As one heat wave ends in the east, another begins in the west. Sizzling temperatures in excess of 110 degrees will spread westward in the Southwest through late week. The extreme heat will build in low elevations east of the Sierra-Nevada Mountains Thursday then spread to Southern California and the Central Valley Friday.
The same upper-level high pressure system responsible for the week-long heatwave in most of the Northeast will slide and expand westward through the weekend. Unlike the heat in the Northeast however, this heat will be exceptional dry . Dew points only in the teens will exasperate the already elevated wildfire risk and worsen the growing Exceptional Drought over the Four Corners Region.
The drought will serve as a medium for a positive feedback loop to worsen the heat and the wildfire risk. Aloft, the high pressure system will expand westward, directing wind to flow over the Rocky Mountains. Moisture will be lost through evaporation up the mountain slopes and in monsoon thunderstorms in eastern Arizona, New Mexico and Colorado. By the time the wind reaches the Great Basin, air will compress and warm as it flows down mountain slopes. With the ongoing drought, there will be little moisture to begin with so air will heat faster and compress more, intensifying the heat and the high pressure system aloft. Stronger high pressure further dries the air and lowers the chance of relief from monsoon storms. At the surface, air will circulate wind down the eastward side of the Sierra Nevada Mountains Thursday, likewise compressing and heating the air to intensify the surface high pressure system.
The worst of the heatwave will be Thursday through Sunday. Temperatures of up to 115 degrees Thursday will fry cities of the Mojave and Sonoran Deserts including Las Vegas, Phoenix and Tuscon as wind heats the air down the dry Sierra-Nevada mountains. The surface high will shift westward Friday, reversing the wind direction to flow westward down the Sierra-Nevada mountains in Southern California. The wind shift will curb the maximum heat intensity to a slightly less oppressive range of 105 to 110 degrees in these deserts. Meanwhile, the infamous Santa Ana winds will bring 100-105 degree temperatures to Southern California just away from the coast to Santa Barbara, Los Angeles and San Diego between Friday and Saturday. Dry winds down the Central Valley will also spread 100 degree temperatures to cities like Fresno, Bakersfield, Sacramento and Redding between Friday and Wednesday.
Spreading wildfires throughout the heatwave will ablaze some of the foothills. They will further act to raise the air temperature and intensify low level winds down the mountains, which will increasingly dry and heat the air, expanding the range of wildfires and worsening the drought. In addition to threatening homes, smoke from wildfires with pollution trapped beneath a night-time inversion layer will contribute to dangerously poor air quality throughout much of California.
Some relief may tone down the heat in parts of the Southwest with thunderstorms from monsoon winds. Isolated to scattered thunderstorms will form over the Four Corners region. Most of the storms will develop just east of the most intense heat in Western Colorado, New Mexico, southeastern Utah, and eastern Arizona. Some of the storms will spread to Phoenix and Las Vegas by Saturday with slight rain chances persisting through next weekend. Unfortunately, these storms will stay east of the Sierra-Nevada mountains. Only the Mojave desert of southern California is expected to receive rain and temporary heat relief from these storms, leaving conditions ripe for drought and wildfires in the Central Valley.