A sizzling summer week looms for Western Montana as a "massive" ridge of high pressure takes hold of the Northern Rockies.

The heat wave packing dangerously hot conditions settles over the region this weekend with triple-digit temperatures possible by the middle of next week. An excessive heat watch in place for the Kootenai and Cabinet region of far Northwest Montana and the Lower Clark Fork region of Sanders and Mineral counties from July 9-13.

"The middle of next week looks to be the hottest period, with valleys in central Idaho hitting the 100-115 degree range and western Montana valleys reaching 90-105 degrees by next Wednesday," the National Weather Service in Missoula warned in its forecast Thursday.

Overnight lows will only cool into the 50s or 60s, "which will make it difficult for those without air conditioning or other means of cooling down to find relief from the heat."

Libby could top out at 103 during the peak of the heat wave. Missoula is also facing highs in the low 100s. The hottest days for Kalispell will be from July 10-13 as highs hit 96.

Heat exhaustion or heat stroke will be possible.

"This level of heat affects anyone without effective cooling and/or adequate hydration," the Weather Service warned, adding that some infrastructure could be affected as well.

"Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors," the Weather Service continued. "Do not leave young children and pets in unattended vehicles. Car interiors will reach lethal temperatures in a matter of minutes."

A chance of thunderstorms returns by next Thursday.