The first significant heat wave of the summer is expected to bring 90-degree and triple-digit temperatures to much of Southern Oregon and Northern California this weekend, prompting heat advisories across several west side valleys, coastal areas and parts of far Northern California.

Southern Oregon will move from showers, breezy nights and possible frost east of the Cascades to its first significant heat event of the season. Temperatures may reach 101 degrees in Medford and Grants Pass by Sunday, while forecasters urge residents to prepare for heat-related illness and remember that area rivers and lakes remain dangerously cold.

Cooler weather arrives Wednesday across Southern Oregon and Northern California as a compact low and cold front move through the region. NWS Medford says temperatures may fall 10 to 15 degrees compared to Tuesday, with light showers possible along the coast and parts of the inland region.