Thursday, January 19, 2017
Weather Station Data (TMY) Tool User Guide

Weather Station Data (TMY)
Red Calc Tool User Guide

What this tool can do for you

First, the embedded Google map feature helps you find the closest (TMY) weather station when your location is close to a state/province or national border and the closest station is actually in a different state/province/country. These are the same weather stations that are used in the ASHRAE 62.2-2013 tool, for example.

Second, the tool's interactive table and chart help you explore the the Typical Meteorological Year (TMY) data for each of 1,100 weather stations in North America. This hourly data is the foundation for most building energy simulation software. (See the "Typical Meteorological Year data" section below.)

Weather station map displayed
Weather data chart displayed

Calculated values

  • Latitude for selected location.
  • Longitude for selected location.
  • Altitude (elevation) for selected location.
  • For the date range selected, a table including low, average, and high values for dry bulb temperature, dew point temperature, and wind speed.
  • For the date range selected, a chart showing daily averaged dry bulb temperature, dew point temperature, and wind speed.


  • Clicking the label for any input or result will cause a popup help box to appear. This help box includes the allowed and normal values (for inputs). Read more.
  • This tool requires a reasonably fast internet connection to perform well, as compared to other RED Calc tools that came before it. A slow internet connection will be most noticeable when using the embedded Google map. You may prefer to uncheck the "Show map" check box to disable the map feature. (It is not required in order to use the rest of the tool.) Also, each time you choose a different weather station, the weather data for that station must be downloaded, causing a noticeable delay with a slow internet connection. The only recourse in this case is to seek out a faster connection.
  • Check "Show map" to show the Google map with the weather stations. The weather stations are displayed as pink dots. The selected weather station is centered in the map viewing area and is displaced as a red dot. Otherwise, the map functions like a typical Google map.
  • The drop-down selectors for selecting the weather station are interconnected with the map; change one or more of the drop-down selections and the map changes. Change the map weather station selection, and the drop-downs change.
  • The date range above the table allows you to select the month and day for the beginning and end dates of the displayed table and chart data. Because the tool uses Typical Meteorological Year data, there is no year selection.
  • Check "Show chart" to display the interactive chart. Refer to Interactive Chart Use below for more information.
  • The low (high) values in the table will most likely be lower (higher) than the lows (highs) in the chart. This is because the chart plots daily average values.
  • For an explanation of the derivation of the TMY3 (US) and CWEC (Canadian) weather data used for this tool, please see the Related external resources below.

Interactive Chart Use

This tool includes a powerful interactive chart that can be used to display the results; it may also be used for educational, sales, and marketing purposes. For example, you can save a chart in one of four different file formats, embed it into your customer reports, or print it separately.

Tips for using the interactive chart:

  • You may zoom in on the chart weather data by dragging an area on the chart with your mouse or by zooming (stretching or pinching) with two fingers on your touch device. [On a touch device, you may swipe the date range forward (left) or back (right) with one finger.] Reset by clicking/touching the "Reset zoom" button.
  • Click/touch the labels "Dry bulb", "Dew point", and "Wind speed" in the legend below the chart to turn the corresponding data lines on or off.
  • Click/touch the menu icon in the upper right corner of the chart to show the choices for printing the chart or downloading it as an image file in PNG, JPEG, PDF, or SVG format. You are free to use the downloaded image in any way, including reports, presentations, websites, as long as the attribution for "Residential Energy Dynamics, LLC" is included.
    • If you save the chart as an SVG file, you can change the title or any other chart element with the use of third-party software. Examples of third-party software include Inkscape (a free version is available) and Adobe Illustrator.

Typical Meteorological Year weather data

The weather station data used for this tool - Typical Meteorological Year (TMY) data - comes from two sets of data: TMY3 with 1020 US locations, and CWEC with 80 Canadian locations. Both of these sets of weather data include many types of hourly weather measurements. For this tool, we have chosen to focus on the three most commonly used. (See the "Related external resources" section below.)

The typical meteorological year data for a location is comprised of twelve separate typical months of data spliced together to form an entire year. Each typical month of data is the actual data for that month at that location, for some year in the past 15 years (or so). It was chosen because it was the most "typical" in the sense that its average temperature, humidity, wind speed, etc. was closest to the 15 year averages for that month. So it is entirely possible that the typical meteorological year at a location includes January data from 2002, February data from 1999, etc. Each month is chosen independently of the others.

TMY data is often used for building energy simulation to assess heating/cooling loads and for solar analysis to evaluate photovoltaic, hot water, and other solar projects.

The map below shows the TMY3 weather station locations for the United States.

Source: National Renewable Energy Laboratory (NREL)

Best practices

Select the weather station closest to the site you are analyzing. If your location is close to a state border, you might find the closest weather station is in another state. The map feature is helpful for determining this.


We recommend you NOT use the uncertainty feature for this tool because the tool is merely reporting weather data for the Typical Meteorological Year. If the uncertainty reporting is on, go to the "Preferences" RED Calc Free tool to set the "Uncertainty feature" to off.

Related tools

  • ASHRAE 62.2-2013 Ventilation: Determine whole-building ventilation requirements for new and existing dwellings, with the choice of using advanced blower door options and the alternative compliance path. It requires the selection of the closest (TMY) weather station.

Related external resources

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