Southwest US Braces for Record-Breaking Heat Wave Under Dome of High Pressure

A heat dome is expected to bring extreme heat to the US Southwest this week, testing temperature records and affecting 7.5 million people. Phoenix is forecast to reach 117F on Thursday, matching its all-time high for August. The heat is due to a high-pressure system blocking cloudier conditions and is increasing the risk of wildfires. Temperatures are expected to ease by the weekend.

Extreme heat is expected to sear the US Southwest this week, with temperatures testing records and affecting approximately 7.5 million people. Phoenix, in particular, is forecast to reach 117°F (47°C) on Thursday, matching its all-time high for August [1]. This heatwave is driven by a high-pressure system that blocks cloudier conditions, allowing temperatures to soar [2].

The National Weather Service predicts that the heat will ease by the weekend, with Phoenix only reaching a high of 108°F (42°C) on Saturday [1]. Heat advisories stretch from Anaheim to the Mexican border, sparing larger coastal cities like Los Angeles and San Diego [1]. Further east, heat advisories extend across the mid- to southern Great Plains from South Dakota to Texas, where temperatures could push into the 90s and Dallas may reach 100°F (38°C) on Friday [1].

The heatwave is not only a concern for residents but also for energy demand. The hot, dry air is boosting energy demand and elevating the risk of wildfires. The US Storm Prediction Center calls for elevated fire weather conditions across parts of Arizona and a more severe critical threat through Utah, Colorado, and Wyoming [1].

The heatwave is expected to bring record-breaking temperatures to the region, with Phoenix, Tucson, and Winslow all forecast to experience record highs. Phoenix's forecasted high of 117°F (47°C) would break the daily record by 5 degrees and tie an all-time record for the month [2].

The heat dome is likely being driven by the Madden-Julian Oscillation (MJO) feature, which has been affecting the region this summer. This feature has led to an unusually strong area of high pressure over the Southwest, resulting in the intense heatwave [2].

The heatwave also coincides with an unusually dry summer in the West, which is exacerbating wildfire risks. Multiple large wildfires are already burning across the region, particularly in Utah, where the governor has declared a 30-day state of emergency due to wildfires and drought [2]. The hot, dry, and at times breezy conditions are expected to worsen the fire weather situation this week, with critical fire conditions outlooked for much of Utah Monday and Tuesday [2].

The heatwave is expected to bring a few days of relief from the worst of the heat this weekend, but hot and dry conditions are expected again much of the following week [2].

References:
[1] https://www.bloomberg.com/news/articles/2025-08-07/a-heat-dome-is-about-to-test-temperature-records-in-us-southwest
[2] https://balancedweather.substack.com/p/major-late-summer-heatwave-for-the