Strong upper-level high pressure built over the region during the 22nd. Surface high pressure over the Atlantic Ocean caused moist air to move into the region from the south. Strong subsidence underneath the upper-level high caused extremely hot conditions with air temperatures over 100 degrees. The combination of the heat and high humidity caused heat indices to soar up to as high as 120 degrees. The worst conditions were across eastern Maryland where the humidity was highest.
Numerous reports of heat-related illnesses were were received by State Health Authorities on the 22nd.

Excessive Heat in PRINCE GEORGES, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: AWOS

Heat indices up to 118 degrees were reported at Andrews Air Force Base. A fatality was reported due to the high heat.

Excessive Heat in CARROLL, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: AWOS

Heat indices up to 114 degrees were reported at Westminster.

Excessive Heat in WASHINGTON, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 110 degrees were reported at the Hagerstown Airport.

Excessive Heat in FREDERICK, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: Unknown

Heat indices in excess of 115 degrees were estimated due to observations nearby.

Excessive Heat in NORTHERN BALTIMORE, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: Unknown

Heat indices in excess of 110 degrees were estimated due to observations nearby.

Excessive Heat in HARFORD, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: Unknown

Heat indices up to 120 degrees were estimated due to observations nearby.

Excessive Heat in HOWARD, MARYLAND
From 22-JUL-11 11:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: Unknown

Heat indices in excess of 115 degrees were estimated due to observations nearby.

Excessive Heat in CHARLES, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: Unknown

Heat indices in excess of 115 degrees were estimated due to observations nearby.

Excessive Heat in CALVERT, MARYLAND
From 22-JUL-11 11:00:00 to 22-JUL-11 19:00:00 (EST-5)
Reported by: Unknown

Heat indices in excess of 110 degrees were estimated due to observations nearby.

Excessive Heat in CENTRAL AND EASTERN ALLEGANY, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: Unknown

Heat indices in excess of 110 degrees were estimated due to observations nearby.

Excessive Heat in SOUTHERN BALTIMORE, MARYLAND
From 22-JUL-11 09:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 123 degrees were measured at the Maryland Science Center. A fatality was reported due to the high heat in the city of Baltimore.

Excessive Heat in ST. MARY'S, MARYLAND
From 22-JUL-11 11:00:00 to 22-JUL-11 19:00:00 (EST-5)
Reported by: AWOS

Heat indices up to 114 degrees were measured at Patuxent River.

Excessive Heat in MONTGOMERY, MARYLAND
From 22-JUL-11 11:00:00 to 22-JUL-11 15:00:00 (EST-5)
Reported by: AWOS

Heat indices up to 117 degrees were measured at Gaithersburg.

Excessive Heat in ANNE ARUNDEL, MARYLAND
From 22-JUL-11 10:00:00 to 22-JUL-11 16:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 117 degrees were reported at the BWI Airport.