An article in the Ashcroft Journal on Aug. 18, 1900 noted that authorities had proposed to establish a convalescent home in British Columbia for the sick or wounded British soldiers sent home from China, with the writer noting that 乌鸦传媒淭he dry clear atmosphere of Ashcroft would, without doubt, be much more beneficial to the soldiers than the liquid air of the coast.乌鸦传媒�
A convalescent home was never built in Ashcroft, but in 1907 the Tranquille Sanatorium was built in Kamloops, to treat those suffering from tuberculosis. Medical thinking at the time was that people suffering from tuberculosis, and lung conditions generally, did better in a dry environment than a moist or humid one.
A century-and-a-quarter later, data bears out what residents of the region have long known: it gets hot here but, as the saying goes, it乌鸦传媒檚 a dry heat. Just how dry? Ashcroft has the lowest average annual relative humidity in Canada, at 58.6 per cent, with Kamloops not far behind.
Of the 10 locations in the country with the lowest average annual relative humidity, six are in Alberta and four (Ashcroft, Penticton at 61.15 percent, Kamloops at 61.4 per cent, and Osoyoos at 62.15 per cent) are in B.C. Lytton, with an average annual relative humidity of 63.95 per cent, is in 11th spot.
Relative humidity is the ratio of how much water vapour is in the air to how much water vapour the air could potentially contain at a given temperature and pressure. It is normally expressed as a percentage, with a higher percentage means that the air-water mixture is more humid.
When air reaches 100 per cent relative humidity, the air is saturated and is at the dew point. Cooling air increases the relative humidity: if it reaches the dew point, and there is an available surface or particle, the water vapour will condense into liquid or deposit into ice. Warming air decreases the relative humidity.
Information on average relative humidity compiled by Junah Birchwater from the Environment Canada database from 1991乌鸦传媒�2020 did not include Ashcroft, he told the Journal, so he downloaded the hourly data for Ashcroft from 2010 to the present and compared it to the Kamloops data to reach his conclusion.
Birchwater乌鸦传媒檚 graph showing the average annual relative humidity of the six locations in Canada where it is below 61.5 per cent shows Ashcroft the highest of all six in January and December, where the relative humidity hovers around the 80 per cent mark. By July, however, Ashcroft is well below the other locations, at around the 40 per cent mark.
Penticton and Kamloops show similar large fluctuations. The three Alberta locations in the top six 乌鸦传媒� Lethbridge, Calgary (airport), and Claresholm 乌鸦传媒� show much more consistent relative humidity levels over the course of the year.
Joey Onley of the Interior Weather & Wilderness Watchers Facebook page says that Ashcroft乌鸦传媒檚 low average relative humidity is a result of the rain shadow effect it experiences thanks to the Coast Mountains to the west.
乌鸦传媒淟arge weather systems throw tons of water against the Coast Mountains, which forces clouds to climb in what乌鸦传媒檚 called orographic lift,乌鸦传媒� he explains. As an air mass gains altitude it cools down, which can raise the relative humidity to 100 per cent, create clouds, and cause precipitation. Since most of the precipitation falls on the windward (upslope) side of the mountains, areas on the leeward (downslope) side are said to be in the rain shadow.
乌鸦传媒淐louds climb on the far side of the mountains, and then you have the dry belt through the Chilcotin and west Cariboo,乌鸦传媒� says Onley. 乌鸦传媒淢oisture sails over, then starts to lose some altitude as it comes over the Cariboo plateau.
乌鸦传媒淎shcroft is so uniquely placed, so far south and on the dry side of the mountains. You乌鸦传媒檙e hidden down deep there. Weather launches off the mountains, and the lower you are the harder it is for precipitation to be triggered. Low humidity is a reflection of that, and you see it in the steep canyons throughout the region.
乌鸦传媒淟ytton has two major rivers, so that increases relative humidity slightly, because of the greater volume of water through there. Ashcroft is a little further from the mountains, there乌鸦传媒檚 only one water source, and it乌鸦传媒檚 down deeper in the valley. Kamloops benefits from some of same things as Ashcroft: it乌鸦传媒檚 very low in the valley, and is at a great angle for sun all year round."
