Watching the Wind

This is a sample lesson page from the Certificate of Achievement in Weather Forecasting offered by the Penn State Department of Meteorology. Any questions about this program can be directed to: Steve Seman


When you've finished this section, you should be able to describe wind direction in both words (like "west," "southwest," etc.) and compass degrees, and determine the wind direction and speed on a station model (including proper units). Please note that wind direction in particular is an important concept that often gives students some trouble, so make sure that you don't leave this section without mastering this skill.


A wind vane and rotating cup anemometer.
A wind vane and anemometer (used to measure wind speed).
Credit: David Babb

Wind is a weather variable that's pretty easy to notice, from a gentle breeze on a summer day to whipping winds that can cause damage during a storm. Really, wind is just about everywhere -- even in music! Wind has captured the attention of songwriters for years, with numerous songs referencing "wind" in some way ("Blowin' In The Wind," "Candle in The Wind," "Summer Breeze," and "Dust in the Wind" are but a handful of examples).

But, just what is the wind? In short, wind is the horizontal movement of air. One of the most fundamental rules that you need to know is that the direction of the wind is always expressed as the direction FROM which the wind blows and NOT the direction toward which the wind blows. Make sure to commit that to memory! So, if the wind blows from the north toward the south, for example, you'll hear a meteorologist say that the wind is "northerly" (or there's a "north" wind), NOT a "southerly" or "south" wind. Meteorologists are always interested in where the air is coming from because it can help with weather forecasting. For example, if a wind is blowing from a region of warm air toward a region of colder air, a weather forecaster would want to know that! If you happen to own a weather vane, remembering this rule should be easy because a wind vane points into the wind and thus toward the direction FROM which the wind blows.

So, wind direction is always the direction from which the wind is blowing. While forecasters commonly brand the wind with a general direction (such as "north" or "southeast"), in practice, they routinely use standard compass angles to fine-tune the wind direction, as shown in the compass below. For sake of illustration, the wind direction from the north blows from a direction of 0 degrees. A wind that blows from the east is a 90-degree wind, while a wind direction of 70 degrees corresponds to a wind that blows from the east-northeast.

A sample station model plot.
Weather forecasters use standard compass angles to describe the specific wind direction. For example, a 270-degree wind would be blowing from the west (a "west" or "westerly" wind), while a 180-degree wind would blow from the south (a "south" or "southerly" wind).
Credit: David Babb

Wind speed is simply how fast the air is moving, and it is the sustained wind speed that is routinely included in weather observations. What is "sustained" wind speed? It's the wind speed averaged over a certain time period (usually 1 or 2 minutes). The rotating cup anemometer shown near the top of the page is a popular instrument for measuring sustained wind speed at home weather stations. To determine the sustained wind speed, the revolution rate of a rotating cup anemometer is typically averaged over a one- or two-minute time period and then mathematically converted to a speed.

The wind is sometimes unsteady, however, with brief, sudden increases in wind speed called gusts. As a general rule, gusts last less than 20 seconds. Weather observers typically only report gusts when the wind speed varies by greater than 10 knots (between the peaks and lulls), so wind gusts are only included in routine weather observations when they're noteworthy.

The units of "knots" may not be familiar to you; in the United States, we often talk about wind speed in mile per hour (just like automobile speed). But, in routine weather observations, wind speed is actually expressed in units of knots (nautical miles per hour). For the record, 1 knot = 1.15 miles per hour. To convert between knots and the more familiar "miles per hour," multiply knots by 1.15. You can find many wind speed converters online, but if you have to make the conversion in your head, it's much like if you were out at a restaurant and wanted to leave a 15 percent tip. Imagine your bill at the restaurant is $25. To leave a 15 percent tip, first multiply your bill by 10 percent, which gives you $2.50. Then add on half of $2.50 (which is $1.25) to get to your 15 percent tip of $3.75. Your total bill, then, is $25 + $3.75 = $28.75. Converting knots to miles per hour is the same as computing your tip and total bill at a restaurant. A 25-knot wind speed converts to 28.75 miles per hour (which we get by multiplying 25 by 1.15).

Now that we've covered the basics of wind speed and direction, you might be wondering, "What if the wind is calm? What's the wind speed and direction?" Technically, if the wind is calm, then its speed is 2 knots or less (which gets reported as 0 knots) and it does not have a reported direction. Keep these ideas in mind as you concentrate on this section's Key Skill -- determining wind speed and direction from a station model.

Key Skill...

See caption.
A sample of a station model with wind direction and wind speed labeled. In this case, winds were blowing from the southeast (or more precisely, 150 degrees) at 15 knots. The long wind barb represents 10 knots, while the short barb represents 5 knots for a total of 15 knots (17 miles per hour).
Credit: David Babb

Wind speed and direction are prominently displayed on the station model. To see the wind information displayed on a station model, check out the image on the right. On a station model, the thin, solid line (often referred to as the "flag") extends outward from the sky coverage symbol in the direction that the wind is blowing from. In this case, it's apparent that the wind is blowing from the southeast (we would say we have a "southeast" or a "southeasterly" wind). More precisely, we could say that winds were 150 degrees (you may want to refer to the image of standard compass angles to confirm).

What about wind speed? On station models, the speed of the wind is expressed as a series of notches, called "wind barbs" on the clockwise side of the line representing wind direction. Each longer wind barb counts as a tally of 10 knots (actually, each longer barb represents a speed of 8 to 12 knots, but weather forecasters operationally choose the middle value of 10 knots for simplicity). The shorter barbs count as a tally of five knots. So, to figure out the wind speed, you need to add the values associated with any long and short wind barbs present. In the sample station model on the right, there's one long barb (10 knots) and one short barb (5 knots), so we add 10 knots and 5 knots together to get our wind speed of 15 knots (which converts to 17 miles per hour).

