Wind direction is a fundamental component of meteorology, providing necessary context for weather forecasting and atmospheric studies. Understanding the terminology used to describe air movement is necessary for anyone following a weather report. When a forecast mentions a West-Northwest wind, it refers to a specific direction defined within a global system of measurement, allowing meteorologists to accurately track and predict weather systems.
Defining West-Northwest (WNW)
A West-Northwest (WNW) wind is defined as the direction halfway between due West (W) and Northwest (NW). This is a tertiary direction on a standard compass rose, falling in the upper-left quadrant. A WNW direction corresponds to an azimuth of 292.5 degrees, measured clockwise from true North (360 degrees). This designation provides detail greater than simply calling the wind “Northwest” or “West.”
The Convention of Wind Measurement
The most important concept to understand about wind reporting is that the direction is always named for the point from which the air originates. The terminology describes the source of the air mass, not its destination. For example, a “northerly” wind is one that is blowing from the North toward the South. This convention is a standard rule used universally in meteorology for consistency in weather reporting.
This means a West-Northwest wind is air that is physically moving from the WNW point on the compass. The air is traveling away from the West-Northwest and blowing toward the opposite direction, which is the East-Southeast (ESE). This distinction allows people to anticipate what kind of weather the wind is likely to bring, as it indicates the region from which the air mass has traveled. A wind vane, the instrument used to measure direction, always points into the wind, indicating the source direction.
Placing WNW on the 16-Point Compass
The designation WNW is part of the 16-point compass system, which offers a greater degree of accuracy than the basic four or eight cardinal directions. The system begins with the four primary cardinal directions: North (N), East (E), South (S), and West (W), separated by 90 degrees. Next are the four secondary intercardinal directions, such as Northwest (NW) and Southwest (SW), which fall exactly halfway between the cardinal points, separated by 45 degrees.
The tertiary directions, like West-Northwest, are known as half-winds. These points further divide the compass rose, with each of the 16 points being separated by 22.5 degrees. Meteorologists use this 16-point scale to describe wind direction with necessary precision, helping to create more detailed and accurate forecasts.