The National Weather Service has upgraded today’s heat advisory to an excessive heat warning for Washington, D.C. and Baltimore and close-in suburbs. Temperatures are likely to be hotter than previously anticipated, prompting the more serious alert.
A heat advisory is issued when the heat index is forecast to reach 105, whereas an excessive heat warning is issued for hazardous heat indices of 110 or higher.
The advisory was not upgraded to a warning in the northern and eastern suburbs of D.C. (including Prince George’s, Montgomery, Howard, and Anne Arundel counties), nor in the suburbs of Baltimore - where heat indices may remain just under warning levels.
An excessive heat warning means a prolonged period of dangerous heat will occur. You are urged to drink plenty of fluids, stay in air-conditioning, stay out of the sun, and check on relatives and neighbors, especially older adults and the sick. Outdoor workers should take special precautions to reschedule strenuous activity to early and late in the day and hydrate liberally.
Current temperatures support the upgrade. At 10:00 a.m., the temperature at Reagan National Airport had already risen to an incredible 96 degrees, 11 degrees higher the 9 a.m. temperature of 85. The heat index, factoring in humidity, was up to 101 degrees. (Note: Mark Richards, the weather observer at Reagan National Airport, said it was up to 97 at 10:10 a.m.)
The record high today of 101 at Reagan National airport, set in 1934, is likely to be threatened. The all-time June high of 102, set in 1874 and 2011 is also in jeopardy.
These conditions have arisen from massive, record-setting heat dome sprawled across the eastern half of the U.S. Heat advisories or heat warnings are in effect in 25 states and the District.