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 over 115 degrees. The worst conditions were east of the Blue Ridge Mountains where the humidity was highest.

Excessive Heat in ARLINGTON, VIRGINIA
From 22-JUL-11 09:00:00 to 22-JUL-11 16:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 120 degrees were measured at Reagan National.

Excessive Heat in ALBEMARLE, VIRGINIA
From 22-JUL-11 15:00:00 to 22-JUL-11 18:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 111 degrees were measured at the Charlottesville Airport.

Excessive Heat in LOUDOUN, VIRGINIA
From 22-JUL-11 15:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 116 degrees were measured at the Dulles Airport.

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

Heat indices up to 118 degrees were measured at Quantico.

Excessive Heat in FAIRFAX, VIRGINIA
From 22-JUL-11 12:00:00 to 22-JUL-11 16:00:00 (EST-5)
Reported by: ASOS

Heat indices up to 116 degrees were measured the Dulles Airport.

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

Heat indices were estimated to be over 115 degrees based on observations nearby.

Excessive Heat in SPOTSYLVANIA, VIRGINIA
From 22-JUL-11 11:00:00 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 STAFFORD, VIRGINIA
From 22-JUL-11 11:00:00 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 KING GEORGE, VIRGINIA
From 22-JUL-11 11:00:00 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 NORTHERN FAUQUIER, VIRGINIA
From 22-JUL-11 15:00:00 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 SOUTHERN FAUQUIER, VIRGINIA
From 22-JUL-11 11:00:00 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 SHENANDOAH, VIRGINIA
From 22-JUL-11 11:00:00 to 22-JUL-11 14:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be around 110 degrees based on observations nearby.

Excessive Heat in PAGE, VIRGINIA
From 22-JUL-11 11:00:00 to 22-JUL-11 14:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be around 110 degrees based on observations nearby.

Excessive Heat in WARREN, VIRGINIA
From 22-JUL-11 11:00:00 to 22-JUL-11 14:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be over 110 degrees based on observations nearby.

Excessive Heat in CLARKE, VIRGINIA
From 22-JUL-11 11:00:00 to 22-JUL-11 14:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be over 110 degrees based on observations nearby.

Excessive Heat in NELSON, VIRGINIA
From 22-JUL-11 15:00:00 to 22-JUL-11 18:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be around 110 degrees based on observations nearby.

Excessive Heat in GREENE, VIRGINIA
From 22-JUL-11 15:00:00 to 22-JUL-11 18:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be around 110 degrees based on observations nearby.

Excessive Heat in MADISON, VIRGINIA
From 22-JUL-11 15:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be around 110 degrees based on observations nearby.

Excessive Heat in RAPPAHANNOCK, VIRGINIA
From 22-JUL-11 15:00:00 to 22-JUL-11 17:00:00 (EST-5)
Reported by: Unknown

Heat indices were estimated to be over 110 degrees based on observations nearby.

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

Heat indices were estimated to be over 110 degrees based on observations nearby.

Excessive Heat in FREDERICK, VIRGINIA
From 22-JUL-11 11:00:00 to 22-JUL-11 14:00:00 (EST-5)
Reported by: AWOS

Heat indices up to 112 degrees were measured at Winchester.