Massive heat wave bakes U.S.

Kids and adults cool off in a fountain on the Rose Kennedy Greenway on the first day of a forecasted summer heatwave in Boston, Massachusetts, July 19. REUTERS/Brian Snyder

A girl cools off in a water feature in the Navy Yard neighborhood during a heat wave in Washington, July 20. REUTERS/Eric Thayer

A man wipes his face with a cloth during hot weather in the Manhattan borough of New York, July 19. REUTERS/Carlo Allegri

A girl cools off from the heat in water from an open fire hydrant in the Washington Heights section of upper Manhattan in New York, July 19. REUTERS/Mike Segar

Birds splash in a fountain on the Rose Kennedy Greenway on the first day of a forecasted summer heatwave in Boston, Massachusetts, July 19. REUTERS/Brian Snyder

Tourists huddle under umbrellas to protect themselves against the sun in the plaza in front of the Lincoln Memorial with the Washington Monument in the background, in Washington, July 21. REUTERS/Will Dunham

Louisa Facini, 17 months old from Brooklyn, plays in a water feature in Domino Park as a heatwave continued to affect the region in Brooklyn, July 21. REUTERS/Andrew Kelly

A couple share a popsicle in High Line Park during a period of high temperatures in Manhattan, July 19. REUTERS/Lucas Jackson

Kids and adults cool off in a fountain on the Rose Kennedy Greenway on the first day of a forecasted summer heatwave in Boston, July 19. REUTERS/Brian Snyder

A woman lies in Domino Park as a heatwave continues to affect the region in Brooklyn, July 21. REUTERS/Andrew Kelly

A man in a wheelchair reaches down to touch a water feature in High Line Park during a period of high temperatures in Manhattan, July 19. REUTERS/Lucas Jackson

People play in the fountain at Washington Square Park in Manhattan, July 20. REUTERS/Gabriella Angotti-Jones

A girl plays in a fountain on the Rose Kennedy Greenway on the first day of a forecasted summer heatwave in Boston, July 19. REUTERS/Brian Snyder

Children play in the fountain at Washington Square Park during hot weather in Manhattan, July 19. REUTERS/Carlo Allegri

Children play in the fountain at Washington Square Park during hot weather in Manhattan, July 19. REUTERS/Carlo Allegri

Children play in a water feature in Domino Park as a heatwave continued to affect the region in Brooklyn, July 21. REUTERS/Andrew Kelly

A child cools off in a water feature at a park in the Shaw neighbourhood during a heat wave in Washington, July 20. REUTERS/Eric Thayer

A child plays in a fountain during a period of high temperatures in New York City, July 19. REUTERS/Brendan McDermid

A man casts his line out as he goes fishing under the Brooklyn Bridge at sunrise as a heatwave continues to affect the region in New York, July 21. REUTERS/Andrew Kelly

Children play in the fountain at Washington Square Park during hot weather in Manhattan, July 19. REUTERS/Carlo Allegri