Persistent Heat Dome Dominates US Weather: 110°F+ Highs Forecast Into Early August

A high-amplitude upper-level ridge is locking another major Heat Dome over the United States, driving peak afternoon temperatures past 105°F to 110°F across the Southwest and central plains into early August. Supported by deep atmospheric compression, the persistent warm plume is sending upper-air thermal anomalies into the 99th percentile, stretching dangerously high heat indices from Southern California across the Great Plains to the Mississippi Valley. The atmospheric feature behind this multi-week thermal spike is a strong high-pressure system trapped over the western and central states. Desert basins will face the most extreme impact with peak highs reaching 115°F to 120°F, while overnight lows struggle to drop below 75°F to 80°F in major urban corridors. This lack of nocturnal cooling compounds physiological strain on vulnerable populations and skyrockets power grid demand. Furthermore, the persistent excessive heat is rapidly accelerating soil moisture depletion across major agricultural belts. The expansion of the upper-level ridge is nicely visible in the video below, which highlights where the highest 850 hPa temperature anomalies will cluster over the coming days and extend into early August. Atmospheric Dynamics: How High-Pressure Heat Domes Compress and Trap Air When significant, record-breaking heatwaves occurred in the United States, Canada, and Europe in the past, the Heat Dome was a contributing factor. The heat dome is usually the dominant feature of summer weather patterns on both continents. We refer to this phenomenon as a heat dome when extremely high temperatures develop. Here’s how it works and why understanding it on a broader scale is essential. The upper-level ridge pattern, or very warm air mass in the higher altitudes, also known as the Upper High (or blocking High), usually forms the heat dome. This weather pattern brings high, and sometimes record-breaking, temperatures to the region below. This term is used when a broad area of high-pressure air parks over a large portion of the continent. If the event is remarkably stable and extreme, it usually lasts several days or weeks. The heat dome works like a lid on a pot. The extensive dome traps warm air at all levels underneath, with layers sinking toward the ground. Therefore, the air mass becomes anomalously warm at the lowest elevations and extremely hot near the surface. Health and Grid Impacts: Managing Nocturnal Heat Stress and Heat Index Extremes Excessive heat in heat domes can significantly impact human health and be dangerous to particularly vulnerable populations, such as elderly individuals, children, and those with pre-existing health conditions that can be worsened by extreme heat. Due to prolonged exposure to high temperatures, construction workers, farmers, and other long-hour outdoor workers are at increased risk of heat-related illnesses. People living in poverty are also more susceptible to the fatalities of heat domes, as their houses are often built with heat-trapping surfaces such as concrete and asbestos. Heat exhaustion occurs with prolonged exposure to high temperatures. It leads to dehydration, dizziness, and, in more severe cases, heat exhaustion can progress to heat stroke. High relative humidity during a heatwave can also significantly affect the body. For this reason, we use the Heat Index to represent the perceived feel of scorching-hot temperatures and high humidity. It illustrates the natural relationship between temperature and humidity. As we can see, when the air mass has a temperature around 90°F, humidity below 60% is much less challenging than when humidity is very high, e.g., above 80%. Thus, the actual feel temperature would be near 113 degrees F. Heat waves have also been associated with increased rates of heart attacks, strokes, and respiratory illnesses. Our additional article, Health risks during a heatwave and sweltering hot weather, provides further details on the health risks. Synoptic Setup: Multi-Week Heat Dome Expands Across the Western and Central US The general weather picture over the Contiguous U.S. through early August indicates a persistent strong upper-level ridge sitting over the Western US and the Northern Rockies into southern Canada. To its east, a shallow low is traveling east from the mid-Mississippi Valley towards the Southeast US. Strong ridging remains stable for multiple days through early August and results in excessive heat from the desert Southwest US through the northern High Plains into Alberta and Saskatchewan, Canada. The warmest air mass is trapped underneath the core of the heat dome aloft, spread across California, Arizona, Nevada, through Utah into Idaho, Wyoming, and Montana. A particularly intense heat develops over Alberta through the weekend. The subsiding air mass under the ridge translates into significantly warmer surface temperatures, with readings already pushing into the mid-90s to near 100 °F in some places this week. And those will continue to increase through Sunday as the Heat Dome aloft traps more heat and pushes daytime peaks towards 105°F. The following chart hints at peak temperatures on Thursday (upper) and Saturday (bottom) afternoon: upper 90s to around 103°F are expected across the Great Plains. The most extreme values are from Texas across Oklahoma to Kansas, peaking into the low 100s °F on Thursday through Saturday. The air mass warms up significantly more over Montana, Wyoming, and the western Dakotas on Saturday as the dome aloft is the strongest. Afternoon peaks should push from 103°F to possibly close to 110°F. Extreme heat continues over the desert Southwest US, with daytime highs from 112°F to 120°F in some of the valleys. Scorching hot weather is forecast to continue into Sunday and Monday, extending into early August. Sunday should bring daytime peak temperatures from upper 90s °F to low 100s °F all across the Plains from Texas to the Dakotas. Arizona, Nevada, and California remain baking with highs from 115°F to 120°F. By Monday, the hottest air mass will push more towards the central and southern Plains, with peaks from 100°F to 105°F across New Mexico, Texas, and the Colorado High Plains. After the weekend and early following week pattern, the general trends in global weather models indicate cooler temperatures spreading from Canada, where a frontal system moves east early next week. This should cool down temperatures in the northern High Plains through Wednesday. We will continue to monitor the evolution of the weather pattern and update the forecasts accordingly. Stay tuned for updates. PivotalWeather and WXcharts provided images used in this article. See also: Super El Niño Is Now Breaking Into the Atmosphere as July Forecasts Show a Pattern Shift for the U.S. and Canada