The United States is being blanketed by a massive heat dome, with millions of people facing life-threatening temperatures as meteorologists predict extreme heat for several days in some regions through the Fourth of July holiday weekend.
The event is likely to affect much of the central and eastern United States, as high heat, combined with high humidity and abnormally warm nights, could result in life-threatening conditions, according to weather officials. When humidity is added to the heat index calculation, temperatures could reach 110°F to 115°F in the areas most at risk.
Hundreds of cities are opening cooling centers, modifying holiday activities, and urging residents to get ready for what could be the largest heat wave of the season in dozens of states as the National Weather Service expands heat alerts.
The temperature rises in the Midwest and moves eastward.
The heat wave of the week started to strengthen over the Plains during the weekend, then increased in strength across the Great Lakes early this week. The hot air mass has then propagated eastward, with an increasing number of communities being placed under threat of extreme heat conditions every day.
The heat index hit 101°F on Monday in Chicago, and was at its highest in the most severe conditions in the first major city to experience them. Authorities set up cooling centers and set out to reach those in need because meteorologists predicted the nighttime heat would stay high for much of the week.
In contrast to the typical summer hot spell, which subsides in the evening, overnight temperatures in parts of the Midwest will be in the upper 70s and will not allow for the cooling of homes, roads, and buildings. This residual heat may cause a greater physical strain on the body and predispose one to heat-related illness for a few days in a row.
The National Weather Service is forecasting a high risk of severe weather to persist in areas throughout the Great Lakes region, including portions of Illinois, Michigan, Wisconsin, and Ohio, throughout the week. As the week continues, more Americans will fall under heat alerts.
Already, over 100 million Americans are in heat alerts, and that could increase significantly on Thursday as the heat begins to reach the Northeast, Mid-Atlantic, and parts of the Southeast from the Midwest. As the weather system moves to the east, it is expected to affect more people, forecasters say.
By that time, at least some of the anticipated 250 million could find themselves under at least some amount of extreme heat from the northern Plains to the Atlantic Coast and south to Florida.
Prolonged periods of high heat index values are expected in communities across Indiana, Missouri, Kentucky, Tennessee, and Iowa, with a few communities expected to top 105°F.
Several days of intense heat are forecast for the East Coast cities.
The heat dome will continue to move east, leaving some of the nation’s biggest cities facing several days of extreme heat.
Temperatures may reach as high as 100 degrees F from Wednesday through Saturday in Washington, D.C., possibly setting a long-standing record of four days in a row of hot weather.
Heat indices are expected to exceed 100°F in New York City for a few days. To that end, Mayor Zohran Mamdani announced an “unprecedented, historic heat emergency plan” to aid residents in dealing with the dangerous situation.
With temperatures reaching 104°F, Philadelphia may soon reach record highs for the month of June.
Some of the hottest weather of the season is forecast for Boston, Baltimore and Richmond ahead of the holiday weekend.
A heat dome is causing the extended event
The high-pressure ridge in the upper level of the atmosphere dubbed a “heat dome” is being blamed for the heat being felt across the entire region, meteorologists said.
The system circulates hot air near the surface of the earth and keeps cooler air from entering into the area. Every day, the air mass is further warmed by the sun, so that the sun continues to warm the air mass and no cooling occurs.
Add to this the high humidity. While many communities will report temperatures in the upper 90s or low 100s, the increased humidity in the air will make it much hotter.
The eastern half of the country is extremely hot, with the western half of the Pacific Northwest and northern Rockies staying considerably cooler than normal. Other areas face other weather risks such as extreme thunderstorms, flooding and high fire danger.
Government officials pay particular attention to safeguarding vulnerable residents
As the hot season has continued, local governments throughout the impacted states have already started putting measures in place.
Cooling centers have opened in several cities, emergency management agencies have stepped up public messaging and health workers are asking residents to make sure they check up on elderly, neighbors and anyone who doesn’t have reliable access to air conditioning.
In Philadelphia, officials had to cut part of an Independence Day parade short due to the hot forecast.
The Ohio governor asked people to reach out to neighbors in need, and emergency personnel in multiple states urged people not to engage in unnecessary outdoor activities during the hottest part of the day.
Experts still say that the No. 1 killer of weather-related deaths in the United States is heat. The biggest risk is when extreme temperatures come in back-to-back, and nights are warm enough to keep the body from recuperating.
The reason why overnight temperatures are significant.
A key part of this heat wave is that it does not feature any nighttime cooling.
Homes, roads and the human body typically “catch up” with the heat of the day during the night. Many urban areas will stay close to 80° F overnight, as concrete and buildings will release the heat absorbed during the day.
Long-term exposure makes dehydration, heat exhaustion and heat stroke more likely, especially for older adults, young children, outdoor workers and those with chronic medical conditions.
Decades of states are currently under heat warnings and alerts.
Extreme Heat Warnings and Watches are in effect, as well as Heat Advisories, in most of the central and eastern United States.
Alerts are in effect for portions of Michigan, Illinois, Indiana, Missouri, Kentucky, Ohio, Iowa, Wisconsin and the surrounding states as the heat rolls east, and other alerts are in effect for much of the Northeast, Mid-Atlantic and Southeast.
Some areas under Extreme Heat Warnings could experience heat index values approaching 112°F.
Will there be any relief before the holiday weekend?
The forecast models show the hottest weather between Thursday and Saturday, with Fourth of July festivities in full swing in the country.
Scattered showers and thunderstorms are expected over parts of the Northeast late Friday through Saturday, but they are not expected to be widespread or persistent enough to bring much relief.
Some relief from the heat is expected in parts of the northern Northeast on Sunday as the heat dome starts to weaken and move to the west. Despite this, above normal temperatures will remain across most of the South, Mid-Atlantic and Great Plains through next week.
Until that happens, officials will keep urging residents to drink water, keep cool in air-conditioned buildings if available, avoid outdoor work during the hottest parts of the day, and watch for the signs of heat-related illness.
