US: High temperatures forecast across western and southwestern regions through at least July 5

Forecast models indicate excessive temperatures are likely across the western and southwestern regions through at least July 5. The US National Weather Service (NWS) has warned of high temperatures across California and Desert Southwest. Temperatures near the daily record highs are possible in parts of central California, and heat indices in the Great Valley may approach 41 C (105 F).

As of late June 30, the NWS has issued excessive heat warnings across western and southern California. Excessive heat watches are in place for southwestern Oregon and northern California. 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.