Climatology, Seasonal Weather and Flight Planning Meteorology
Global and regional climate
Know the general circulation: the equatorial trough with the intertropical convergence zone (ITCZ), the subtropical highs with descending air and deserts, the mid-latitude westerlies with travelling depressions, and the polar highs. The ITCZ migrates seasonally, bringing the wet season to the tropics. The Asian monsoon reverses seasonal winds and brings heavy rain in summer. In the northern hemisphere, the polar front jet stream steers depressions and is strongest in winter, when the temperature gradient is greatest.
Seasonal weather and aviation planning
Seasonal patterns matter for flight planning. Winter brings radiation fog in moist valleys, low stratus in anticyclones, and strong jet streams. Summer brings convective activity, thunderstorms and hail, especially in the afternoon. Tropical revolving storms form over warm oceans (sea temperature above about 27°C) and require avoidance. Easterly waves affect the tropics. Know the difference between climatology (long-term averages) and a forecast.
Planning traps
Candidates mix up the ITCZ with the subtropical high, or forget the seasonal migration of the ITCZ. They also forget that the jet stream is stronger in winter and that the tropopause is higher in the tropics, which affects cruise levels and turbulence. Always check the relevant charts, winds aloft and significant weather for the route and time.
Worked example
Planning a flight across the North Atlantic in January, expect a strong polar front jet with a large tailwind eastbound and headwind westbound, plus CAT risk near the jet. Choose a route and level that exploit or avoid the jet accordingly, and check SIGMETs for turbulence and icing.