Near record heat in some parts of the region Monday — with temperatures topping out at 98 degrees at Baltimore-Washington International Marshall Airport — turned Memorial Day cookouts into cook-ins and sent more than a dozen parade-goers and baseball fans to area hospitals with heat-related illnesses.

Pete Piringer, the spokesman for the D.C. fire department, said 12 people were transported to hospitals after being stricken with illnesses such as heat stroke and exhaustion during the National Memorial Day Parade along Constitution Avenue. Six others became ill in the stands at the Washington Nationals game.

Monday’s temperature of 98 degrees at BWI tied the record for 1991, with temperatures reaching 96 at Reagan National Airport and 93 at Dulles International Airport.

Jason Samenow of The Washington Post’s Capital Weather Gang said Tuesday’s outlook is even worse — with hot and muggy conditions and temperatures between 93 and 97 degrees. No relief is forecast until at least Wednesday, when showers are expected later in the day. The National Weather Service has issued a heat advisory for the Washington and Baltimore region that is in effect until 8 p.m. Tuesday.

Officials advised residents to stay hydrated and spend time in cool public spaces if they don’t have air conditioning.

Dan Stillman, also on The Post’s weather team, said early season heat waves are especially dangerous because people’s bodies aren’t used to or ready for the heat.