Topography
The Airport is situated on the flat floor of a deep, narrow east/west orientated valley dissecting the Fraser Plateau. Eight km to the east, the North Thompson river flows in from the north to meet the South Thompson river, entering from the east. The combined Thompson rivers forms the south boundary of the airport and enters the 40 km long Kamloops Lake 6 km to the west. The side hills to the north and south rise steeply to an elevation of 900 m within 4 km of the Airport and there are ridges of over 1500 m elevation within 19 km in all directions. Peaks of the Lillooet Range of the Coast mountains rear to over 2700 m 113 km to the west and the Monashee mountains with similar elevations within 113 km to the east.
The adjacent hillsides are grass-covered with considerable sagebrush but little tree growth to the 900 m level. Above this, the terrain is generally covered with an open coniferous forest. The valley floor is green where irrigation is applied to the rich alluvial soil, however, residential and industrial development has largely replaced farmland immediately to the east of the airport in the suburbs of Brocklehurst and North Kamloops. The City centre is located on the south side of the river on the slopes extending up from the confluence of the North and South Thompson rivers. The suburbs of Valleyview, Juniper, Dallas and Barnhartvale stretch 29 km to the east on the south side of the South Thompson River while the suburbs of Sahali, Mt. Dufferin and Aberdeen lie in the hills directly west of the City centre. The suburb of Westsyde stretches 21 km north along the west side of the North Thompson River.
Climate
Although Kamloops is situated only 258 km from the Pacific Ocean, the climate must be classed Continental with aridity as its outstanding characteristic.
Movement over the Coastal mountain barrier condenses much of the water vapor from the moist Westerlies with one of the driest areas in Southern Canada extending up the Thompson River Valley from Spences Bridge to Kamloops. In fact, the climate in this "rain shadow" is semi-arid and borders on desert. However, in the mountainous Interior of Southern B.C. topography exerts a major effect on Climate and, in general, the adjacent highlands receive much more precipitation than the valley. The normal annual precipitation for the airport is 256.5 mm, of which 174.8 mm is rainfall. Most of the winter precipitation falls in the form of snow and averages 91.5 cm. June is generally the wettest month, summer precipitation is in the form of showers and thundershowers but these are usually of short duration with summer a season of abundant sunshine, in contrast to the rather cloudy winters.
Though incursions of mild maritime air occur, the Kamloops winters are in general cold with a long term mean temperature for January of ~6.1 C.Temperatures will, in most winters, drop to -29 C for short periods while an extreme of -38.3 C has also been recorded. However, temperatures rise rapidly in the early spring and summers are warm with a mean July temperature of 20.8 C. Most summers experience maximums over 38 C on several days while the extreme maximum soared as high as 41.7 C.
Winds usually follow the valley with a prevailing direction from the east, though summer months have a predominately westerly component. Calms are frequent, particularly during winter nights. However, strong winds are not uncommon and it is of particular interest that the highest gusts recorded, up to 137 km/h, have been most frequently associated with cross-valley wind flows.
Most of the farm holdings are located along the North Thompson Valley from Heffley Creek to Vavenby. Also, small farm holdings are situated in the Louis Creek valley near Tod Mountain. The average farmer is a small operator and primarily raises between 75 to 100 head of cattle. In addition to cattle ranching, the Vavenby area has a few sheep farmers. The forage grown is primarily barley, oats and some corn and is used to feed the cattle. Although most of the hay harvested is for their own consumption, some of the larger hay farmers sell most of their harvest.
Local Effects and Climate Information Kamloops
Publicly Orientated
Terrain has a major effect on the weather. The Kamloops area is no exception. Just a few examples serve to show how the local climate is influenced by the surrounding terrain.
The most obvious effect is the near desert conditions locally around Kamloops. As moist air rises it condenses into cloud and often results in precipitation. When air descends it warms and expands causing temperatures to increase and cloud to dissipate. Since the Coast Mountains act as a significant barrier to the prevailing winds in Southern B.C., the air must rise up over them before sinking down onto the Southern Interior. The rising air drops great amounts of precipitation on the windward slops of the Coast Mountains while the lee side of the mountains remain dryer and warmer. The Thompson Valley lies in an area where this warming and drying is quite extreme and results in the near desert conditions in Kamloops and the area just to the west towards Savona, Ashcroft and into Spences Bridge.
To the east, where the terrain rises again, the air is lifted as it crosses the Monashee, Selkirk and Rocky Mountains. There are several windward slopes which receive much heavier precipitation. The Shuswap Lakes area, for example, receives almost double the precipitation that Kamloops receives.
The winds at Kamloops Airport are predominantly easterly. As the air comes over the Coast Mountains it is warmed and then becomes less dense thus forming an area of low pressure at the eastern foot of the range. At the same time, air is packing up onto the Monashee Range, becoming increasingly dense and forming an area of high pressure. The air will tend to move from higher to lower pressure and where there is a deep valley to direct the flow, like the South Thompson, the wind takes on the direction of the valley. This results in a prevailing easterly wind in the Kamloops area.
Another wind effect is experienced on a stable day when no great pressure differences are experienced in the area. The wind will flow from areas with a greater potential for higher density. Since the air is generally colder to the north up the North Thompson and to the east over the Shuswap Lakes, it has an increased density which in turn raises the pressure. This provides the gentle easterly winds along the South Thompson valley and the northerly winds down the North Thompson valley.
Many people have noticed the gusty winds in the Valleyview area late on a warm summer afternoon. These are also a valley type of wind. As the air heats up, the valley bottom becomes much warmer than the air under the trees on the ridge tops and at the top of many draws and creek beds. The air from the valley, then warmer and buoyant, rises up the draws into these areas. The cooler air at the higher elevations is trapped as it is won't rise because it is too dense, and it won't flow down the draws because the rising warm valley air has blocked it. Once the intense heating stops in the late afternoon, the cooler air is released and surges down the creek beds and draws into the South Thompson, frequently as strong gusts.
A similar effect occurs near the local lakes. When the air is cooler over the water during the day, it maintains its density and high pressure. As the air over the land heats more rapidly, it begins to rise with the cooler air over the water rushing in to take its place. The effect so may of us enjoy on a summer afternoon is known as a sea breeze or lake effect.
A very common fall, winter and early spring occurrence in the Kamloops area is the presence of low cloud, capped just above the valley ridges. With clear skies the ground surface cools more rapidly in the valley bottoms that at the ridge tops. This causes a situation where the air is warmer at the top of the valley than on the valley floor. This is know as a valley temperature inversion. The air will naturally rise so long as it is warmer than its surroundings, then it will stop. In the fall, winter and early spring when an inversion has formed there are still some pockets of warmer air in the valley such as air over open water, chimney smoke, automobile exhaust and industrial emissions. This warmer air picks up pollutants and rises to the inversion level. As it rises it cools and condenses thus forming a layer of low cloud covering the valley areas. Since the best conditions for this development occur with a clear night and rapid cooling temperatures, they are usually associated with a strong ridge of high pressure. A typical day in these circumstances will include a low grey overcast over the valley floor and the downtown area, fog just below the inversion level in Sahali and Aberdeen with bright sunshine over the mountains such as experienced at the Sun Peaks Ski Resort.
