Final answer:
A winds aloft forecast omits the wind speeds and directions at lower altitudes, usually near the Earth's surface. This is because surface friction and the primary focus on aircraft navigation make it difficult to accurately predict these values. Surface winds can be obtained from other weather observations such as weather stations and radar.
Step-by-step explanation:
A winds aloft forecast is a forecast of winds at different altitudes in the atmosphere. In a winds aloft forecast, certain values may be omitted due to various factors such as measurement limitations, data gaps, or prediction uncertainties. However, the primary values that are typically omitted are the wind speeds and directions at lower altitudes, especially near the Earth's surface.
- One reason for omitting the surface wind values is that surface friction, caused by features such as mountains, buildings, and vegetation, can disrupt and alter the wind flow, making it difficult to accurately predict the wind speeds and directions at lower altitudes.
- Another reason is that the primary purpose of a winds aloft forecast is to provide information for aircraft navigation and flight planning. Therefore, the focus is on the winds at higher altitudes, usually above 2,000 feet, where aircraft operate.
- Additionally, surface winds can be obtained from other weather observations such as weather stations, buoys, and weather radar, which provide more accurate and detailed information for surface-based activities and forecasts.