A dangerous combination of extreme heat, severe thunderstorms, flash flooding and monsoon-driven rainfall is expected to affect much of the United States through July 29, according to the National Weather Service’s (NWS) Weather Prediction Center (WPC).
While a powerful heat dome continues to bake the central and southern US, multiple storm systems are forecast to bring damaging winds, hail and flooding from the Upper Midwest to the Northeast. Meanwhile, the annual North American monsoon is triggering heavy downpours across the Southwest.
Here’s what is happening and which places are most at risk.
Why is the US facing such extreme weather?
The Weather Prediction Center says a broad upper-level high-pressure ridge, often called a “heat dome,” is parked over the central and southern United States.
High-pressure systems suppress cloud formation and trap hot air near the surface. The result is prolonged sunshine, soaring daytime temperatures and unusually warm nights that prevent people and infrastructure from cooling down.
At the same time, disturbances moving along the northern edge of the ridge are colliding with warm, humid air from the Gulf of Mexico, creating ideal conditions for severe thunderstorms.
Meanwhile, the Southwest remains under the influence of the North American monsoon, bringing moisture from the tropics that fuels heavy rainfall and thunderstorms.
Which states are under the dangerous heat wave?
The most dangerous heat is expected across:
Texas
Oklahoma
Kansas
Nebraska
Arkansas
Louisiana
Mississippi
Alabama
Georgia
Parts of Tennessee
Portions of the Southern Rockies
The Desert Southwest, including Arizona, Nevada and southeastern California
Daytime temperatures are forecast to reach:
-Upper 90s to low 100s°F (37°C-40°C) across much of the Plains and Southeast.
-Between 115°F and 120°F (46°C-49°C) in isolated parts of the Desert Southwest.
-Humidity will make conditions even more dangerous, with heat index values expected to exceed 105°F to 115°F (40°C-46°C).
-Overnight temperatures are also expected to remain unusually warm, staying in the 70s°F in many locations, increasing the risk of heat-related illness.
The Weather Prediction Center has issued Major to Extreme HeatRisk for large portions of the Southern Plains, Mississippi Valley and Southeast.
Where are severe thunderstorms expected?
A cold front stretching from the Upper Midwest into the Ohio Valley will interact with warm, humid air to produce widespread thunderstorms.
On Monday, the greatest severe weather risk covers parts of:
Minnesota
Wisconsin
Michigan
Illinois
Indiana
Ohio
The Storm Prediction Center has placed these areas under an Enhanced Risk (Level 3 of 5) for severe thunderstorms.
Forecasters warn the storms could produce:
Damaging wind gusts
Large hail
Frequent lightning
Heavy rainfall
Why is flash flooding a concern?
Heavy rain falling repeatedly over the same locations—known as training thunderstorms—could quickly overwhelm drainage systems.
The Weather Prediction Center has highlighted flood risks across:
Michigan
Ohio
Pennsylvania
New York
Vermont
New Hampshire
Massachusetts
Connecticut
Rhode Island
New Jersey
By Tuesday, a Slight Risk (Level 2 of 4) for excessive rainfall extends from parts of the:
Mid-Atlantic
Maryland
Delaware
Virginia
Pennsylvania
New Jersey
New York
New England
Urban flooding, overflowing streams and rapid rises in water levels are possible, especially where storms repeatedly move over the same communities.
Which places face the greatest severe weather on Tuesday?
As another upper-level disturbance moves into the Great Lakes, severe thunderstorms are expected farther east.
Areas under a Slight Risk (Level 2 of 5) include portions of:
Virginia
North Carolina
West Virginia
Maryland
The Appalachian Mountains
The storms may again bring:
Damaging winds
Isolated hail
Torrential rain
Localized flooding
What’s happening in the Southwest?
The annual North American monsoon continues to bring moisture into:
Arizona
New Mexico
Utah
Colorado
Parts of Wyoming
The central and northern Rockies
The High Plains
Frequent afternoon thunderstorms are expected across the Four Corners region, where Arizona, New Mexico, Utah and Colorado meet.
The Weather Prediction Center warns that burn scars from previous wildfires, slot canyons, steep mountain terrain and urban areas remain particularly vulnerable to flash flooding.
Some thunderstorms over southeast Arizona could also produce severe wind gusts.
Which other regions could see flooding?
Repeated thunderstorms are forecast along the:
Texas Gulf Coast
Louisiana
Mississippi Gulf Coast
Alabama Gulf Coast
Florida Panhandle
East Florida, including parts of the Atlantic coast
Some areas could receive up to six inches (15 cm) of rainfall, raising the risk of flash flooding.
When will the heat ease?
The arrival of a cold front will bring some relief to parts of the Midwest and Great Lakes.
However, dangerous heat is expected to persist across:
Texas
Oklahoma
Southern Kansas
New Mexico
Arizona
Louisiana
Mississippi
Alabama
Georgia
through at least the middle of the week.
What should residents do?
The National Weather Service advises people in affected areas to:
Stay indoors during the hottest part of the day whenever possible.
Drink plenty of water and avoid strenuous outdoor activity.
Never leave children or pets in parked vehicles.
Monitor weather alerts for severe thunderstorms and flash floods.
Move immediately to higher ground if floodwaters begin to rise.
