Ministry of Environment
Current Snow Survey and Water Supply Bulletin
The February 1st snow survey is now complete. Data from 113 snow courses and 53 snow pillows around the province and out-of-province sampling locations, and climate data from Environment Canada, have been used to form the basis for the following reports.
The entire document including text and data can be viewed as an Adobe pdf file.
The detailed snow survey data can be viewed as an Excel file or PDF file.
Weather
Weather across British Columbia transitioned in early January from warmer and wetter weather, to an outbreak of cold, arctic air which persisted through the middle of the month. The breakdown of this cold air mass occurred as warmer, moist air masses from the Pacific worked their way onto coastal British Columbia, and then into the interior. This transition saw some significant snowfall across much of the province, including lower elevation areas along the coast. Continued moderate storm events through the latter part of the month contributed to additional snowpack accumulation, particularly in the mountainous regions of the province.
As a result of the mix of both cold and warmer weather events, the overall average temperature through January was near normal or slightly above normal through most of the province. On average the province was slightly wetter than normal through January, with areas in the central interior, north-west, Peace, Kootenay and Columbia typically receiving higher than normal precipitation, and the south interior receiving below normal precipitation.
Snowpack
Weather patterns through January allowed for the continued development of snow packs across the province, with significant increases in snow basin index values in the Nechako and Lower Fraser. Snow basin indices are well above normal through the Upper Fraser, Nechako, Peace and Skeena-Nass, with a high of 168% of normal in the Nechako basin. Note the Nechako basin index is based on surveys from Mount Wells (1B01), Tahtsa Lake (1B02) and Kidprice Lake (4B01). The overall Fraser Basin index is currently at 125% of normal, with low to mid-elevation snow packs being near normal. Below normal snow basin indices are present in the South Thompson, Okanagan-Kettle, and Vancouver Island, with a low of 81% of normal in the Okanagan (see Map 1).
BC Snow Basin Indices – February 1, 2012
Basin |
% of Normal |
Basin |
% of Normal |
Upper Fraser |
149% |
Kootenay |
104% |
Nechako |
168% |
Okanagan-Kettle |
81% |
Middle Fraser |
111% |
Similkameen |
99% |
Lower Fraser |
118% |
South Coast |
109% |
North Thompson |
116% |
Vancouver Island |
92% |
South Thompson |
92% |
Peace |
145% |
Columbia |
118% |
Skeena-Nass |
139% |
Outlook
By this date, generally about two-thirds of the annual BC snowpack has accumulated, with another 2 or more months of accumulation still to come. At a provincial level, snow pack levels are above normal through most of the province except for the south interior and Vancouver Island. Seasonal runoff volume forecasts indicate a similar trend of below normal runoff volumes forecast in the Okanagan and south interior, and higher than normal runoff volumes for the Upper Fraser, Middle Fraser, North Thompson and Skeena basins. Note that forecasting skill is typically low for February 1st forecasts, reflecting the uncertainty over weather for the remainder of the winter and early-spring. Seasonal volume runoff forecasts are available on the River Forecast Centre website.
At this stage the two main issues are the below-normal snow packs and seasonal flow outlooks for the south Interior, particularly the Okanagan (and the potential for water supply issues into the summer of 2012), and the above-normal snow packs (and potential for increased spring flood risk) in the Upper Fraser, Nechako, Peace, and Skeena-Nass regions, and the Fraser River basin as a whole. Current snow pack levels are above the February 1st 2007 levels in the Upper Fraser, similar to 2007 levels in the Nechako, Peace, and Skeena-Nass basins, and below 2007 levels for the entire Fraser River basin.
La Niña conditions are present across the equatorial Pacific Ocean, though temperature anomalies are weaker than were observed during last year’s La Niña event. The Climate Prediction Centre with the U.S. National Weather Service (NOAA) is predicting the weak to moderate La Niña event to persist into the spring of this year. In combination with La Niña, cool-phase Pacific Decadal Oscillation (PDO) conditions are present in the north-east Pacific (cooler than normal temperatures in the Gulf of Alaska). In-phase La Niña and PDO conditions tend to enhance seasonal climate effects. Current probabilistic seasonal weather forecasts from Environment Canada are similar to what would be expected under La Niña and cool-phase PDO conditions, with cooler than normal and normal to wetter than normal conditions forecast for the next 3 months throughout most of British Columbia. Cooler temperatures and wetter than normal conditions are forecasted to be more likely in the western, coastal portions of the province than in the interior. It is important to note that forecast skill is typically low for seasonal precipitation forecasts.
The current seasonal climate outlook is favourable for the maintenance or enhancement of snow packs, relative to normal, through most of the province. This would further develop the snow pack in regions that are currently below-normal (eg Okanagan), but may exacerbate snow pack and flood risk in the areas that are currently above-normal. While snow pack is one important factor in determining seasonal flood risk, whether or not major flooding occurs is largely dependent on the weather during the snowmelt season in May and June.
Produced by: BC River Forecast Centre
February 8, 2012
Top