Aircraft Icing Environment in Low Ceiling Conditions near Washington, D.C.

Abstract

Radiosonde temperature and humidity data were used to deduce the vertical distribution of clouds and aircraft icing conditions near Washington, D.C. when low ceilings occurred with surface temperatures near freezing. Twenty-three soundings from 12 cold, low ceiling episodes during the winter of 1981/82 were examined for this study. Results indicate the following: (a) generally, a deep, apparently unbroken cloud layer existed above the low ceilings; (b) typically, a cold surface layer existed under a relatively strong inversion; (c) while icing conditions above the cold, low ceilings are mitigated by inversion or isothermal layers, 70% of the cases still required flight into significant icing conditions; and (d) local geographic effects can noticeably influence ceiling height and visibility. Automated predictions of the icing probability, type, and.severity were generated from the radiosonde data and were supplemented with pilot reports; reasonable agreement was found.