VisualWeather™ Software Version 3.1 Revision: 6/12 C o p y r i g h t © 2 0 0 1 - 2 0 1 2 C a m p b e l l S c i e n t i f i c , I n c .
License for Use This software is protected by United States copyright law and international copyright treaty provisions. The installation and use of this software constitutes an agreement to abide by the provisions of this license agreement. Campbell Scientific grants you a non-exclusive license to use this software in accordance with the following: (1) The purchase of this software allows you to install and use the software on one computer only.
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Limited Warranty The following warranties are in effect for ninety (90) days from the date of shipment of the original purchase. These warranties are not extended by the installation of upgrades or patches offered free of charge. Campbell Scientific warrants that the installation media on which the software is recorded and the documentation provided with it are free from physical defects in materials and workmanship under normal use.
VisualWeatherTM Software Table of Contents PDF viewers: These page numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Introduction..................................................................1 1.1 Background...............................................................................................2 1.2 What’s New in VisualWeather 3.1 ...........................................................2 2. Installation.................
VisualWeatherTM Software Table of Contents 7. Reports .......................................................................12 7.1 Manually Generated Reports ................................................................. 12 7.2 Report Parameters .................................................................................. 13 7.2.1 Wind Rose.................................................................................... 13 7.2.2 Evapotranspiration (ETo)..........................................
VisualWeatherTM Software Table of Contents Appendices A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs ......................................... A-1 A.1 Evapotranspiration .............................................................................. A-1 A.2 Vapor Pressure Deficit of the Air ....................................................... A-8 A.3 Crop Water Needs, Crop Coefficients ................................................ A-9 B.
VisualWeatherTM Software Table of Contents iv
VisualWeather™ Software 1. Introduction VisualWeather software is designed to work with Campbell Scientific's preconfigured weather station models ET106, ET107, Toro T107, and MetData1, or custom-configured weather stations. This software will allow you to: • • • • • • • • • • • Create and send programs to one or more weather stations. Select a mode of communication (e.g., phone modem or RF) for each weather station. Define a data retrieval schedule for each station.
VisualWeather™ Software 1.1 Background Each weather station consists of a datalogger and a group of sensors. The sensors are designed to measure environmental factors such as air temperature or solar radiation. The datalogger measures the sensors and processes and stores the results. The stored results (final storage data) can be retrieved with a PC using communication software.
VisualWeather™ Software 2.1.2 For Users Upgrading from VisualWeather 1 VisualWeather 3.X will not upgrade an existing VisualWeather 1 installation. Significant changes were made to the database structure for VisualWeather 2. Existing VisualWeather databases and reports are not compatible with, nor will they import into, the new software. If VisualWeather 1 is detected on your computer system during installation of VisualWeather 3.
VisualWeather™ Software To install the software, insert the VisualWeather CD into the CD ROM drive of your computer. The installation process should begin automatically. If it does not begin, access your CD ROM drive and double-click the SETUP.EXE file. Follow the on-screen instructions to complete the installation. 2.3 Configuration of TCP/IP and Telephony Services TCP/IP and Telephony services must be installed and enabled on the computer for VisualWeather to run.
VisualWeather™ Software 3.3 Getting Help VisualWeather has a complete on-line help system. Most screens have a Help button that, when pressed, will bring up help about the screen. In addition, help for any screen can be displayed by pressing the F1 key on your computer. A Help file Table of Contents, an Index, and a Search function can be displayed by selecting VisualWeather Help from VisualWeather's main menu. 4.
VisualWeather™ Software After you have progressed through all steps of the wizard, press the Finish button to save the configuration and return to the main VisualWeather window. 5.2 After Configuring a Weather Station After setting up your weather station, VisualWeather will automatically collect data at the intervals specified (if scheduled collection is enabled). If batch reports have been created (see Batch Reports section 7.3), VisualWeather will automatically create reports using the collected data.
VisualWeather™ Software All weather stations that have been configured using VisualWeather will be listed on the left side of the screen under the Station Selection field. Select the weather station you wish to communicate with and click the Connect button. VisualWeather will attempt to communicate with the weather station. Once connected, the Connection Status will display Connected and other buttons on the window will be enabled.
VisualWeather™ Software 6.2 Monitoring Current Conditions Current weather conditions can be viewed after connecting to a weather station. Click the Current Conditions button to show the Current Conditions Screen. The data displayed will be based upon the sensors that were selected when the weather station was configured. Custom stations will show only those values that were set up in the Data Files/Mapping section when configuring the weather station (see Section 11.2 Real Time Field Mapping).
