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National Water and Climate Center

Wind Rose Data

Wind Rose Plots (ftp site)

The above link takes you to an ftp server that houses the wind rose plot images.  The directory is organized by State and Climate Station name.  Within each Climate Station directory, there are images in both .emf and .gif formats for each of the twelve months.  The .emf images can be viewed using Internet Explorer 6.x or by using the "insert picture" option in MS-Word.  The .emf images are larger than the .gif images as shown in the example below, and show more detail.

Note: Wind speeds shown are in meters per second. To convert meters per second into miles per hour just multiply by 2.237. Thus, a 5 m/sec wind is an 11.19 mph wind, and a 10 m/sec wind converts to 22.37 mph
.

Additional note: Anemometer heights were not adjusted to a common height in the SAMSON database (see below). For user's information, a file containing the anemometer height history at each of these stations is available HEREExcel Spreadsheet (MS Excel Required) Two files are shown: one in meters, and the other in feet. Only data from 1961 to 1990 were used in SAMSON, and in the development of these wind roses.

A wind rose gives a very succinct but information-laden view of how wind speed and direction are typically distributed at a particular location. Presented in a circular format, the wind rose shows the frequency of winds blowing FROM particular directions. The length of each "spoke" around the circle is related to the frequency of time that the wind blows from a particular direction. Each concentric circle represents a different frequency, emanating from zero at the center to increasing frequencies at the outer circles. The wind roses shown here contain additional information, in that each spoke is broken down into discrete frequency categories that show the percentage of time that winds blow from a particular direction and at certain speed ranges. All wind roses shown here use 16 cardinal directions, such as north (N), NNE, NE, etc.

An example is shown here. It is the April wind rose for Fresno, California, based on 30 years of hourly wind data (all hours of the day). This rose shows that the winds at Fresno in April blow from the northwest much of the time. In fact, the 3 spokes around the northwest direction (WNW, W and NNW) comprise 50% of all hourly wind directions. This is quickly calculated by taking the sum of the frequencies of each of these directions (16+25+9=50%). This also shows that the wind rarely blows from the northeast or the southwest. These wind roses also provide details on speeds from different directions. Examining winds from the northwest (the longest spoke) one can determine that approximately 8% of the time in April at Fresno the wind blows from the northwest at speeds between 1.8 and 3.34 meters per second. Similarly, on this spoke it can be calculated that winds blow from the northwest at speeds between 3.34 and 5.4 m/sec about 10% of the time (18% - 8%), at speeds between 5.4 and 8.49 m/sec about 6% of the time (24-18), between 8.49 and 11.06 m/sec about 1% of the time (25-24), and less than 0.5% of the time at speeds greater than 11.06 m/sec. Please note the legend at the bottom of the wind rose that gives the speed categories and their associated colors.

Example Wind Rose Plot - Select for Full GIF Image

Select the above example for full GIF Image

The legend at the bottom gives additional information such as the unit (m/sec), the average wind speed for the month over all hours (in this case 3.61 m/sec), and percentage of time that the winds are calm (7.53%), and the years and month and hours of data on which each rose was constructed. Note: Even though it says 1961 as the year, these data are for 30 years (1961-1990).  The software only prints the beginning year.  All hours of the day (24 readings per day) are used to construct these wind roses. All wind roses available here are for the period 1961-1990.

The software used to generate these high-quality wind roses is courtesy of Lakes Environmental Software and is called WR-PLOT.

To calculate the typical amount of time that the wind blows from a particular direction and certain speeds just multiply the respective frequency by the appropriate amount of time. In our example with Fresno in April, there are 30 days x 24 hours/day in April, or 720 hours. From the wind rose we calculated that winds blow from the northwest at speeds between 5.4 and 8.49 m/sec 6% of the time. This represents 0.06 x 720 = 43.2, or about 43 hours typically have winds from the northwest at these speeds at Fresno in April.

A note on the wind database: These wind roses are based on hourly data from the Solar and Meteorological Surface Observation Network (SAMSON) CDROM, available from the National Climatic Data Center (http://ols.nndc.noaa.gov/plolstore/plsql/olstore.prodspecific?prodnum=4458). The period of record is for 1961-1990. SAMSON is a 3-volume CD-ROM set is divided geographically into regions: Eastern, Central, and Western U.S. It contains hourly solar radiation data along with selected meteorological elements for the period 1961-1990. It encompasses 237 NWS stations in the United States, plus offices in Guam and Puerto Rico. The dataset includes both observational and modeled data. The hourly solar elements are: Extraterrestrial horizontal and extraterrestrial direct normal radiation; global, diffuse, and direct normal radiation. Meteorological elements are: Total and opaque sky cover, temperature and dew point, relative humidity, pressure, wind direction (true north) and speed, visibility, ceiling height, present weather, precipitable water, aerosol optical depth, snow depth, days since last snowfall, and hourly precipitation. Joint NCDC and NREL product. DOS only. SAMSON can be ordered from NCDC by clicking on the above link.

The hourly winds measured at airports are normally 2 or 3 minute averages of 3 or 5 second samples at the top of every hour. These are not gusts. Newer equipment, particularly the Automated Surface Observation System (ASOS) used at most locations since 1996 or so, automatically records these values from cup anemometer values. Older observations (generally prior to 1996) represent data recorded by personnel working at weather stations who manually observed wind speed and direction at the top of every hour, and made an estimation of hourly winds over some time period, typically 2 to 5 minutes in length.