When will the heatwave end? Forecast suggests above-normal temperatures to persist in July

Extreme heat and dry conditions have blanketed the Pacific Northwest for almost one week, causing increased death tolls and dangerous heat conditions.

Temperature records were broken across states in the United States like Washington, Oregon, and Idaho – while portions of Canada were hit with as high as 49.5C (121F) weather.

Hundreds of deaths across the Pacific Northwest have been credited to the unprecedented heatwave, which even left residents of the British Columbia province town of Lytton fleeing after several wildfires engulfed portions of the area.

So when might people experience relief from the extreme heat?

The National Weather Service has forecasted that temperatures should start to decrease in portions of the Northwest US such as the western part of Washington and Oregon. But there will still be “well-above average temperatures will persist across the region into the Upper Midwest” into July.

“Above normal highs are also likely in the Mid-Atlantic,” the agency forecasted.

The National Weather Service issued excessive heat-warnings for most of Washington and Oregon on Tuesday, which was expected to last through the Fourth of July.

Portions of Idaho have been blasted with extreme heat for the last week, and that was likely to continue through mid-July.

In Shoshone, Idaho, for example, forecasts show the town experiencing 37.2C (99F) to 38.8C (102F) through 15 July.

In other areas of the Pacific Northwest, forecasters have said temperatures should remain higher than normal through to next Tuesday.

Portland, Oregon, saw record-high temperatures of (116F) on Monday afternoon. But those high temperatures have since dropped to 25.5C (78F) on Thursday.

High temperatures were expected to bounce back to around 32C (90F) next week in Portland, making it about five to 10 degrees higher than normal.

Environment Canada said the weather system shattered heat records across portions of British Columbia, Alberta, Yukon, and Northwest Territories in Canada on Monday.

In the British Columbia town of Lytton, a shocking 49.5C (121F) was recorded at one point – breaking the country’s all-time high temperature record.

The heatwave was caused by an atmospheric blocking pattern that led to a “heat dome” of high pressure with low pressure on either side. The weather was unable to move along by the jet stream, the World Meteorological Organization said.

David Phillips, senior climatologist at Environment and Climate Change Canada, said climate change looked to be a key contributor – given the heatwave’s duration, extremes, and the fact it is setting new temperature highs a month earlier than the usual hottest time of year.

“In some of these places, their records are being annihilated,” Mr Phillips said. “It really is spectacular, unprecedented for us.”

Residents in the Pacific Northwest have been warned that higher temperatures could become the new normal for these areas.