VisualWeather™ Software 6.3 Monitoring Station Status When you have a connection established with a weather station, you can view the station’s status. This can be done by clicking the Station Status button. The Station Status window has three tabs. The Summary tab provides an overview of important status information in the datalogger, including the information about the datalogger model and its firmware, program details, battery voltage levels, and card memory (if one is present).
VisualWeather™ Software table size. A data table can be reset from this window by pressing the Reset Tables button. NOTES No Table Fill Time statistics will be shown for a CR200 Series datalogger, because they cannot be calculated for this datalogger model. For the CR10XTD, CR10XPB, CR510TD, CR510PB, CR23XTD, and CR23XPB, the Time of Fill will not be shown and you will not have the option to Reset Tables. Resetting a table will erase the data in the datalogger and in the data cache.
VisualWeather™ Software 6.4 Field Monitor Clicking the Field Monitor button will bring up a screen that allows you to view the numeric values for a table. Select the table you want to view from the Table list box; the values for that table are displayed in the cells. Right-clicking on a value and then selecting View/Edit will display the value in a separate dialog box and allow you to change the value (if it is editable).
VisualWeather™ Software NOTE It is nearly impossible to synchronize the two clocks exactly, since it takes time to transfer the clock setting to the weather station. 6.7 Sending/Retrieving Programs to a Weather Station The name of the program currently running in the weather station is displayed in the Station Program Group box. For debugging purposes it may be necessary to retrieve the program from the weather station. Click the Retrieve button and choose the location to save the file.
VisualWeather™ Software After a station is selected, use the option buttons to select the time range that the report should cover. Note that VisualWeather will not let you enter a time range for data that is outside of what is currently available in the database. The following report options are available: 24 hour Creates a 24 hour report, with a user-specified start date and time. As the start parameters are entered, the end date and time change accordingly to reflect a 24 hour period.
VisualWeather™ Software desired for each bin. Any wind speeds that fall in between the low and high will be placed in the corresponding bin. Any value below the low value of the first bin will be placed in the calm bin. The default values give the lows and highs that follow the Beaufort wind scale boundaries. If you have edited the wind rose parameters, at any time you can restore the defaults for the bins by clicking the Restore Defaults button.
VisualWeather™ Software 7.2.2 Evapotranspiration (ETo) EVAPOTRANSPIRATION (ETO) — Select the ETo Method to be used and enter the anemometer height in meters. The latitude, longitude, and elevation are also used to calculate Evapotranspiration. These can be entered/changed in the EZSetup wizard by selecting Network | Edit Weather Station from the main menu of the Home Screen.
VisualWeather™ Software 7.2.3 Crop Water Need CROP WATER NEED — Select the Crop Name and enter the Planting Date. Next enter the Duration (Days) for each crop stage (initial, development, midseason, late-season). The beginning date of each stage will be automatically calculated. Next enter the Crop Coefficient for each stage. NOTE 16 Alternatively, you can enter the stage start dates instead of the duration. The duration of each crop stage will be automatically calculated.
VisualWeather™ Software 7.2.4 Growing Degree Days and Growing Degree Days 2 GROWING DEGREE DAYS AND GROWING DEGREE DAYS 2 — Enter the Crop Name. Next enter the Lower and Upper Temperature Limit for the crop. If Fahrenheit is entered, the Celsius value will be calculated automatically. If Celsius is entered, the Fahrenheit value is calculated automatically. 7.2.5 Chill Hours CHILL HOURS — Enter the Reference (Base) Temperature in either Fahrenheit or Celsius.
VisualWeather™ Software 7.2.6 Custom Reports Custom reports are available that let you plot one or more traces on a graph and/or monitor one or more data values in a table. To create a custom report, press the New Custom button on the Custom/Edit Reports screen. The Report Title and Sub Title fields are used to provide headings for the graph. The Left and Right Axis Description fields are used to provide a label for each axis.
VisualWeather™ Software 7.2.7 Custom X-Y Reports Custom X-Y report are available that allow you to plot one or more X-Y traces on a graph and/or monitor one or more data values in a table. The user specifies what will be used for both the X axis data values and the Y axis data values on the graph. Each Y axis data value is plotted against the X axis data value with an identical timestamp. The Report Title and Sub Title fields are used to provide headings for the graph.
VisualWeather™ Software right-clicking and choosing Delete. Selecting the Generate daily values if time range > 1 day will cause only daily values to be monitored if the time range for the report is greater than two weeks. Press the Delete This Report button to delete this custom X-Y report. 7.2.8 Custom GDD Reports Custom GDD report are available that are similar to the GDD and GDD2 reports, but allow the user to choose the algorithm used to calculate the GDD.
