At least two students at Magruder High School in Rockville were treated for heat exhaustion Wednesday as temperatures soared to record highs, said Montgomery County Fire & Rescue officials.
Two 8th-grade girls passed out during a choral festival in the school, officials said.
After weeks of chilly weather that included snow during many area schools' spring breaks, the heat arrived so suddenly Wednesday that some public buildings -- including the Rockville school -- hadn't turned on their air-conditioning yet.
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The D.C. area hit a record high temperature of 91 degrees in D.C., said Storm Team 4 Meteorologist Doug Kammerer.
The mercury rose steadily throughout the day, making it into 60s around dawn and hitting 86 degrees by noon.
The previous record temperature for April 10 was 89 degrees, set in 1922. The record high temperature for April is 95 degrees.
In the District, library officials decided to close nine of the city's 26 libraries "based on comfort levels for customers and staff," they said.
The shuttered libraries are: Deanwood, Juanita E. Thorton/Shepherd Park, Lamond-Riggs, Southeast, Southwest, Takoma Park, Watha T. Daniel/Shaw, West End and Woodridge.
The warm weather has led to high pollen counts in the region, particularly from maple, juniper and elm trees.
However, it has also caused the cherry trees that famously line D.C.'s Tidal Basin to bloom at last.
Just a week ago, temps were in the 30s and 40s, with tourists wrapped up in down jackets. On Wednesday, T-shirts and shorts were a far more common sight.
"I love it," said a man enjoying a run with three friends.
"Spring's out. We're going to enjoy the moment," said a woman visiting the Tidal Basin.
During the National Cherry Blossom Festival, as many as 1.2 million people are expected to check out the blossoms. The trees are considered to be in peak bloom now.
We want to see your Cherry Blossom pictures! Tweet them to @nbcwashington with #nbcblossoms.