Utah's state capital Salt Lake City just had its equal hottest day on record as an oppressive heatwave raises bushfire concerns across the drought-weary Western United States.

A large and slow-moving upper-level high pressure system above the US has allowed extreme heat to develop across the country's western states this week. This heat is hitting one week out from the start of summer, which begins on June 21.

Image: Forecast surface temperature on Wednesday afternoon, showing extreme heat in the Western United States.

On Tuesday, June 15, the temperature at Salt Lake City reached 41.7ºC (107ºF), which was its equal highest temperature in records dating back to 1874. In this 147-year history, the only other days this hot were July 7, 2002 and July 26, 1993.

Across the border in Arizona, Phoenix Airport hit 46.1ºC (115ºF) on Wednesday afternoon as a large fire sent a plume of smoke billowing into the sky around 100km to the east.

Unfortunately, bushfires will continue to be a side-effect during this week's intense heatwave, with some of the highest temperatures occurring over areas that are experiencing a crippling drought.

According to the latest US Drought Monitor data, roughly one third of the country is in either Extreme or Exceptional Drought. These are the two highest tiers of drought rating on a six-tiered scale.

The National Weather Service has issued numerous warnings for excessive heat and fires across a broad area of the Western United States in response to this week’s heatwave.

While there are a lot of extreme and record-challenging temperatures coming out of the US this week, one of the hot spots to watch in the next few days will be Furnace Creek in Death Valley, California.

This aptly named place hit 51.1ºC on Tuesday and is forecast to reach 52-53ºC between Wednesday and Saturday. This could challenge the site's June record of 53.9ºC, although its all-time record of 56.7ºC (July 10, 1913) - which is also the current official world record – looks safe for now.