A strong rainshadow and a dry April

Victoria is often in the rainshadow of the Olympic Mountains, and as a result it generally gets much less rain than surrounding areas.  This phenomenon was really on display in April.

Below is the radar image for April 6, 2023.  The rainshadow "hole", to the northeast of the Olympic Mountains is clearly visible.  

Here is another radar image from April 6, showing a closer view of Victoria.  A great rainshadow, extending across Greater Victoria, the San Juan Islands, and over towards Anacortes.

Southwestern B.C. and the US Pacific Northwest experienced an atmospheric river event from April 6-9, 2023.  However, the rainshadow kept Victoria extraordinarily dry.  Below is a chart comparing the rainfall totals for April 6-9.  Rainfall in the core area of Greater Victoria ranged between 0.8  and 2 mm.  Victoria Airport (located 25 km to the north and typically less protected by the rainshadow) received 8.3 mm.  Other locations in the region received 25 mm or more, including 64 mm at Vancouver Harbour and 77 mm at West Vancouver - nearly 100 times as much rain as the University of Victoria received.

While the April 6-9 event was the most dramatic, Victoria stayed significantly drier than other locations in the region for the whole month.  The chart below compares April rainfall totals.  Again, locations in the core area of Greater Victoria were much drier, receiving between 17.8 mm and 22 mm of rain for the entire month (normal April rainfall for Victoria Gonzales is about 34 mm).  The Victoria Airport and the Cowichan Valley each received more than 3 times as much rain as Victoria Gonzales.  Seattle received more than 5 times as much rain as Victoria, and Vancouver Harbour received nearly 9 times as much rain.   Port Alberni and West Vancouver received 11-12 times as much rain as Victoria Gonzales.

April continued the trend of a dry start to 2023.  During the first 4 months of the year, Victoria Gonzales has only received about 128 mm of precipitation - half of the normal 257 mm for that period.

A very rainy day in Victoria!

Up until Sunday, it had been a dry start to the year, with just 81 mm since January 1, compared with our normal of 134 mm in the first 45 days of the year.  Then came yesterday (February 15) - what a very rainy day!  There was 61.6 mm of rain recorded at Victoria Gonzales.    Average rainfall for the entire month of February is 61 mm, so that's a month's worth of rain in one day.  It was also far more than the 47 mm of rain we had in the entire month of January 2016, even though we had 20 days with measurable precipitation during that month.  Yesterday's rainfall was quite rare for Victoria.  It certainly blew away the old record for the date of 28.2 mm of rain back in 1949.  It was the most rain recorded at Victoria Gonzales in a single day since since November 6, 2006 - more than 9 years ago.  It was also the second rainiest February day ever recorded at Victoria Gonzales in more than 117 years of recording-keeping, and the 17th rainiest day ever recorded in any month!  On average, Victoria gets a day like yesterday with more than 60 mm of rain only once ever 7 years.

As the chart below shows, yesterday's rain completely closed the rain deficit we'd had so far this year.  The blue line shows the 30-year average rainfall to date while the red line shows the cumulative total rainfall for 2016.  You can see that we've been well below average so far this year, but with yesterday's deluge, we have jumped to just above average.  The green bars show the daily rainfall amounts, and you can see how much rainier yesterday was compared with any other day this year.

Why did we get so much rain?  There were two factors.  The first was an atmospheric river or "pineapple express" carrying subtropical moisture directly to our area.  Usually during a pineapple express, as the moisture streams in from the southwest, Victoria is protected by the rain shadow of the Olympic Mountains, and our rainfall totals are a lot less than areas to the north and west of us.  However, this pineapple express, rather than coming from the southwest, was coming from a more westerly direction.  When that happens, the rain shadow shifts from being northeast of the Olympics (and usually including Victoria) to be more east of the Olympics (giving more protection to Seattle).  Westerly flows are often when Victoria will get it's heaviest rainfall.   When I saw in the forecast on Sunday that there was going to be an atmospheric river coming at us from the west, I expected we'd get more than our usual light showers!

Below is an interesting radar image from about noon yesterday.  Instead of being in the hole of the donut, as we often are, Victoria is right in the bulls eye!

