Weathering Wells Gray
“This is the third season that I have spent on survey in this district, and I have not the slightest hesitation in saying that the climate is first class…”— Robert H. Lee, 1913
Broadly speaking, Wells Gray’s climate is controlled first and foremost by its geographic position relative to the Rocky and Columbia Mountains to the east, and the Coast Mountains to the west.
The former ranges tend, particularly in winter, to protect the park from outbreaks of arctic air originating in central Canada. As for the latter, they do equal service against the warm, sopping winds that blow off the Pacific, and that make such a muck of coastal British Columbia during that season.
Mild, snowy winters. Pleasant, sunny summers. About the only argument that can be brought to bear against Wells Gray’s candidacy for the title of Canada’s climatic Eldorado, is June. June is the month when, in most, the Clearwater Valley turns humid and wet. Even in the driest portions of the valley, rain can be expected on 13 days out of 30 in a typical year, and heavy cloud on perhaps 20 days.
By the second week of July (in most years), the skies have cleared, and the lakes are sparkling with reflected sunlight. Most years, too, August is even sunnier, and September, sunnier still. Blessed are they who visit the park late rather than early.
Very few climatic data exist for Wells Gray. To date, only a single long term weather station has operated here, and even that (at Hemp Creek, a frost pocket) has failed to record climatic patterns typical of the area as a whole. Most of the following figures are educated guesses only, based on available short-term measurements.
July is the warmest month, daytime temperatures then averaging a comfortable 22°C to 25°C at valley elevations, though slightly cooler on the lakes, where the evaporating surface of the water uses up a disproportionate amount of the sun’s radiant energy. Moving up the mountain slopes, average temperatures decrease some 9°C for every 1000 m. Thus, at treeline, midday temperatures probably average 14°C.
On a typical summer night, valley temperatures generally fall to a cool 7°C to 12°C, reflecting the relative nearness of glaciers, snowfields and small side drainages. Summer frosts are rare, except at treeline and above, where they may occur even in mid July.
In January, daytime highs average roughly -5°C at all forested elevations, and nighttime lows about -10°C. The vertical temperature gradient in winter is much less than in summer, with a typical midday decrease of only about 1°C for each 1000 m rise. At night, temperatures are often actually warmer at treeline than in the valley, owing to the existence of a cold inversion layer at lower elevations.
Although Wells Gray’s skies are frequently cloud-covered in winter, for the park visitor this is usually more of a plus than a minus: clouds block the flow of heat from the earth into space, and so help to keep air temperatures moderate. As a result, the thermometer seldom dips far below about -25°C, and when it does it seldom holds there for very long.
Against these averages, it is important to realize that temperatures can vary tremendously from place to place, even over short distances. A south-facing slope can be as much as 5°C warmer on a sunny afternoon than a north-facing slope mere metres away.
Temperature differences are even more pronounced at night when, under clear skies, small topographic depressions can be 15°C colder than the adjacent slopes. Pay attention to these subtleties: for the backpacker, they can mean the difference between a restful night’s sleep, and eight hours of shivering. During cloudy weather, or when it is windy, temperatures are much more likely to be uniform for any given elevation.
Generally speaking, precipitation is evenly distributed through the year in Wells Gray, with spring, however, being somewhat the driest season, and summer (especially June) the wettest.
Precipitation is lightest in the valleys of the south and west, and heaviest in the high Cariboo Mountains of the north and east. A total annual precipitation of about 450 mm at Clearwater Village increases to 550 mm at the park entrance, and then to as much as 700 mm at the south end of Clearwater Lake. Azure Lake is even wetter, possibly receiving more than 1000 mm per year. In the wettest portions of the Cariboo Mountains, amounts probably exceed 1500 mm. The wetbelt outlier at Spahats Creek provides an fascinating exception to this general pattern.
Few days are so grey that the evening sun doesn’t light up the sky for at least a few moments prior to setting. Evening sun is, in fact, one of Wells Gray’s meteorological specialties.
This curious phenomenon has to do with the park’s position relative to the Coast Mountains to the west. The Coast Mountains are cloud makers; that is, they cause the moist Pacific air that blows against their western slopes to rise and, as it rises, to cool and so condense into cloud – often raincloud. Once, however, this cloud has crossed the Coast Mountains, it descends again and, as it descends, it warms and thus dissolves. The result is a window of sunshine in the lee of the Coast Range. Climatologists call that window a rain shadow. Geographers refer to the area it covers as the Chilcotin or, east of the Fraser River, the Cariboo.
Eastward of the Cariboo, the cloud begins to form again, banking up against the next range of cloud makers, the Cariboo Mountains. Southern Wells Gray lies just to the west of the Cariboos, so here it may have been raining all day. When, however, the evening sun finally touches down on the western skyline, its angle is such that it now shines directly through the opening provided by the rain shadow. Suddenly, a flash a colour lights up the sky.
Under certain circumstances, this evening performance may go one better, casting reflections of the park’s larger lakes upon the cloud bottoms overhead. Also, if rain is actually falling, this is the time of day to check for a rainbow.
In northeastern Wells Gray, snowfall amounts can be spectacular. At one upper level snow station, snow depth averages about 350 cm during May, the month of maximum accumulation, with a water content of roughly 1500 mm. Using a multiplier of ten (on average 1 cm of water is equivalent to 10 cm of snow), this represents about 15 m of fresh-fallen snow: roughly the height of a five-storey building! In Canada, only B.C.’s Coast Mountains are charged with a (marginally) deeper snowpack.
Amounts are, of course, considerably less in the valleys, with Azure Lake, for example, experiencing a settled snowpack of approximately 150 cm. Moving south out of the Cariboo Mountains, the snows become even lighter: 110 cm at the south end of Clearwater Lake; 70 cm at the park entrance; and 50 cm at Third Canyon. In an average year, at lower elevations, the snowpack is at its deepest already by the end of February, whereas at treeline it continues to accumulate until mid April.
Each summer, Wells Gray rocks to the rhythm of thunder and lightning on about 40 days each year. June is the stormiest month, averaging three to five thunderstorms every week, though of course not all affect the entire park. One study in 1980 recorded, from May through September, a total of 707 cloud-to-ground strikes in the Clearwater area, and 1697 strikes near Blue River. These numbers pale, however, when you realize that lightning touches down on earth approximately 100 times every second!
At valley elevations in Wells Gray, winds are generally light. Presumably this reflects the Clearwater Valley’s north-south orientation, which thus cuts at right angles to the prevailing westerly flow.
The strongest winds tend to develop in such east-west gaps as Azure and Mahood Lakes, which thus provide major exceptions to the no-wind rule. (Tradition has it that Mahood Lake was formerly called “Windy Lake” in the tongue of the Canim Lake people). Another major exception will be found wherever the Clearwater Valley narrows, as it does for example near Spahats and at the north end of Clearwater Lake. Here the winds can at times be very strong. Boaters beware!
In the mountains, winds are much more prevalent, owing to a decreasing drag of the earth’s surface on atmospheric circulation.