The wind direction will have an important influence on the expected weather. You can often be given a wind direction and you will have a pretty good idea of how the weather will change and what weather can be expected with that wind direction. The typical wind direction that a location has for a certain time of the year is called the prevailing wind. When the wind is from the prevailing direction then the weather is generally typical. When the wind shifts away from the prevailing direction then it often indicates atypical or changing weather. For your forecast location, note what type of environment is located in every direction from the location. Take Dallas for example, toward the southeast is the moisture source of the Gulf of Mexico; toward the east is the typically warm and humid southeast; toward the north are the plains which can bring in cooler air in the cool season; toward the west and southwest is a very dry high elevation climate; toward the south is the transition between the coastal area and dry portions of Texas. A wind from the north in Dallas will tend to bring in cooler and drier air; a wind from the southwest will bring in very dry air; a wind from the southeast will bring in warm and humid air. Just by noting the wind direction a forecaster gains an idea of what type of air mass is moving toward the forecast area. Wind direction changes often accompany changes in the weather. The air flows cyclonically around low pressure systems. If the wind changes direction in a cyclonic fashion it often means a low pressure or front is influencing the forecast area. A wind shifting from the south often means warmer air is approaching and a wind from the north often means cooler air is approaching. When the wind changes abruptly it could be a frontal passage or wind direction change caused by thunderstorm outflow. When the wind speeds are light then a change in wind direction is not as significant. You may have heard the phrase "winds will be light and variable". When the winds are light it indicates there is not much of a steering current to move the wind. When winds are light, mesoscale influences will tend to start influencing wind direction. The winds can continue shifting from a variety of directions when winds are light. When analyzing MOS data make sure to note the wind speed and direction over the course of the forecast period. That information alone can give you clues to what weather to expect. |