HEADLINERS:
Heat and air quality issues expand to cover parts of B.C., and most all of Alberta and Saskatchewan.
Heat shifts toward the Northern Rockies/Northern High Plains.
Thunderstorms with heavy rainfall are expected in the Four Corners region and from the western Gulf Coast into parts of the East.
A strong Pacific storm will drench Northern California through midweek. An Arctic front follows this weekend with much colder air and a wintry mix for parts of the Great Lakes, Northeast, and Northern Plains.