Icing AIRMETs for the coterminous United States issued during the winters of 1994-2000 are evaluated. IIDA is only available for two winter seasons, 1999-2000 and 2000-2001. Contour maps of the relative frequency of both information sources are presented for the winter season in addition to individual months. Icing conditions vary by altitude, so climatological characteristics in certain altitude ranges are also considered. Finally, these climatologies are compared and contrasted to those presented in parts I and II of this series.
None of these sources directly and systematically measure aircraft icing, so they are not ideal. However, taken together they can paint a reasonably good picture of the climatological nature of aircraft icing conditions.