If the surface wind is calm, a larger circle is drawn around the circle that represents sky coverage, as shown in the example map of station models over the western United States below. The two stations I've highlighted (Havre and Glasgow, Montana) were both reporting calm winds.

A station model plot for the interior northeast United States, showing a few stations with calm winds.
Stations with calm winds have a larger circle drawn around the sky coverage circle, as shown at the two highlighted stations -- Havre and Glasgow, Montana.
Credit: NOAA

On the other hand, for very strong winds, a "triangular" barb counts as a tally of 50 knots. The use of the 50-knot symbol doesn't happen at the surface very often in most locations, however, because sustained winds rarely reach such speeds. Of course, wind gusts of 50 knots occur a little more frequently (severe thunderstorms, strong cold fronts, etc.). You're more likely to observe a sustained 50-knot wind near the Atlantic and Gulf Coasts with a hurricane nearby. For example, check out the sustained 50-knot wind at Apalachicola, Florida at 17Z on October 10, 2018. The culprit in this case was Hurricane Michael, which was about to make landfall in the Florida Panhandle.

Want to see a few examples of interpreting wind direction and speed using the interactive station model tool? Check out the short video (2:25) below:

Wind on the Station Model
Click here for a transcript of the video.

This short video should help reinforce conventions relating to wind speed and direction on station models.

For starters, always remember that wind direction is expressed as the direction that the wind is blowing from. So, on our compass here, a “west” or “westerly” wind would blow from 270 degrees like this. A “north” wind or “northerly” wind would blow from 0 degrees like this. A 130 degree wind blows from the southeast like this, and would be called a “southeast” or “southeasterly” wind.

Now let’s apply those ideas to the station model. We’ll assume that north is that the top of the image, south is at the bottom, west is on the left, and east is on the right. The tool defaults to a wind from 180 degrees, so the wind is blowing from the south.

We can change the wind direction to, say, 50 degrees. Now we have winds from the northeast to the southwest, and that's what it would look like on the station model. We would call this a northeast wind, or a northeasterly wind. Of course, we can also tell wind speed from a station model. The speed here is 25 knots, as indicated by the two long wind barbs and one short wind barb. Each long wind barb represents 10 knots, and the short wind barb represents 5 knots. So we sum those together, and we get a total of 25 knots.

If we had calm winds, or a wind speed of 0 knots, we would just have an extra circle around the sky coverage because the wind doesn't have a direction or speed.

Or, on the other hand, we could make it really windy, and have 75-knot sustained winds –say maybe a hurricane is making landfall nearby. The pennant, or triangular barb, represents 50 knots, the 2 long wind barbs represent 10 knots each, and the short barb represents 5 knots. Add those together, 50 + 10 + 10 + 5, to get our total of 75 knots.

Credit: Penn State

Finally, I highly recommend practicing with the interactive station model tool below. The tool defaults to a 180º (south) wind at 25 knots, but you can experiment with different wind directions by entering different compass directions into the "Current Conditions" field to see how they would be represented on the station model (remember the wind direction is represented by the flag stick). Try a 220-degree wind, a 90-degree wind, and 340-degree wind for starters. You can also try out different wind speeds and examine the resulting group of wind barbs (remember that a long barb counts for 10 knots, a small barb for 5 knots, and a black triangle for 50 knots). Try a 10-knot wind, a 35-knot wind, and a 60-knot wind for starters. Don't forget to try an observation with calm winds, too!

One last thing to keep in mind. Remember that station models report sustained wind speeds. Reported wind gusts often do not appear on station models, but if they do, you might see something like "G28" near the wind barbs, which would indicate gusts to 28 knots (the interactive tool does not show gusts).

Quiz Yourself...

Think you have a good handle on wind speed and direction on a station model? Take this self-quiz below to see how you do. Begin by hitting the "Quiz me" button. Fill in the missing wind direction and speed, and then hit "Submit" to check your answer. Wind direction can be rounded to the nearest 10 degrees and wind speed is to the nearest 5 knots. You may also turn on some directional hint lines if you have trouble estimating angles. Since some visual estimating is involved with wind direction, if your answer is only 10 or 20 degrees off from the tool's answer, that's a reasonable estimation. If you can get five in a row, you've likely got the hang of it!

Explore Further...

Why do meteorologists bother detailing wind directions with compass degrees instead of just saying things like "northeast" winds? If the wind is from the northeast (or any other general direction), do the specifics really matter? They certainly can! Slight changes in the wind direction can translate into large changes in the weather forecast.

For example, suppose it's December along the Northeast Seaboard. At this time of year, sea-surface temperatures over the offshore waters of the Atlantic are typically in the 40s (Fahrenheit). Thus, the temperatures of the air overlying Atlantic waters are often higher than air temperatures over the colder land. Now suppose a storm system approaches New York City and the wind direction at Central Park is 20 degrees (depicted on the left below). Such a north-northeast wind would bring cold air into the Big Apple strictly via a land route, which, as you might guess, increases the chances of snow. If the wind direction were 70 degrees, however (meaning that the trajectory of the air comes into New York City from the Atlantic, depicted on the right below), milder air might make a change to rain more likely.

Two images showing the effect on wind direction for temperatures of Long Island, New York.
During winter, a wind with a trajectory over land heightens the risk of snow at New York City (left), while a trajectory over water favors a changeover to rain (right).
Credit: David Babb

As we go deeper into the course, the idea that meteorologists are interested in where the air is coming from will come up again and again, because it can have impacts on temperature, moisture, etc. So, keep "air trajectories" (where the air is coming from) in your mind going forward. They're an important part of forecasting!