The Pacific Northwest is facing another summer heat spike, with temperatures likely to rise into the triple digits this week across parts of the region and in Northern California.

Heat advisories from the National Weather Service have been issued for Wednesday and into the weekend.

The Pacific Northwest is one of the few remaining parts of the United States where many buildings are not air-conditioned, increasing the risk of heat-related illnesses.

Widespread 90-plus temperatures are expected across central and eastern Washington and Oregon and in northern Idaho this week. Highs could reach the 100s in some areas, especially in the valleys of the Cascade Mountains in Washington state.

Overnight lows will also be warm, making it harder for the human body to cool down and potentially increasing the risk of health issues. Forecasters say the heat wave will last into the weekend.

In California, higher-than-average temperatures are expected throughout the week in the Sacramento and San Joaquin valleys, with a heat advisory in effect at least through Friday night.

The worst of the heat will be on Tuesday and Wednesday, with highs that could reach 109 degrees in the Sacramento Valley and 106 in the foothills — seven to 15 degrees above normal for this time of year, according to the Weather Service.

Temperatures will remain above average for the rest of the week, but the chances of triple-digit heat will be lower on Friday and over the weekend.