U.S. Forecasters Predict Record Summer Heat as El Niño Strengthens

New data released on Tuesday showed the first six months of the year were the hottest ever measured for parts of eight western states. A heatwave is underway in the east, with the National Weather Service forecasting temperatures that could approach all-time highs from Washington DC to New York over the 4 July weekend.

Sweltering heat indexes topping 115F (46C) are expected. This week's heatwave will affect more than 100 million people and is intensified by the growing influence of El Niño and a massive drought affecting 45 states.

Across the western U.S., numerous wildfires have broken out, including in the mountains of Colorado. Local officials have been working for months to strengthen preparations for what is expected to be a brutal fire season, including sourcing additional equipment and seeking federal support from the U.S. Wildland Fire Service.

Last week, high temperatures were in the 90s in Seattle and Portland, Oregon, about 20F warmer than usual. A state climatologist said snowpack is very low across the western U.S. and that low April snowpack is tied to higher risk of mountain wildfires.

In the Colorado River basin, water levels are on pace for new record lows and have triggered new mandatory water restrictions affecting Nevada and Arizona. Later this summer, water levels could fall below critical thresholds needed to continue operating major hydropower dams along the river.

Wildfires in Colorado and other western states have already begun sending persistent smoke plumes toward the midwest and eastern states. Minnesota, Wisconsin and Michigan have warned residents about a heightened potential for unsafe air quality from wildfire smoke this summer.