With the mountain snowpack beginning to dwindle, forecasters pondering a rising Osoyoos Lake are turning their gaze skyward and watching for storm clouds.
Rain is the latest nemesis in the community’s bid to protect property and infrastructure.
“The biggest piece of uncertainty is how much rain do we get over the next 24 to 36 hours,” said Dave Campbell, manager of the BC River Forecast Centre, when asked Thursday afternoon about how high Osoyoos Lake could rise over the weekend.
“I think that’s really going to determine where we go with things.”
Mr. Campbell told media Thursday afternoon that most of the low- and mid-elevation snowpack has melted now as a result of record-setting heat this week.
That doesn’t end the threat from the Similkameen River, however, which is likely to increase in both depth and ferocity with the rainfall.
Despite showers through the night, Osoyoos Lake’s water level remained constant at 916.29 feet until just after 6 a.m. when it ticked up to 916.30, according to the US Geological Survey, which measures the lake’s level at a station in Oroville.
The Town, opting for caution, yesterday afternoon issued evacuation alerts to 20 properties along Spartan, Cottonwood and Lakeshore Drives and three others in Crab Apple Court.
That brings to 76 the number of residential properties either under an evacuation order or on evacuation alert.
Two hotel properties — the Coast Osoyoos Beach Hotel and Poplars Hotel — also have an evacuation order.
“There is the expectation of rain . . . and this will really push the risk of extreme flooding through the Similkameen, the Okanagan, the Shuswap, the Boundary — where we’ve been experiencing obviously significant challenges — but also the Kootenays where we haven’t seen significant high flows yet,” said Mr. Campbell.
He also noted “ongoing hot weather is expected through the weekend.”
With an expectation Osoyoos Lake will begin to settle, flood watchers are now turning their attention to Okanagan Lake, which is expected to reach potential flood levels in early June.
“It’s important to understand I’m not necessarily saying we’re going to reach that 343-metre elevation, but I think it’s very prudent that people who were flooded (and) local governments plan for that in terms of where they want to put their flood-protection measures,” noted Shaun Reimer who manages the province’s dam structure system in the Okanagan.
The lake’s level is currently increasing about five centimetres per day, Mr. Reimer told media, but the rise is expected to taper off as snowmelt eases.
As of Thursday, the lake was 32 cm lower than where it was at this time last year, but water was flowing in faster than in 2017, when the lake topped out at a record-setting 343.27 m on June 8.
Outflow from the Penticton dam was cut 13 days ago, he added, to avoid damaging equipment downstream. He hopes to increase flows again once the lake inflow starts slowing.
— with files from the Penticton Herald