Climate

To report a fire: call 1-800-663-5555 or *5555 from a cellular phone

Wildfire Information (Forest use restrictions, campfire bans, and current information on wildfires): Call 1-888-3FOREST or Call 1-888-336-7378

History

The longest-running continuous (up to June 2002) weather records for the Cariboo Forest Region are for Barkerville, the historic gold mining and panning site in the mountains east of Quesnel, starting in 1888. Another site with long-term records is Tatlayoko Lake (north end) along the eastern edge of the Coast Mountains, with records back to 1928. For the two cities in the Region, Quesnel and Williams Lake, the official records at the airports go back to 1946 and 1960, respectively. All of these weather records are compiled under the direction of Environment Canada. The B.C. Forest Service started its organized network of daily reporting fire weather stations throughout the Cariboo Forest Region in the early 1970's and it has expanded to the present 30 active stations (as of June 2002), all but two of which are fully automated.

Topography Affecting Weather

Two main mountain ranges dominate the edges of the Region: the Coast Mountains in the west, with many peaks above 3000 meters, and the Cariboo Mountains in the east, with the general ridgeline elevation above 2400 meters. Since the prevailing airflow is from the west to southwest, these ranges are major weather modifiers, creating a rain shadow in the west and a wet belt in the east. When winds occasionally develop from an easterly direction, this pattern of wet and dry sides is reversed to some extent. Between these two ranges there are a wide variety of topographical features that have a more localized affect on weather. Moving from west to east, there is the broad, rolling Fraser Plateau extending eastward for approximately 250 kilometers from the eastern slopes of the Coast Mountains, with a general elevation of 1100 meters or more. It is broken here and there by small ranges, occasionally rising above 1800 metres, that have wetter and drier sides.

The two main rivers crossing the plateau are the Chilcotin, running generally west to east, and the Fraser, running north to south. The Fraser runs 700 meters or more below the surrounding ridge tops in the south while the Chilcotin also forms a deep depression as it nears its confluence with the Fraser south of Williams Lake. These deep valleys or canyons are much drier than the upper hillsides and plateau due to the warming and drying of air as it spills down into the valleys. East of the Fraser, and especially east of Highway 97, the land becomes increasingly hilly as it approaches the Cariboo Mountains, with many river and creek valleys that channel winds in different directions. The largest river in the east is the Quesnel which starts in the Cariboo Mountains and joins the Fraser at Quesnel.

Several big lakes also affect this Region's climate, by moderating temperatures and by providing a source of moisture to the air where it blows across the water for long stretches. Chilko Lake, on a north-south axis on the eastern edge of the Coast Mountains, is the largest lake in the western half of the Region and is in the general vicinity of two other long north-south oriented lakes, Tatlayoko and Taseko. In the east, Quesnel Lake, the largest lake of all at close to 90 km long, sends two main arms far into the Cariboo Mountains. Its general orientation is west-east, with one arm going off to the northeast, while the second largest lake in the east, Horsefly, also runs west-east. The east is covered by a vast number of smaller lakes while the west has significantly fewer lakes, especially once you are out of sight of the Coast Mountains, and thus fewer sources of localized moisture in the prevailing airflow from the west to southwest.

Climate and Vegetation

This Region is divided into two main climatic belts: the western dry belt and the southern wet belt. The western dry belt extends from the eastern slopes of the Coast Mountains eastward to near Nazko in the north, near the Fraser River in the middle of the Region and slightly east of Highway 97, at the southern edge of the Region. The southern wet belt east of Highway 97 has extensive cedar and hemlock. Between these two areas there is a transition zone, roughly between the Fraser and Highway 97. The southeastern boundary area, centred around Clinton, has similar vegetation in the valleys to the adjoining part of the Kamloops Region, with well-spaced Douglas fir and some areas of mainly ponderosa pine, with many semi-open grassy areas, and a milder climate, due to the more southerly latitude and lower elevations in the deeper valley bottoms.

Annual temperature is largely determined by latitude and elevation, and to a lesser extent by topography. There are about 2.5° of latitude between the northern and southern edges of the Region while elevation varies by close to 3000 meters from the highest mountaintops to the Fraser River at the southern boundary. The influence of elevation on temperature is highlighted by the 1.7° C drop in the average annual temperature between the Quesnel Airport and Kersley, about 22 kilometers further south along Highway 97 but 126 meters higher.

The dry belt is generally at its driest along the benches and plateaus of the lower Fraser and Chilcotin Rivers, typically showing patches of bare ground between sagebrush bushes, with lone Douglas firs here and there. Trees here are widespread only on the upper parts of ridges where more rain falls. In the northern and western parts of the dry belt there is general cover of mainly well-spaced lodgepole pine, Douglas fir and spruce, with little or no underbrush, along with some thinly grassed meadows. The densest tree cover is usually at the higher elevations. Dry, late winters and early springs often result in a risk of grass fires in the dead stalks and blades until the new grass starts growing vigorously. Summer precipitation can vary widely from year to year and droughts can last for substantial periods of time. Western parts of the dry belt receive less lightning than elsewhere in the Region although the dryness makes any strikes more dangerous due to the usually dry fuels.

Large parts of the natural landscape have been altered by farming and timber harvesting, although many areas of virtually untouched land exist. Ranching in the west utilizes natural grassland to a large extent, together with some forest clearing. Logging in the west is widely scattered throughout but limited to areas of better growth while large areas of rather straggly growth are undisturbed. In the eastern wet belt any farming is along the western, drier, fringe and logging is the main man-caused alteration. The transition zone has the largest amount of clearing for farming, mostly for cattle grazing and some hay pasture. Wildfire also continues to be a very significant modifier of the landscape, however.