What is the sunniest location in British Columbia? Victoria

Victoria has a well-known reputation for having the mildest climate in Canada, but fewer people seem to be aware that it is also among Canada's sunniest cities, with an average annual 2,203 hours.  Sunshine was measured at Victoria Gonzales from 1914 to 1988, so this average was calculated based on the most recent 30-year period (1958-88) rather than the standard 30-year climate normal period (currently 1981-2010).

The Olympic Mountain rainshadow, discussed earlier for its impact on precipitation in Victora, also affects the amount of sunshine.  As winds flow down over the Olympics, the sinking air warms and dries, often resulting in a hole in the clouds.  In fact this is so prevalent that airplane pilots often use this "hole in the clouds" as part of the visual navigation in the region around Victoria.

Victoria is the sunniest city in B.C. and one of the sunniest cities in Canada.  Compared with 2,203 hours at Victoria Gonzales, the Victoria Airport averages 2,109 hours and Vancouver Airport gets 1938 hours.  People are often surprised that Victoria gets more annual sunshine than the "sunny Okanagan" and other spots in the B.C. interior, including Kelowna (1949 hours), Penticton (1923 hours), and Kamloops (2,080 hours).  Victoria also gets more sunshine than places like Toronto (2,066 hours), Montreal (2,051 hours).  In Canada, only Prairie cities like Calgary (2,396 hours) get more annual sunshine than Victoria.

Obviously, the  amount of sunshine varies throughout the year.  In part, this is due to the seasonal changes in day length: Victoria gets roughly 16 hours of daylight in late June, but only about half that amount in late December.  In addition, the percent of possible sunshine in Victoria varies significantly throughout the year.  In July, it's sunny in Victoria for 70% of daylight hours while in December it is only sunny for 24% of possible daylight hours.  As a result of these two factors, sunshine in Victoria ranges from an average 338 hours in July (nearly 11 hours per day on average) to just 63 hours in December (about two hours per day).  Late spring and summer tends to be very sunny in Victoria, and just four months - May, June, July, and August - account for 54% of Victoria's annual sunshine.  During the summer months, Victoria gets more sunshine than any other major city in Canada, including those on the Prairies.

On average, Victoria gets 317 days each year with  at least some measurable sunshine.  Not surprisingly, virtually every day in July -  30.3 out of 31 days - has measurable sunshine.  However, even in sometimes gloomy December, there is at least some sunshine on an average 20.5 out of 31 days.  On the flip side, Victoria gets just 48 days annually with no sunshine, compared with 76 days in Vancouver, 60 days in Toronto, and 32 days in Calgary.

The sunniest month on record at Victoria Gonzales was 426 hours in July 1985.  That works out to an average of nearly 14 hours of sunshine per day.  In July 2013, 432.8 hours of sunshine was recorded at the Victoria Airport - the sunniest month on record for any location in Canada (not including the Territories where northern locations can get 24 hours sunshine during the summer, resulting in very high monthly totals).  While sunshine was no longer being recorded at Victoria Gonzales in 2013, Gonzales on average gets about 6% more sunshine than the Airport, so there is a good chance that it received even more sunshine than the Airport site.  The least sunny month ever recorded at Victoria Gonzales was January 1982, with just 28.2 hours of sunshine - less than one hour per day.

The sunniest year on record in Victoria was 1951 when 2545 hours of sunshine were recorded, making it the sunniest year recorded for any location in B.C.  The least sunny year in Victoria was way back in 1914 with just 1948 hours of sunshine, but keep in mind that this is still more than the average annual sunshine in Vancouver.

	Hours	% possible	Days with measurable
Jan	69.8	25.5%	21.3
Feb	97.9	34.1%	22.5
Mar	152.9	41.5%	27.9
Apr	195.7	47.8%	28.7
May	274.0	58.2%	29.9
Jun	281.9	58.6%	28.8
Jul	338.3	69.7%	30.3
Aug	294.3	66.2%	29.6
Sep	206.5	54.5%	28.2
Oct	145.9	43.4%	26.5
Nov	82.6	29.7%	22.6
Dec	63.2	24.3%	20.5
Annual	2202.9	46.3%	316.8

How much does it rain in Victoria?

