The eastern half of the United States faces an intense heat wave starting late this week and peaking next week that could produce dangerously high temperatures over a large area for an extended period. It could threaten records and place vulnerable groups of people at risk from heat-related illnesses.
Over the weekend, widespread highs in the mid-90s to around 100 — some 10 to 20 degrees above normal — will spread across the southern Plains, South and Midwest. By Monday, the heat will swell into the Ohio Valley before reaching the Mid-Atlantic and Northeast shortly thereafter.
For much of next week, a punishing combination of heat and humidity will remain lodged over the East — although some relief may arrive in the Upper Midwest during its second half.
The source of the heat is a sprawling heat dome — or strong zone of high pressure — that is centered over northern Mexico and the southwest United States, where record high temperatures are occurring in some areas. It is forecast to shift eastward this weekend and will become centered over the southeast. Next week it will drift northward toward the Mid-Atlantic while strengthening and expanding in all directions.
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Some models indicate that the heat dome could reach historic strength for the time of year. The European weather model simulation, shown above, shows its intensity even surpassing the heat dome of June 29, 2012, during which Washington set a June record of 104 degrees. It hit 109 degrees in Nashville and 105 in Raleigh, N.C., that same day.
It’s already been one of the warmest years on record in the East because of a largely absent winter and mild spring. But since the start of June, the nation’s most extreme heat has occupied the West. That’s about to change in a big way.
Brutal heat in the South this weekend
While the heat dome shifts and reconfigures over the South and southeast, the potential for record highs will arrive as soon as Friday in Atlanta and Raleigh, where temperatures could rise to near 100. Over the weekend, record highs near and above 100 should be common from Arkansas to coastal Georgia.
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As the heat dome shifts north and strengthens, record highs are probable across the Ohio Valley on Monday and into the Mid-Atlantic by Tuesday. More record heat is probable in the East after that, too.
Few areas will escape escalating heat risk
The National Weather Service has developed a new HeatRisk product, which evaluates the threat of predicted temperatures on a 0 to 4 scale. Most of the Lower 48 states will experience at least Level 2 or 3 HeatRisk levels over the next week as the heat dome evolves.
Large areas of Missouri, Illinois and Indiana as well as portions of Kansas, Iowa, Michigan, Ohio, West Virginia and Georgia are forecast to experience Level 4 or “extreme” conditions. Des Moines, St. Louis, Chicago, Indianapolis and Atlanta are some of the cities in this zone.
A Level 3 or “major” HeatRisk is forecast for Pittsburgh, New York City, Washington, Nashville, Little Rock and Wichita.
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The HeatRisk levels take into account how unusual the heat is, its duration and its potential health effects. At Levels 3 and 4, the Weather Service says the heat will pose a threat to individuals without adequate cooling and hydration. The most vulnerable groups are typically outdoor workers, the homeless, older adults and anyone without access to air conditioning.
Heat indexes to top 100 degrees over sprawling area
It’s not just the heat but also the humidity that will make this episode potentially hazardous. Heat indexes, a measure of how hot it feels factoring in the humidity, are forecast to reach 100 to 110 degrees across the South by the weekend, according to the Weather Service. Some areas near the Gulf of Mexico could even surpass 110.
The heat dome should produce multiple days of heat indexes of at least 100 from Texas to Washington, and even stretch as far north as Iowa and the lower Great Lakes.
No end in sight
This heat dome may have substantial staying power. It developed in May this year and has already been stubbornly persistent and unseasonably intense — contributing to historic heat in Mexico, the Desert Southwest, Texas and Florida.
The outlook ahead is for more of the same. While the heat dome may relax or move around, it seems likely that most of the Lower 48 will remain under its influence and see warmer to much warmer than normal weather through at least the end of June.
Jason Samenow contributed to this report.
