June’s weather across the United States is soon flipping into more stable conditions, especially across the eastern two-thirds of the country. A sweltering hot weather is forecast to develop and intensify a heatwave over the weekend and continue next week as a powerful Heat Dome takes place.
So far, June has brought active weather across the nation, with multiple waves supporting severe weather, as is typical late spring in the U.S. Now, the weather models are in good agreement that a significant change is coming up.
A major Heat Dome will first build up into the central U.S. by Friday and gradually expand north and east across the nation over the weekend and continue next week. Temperatures will significantly increase, and combined with high humidity, will lead to sweltering hot weather with high Heat Index.
The following animation provides an overview of the changing and developing general weather patterns across the Contiguous United States through the end of June 2025.
One can notice how a blocking High will dominate the eastern two-thirds, meaning much more stable, and hot weather is forecast.
The heat will spread across a large part of the country and become significant, particularly across the eastern U.S. Attached is the Meteogram for Washington, D.C., over the following 14 days. It reveals that some short-term refreshment will follow the ongoing frontal system before Friday, and then a rapid warming is expected to occur.
Temperatures will push much higher throughout the whole atmosphere, meaning a significant blocking ridge (High) will take place. Thus, developing a much warmer weather period with excessive heat.
So, the upcoming heatwave will be intense, and it occurs with the establishment of a heat dome aloft. Let’s examine what this large-scale feature is.
What is a Heat Dome?
When significant and historic record-breaking heatwaves occurred in Europe, the United States, and Canada 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.
When extremely high temperatures develop, we refer to this phenomenon as a heat dome. 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 very high and sometimes record-breaking temperatures to the region underneath.
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.
How does it impact the life underneath?
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 agricultural workers who work outdoors for long hours 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 upon exposure to high temperatures for extended periods. 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 a Heat Index to represent the natural feel of scorching hot temperatures and high humidity. These graphics illustrate the natural relationship between temperature and humidity.
As we can see, when the air mass has a temperature around 90°F, humidity below 60 percent is much less challenging than when the 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.
For further details on the health risks, please refer to our additional article, “Health Risks during a Heatwave and Sweltering Hot Weather.”
The upper ridge develops over the central U.S. by Friday, intensifying the Heat Dome into the weekend
The general weather picture over the Contiguous U.S. for Friday indicates a deep upper wave/low emerging into the Pacific Northwest and northern Rockies, resulting in another potential increase in the severe weather for the Northern High Plains.
To its east, a broad area of high pressure is forecast, gradually developing beneath the upper ridge. At the same time, a Heat Dome begins forming aloft. Thus, stabilizing the ridge and strengthening its core even further, trapping a much warmer air mass underneath. It leads to increased sweltering hot conditions and high humidity.
The warmest air mass first spreads across the central U.S. and Midwest from Friday into Saturday, with the highest anomalies reaching around 15 °C above normal at the 850 mbar level. Precisely across the central High Plains into the Upper Midwest and the Great Lakes on Saturday.
This translates into significantly warmer days at the surface, with temperatures already pushing into the 90s to near 100°F in some places by Saturday. And those will be further increasing through Sunday into early-mid next week as the Heat Dome aloft matures. Heat Index will exceed 100°F after Sunday in many states.
So, by early next week, the upper blocking High and ridge will mature across the eastern two-thirds of the country, with excessive hot weather trapped underneath the heat dome.
The following weather pattern chart hints at the major country’s dominance of the blocking High on Monday. Centered over the Great Lakes and Mid-Atlantic.
After multiple rounds of fronts and storms through May and June, an above-normal amount of rainfall has been observed across the central, south, and eastern parts of the United States. With the arrival of hot summer weather, hot temperatures also introduce significant evapotranspiration from the crops, combined with moist air mass advected from the Gulf.
Thus, this leads to high Heat Index values across the nation, a mixture of high temperatures and high relative humidity.
As we see on the following chart for Sunday afternoon, upper 90s to around 105°F will develop across a large part of the country. With the most extreme values across the Mississippi and the Midwest, precisely where the highest moisture will be present.
Very hot weather is forecast to continue at least through mid-next week, with the potential to last until the end of the month. On Wednesday, temperatures in the mid-90s will remain across the south-central Plains, Midwest, Mississippi, Ohio, and Tennessee Valley, as well as further east.
The Southeast U.S. and the East Coast will see particularly excessive heat, as the High aloft parks over the region for days. The air mass underneath will be ‘overheating’, which is a typical occurrence during intense Heat Dome events.
The peak temperatures on Wednesday could reach up to 105 °C across the eastern states, which is pretty extreme for late June across Georgia and the Carolinas.
This is also where the most significant Heat Index will develop. The following chart for Wednesday afternoon indicates that most eastern states are expected to experience an index above 100°F. This is the result of the overheating air mass, trapped underneath the Heat Dome since the weekend.
Above 100°F heat index is forecast across the Midwest, Ohio, and Tennessee Valley, Mississippi Valley, and will be the most excessive from Georgia across both Carolinas to Virginia and Washington D.C. on Wednesday.
After the weekend and early following week pattern, the general trends in global weather models indicate some uncertainties regarding the persistence of the heat dome. However, the general idea is that the upcoming heatwave could persist for longer and may extend into the end of June.
We will continue to monitor the evolution of the weather pattern and update the forecasts accordingly. Stay tuned.
Pivotalweather, Wxcharts, and Wetterzentrale provided images used in this article.
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