VisualWeather™ Software • Upper-Lower – Uses both the Upper Temperature Limit (upperThreshold) and Lower (Base) Temperature (lowerThreshold) to calculate the GDD. The method of calculation changes based on both the Temp Values to Use field and the Cutoff Method field as described below: o Average Temperature None – Not adjusted for upper threshold. Basically the same as the Simple GDD Method.
VisualWeather™ Software NOTE • Sine – This GDD Method is an industry standard also known as the Baskerville-Emin (BE) method. The method of calculation changes based on the Cutoff Method field. • DoubleSine - This GDD Method is an industry standard. The method of calculation changes based on the Cutoff Method field. The Lower (Base) Temperature and Upper Temperature Limit can be entered in either the Fahrenheit or Celsius field.
VisualWeather™ Software 7.3.1 New To create a new batch report click the New button on the Batch Reports Schedule screen. The Batch Report Selection screen is displayed. This screen is much like the screen shown when manually generating a report except you have additional fields to enter. Batch reports can be created only for current weather stations (that is, you cannot create Batch Reports for historical data of deleted weather stations). Select the Output types desired.
VisualWeather™ Software Select whether you want to generate on Demand (user initiated creation) or according to Schedule (automatically generated). When Generate on Demand is chosen, a defined report will be run when it is selected from the Reports | Batch Reports menu. When Generate According to Schedule is chosen, the report will be run automatically based on the additional fields. The additional fields enabled will be based on the Report Type selected as follows: 24 hour Creates a 24 hour report.
VisualWeather™ Software 7.3.2 Edit To Edit a batch report that has already been created, select it in the list and click the Edit button. The batch report will be loaded in the Report Selection screen. Edit the selections and click the Save Batch button. The changes will be saved. 7.3.3 Run All batch reports, including those set up as scheduled, can be run on demand. Select the batch report you wish to run and click the Run button. The report will be generated.
VisualWeather™ Software The following components are available in Station Data. Listed below each component are the sensors (for pre-configured weather stations) and real time fields (for custom stations) required for each condition to be displayed.
VisualWeather™ Software Note that when using Air Temperature and RH to calculate the Heat Index, the Air Temperature and RH must fall within these boundaries in order for Heat Index to be calculated: Air Temperature ≥ 80 °F RH ≥ 40% If either measurement is outside the boundary, the Heat Index will be reported as N/A. The condition that caused the Heat Index not to be calculated will also be specified. See Appendix F for more information on Heat Index calculation.
VisualWeather™ Software Rain Last 24 Hours Rain Last 24 Hours Sensors: TE525-T Tipping Bucket Rain Gage, TE525WS Tipping Bucket Rain Gage, TE525mm Tipping Bucket Rain Gage, or CS700 Tipping Bucket Rain Gage w/syphon Real Time Fields: Rain Fall Relative Humidity Relative Humidity Sensors: HMP50-ET Temp/RH Sensor, HMP35C, or HPM45C Real Time Fields: Relative Humidity 28
VisualWeather™ Software Barometric Pressure Barometric Pressure Sensors: CS105MD Real Time Fields: Barometric Pressure Solar Radiation Solar Radiation Sensors: CS305-ET Solar Radiation or LI200X Real Time Fields: Solar Radiation 29
VisualWeather™ Software Air Temperature and Relative Humidity Air Temperature and Relative Humidity Sensors: Sensors that measure Air Temperature and Relative Humidity Report Fields: Air Temp Avg and RH Avg (backfills last 7 days) Soil Temperature and Soil Water Content Soil Temperature Sensors: 107 Temperature Probe or 108 Temperature Probe Real Time Fields: Soil Temperature Soil Water Content Sensors: CS615 or CS616 Real Time Fields: Soil Water Content Battery Voltage Datalogger Battery Voltage Real
VisualWeather™ Software Enclosure RH Enclosure RH (inside the weather station enclosure) Real Time Fields: Enclosure RH 9. Monitoring the Data Collection Status To view the current status of scheduled collection for stations, select the Collection Status heading or Network | Collection Status menu item from the main menu of the Home screen. The Collection Status screen shows the current status of all stations currently configured in VisualWeather.
VisualWeather™ Software Network Paused - VisualWeather has paused communication in the network. Unreachable - The device cannot be reached through the network. Comm Status - A device has four communication states: Normal, Marginal, Critical, or Unknown. The current status of the device will be reflected in this column. Line State - The state of communication with the device in the network. Off-line - No communication is taking place with the device.
