While many of us are in the habit of checking the weather forecast on a daily basis, this is usually only to make decisions that impact our personal lives; the information can help us decide what to wear, where to go, and when to plan certain activities.
For pilots, however, the forecast is much more important, and can sometimes mean the difference between life and death.
Winds and temperatures aloft are particularly important; they help pilots to determine and understand the various atmospheric conditions that are currently in action at a range of altitudes, and this information can be crucial.
What Does Winds & Temperatures Aloft Mean?
The term “winds aloft” refers to the speed and direction of the wind at different heights in the atmosphere.
The most common winds aloft are the surface winds (also known as ground or surface winds), which are the winds blowing over land surfaces.
These include the trade winds, which blow from east to west across the equator, and the jet streams, which flow north and south along the polar regions.
Other types of winds aloft include those associated with thunderstorms, which occur above clouds, and the boundary layer, which occurs just below the cloud base.
Winds aloft also play an important role in determining the weather pattern for a given area. If the wind blows from one direction, then it will tend to cause a low-pressure system to develop.
This means that air flows into the region from all directions, resulting in the formation of a high-pressure cell.
Conversely, if the wind blows in another direction, then it will create a high-pressure system, causing air to move away from the region.
In other words, the wind determines whether there is going to be rain, snow, or sunshine.
Winds Aloft – What Do They Tell Us?
There are several ways in which you can use the information provided by winds aloft to help you decide what to do next:
- When flying near mountains, you should know how the wind changes as altitude increases. A strong southerly breeze may become light northerly breezes as you climb higher up the mountain.
You should also note the change in temperature with increasing height. As you get closer to the top of the mountain, the temperature will drop significantly.
- If you are planning to fly through a thunderstorm, you need to know what the wind speeds are at different levels within the storm. The strongest winds will generally be found closest to the lowest level of the storm, while the weakest winds will be found at the highest level of the storm.
- If you are planning to cross a front, you need to know how fast the fronts are moving. Generally speaking, the faster the front moves, the stronger the winds aloft will be.
- If you want to avoid turbulence, you need to know where the strong updrafts and downdrafts are located. If these areas are close to your planned route, you should take extra care when approaching them.
Readings From The Forecast Wind Aloft Chart
You can access the forecast winds aloft chart online at www.weather.gov/afcw/forecasts/aloft/.
It shows the latest forecasts for winds aloft, including the expected wind speeds and directions at different levels throughout the troposphere.
Note that this forecast only applies to the United States. The chart contains three sections:
1. Surface winds
2. Boundary layer
3. Upper tropospheric winds
Surface winds are the winds blowing over the earth’s surface, such as the trade winds, jet stream, and local winds.
Boundary layer winds are the winds occurring between the surface and the upper troposphere.
Upper tropospheric winds are the winds occurring above the stratosphere.
How Are Winds Aloft Measured?
The National Weather Service uses a combination of instruments and computer models to measure the winds aloft.
Instruments used include radiosondes, sonic anemometers, and microwave radiometers.
A sonic anemometer consists of a microphone that measures the speed of sound (the speed at which sound travels) in the atmosphere.
By measuring the time it takes for the sound waves to travel across the instrument, you can calculate the wind speed.
A microwave radiometer works on the same principle as a radar gun. It sends out radio waves that bounce off objects in the atmosphere, allowing us to see the object.
We can determine its size and shape from the amount of energy reflected back to the antenna.
A radiosonde is a weather balloon equipped with sensors that measure air pressure, humidity, temperature, and other atmospheric conditions.
After being launched into the atmosphere, the radiosonde descends to the lower layers of the atmosphere until it reaches the boundary layer.
Once there, the radiosonde releases a small parachute so that it floats down to the ground, where the data collected by the instruments inside the radiosonde are recorded.
At each stage of descent, the radiosonde records the wind speed and direction, as well as the temperature and humidity of the air.
This information allows meteorologists to estimate the strength of the winds aloft.
- What Is A Boundary Layer?
The boundary layer is the region of the atmosphere closest to the earth’s surface. In general, the boundary layer is about 10-20 km thick.
In the boundary layer, the air has a very low density because it is so hot or cold relative to the surrounding air. As a result, the air tends to flow downward rather than upward.
In some cases, the boundary layer may be thicker than 20 km.
For example, if a thunderstorm forms over a large area, the resulting updraft will cause the boundary layer to extend even farther up into the atmosphere.
Why Do We Care About Winds Aloft?
Winds aloft affect our lives in many ways. They influence the movement of clouds and precipitation, they help control the temperature of the earth, and they affect how we fly airplanes.
Winds aloft also play a role in determining the location of hurricanes and typhoons. Hurricanes form when warm tropical waters rise toward cooler water temperatures near the surface.
The rising warm water creates strong vertical motion in the ocean, which causes the water to rotate around the center of circulation.
When this rotation becomes unstable, the storm begins to spin clockwise, wind levels increase, and a hurricane is born.
If aviation weather services, and other weather center experts can track and monitor these changes, they can help to predict the path, strength, and potential risks of extreme weather events.
Hurricanes move counterclockwise due to the Coriolis force, but winds aloft can change their course. If the winds aloft are stronger than expected, then the hurricane will track closer to land.
If the winds aloof are weaker than expected, then the storm will track further away from land.
Airplanes use the winds aloft to maintain altitude during flight. If the wind is too weak, then the plane will descend; if the wind is too strong, then the plane will ascend.
Airports have wind indicators to show pilots what the prevailing winds are at different altitudes. These indicators are called “wind shears.”
How Do You Read Winds Aloft Charts?
To read the winds aloft chart, first, locate the time period you want to look at on the chart. Then find the wind indicator for the desired height range.
For example, suppose you want to see the winds aloft for the past 24 hours. First, find the time period (in this case, the last 24 hours) on the top line of the chart.
Next, find the wind indicator for heights between 0 and 1,000 meters above sea level. Finally, find the date that corresponds with your reading.
When you find the date, click on it to bring up the details for that day. Now you should see the wind speeds and directions recorded by the radiosondes.
You will also need to know the following information to interpret the charts:
- What is the type of radar used?
- How high does the radar penetrate into the atmosphere?
- Is there any cloud cover?
- What is the wind speed and direction? Is there an indication of whether the winds are coming from the east or west?
- Does the wind come from one direction only, or do both sides have equal amounts of wind?
- Are there any special notes about the conditions?
- Is there any mention of rain or snow (see also “Can Planes Fly In Snow?“)?
- Is there any mention of whether the winds are blowing steady or gusty?
- Is there any mention of turbulence?
- Is there any mention regarding the pressure?
- Is there any mention concerning the visibility?
- Is there any mention as to whether the winds are calm or variable?
- Is there any mention that the winds are increasing or decreasing?
- Is there any mention of how long the winds were blowing?
These details will help you to understand the winds aloft chart more completely, and ensure that you have the information that you need to make your decisions.
The winds aloft chart is very important because it gives us a general idea of the atmospheric conditions over our area.
It helps us determine where we might be able to fly safely, and where we cannot, and can also help us to plan ahead so that we don’t waste fuel flying in areas where the winds are not favorable.
It’s always good to keep these things in mind when planning flights, and one of the most commonly cited aviation tips is to keep a close eye on winds aloft – this can make a substantial difference to the safety, quality, and nature of your flights.