Declining Snow and Summer Rain in the Alberni Valley

"During my childhood, Mt. Arrowsmith and surrounding peaks tended to have a fair amount of snow cover; it was into the summer months before it totally disappeared."

Michelle Dyler wrote:

My anecdotal observation from childhood to the present is that the amount of rain and snow in the Alberni Valley has declined over the past twenty years.

During my childhood, Mt. Arrowsmith and surrounding peaks tended to have a fair amount of snow cover; it was into the summer months before it totally disappeared. In current days, the snow leaves bare patches, even in the middle of winter, that never get snow pack, and it melts much sooner - often being totally bare of snow by mid-spring.

The summers have also become drier. I remember the temperatures dropping and it raining semi-frequently in my childhood summers, but in the past few years it's been a much longer and more severe drought than anyone can remember. The valley is also experiencing wildfires in the summer that never seemed to occur when I was younger.

Tom Okey, LEO BC Coordinator, wrote:

Historical data and future projections for Port Alberni from Canada's climate data portal (climatedata.ca) strongly support Michelle Dyler's observation of declining snow cover on Mt. Arrowsmith and surrounding mountains during the last 20 years. These data and projections show dramatic declines in 'frost days' since the mid-1990s (78 to 47 frost days per year) and considerable declines in 'ice days'.

My own photographic record illustrates this change visually. I took a photo of the west face of Mount Arrowsmith on 26 March 2008 just after moving to Port Alberni with my family, and again a decade later on 27 March 2019, 18 May 2018, and 8 August 2019. This photographic comparison consists of snapshots of these two points in time rather than a time series, and so they are shared here simply to illustrate the observed change described in the present observation by Michelle Dyler and in the Port Alberni frost and ice observations/projections data.

Comparing satellite photos from 8 June 2003 and 11 June 2019 (also inserted below) also shows less snow cover in 2019, including on Mount Arrowsmith to the SE of the highlighted city of Port Alberni. But again, determining a real trend from these images would require examining an entire time series of annual satellite photos, and this is extremely challenging in this region given the frequent cover of clouds and, more recently, wildfire smoke. Such a time series is not necessary, however, given the compelling frost and ice observations/projections.

Regarding the observation of declining summer rain, the climatedata.ca portal does not currently distinguish summer rain, or any season, from annual precipitation, which is projected to continue somewhat unchanged in Port Alberni. This means that any trends of summer rain are not possible to evaluate using these summaries. This information does exist for evaluation, but it is simply not summarized on this portal.

The temperature observations and projections for Port Alberni do, however, indicate that mean annual temperature has increased about 0.8°C in Port Alberni since the mid-1990s. Hotter and dryer conditions in the Alberni Valley summer microclimate can be seen to "consume" summer clouds as they enter the Valley from the more maritime west coast of Vancouver Island (T. Okey, pers. obs., August 2019).

This rapid incoming cloud consumption phenomenon can be seen during summer over the ridges on the west side of the Alberni Inlet, and is reminiscent of (and analogous to) the rapid consumption of fog and clouds as they flow from west to east over the San Francisco Peninsula (California) towards San Francisco Bay during summer. Decadal-scale temperature increases in the Alberni Valley likely lead to increasingly effective consumption of incoming clouds and fog from the Pacific by the warmer and drier air in the valley, thereby likely decreasing summer rainfall.

Resources

Canada's climate data portal climatedata.ca