US: High temperatures forecast to continue across western, northwestern, and southwestern regions through at least July 12 /update 2

Forecast models indicate excessive temperatures are likely to persist across western, northwestern, and southwestern regions through at least July 12. Temperatures of up to around 38-46 C (100-115 F) are possible across parts of the affected area, with even higher temperatures possible in the Desert Southwest. A slight cooling is expected in Pacific coastal areas over the coming days as the expanse of heat shifts eastward inland. The US National Weather Service (NWS) has warned that the combination of high temperatures and high relative humidities will produce potentially major to extreme heat impacts over the coming days. Record high temperatures are possible through parts of the region. Fire risks will also be a threat due to the combination of hot temperatures and very low chances of precipitation.

As of early July 8, the NWS has issued excessive heat warnings across parts of central, northern, and southern California, eastern, northern, and western Oregon, central and eastern Washington, north-central and western Idaho, central, northwestern, southern, and western Nevada, far southern Utah, and southern and western Arizona. Excessive heat watches have been issued for parts of eastern and southeastern Idaho, northeastern Nevada, and northwestern southern, and western Utah. Heat advisories are in place across much of the rest of the affected area. Minimum nighttime temperatures will also be well above average for the time of year, providing little relief from the excessive heat. Officials could update and extend the coverage of weather alerts over the coming days.

The high temperatures may result in increased energy and water demand and an increased risk of heat-related illnesses such as heat exhaustion and heat stroke. Authorities advise the general public to avoid prolonged exposure to direct sunlight, wear loose and light clothing, and stay hydrated.

The extended period of oppressive heat and dry conditions may produce ideal circumstances for wildfire growth throughout the region. Heatwaves also pose a threat to vulnerable groups - such as the elderly, children, pregnant women, and those with respiratory illnesses - due to the increased possibility of heat stroke or heat exhaustion during prolonged exposure to high temperatures. These health risks could also extend to relatively healthy individuals during significant heatwave events.

Very high temperatures may warp rail tracks and force passenger and freight trains to operate at reduced speeds. Road surface damage is also possible, and overheated vehicles may worsen traffic problems in urban areas where congestion is already a problem. Commercial trucking disruptions might occur as very high temperatures put more stress on vehicles, making tire blowouts more common. Major flight disruptions are unlikely, but general aviation disruptions are possible, and some airfreight carriers could reduce cargo loads. High temperatures could lead to an increased demand for electricity, which might trigger localized brownouts or blackouts, exacerbating hazardous conditions when air conditioning is no longer possible.