One question I should have asked during today’s webinar: on eastern Vancouver Island (south of Nanaimo), we often get a dump on us greater than anticipated when the cold and warm airs runs into each other during transitions. Can you comment on the likelihood that the snow amounts will change significantly if the warm/cold collision differs from the current predictions? We can watch the radar images tomorrow to help understand the amounts of precip expected but my question is do you foresee a high or low likelihood that it will turn to rain before the quantities of precip mount?
This is an excellent question and a natural one given the recent 15 cm snowsquall at Nanaimo.
We think the odds of a locally heavy snow fall anywhere on the East Coast of Vancouver Island are low and that the transition to rain on EVI will be fast in the south near Victoria and slower further north toward Campbell River. This weekend’s pattern is significantly different than February 3rd. The outflow will be dying as the warm Pacific system approaches, not strengthening as per February 3rd in deepening Arctic air.
Additionally, we don’t foresee an upper low parking itself off the west coast of Vancouver Island and injecting the swirling streams of moisture overhead EVI that can combine with strong NE outflow winds to produce those enormous local 30-70 centimetre snowfalls that Roger Wu has researched. The odds are low because south of Nanaimo, the snow will be limited in duration and intensity.
Technically, this is a synoptic scale event (larger) rather than a meso-scale event (smaller!) like February 3rd or a synoptic+meso-scale event that can produce widespread and locally huge snowfalls in the snow-belt zones of EVI.
On freezing rain potential…
Interesting… the main threat from this storm seems to be shifting and evolving from snow to freezing rain:
Freezing rain can be deadly and is one of our climate’s worst hazards causing treacherous travelling conditions for planes, trains and automobiles.
Here’s a quick look at a couple of meteograms from the 10am run of the Regional model (10km resolution) that show precipitation type for the next 54 hours through Monday afternoon:
The first graph is total precipitation, liquid-water equivalent.
The second graph is rain and snow.
The third graph is freezing rain and ice pellets.
Note how the forecast threat of freezing rain increases as we move east from Victoria to Vancouver and Abbotsford. This is what we expect given that the Arctic air is pouring out of and persists longest in the Fraser Valley. Snow at Hope and Squamish may persist much longer before changing to rain or freezing rain.