Baltimore broke an 85-year-old heat record Wednesday when the temperature reached 91 degrees, the highest ever recorded on April 15 in the city, according to the National Weather Service.

Andrew Snyder, a meteorologist with the weather service’s Baltimore/Washington office, said the city’s last record was set in 1941 at 88 degrees. He added temperatures could still tick up late Wednesday afternoon.

The record-breaking day comes as a spring heat wave settles over much of the eastern United States. While high temperatures will continue in Maryland this week, Wednesday is expected to be the hottest day.

Thursday’s temperatures are expected to reach 91 in Central Maryland. The record high for April 16 in Baltimore is 90 degrees, set in 2012.

Samantha Timmers of the weather service said spring has featured persistent high pressure, largely undisturbed due to a lack of rain.

“And when that happens, it just gets warmer and warmer,” she said.

People working outdoors should be extra cautious as dry heat can sneak up on you, Timmers said. It’s important to stay hydrated.

The weather service and county officials also warned of possible elevated fire conditions Wednesday afternoon.

Commuters on MARC trains may experience 10- to 15-minute delays on the Camden and Brunswick lines until 7 p.m., according to the Maryland Transit Administration. Trains will travel at reduced speed due to the heat.

CSX Transportation, the owner of the Brunswick and Camden lines, reduces the maximum speed of trains by 20 mph whenever temperatures reach 85 degrees.

When steel tracks heat and expand, they can buckle or snap out to the side. Trains cannot move when this happens. Slowing trains down creates less pressure on the steel, which means less force that could cause buckling.

Temperatures are forecast to cool down Friday and over the weekend as a cold front moves into the region, bringing some much-needed rain.

The heat wave will drive temperatures up across the eastern U.S. for an unusually long time, likely shattering records from Georgia through the New York City area.

“That’s borderline unprecedented as far as the duration of it this time of year,” said John Feerick, senior meteorologist at the forecasting firm AccuWeather.

Early-season heat can be more stressful on people’s bodies as they haven’t acclimated yet.

The Associated Press contributed to this story.