The eastern parts of the wet belt, along and in the Cariboo Mountains, get as much precipitation as many coastal areas, resulting in an almost pure coniferous forest, mainly of hemlock, cedar, spruce and Douglas fir, with heavy undergrowth and virtually total ground cover. Precipitation is normally at least moderate for every month of the year and droughts are usually mild and short-lived. This belt gets frequent lightning, occasionally in major outbursts, although strikes in the frequently damp to wet fuels often do not erupt into flames and are more likely to smolder until some drying occurs.

The west typically has a cold to very cold but relatively dry and generally sunny winter, followed by a very dry spring. Even though the western boundary of the Region is only about 40 kilometers from the nearest ocean water (Knight Inlet) the mild maritime air is effectively blocked out by the Coast Mountains. In the summer rainfall usually comes as showers and amounts can vary considerably from year to year. Summer often sees long dry stretches followed by brief periods of substantial but erratic moisture. The exception to this pattern is the belt next to the Coast Mountains where winter snowfall is greater and summers are drier.

In the eastern wet belt there is substantial precipitation throughout the year, with some drying in the spring. Snowfalls are very heavy and can take a long time to melt in the spring in the thick forest whereas the dry west usually loses its sparse snow cover much earlier. Areas in the transition zone between the dry and wet belts, on both sides of the Fraser, have considerably more precipitation in the summer months than in winter or early spring. Williams Lake Airport, for instance, receives 38.5 mm total precipitation in January, only 19.5 mm and 21.5 mm in March and April, while receiving 51.4 mm on average in July, its wettest month. Quesnel Airport, in the northern part of the transition zone, has somewhat less variation through the year, with 50.5 mm in January, a maximum of 59 mm in July and a minimum of 22.6 mm in April. The only site with sunshine records is the Williams Lake Airport and it receives slightly more sunshine hours per year than the Kamloops Airport (although hillsides at Kamloops cut off some potential sun in morning and evening). Many parts of the west are probably sunnier than Williams Lake, especially in winter, while the wet belt is much cloudier through the year.

Climate Statistics

Williams Lake Airport (elevation 940 meters), almost in the geographical centre of the Region and in the transition zone from dry to wet, Quesnel Airport (elevation 545 meters), in the northern heavily forested area and just east of the wet belt, Barkerville (elevation 1265 meters), in the northern wet belt in the Cariboo Mountains, and Tatlayoko Lake (elevation 853 meters), on the eastern edge of the Coast Mountains and in the dry belt, have the most extensive weather records in the Region and are used here as a guide to the general climate, keeping in mind that many other areas have wetter or drier and warmer or colder conditions.

Climate Statistics: 1971-2000

* Averaged between daytime highs and lows
** Based on 1961-1990 data

The Fire Season

As is to be expected from the previous description of the Region's weather and vegetation, there is a significant variation in fire danger between the dry and wet belts. The fire season starts in April when the main hazard is from fires in the dead winter grass, principally in the valleys and the lower river benches of the southwest and on the western plateau. These fires are typically short-lived and limited in area, although they may threaten buildings and property. The most important factor in the behaviour of these fires is the wind and they can burn even on quite cool spring days, if the wind is strong enough and the grass is not soggy. This hazard ends when new green grass starts growing vigorously, usually by the latter part of May. There is also a spring hazard in deciduous trees, such as poplar and birch, before the leaves are fully out, when the moisture content of the twigs and branches is low. After greenup, there is a moisture balance in both live and dead fuels, whereby rain and, to a much lesser extent, high humidity, add moisture to dry fuels while warm temperatures, low humidities, and winds dry out fuels. There is a normal drying of dead fuels through the latter part of May through to the end of August and into early September, although heavy rain can reverse this pattern for many days and cool temperatures and high humidities slow down the rate of drying. Live vegetation can largely replenish moisture loss through the roots until available soil moist becomes significantly depleted. Drying of different types of dead fuels also varies greatly since litter such as dropped needles on a forest floor can dry out in one day after a good rain while large logs slowly dry out through the summer unless conditions are very wet and cool. Specific fire weather indices calculate the different rates of drying in the various fuel categories.

Fire Danger History

The B.C. Forest Service monitors the fire hazard through the fire season by maintaining a daily record, as of 1:00 p.m. daylight time, of the temperature, relative humidity, wind speed and 24 hour precipitation at numerous sites that are representative of the different areas of climate, forest fuel types, and fire history around the Region. These weather factors are input into the Canadian Fire Weather Index to provide a standardized assessment of the fire danger in the different parts of the Region. From these indices five danger class ratings are determined, from very low to extreme (very high). When these indices reach certain levels various prescribed steps are taken, such as manning lookouts, banning campfires, etc.

The following table shows what percent of the time various sites have been in the high to extreme danger class for the months April through September during the 20 year period of 1981-2000. As is to be expected, western and southern dry belt sites are typically in the high to extreme danger class range much more frequently than eastern wet belt sites. When reviewing the last 22 years it is very noticeable how much lower the fire danger has been generally from about 1995 onwards, with the exception of the warm and dry spring and summer of 1998, in comparison to the 1981 to 1994 period. Quesnel has had the highest percentage of days in high to extreme danger class for that period, probably reflecting the fact that it is the lowest elevation weather station in the Region. At the other extreme is the Baldface station, in the northwest corner of the Region and the second highest station, which has reported only 52 days, or 2.8% of the total days, in high to extreme danger class since it started in 1991. Big Valley, in the far northeast corner of the Region in the wet belt at 1355 meters, has had 118 days or 4.2% of the time in high to extreme danger class during the April-September period since 1987.

Number of days in High and Extreme Danger Class During Fire Season (April 1-September 30) For Period 1981-2000