Snow packs in the East Kootenay gained a small amount in the month of April, according to the B.C River Forecast Centre’s May 1 measure. The snow pack is at 114 per cent of normal. Most basins across the province are at or near 100 per cent of normal, with the driest area being Vancouver Island with 68 per cent of normal.
Despite cooler than normal temperatures, very dry weather contributed to modest snow pack accumulation in April; additionally, a short warm spell in late April rapidly melted low-elevation snow, especially in the Middle Fraser, the report says.
114 per cent of normal is considered moderately high.
“Cool weather in the first half of April led to a delay in the onset of low elevation snowmelt. A moderate warm spell with slightly above normal temperatures resulted in rapid thaw of frozen rivers and quick melt of low elevation snow. Low-elevation rivers in the Chilcotin Plateau, the Cariboo Region near Williams Lake, rivers surrounding Prince George, and the Bonaparte River at Cache Creek experienced flood levels in late April. Extreme cold weather over the winter and early-spring may have also contributed to increased ice-jamming and rapid runoff during the warming in mid-April. Many rivers in the province are experiencing above-normal flows for early-May. This reflects early melt of low-to-mid elevation snow, with flows 2-to-3 weeks ahead of normal in some areas. In watersheds with an increased proportion of high elevation, mountainous terrain, streamflow is more typical for this time of year and flows are expected to increase as high elevation melt proceeds.
The outlook for the coming months indicate the likelihood of a warmer than normal May June July. But any worry of spring flooding depends on the amount of rain.
“Typically, 100 per cent of the annual BC snow pack has accumulated by early May as the provincial snow pack normally peaks in mid-April,” the report says.
In the Kimberley Cranbrook area, there was fresh snow in the mountains this week.
Lower elevation snow sites usually start to melt prior to May 1, while high elevation snow stations can continue to accumulate snow in May depending on weather conditions. Warm weather forecasted for this weekend (May 9-10) is expected to initiate high elevation melt, but it is not expected to substantially increase flows in most rivers. Seasonal temperatures the following week should keep most rivers fairly level.
“Seasonal temperatures the following week should keep most rivers fairly level. While snow pack is one risk factor for freshet flooding, snow pack alone cannot predict whether flooding will occur or not. Spring weather is also a critical flood risk factor, where the timing and severity of temperature and rainfall patterns are important drivers of flooding irrespective of snow pack levels. Spring freshet poses a seasonal risk across the BC Interior. Scenarios that could exacerbate flood risk this year include prolonged cool weather followed by a rapid shift to persistent hot weather (particularly in mid to late-May), or persistent wet weather or extreme short-term rainfall. Favourable scenarios would include continued dry weather and seasonal temperatures.”