VisualWeather™ Software NOTE Total Retries and Total Failures will equal Total Attempts. A graph is shown for each station to help show historical communication information about the station. A maximum of 72 bars are shown. Each bar represents 15 minutes. The communication failure percentage determines the height of the bar. It is calculated as: (Failures + Retries) / Attempts.
VisualWeather™ Software To remove a station from the network, select it and click the Remove Station button. The station will become a past weather station. Reports may still be generated for the station with historical data, but no new data can be collected from the station. A station may be removed from the network completely from the Network | Remove Station menu item. NOTE The Remove action cannot be undone. To edit the configuration for a weather station, select it and click the Edit Station button.
VisualWeather™ Software Air Temperature (requires one of the following) • • • Air Temperature Min Air Temperature Max Air Temperature Avg Solar Radiation • Solar Radiation Avg Relative Humidity (requires one of the following) • • • RH Min RH Max RH Avg Rain • Rain Fall Total Wind Speed • Wind Speed Max Wind Rose • • Wind Speed Avg Wind Direction Avg Barometric Pressure (requires one of the following) • • BP Min BP Max Leaf Wetness • • • • Leaf Wet AVg Minutes Wet Leaf Transition Point Leaf W
VisualWeather™ Software Soil Water • Soil Water Avg Fuel Moisture • Fuel Moisture Avg Evapotranspiration • • • • Air Temperature Avg RH Avg Wind Speed Avg Solar Radiation Avg Crop Water • • • • Air Temperature Avg RH Avg Wind Speed Avg Solar Radiation Avg GDD • Air Temperature Avg GDD2 • Air Temperature Avg Chill Hours • Air Temperature Avg Dew Point (requires one of the following) • • Dew Point Min Dew Point Max Wind Chill (requires one of the following) • • Wind Chill Min Wind Chill Max
VisualWeather™ Software 11.2 Real Time Field Mapping Data mapping required to monitor Current Conditions and view Station Data is done from the Real Time Field Mapping screen of the EZSetup Wizard. (Real Time Field Mapping is the fourth screen under the Data Files/Mapping section of the EZSetup Wizard.) The goal is to associate the RealTime Parameter with a value, or Data Field, in the datalogger.
VisualWeather™ Software • NOTE If FTP Enabled is checked, all files that are being output to the Local Output Folder will also be sent to the Remote Folder using the specified FTP settings. These files include station data images, WebData.xml, and batch reports. In order to set up the web page, the user will initially need to copy default.htm and the \Web\yui directory to the FTP location. These will not be copied automatically.
VisualWeather™ Software 13. Exporting and Importing Data 13.1 Exporting Data Data retrieved from a weather station can be exported to a file for further data processing. From VisualWeather’s main menu, select Tools | Export Data. Highlight the desired weather station name from the list of Current or Past Weather Stations. The names of the data tables associated with the selected weather station will be displayed. Select the desired table to be exported in the Select a Data Table list.
VisualWeather™ Software 13.2 Importing Data The Import Data function can be used to import data from a data file into VisualWeather’s database for a specified weather station. From VisualWeather’s main menu, select Tools | Import Data. Type in the filename to be imported in the Data File field or press the browse (…) button to browse to the desired file. If the data file is from an array-based logger, you will also need to specify an associated *.
VisualWeather™ Software 15. Programming Custom Weather Stations When an ET106, ET107, Toro T107, or MetData1 station is configured in VisualWeather, a program for that weather station is automatically generated based on the sensors chosen during setup. When custom stations are configured in VisualWeather, you must generate the program yourself if the station has not been previously programmed. Short Cut for Windows (SCWIN) has been included in VisualWeather for this purpose.
VisualWeather™ Software Object State Log (state$.log) - This log is used for troubleshooting an object in the weather station network. The information in this log conveys the state of an object at a given time. Low Level I/O Log (io$SerialPort_1) - This log displays low level incoming and outgoing communications for a root device (i.e., serial port). 16.2.2 Using LogTool When the LogTool is first opened, two logs are displayed: the transaction log and the communication log.
VisualWeather™ Software Log files can be saved to individual files automatically by selecting Options | Log File Settings from the LogTool menu and selecting To Disk for the appropriate log. In addition to controlling whether the logs are saved to files, Log File Settings also lets you set the size and number of log files that are created. One set of log files each is created for the Transaction, Communication, and Object State logs.
