Intense heat is beginning to develop across the Desert Southwest and will spread northward through the Great Basin and Central Valley of California; before it's over, the Pacific Northwest will also be enveloped in the swath of hot air.
The culprit is an atmospheric ridge, a northward bowing of the jet stream along the outer rim of a high pressure dome. Within the ridge (beneath the dome), sinking air heats up and dries out and cloud formation is impaired; Santa Ana winds may also develop in Southern California. Triple-digit heat is forecast for much of the region, with upper 90s (F) expected in Oregon and Washington. Meteorologists warn that the high pressure ridge will remain in place through the upcoming weekend.
As one might expect, the Western heat wave is tied (meteorologically) to the Texas floods. East of the ridge, the jet stream dips southward and this trough has spawned an upper level low over central Texas. Counterclockwise winds around the low are combining with clockwise winds around a high pressure dome over the Southeast, pulling copious Gulf moisture across East Texas, Louisiana and the lower Mississippi Valley. Once this atmospheric pattern shifts eastward, the flooding rains in Texas will cease and the Western heat will abate.