National Weather Service United States Department of Commerce

Severe Weather Expected for Portions of the Midwest; Excessive Heat for the Central and Eastern U.S.

Severe storms capable of producing severe winds, large hail, tornadoes and heavy rainfall are expected through this evening across portions of the Midwest. A Moderate Risk (level 4 of 5) of Severe Storms and Excessive Rainfall is in effect. Excessive heat will continue to impact the Central and Eastern U.S. this week. Read More >

 

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Density Altitude

diagram Density Altitude Concept
diagram

On a hot, muggy day, the air becomes “thinner” or less dense, and its density at a pilot’s location is equivalent to a higher altitude in the standard atmosphere.  It is hazardous to aircraft during takeoff and climb because:

- Aircraft power is reduced. The engine will ingest less air to support combustion.

- Aircraft thrust is reduced.  A propeller will have less "grip" on the air, while a jet engine will will exhaust less mass.

- Lift is reduced.  The thinner air will exert less upward force on the airfoils.

As a result, a longer takeoff and landing roll is required, especially for a fully-loaded aircraft.  After takeoff, the aircraft will have a smaller rate of climb and will have a lower service ceiling.

Density altitude is usually reported at each AWOS/ASOS station in the Remarks section of the METAR, if the value is greater than 1000ft higher than the elevation of the airfield.  Here's an example:

METAR KMSY 291400Z AUTO 18006KT 10SM CLR 28/13 A3001 RMK SLP161 DENSITY ALT 1000FT

 

 

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Density Altitude