The US National Weather Service maintained warnings for excessive rain and potential flash and urban flooding in the central High Plains into the Upper Midwest for Wednesday, with risk of hail and damaging winds.
The NWS also warned that extreme heat over the Desert Southwest would continue until at least Thursday.
Red flag warnings were in place over critical fire risk in Central to eastern Washington, covering Omak, Colville, Winthrop, Chelan, Wenatchee, Moses Lake, Ritzville, Pullman and Spokane.
Puget Sound Energy is one of the main power providers in Washington State.
In southwestern Idaho, thunderstorms, excessive rainfall as well as extreme heat would be experienced on Wednesday in areas including Twin Falls, Jordan Valley and Burley.
The thunderstorms are expected to be severe and capable of yielding large hail and damaging winds. The extreme heat will be experienced in the Desert Southwest.
Idacorp's (IDA) Idaho Power and PacifiCorp's Rocky Mountain Power are the main service providers in the state.
A heatwave expected in Utah looks strong enough to have prompted a red flag warning covering Nephi, Delta, Manti, Millford, Cedar City, Escalante, Bryce Canyon National Park, Zion National Park, St. George and Richfield.
Rocky Mountain Power is the main electricity provider in the state.
In Arizona, the NWS continued to warn of an extreme heat wave, with temperatures potentially reaching 115 degree-Fahrenheit (46 Celsius), with potential dangers for human health. The warning applies unti Thursday evening.
Areas covered by the warning are Gila Bend, Ajo, Tucson, Globe, Casa Grande, Sells, Green Valley, Satford, Oracle and San Carlos.
The state is primarily served by Pinnacle West Capital (PNW) unit Arizona Public Service, and UNS Energy subsidiaries Unisource and Tucson Electric Power. UNS is a subsidiary of Fortis (FTS).
The warning stretched to across the border to California's El Centro, Desert Center and Blythe.
The primary service provider there is Edison International's (EIX) Southern California Edison.