Tuesday, 25 October 2016

So you are off on a trip away from civilization, but you forgot to take your NOAA Weather Radio. Do you have any way of making more than a guess about the forthcoming weather for the next half-day or so? Sure, you can.

Stand out in the open with your back to the wind. Raise your left arm to a horizontal position and then move your arm slightly forward. Your left hand is now pointing toward low pressure.

Why is that relationship so? Check it out by using the knowledge you have learned in the DataStreme Atmosphere course, while keeping in mind that you are in the Northern Hemisphere. On a piece of paper, draw a couple of concentric isobars around an "L". Draw some curved arrows showing the winds circulating counterclockwise around the low-pressure center. Imagine yourself on the map you just drew (but not at the "L") with the wind to your back and your left arm extended. Your arm would be pointing toward the "L". Buys-Ballot, a Dutch meteorologist, noticed this rule on weather maps in the mid-1800's. If you stand with the wind at your back, the low-pressure center will be to your left.

To make a weather prediction, you also have to recall that weather systems tend to travel from west to east. So, if you are facing north while the wind is to your back, lower pressure is to your left (to the west of you). And, the low would be coming toward you. As you know, low pressure approaching you often means stormy weather is on the way. That would be your forecast. Conversely, if you observe a northerly wind, the low would be to your east, and you could forecast that the weather should improve as the low pulls away and the high pressure moves toward you.

So how can we make our own wind observations, and what can we learn from our observations? If you are curious, refer to the Supplemental Information…In Greater Detail below.


To be submitted on the lines for Tuesday on the Investigations Manual, Week 8 Chapter Progress Response Form.

  1. If you were standing in a large, flat open area with your back to the wind, higher air pressure would be to your [(left) (right)].
  2. If your back were to the wind and you are facing south, you could expect to experience [(fair) (stormy)] weather during the next half-day or so.



We have learned that the wind can be of use to us -- helping power our sailboats or turn our wind generators or cooling us during the summer. But, we also know that it can make us feel uncomfortable during the winter, robbing us of body heat when the wind-chill equivalent temperatures drop to low values. We can also look to see how the wind changes over time, and we can then make an intelligent forecast of the weather for the next several hours.


In order to make reasonably accurate wind observations, you do not need a sophisticated system. All you need is a free flying flag. A windsock, similar to those used at small airports, could be used to help you estimate both wind speed and direction. Many novelty stores also stock windsocks. You could even construct a windsock easily from inexpensive materials, keeping in mind that the small end should remain open. The decorative wind vanes on rooftops may be an adequate indicator of wind direction, but often they may be affected by a distorted wind flow over the roof. If possible, the flag or windsock should be away from obstacles that could influence the wind. Ideally, the wind indicator should be mounted approximately 10 meters above the surface.

You can determine the direction of the wind motion by looking at the direction that a free flying flag or windsock is pointing. If you are making your observation from home or school, you should determine the cardinal points (such as North, East, South and West) from local landmarks using the noonday sun or a compass. When you make your observation, remember that traditionally the wind is named for the direction from which the wind blows. That is, a north wind blows from the north. You can record your wind directions using a simple 8-point notation (N, NE, E, etc.).

You can estimate the wind speed by looking at the movement of recognizable objects produced by the wind, such as flags, trees, smoke plumes or the water surface. The Beaufort scale was devised by Admiral Francis Beaufort (1774-1857) of the British Navy in the early 19th century to provide an expedient means for estimating wind speed for use on sailing ships. With a little practice, together with the modernized Beaufort wind force table appearing in Table 8.1 of the Weather Studies text, you can gain the experience needed to estimate wind speed. Compare your observations with the current weather observations from your local National Weather Service Office.


If you keep track of your wind observations for any length of time, you will soon realize that some graphical means for displaying the results would help you visualize the time sequence of the winds more so than a tabular listing of the wind speed and wind direction. By now you should be familiar with the meteogram (short for meteorogram) format for several selected cities on the RealTime Weather Portal. You could use this same type of meteogram format to plot your observations for one or more days. In a meteogram, the hourly wind speed and direction observations are plotted along the entry marked WINDS, using the same familiar wind arrow format used on the surface weather map. Using this format, the direction of the plotted arrow on the meteogram indicates the observed wind direction (a south wind would be plotted as wind arrow directly below the circle) and the number of feathers denotes the wind speed, where a half feather identifies a 5-knot increment and a full feather is a 10-knot wind increment.


By keeping track of the winds for several days and comparing your record with the daily surface weather maps, you can begin to formulate some relationships between the wind and weather systems. As discussed above in the Concept of the Day, you can locate the directions of the low and high-pressure systems come from by facing downwind. As the winds shift direction over time, you should be able to tell how the pressure systems move. You may also be able to note that wind speeds often increase and become gusty as a storm system or front approaches. (A gust is a variation in wind speed of at least 10 knots between peaks and lulls.) Wind speeds usually slacken as a high-pressure cell nears. Unless local or regional factors such as nearness to a large body of water predominate, winds generally from the south usually signal a warming trend as warm air advection occurs.

The following descriptive terms are often used by the local National Weather Service Offices in public forecasts to describe the prevailing wind speed in miles per hour. The range of wind speeds may differ in various parts of the country due to factors such as terrain and elevation.

WINDS (from NWS, Media Guide to National Weather Service Terminology, 1996)

Sustained Wind Speed

Descriptive Term

0 - 5 mph

Light, or light and variable wind

5 - 15 mph, 10 - 20 mph


15 - 25 mph

Breezy (mild weather)


Brisk or Blustery (cold weather)

20 - 30 mph


30 - 40 mph

Very Windy

40 mph or greater

Strong, dangerous, damaging. High wind warning required


Thompson, S. and A.F. Kapela, 1996: Media guide to National Weather Service Terminology. National Weather Service. NWS Forecast Office, Milwaukee/Sullivan, WI. 21 pp.

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Prepared by Edward J. Hopkins, Ph.D., email
© Copyright, 2016, The American Meteorological Society.