The heat has been attributed to a dome of atmospheric high pressure over the upper U.S. Northwest and Canada, similar to conditions that punished California and southwestern states earlier this month. The Canadian city of Vancouver also set an all-time heat record on Sunday and was not expected to cool off until Tuesday. Temperatures were expected to shatter records in the Pacific Northwest again on Monday, bringing the city of Portland to a standstill as residents hunkered down in air conditioned homes or cooling centers. One day after Portland saw temperatures reach 112 degrees F (44.5 degrees Celsius) on Sunday, the hottest recorded there since daily record-keeping began in 1940, the National Weather Service predicted more of the same for Monday.