Precipitation is another key aspect of Victoria's climate - and one that makes it quite unique among places along the B.C. coast - thanks to the rainshadow effect.  The east coast of Vancouver Island as well as the Gulf Islands, are in the rainshadow of the Vancouver Island mountains.  Moisture from the Pacific is dropped in abundant amounts on the west coast of Vancouver Island as the air lifts up over the mountains.  As the air flows back down to the east coast lowlands of Vancouver Island, it tends to warm and dry out, resulting in much less rain.  Victoria is unique because it is also in the rainshadow of the Olympic Mountains in Washington State.  The Olympics are higher than the mountains on Vancouver Island and the resulting rainshadow effect is stronger. Even though Victoria is on the edge of the Olympic rainshadow, this still results in much less rain than other areas of Vancouver Island or the Gulf Islands.  This is especially true around the southeast part of Greater Victoria (the City of Victoria, Oak Bay, and the southeast part of Saanich), which is most affected by the Olympic Mountain rainshadow.  Below is a radar image from February 22, 2014 of the southern Vancouver Island and western Washington.  You can clearly see the rainshadow,  which appears as a hole in the rain that includes Victoria as well as parts of Washington State (around Sequim and Whidbey Island).  This is a pretty typical location for the rainshadow.

Average annual precipitation at Victoria Gonzales is 641 mm for the 1981-2010 period.  Victoria Airport, 25 km to the north, receives 883 mm - nearly 40% more precipitation.  Even more astounding is the change in precipitation amounts as you head west from Victoria and out of the rainshadow.  Port Renfrew, located just 80 km west of Victoria on the exposed outer coast of the Island, receives an average of 3,671 mm of precipitation annually - nearly six times as much as Victoria.

Victoria receives less than half as much precipitation as Vancouver (1560 mm at Vancouver Harbour).  Victoria also receives less annual precipitation than all major cities in Canada east of the Prairies.  For example, Toronto averages 786 mm, while Montreal gets 1,000 mm and Halifax gets 1,396 mm.

Aside from the amount of precipitation Victoria receives, the other interesting thing is the seasonal pattern.  The Prairies receive the bulk of their precipitation during the summer, while winters are typically quite dry.  Most locations in Canada east of the Prairies receive roughly similar amounts of precipitation throughout the year.  B.C., especially along the South Coast, is quite unique in having a late fall/winter rainy season and a summer dry season, and this is most pronounced in Victoria.  Victoria Gonzales gets 119 mm of precipitation in November, its wettest month.  That's nearly ten times the average July rainfall total of 12.6 mm.  Victoria receives over half of its annual precipitation during just three months  - November, December, and January.  In contrast, it receives less than 8% of its annual precipitation during the three summer months (June to August).  In fact, Victoria is by far the driest major city in Canada during the summer.  It's 50 mm total average summer rainfall compares with 160 mm for Vancouver, 217 mm for Calgary, 225 mm for Toronto, 270 mm for Montreal, and 285 mm for Halifax.  Even desert-like  Osoyoos gets 84 mm of rain during the summer - nearly 70% more than Victoria.

Victoria gets 140 days annually with some measurable precipitation.  This varies from fewer than 5 days with measurable rain in both July and August, to nearly 19 days in November.

The wettest month on record at Victoria Gonzales is 337 mm in January 1935.  Although measurements weren't recorded for Gonzales, November 1990 was a very wet month in Victoria.  Nearby Victoria Phyllis Street received a record 395 mm that month.  For its driest month on record, Victoria has experienced calendar months with  no precipitation eight times: August 1901, July 1914, July 1922, July 1926, July 1958, August 1986, September 1991, and August 1998.  Victoria has had months with less than 1 mm of rainfall 23 times: once in May, twice in June, eleven times in July, eight times in August, and once in September.  The driest year at Victoria Gonzales was 1978, with 383 mm, while the wettest year on record was 1933 with 945 mm.  Again, although precipitation wasn't measured at Gonzales in 1990, the annual precipitation at nearby Victoria Phyllis Street was a record-breaking 1,084 mm.

The table below shows average monthly rainfall, snowfall, and total precipitation at Victoria Gonzales, as well as days with measurable precipitation.  Nearly 97% of the precipitation at Victoria Gonzales falls as rain.  We'll look at snowfall in more detail in the next post.