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Clifford E Carnicom
Apr 12 2001

A preliminary model has now been developed which can be used to predict whether contrails will form or not under reported meteorological conditions at flight altitude. Analytical models for contrail prediction appear to be difficult to acquire publicly, and this model is therefore offered for investigative purposes. This is an original development that results from a variety of sources and methods, including unclassified aerographic manuals, meteorological theory, least squares analysis and regression analysis. It is to be interpreted as an empirical model, and it is subject to further refinement depending on the results that are obtained from its use.

The model offered is as follows:


c + (.02c – .41)t

RHmin =



(.003c – .14)

where c = e(151 – alt) / 19. 5

and t = temperature of the atmosphere at flight altitude in degrees centigrade

and alt = altitude of the jet aircraft in thousands of feet.

RHmin is the minimum relative humidity (with respect to water per conventional standard) that is required at flight altitude for contrails to form. The contrails referred to are those classically and conventionally defined as condensation trails, i.e., composed of water vapor. A standard atmospheric model is assumed within the development. The model is intended to be used only within the range of 30,000 to 40,000 ft. MSL. The model is quite sensitive to small changes in temperature, and consequently, any errors in temperature.

Commercial flight traffic usually ranges between 35 and 37 thousand feet MSL. A representative case may be considered, therefore, at approximately 36,000 ft. MSL. Standard temperature at 36,000 ft. MSL is approximately -53.5 deg. centigrade.

This model can and will now be evaluated with actual observations in an effort to test it for reliability. Citizens are welcome to submit their own observations for inclusion if they so desire. The value of this model is to identify those meterological conditions which are supportive of conventional contrail formation. Anomalous persistent contrails and subsequent “cloud” decks that result from frequent aerosol operations can also be examined in conjunction with this model.

Contrail formation/dissipation and cloud formation are to be recognized as two separate physical processes resulting from differing conditions and variables for each. It is important that any analysis of these two processes be appropriately and separately understood before any mutual connection is to be made.

A history of observations is available on the aerosol report page.

This model is in addition to that previously developed that predicts contrail dissipation times, as well as a model to predict the distance behind the engines that the contrail is expected to form.

The model presented will be modified, revised or further developed as circumstances require.