.
Sure enough with a little bit of digging Oct. 31st, 1984 revealed something quite extraordinary — an event of epic proportions.
In the evening, much to the surprise of trick-or-treaters, snow began to fall along eastern Vancouver Island in Campbell River (YBL) and Comox (YQQ). By the early morning hours of November 1st 30-50 cm of heavy wet snow fell on portions of Vancouver Island, but to the dismay of kids across the school district, school was still in session.
Reanalysis by NOAA, reveals the historic upper air pattern is extremely unusual for fall with an exceptionally strong arctic outflow event for portions of the coast. This combined with a juicy pacific low produced the bountiful snowfall amounts.
How's our long range pattern shaping up for Halloween?
Well, this upcoming week is still looking exceptionally damp, dreary, and breezy with short breaks in between systems, although there's a little uncertainty with exactly how much rain will fall. I'll explain.
In particular Tuesday and Wednesday looks to be severe enough for Environment Canada to consider issuing some rainfall warnings, as we're currently forecasting a lot of rain, even for portions of Metro Vancouver.
I'll admit there's still some inherent uncertainty when it comes to direct model quantitative precipitation forecasts (QPF). Large swings can be common in the 5-7 day time period from run-to-run.
The grid below is an excellent visualization showing the past 11 runs of the US global weather model (GFS). As a side note, there's excellent confidence run-to-run for a dry slot on Sunday, so if you're planning any outdoor activities Sunday looks to be a safe bet!
The second system into Wednesday is causing the GFS model some grief. For example, from the period of hour 108-136 the recent run has modeled a rainfall warning worthy 100 mm of rain (see circle below).
For reference, the previous run produced a measly 30 mm or roughly an inch of precipitation for the same time period. So what to believe? We'll have to wait for a couple more model runs to hopefully lower the level of uncertainty and produce a reliable forecast. But enough about rain, how about frost?
As our nights get longer, and the sun angle gets lower as we trudge into fall, we're closing in on that dreaded first freeze. Typically, the Lower Mainland sees it's first frost in early November (Be jealous, rest of Canada).
Now, consulting the North American Ensemble Forecast system, it appears to be trending towards seasonal (or rather following climatology), so bet on a typical Halloween for Vancouver (highs in the low double digits with lows 4 or 5)
Oct 31st 2014: Mainly cloudy with an isolated shower. High 12
There, I've just predicted the future.
Do other sources predict such a cool down for the west coast?
Yes, even a little bit below what would be expected following the downward linear trend of climatology. So with this guidance, expect some towns inland and away from the major bodies of water to fall to the low single digits. So patchy frost is likely away from the water, especially if we get some clearing skies.