What's the chance of rain and the likelihood of sunshine throughout the year in Victoria?

The chart below shows the % chance of precipitation and the % of possible sunshine on any given day during the year in Victoria.  It's really striking how the likelihood of precipitation and sunshine form a mirror image of each other.

Let's start by looking at the blue line - the chance of precipitation on any given day.  This starts in the 50-60% range during January and February, drops below 50% in March, and gradually declines until it reaches about 20% in June and early July.  Then we see something that is very distinctive of the climate in our area - a sharp drop down to about a 10% chance of rain on any given day from roughly the second week of July until mid-August.  That's definitely the time to plan your camping trip or outdoor event if you want to almost guarantee dry weather!  Beginning in mid-August, the chance of rain begins to increase, back to about 20% by the end of August, then gradually increases to about 25% by the end of September.  Unlike the spring, when there is a very gradual decrease in the likelihood of rain, the increase in the fall is much more abrupt, doubling from roughly 25% at the end of September to more than 50% by the end of October.  November and December put the chance of precipitation back in the 50-60% range where they started the year.

This pattern is quite different from other locations in Canada.  In Toronto, for example, the chance of precipitation on any given day varies much less throughout the year, from a high of about 50% during the winter months dropping to 30-35% during the summer.  The pattern is even more different in the Prairies.  In Calgary, there is only a 20-25% of precipitation on any given day during the winter months, but that increases to a 40-50% chance during June and July.

As I mentioned earlier, the % of possible sunshine in Victoria - the red line on the chart - follows almost the exact opposite pattern that chance of precipitation does throughout the year.  Victoria gets less than 30% of possible sunshine in December and January.  This gradually increases to about 60% by the beginning of May and stays at that level until the very beginning of July.  Then just as the chance of precipitation plummets from 20% down to 10% in the second week of July, the % of possible sunshine shoots up from about 60% to over 80%.  Again, this is the time to plan those outdoor activities!  The % of possible sunshine begins to drop off in the second week of August, and by the end of the month it is back down around 60%.  Possible sunshine declines very gradually at around 55% through September and the first half of October, then there is a sudden drop down to 30% by the beginning of November.  I've always noticed that the first half of October tends to have much nicer weather in Victoria than the second half -there's often a very abrupt change midway through the month - so it was nice to see this validated by the statistics!

In some ways, the seasonal pattern of sunshine in Victoria is quite similar to that in Toronto, where % of possible sunshine varies from about 30% during November, December, and January then gradually increases to around 60% in July before gradually declining once again.  The big difference is that Toronto doesn't experience Victoria's very high midsummer sunshine levels (80%).  So why is that?  As I explained in this post, the main reason is the North Pacific High, which tends to park itself over the northeastern Pacific in the summer months, deflecting weather systems to the north and providing Victoria with sunny, dry weather.  This is enhanced by the Olympic Mountain rain shadow and by Victoria's location surrounded by the cool water of the Strait of Juan de Fuca, which inhibits the formation of convective clouds and thunderstorms, resulting in exceptionally clear skies in the summer.  That's also why Victoria holds the record for the sunniest month ever recorded in Canada, outside the far north (in fact it holds the top three spots).

I should just mention one more thing.  While I have talked about the chance of precipitation and the % of possible sunshine as forming mirror images of each other, you should note that the way we're measuring chance of rain versus chance of sun is quite different.  For precipitation, we're looking at the % chance of any measurable precipitation on a given day.  That means a day where it there is a light shower for 10 minutes resulting in 0.2 mm of rain would be classed as a day with precipitation.  On the other hand, for sunshine we are not looking at the % chance of measurable sunshine, we are looking at % of possible sunshine.  The % chance of measurable sunshine would be much higher: throughout the year, Victoria averages about 51% of possible sunshine, but on average there is measurable sunshine (at least 0.1 hours) on 317.7 days, or 87% of days during the year.    So just keep in mind that while the chart above might make it seen like the likelihood of rain and sunshine is about the same in Victoria - just a mirror image - in fact we get a lot more hours of sunshine annually than we get daylight hours with rainfall.