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Experts issue warning for change in weather

A teleconference was held on Tuesday for media to inform the public of the ongoing flood risks and the upcoming change in weather forecasted for the next two days in the Okanagan and other parts of the province.

Matt MacDonald is with Environment Canada.

<who> Photo Credit: Twitter.

He said that the cooler weather in April and May led to continued growth of the snowpack in the alpine.

Once the valley bottom temperatures rose to 20 and 30 degrees over the weekend, "that set the stage for accelerated snowmelt," said MacDonald.

"Back to back days of sustained heat has definitely turned the taps on in regards to snow melt," he said.

However the big change in Tuesday's weather is the cold front and it's expected to sweep across the province from the north between Tuesday afternoon and Tuesday evening.

The two major concerns with the cold front are wind and thunderstorms.

"As this cold front sweeps through, we're going to see some really strong northwesterly gusts and those can be expected for the Okanagan area anywhere between 7 p.m. and midnight."

As well, the Okanagan may see winds of up to 70 kilometres an hour.

<who> Photo Credit: KelownaNow

"We see impacts when wind exceeds 60 kilometres an hour."

The other issue is that the soil is high in moisture and with lots of new tree growth, there is more potential for wind damage over night.

With water levels already high, wave action from the northwesterly winds can also cause potential damage on the southern shores of lakes.

"In terms of thunderstorms - a little bit of good news for the Okanagan area - they're going to dodge that bullet," said MacDonald.

The the most severe thunderstorms are expected to hit Prince George and westwards over the Chilcotins.

Still the Okanagan should see about five to ten millimetres beginning this evening into tomorrow morning.

With the cold front, the freezing levels are going to impact the mountains overnight and slow down the snowmelt.

However, by Wednesday, temperatures are expected to rise again and stay warm (20's to 30's) all the way through until the end of May and into June.

David Campbell is with the River Forecasting Centre.

<who> Photo Credit: David Campbell

He said that areas where there have been flood issues have mostly been fed by mid-elevation snowpacks and that most of the mid-elevation snowpack melted in the last couple of weeks.

However, now the higher elevation snowpack is starting to melt.

"Mission Creek and the headwaters there at 16 to 1800 metres, still have the vast majority of the snow about 80-90% of what fell this year still remains up high and that is consistent at most sites across the province," said Campbell.

"We really have only started to melt that high-elevation snowpack."

Campbell said to expect a couple of days of reprieve when cold the system comes through but then another bout of rising river levels should come near the end of this week and next week.

<who> Photo Credit: KelownaNow

Brian Symonds is with the Ministry of Forests, Lands and Natural Resources.

His job is to oversee the management of the Okanagan mainstem lakes, which Includes Kalamalka, Okanagan, Skaha, Vaseux, and Osoyoos,

There are dams on each of those lakes and each dam allows Symonds and his team to adjust the water outflow levels when needed, to a point.

"We don't have total control on the lake and we are at the mercy of what the weather does," said Symonds. "You heard the forecast - you understand that we're getting high inflows now with the melting snow and the change in weather."

Symonds has to consider all the factors at play - including changes in weather and varying levels of each lake in the system.

"The inflows have been exceeding what our ability is to let water out of the mainstem lakes - in particular out of Kalamalka Lake and Okanagan Lake," said Symonds.

Okanagan Lake has been rising three to four centimetres daily over the past few days.

"That’s a lot of water coming in within a short period of time every day," he said.

Meanwhile, they are letting out as much as water as they can through Penticton and Osoyoos Lake and into the US. Currently, they are releasing more than what the channel was designed to release from in Penticton.

"People often ask us, 'Are the gates wide open?' They are not wide open...but they are as wide open as the channel is designed to handle, plus some and it's not just in Penticton."

"What does it mean if we dump too much water further down the system and how does that transfer into levels in Skaha Lake, Vaseux Lake and the Okanogan River."

<who> Photo Credit: KelownaNow

Currently the flows in Oliver are above the design capacity.

Symonds said the gates on Skaha Lake and Vaseux Lake are wide open.

"The only way we'll get more through them is if we raised both those lakes by releasing more water out of Okanagan," he said.

But the channel, he said was designed to release about 1 and a half centimetres per day out of Okanagan Lake.

As Okanagan Lake's levels continue rising about three to four centimetres per day, Symonds suggests that what's coming into the lake is about three times more what they are physically able to let out of the lake.

"And it's important to understand that even when the flows start to drop, the lake will continue to rise until we have an equilibrium where the water that is coming into lake is equivalent to what we are physically able to let out of the lake. At that point we'll slowly start to go down."

Because of backing up of the systems, Symonds said the lake levels will stay high throughout the summer.

"So we are concerned about wind - we are going to expect these levels to be high into the summer. They will come down as we pass our peak. but they'll still be high into the summer and so we will be exposed to potential damages from wind events and other things like wave action from both well into our summer period," he said.

Meanwhile, the dam that lets water into Osoyoos Lake on the US side has no restrictions on the amount of water flowing down. However, Symonds said they are still mindful of both the Americans and Canadians that live around the lake.

Because the Similkameen river joins the Okanogan River just below the dam on Osoyoos Lake, that river can lead to overflowing the dam. Therefore, they are also keeping an eye on the Similkameen.

"We're starting to see that condition develop a bit with the high flows coming down the the Similkameen where we we can't reduce the water that we're letting down the system - pretty much maxed out flow from the lake is being restricted."

"Under really bad conditions, it can actually cause a reversal," said Symonds.

However, currently the Similkameen levels are starting to slow down and they're able to let some out.

Overall, the speakers emphasized that residents should still continue to be prepared. They stated that residents may see some reprieve with the cold front moving in over the next couple of days, but then it's back to warming temperatures and still the snowmelt of higher elevations to fill the rivers.

The dams are being watched closely, as to which ones are able to let water out safely, while measuring the impact of residents surrounding the various lake systems.



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