VisualWeather™ Software 44 1. Click on “Tools” while in the main VisualWeather screen. Click on “Options…” from the drop down menu. 2. In the “Options” window uncheck the box next to “Show Hints”. Click on “OK” to save the changes.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs A.1 Evapotranspiration This appendix explains the process of evapotranspiration (ET) and the methods VisualWeather uses to calculate hourly ET values. It also explains the calculations for vapor pressure deficit of the air and crop irrigation based on ET. Evapotranspiration is the process of water loss in vapor form from a unit surface of land both directly (evaporation) and from leaf surfaces (transpiration).
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs Over the years the Food and Agriculture Organization of the United Nations (FAO) has published several documents related to evapotranspiration and other agriculture related issues. We allow the option of switching between three ETo methods: 1. Standardized Reference ETo for Short Crops (~0.12 meter in height), Grass Reference 2. Standardized Reference ETo for Tall Crops (~0.50 meter in height), Alfalfa Reference 3.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs 2. Calculations for Rn (net radiation at the crop surface). The net radiation, Rn, is the algebraic sum of radiation at the crop's surface, with the sign convention that the incoming radiation is positive and the outgoing radiation is negative. The incoming radiation is higher in energy (i.e., shorter in wavelength) than the outgoing radiation (which is longer in wavelength).
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs 2b. Calculation of the Radiation Ratio (Rs/Rso) Rs = measured value of solar radiation (MJ/m2 /hour) Rso = clear sky solar radiation; i.e., solar radiation with no cloud cover (MJ/m2 /hour) The general equation used to calculate the solar radiation is: Rs = (as + bs (n/N))Ra (4) where as = constant = 0.25 bs= constant= 0.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs Where n = number of hours of actual sunshine (hours) N =maximum possible number of hours of expected sunshine (hours) For a completely overcast day n = 0; therefore, RS= aS Ra, the constant aS = fraction of extraterrestrial radiation reaching the earth on a overcast day. For an entirely clear day n = N RS= (aS + bS )Ra = clear sky radiation , aS + bS = fraction of extraterrestrial radiation reaching the earth on a clear day.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs Lz = Longitude of the center of the station's time zone (west of the Greenwich line as 0o ) around the earth in clockwise direction (degrees west of Greenwich) Lm = Longitude of the measurement site (west of the Greenwich line as 0 o) 3. Sc = seasonal correction for the solar time (hour) = 0.1645 sin (2b) -0.1255 cos(b) -0.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs where the atmospheric pressure is obtained from the following equation: ⎡ 293 - 0.0065Z ⎤ P = 101.3 ⎢ ⎥ 293 ⎣ ⎦ 5.26 (18) where, Z = Elevation in meters. In the above calculation the temperature is assumed to be 20°C; hence, T (Kelvin) = T (°C) + 273 =293. Note that by taking the value of temperature to be 20 °C at all altitudes the temperature dependence of γ has been ignored. At sea level Z= 0; therefore, P = 101.3 kPa.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs The 24 hourly values of ETo calculated using equation (2) are added to derive an ETo (mm/day) value for a day. This process is repeated 7 times for weekly reports and 30 times for a monthly report. 7. Cn, Cd constants The value of Cn and Cd are dependent upon the ETo method used and whether it is day or night. The following table shows the values used for each method and time of day.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs This difference is calculated by calculating the saturated vapor pressure of the air VP deficit = (e°(Thr)-ea)) Where, e°(T) saturated vapor pressure (kPa) of the air at temperature T (Ref. Equation (19) above) ea actual vapor pressure (kPa) of the air (Ref. Equation (20) above) A.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs Table 1. Names, symbols and units of all quantities used in calculations of hourly ETo values.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs Latent heat of vaporization of water λ=2.45 MJ/kg Atmospheric pressure P kPa Psychrometric constant γ kPa/oC Saturation vapor pressure at T eo(T) kPa Actual vapor pressure ea kPa Vapor pressure deficit of the air at T eo(T)-ea kPa Solar constant GSc= 0.
Appendix A. Evapotranspiration, Vapor Pressure Deficit, and Crop Water Needs SIGMA = 2.043 x 10 -10 Stefan-Boltzmann constant SIGMA*(absolute temp)4 MJ/m2/K4/hour MJ/m2/hour Long wave, low energy radiation Rnl MJ/m2/hour Net radiation (short wave-long wave radiation) Rn MJ/m2/hour Soil heat flux (if Rs>0 then 0.1*Rn, else 0.5*Rn) G MJ/m2/hour Net radiation - soil heat flux (Rn-G) MJ/m2/hour Denominator (Denom) in the equation for calculating ETo Denom = Δ + γ (1+0.
Appendix B. Growing Degree Days (GDD) B.1 Growing Degree Days This section explains the concept of growing degree-days (GDD) and methods used in VisualWeather to calculate its hourly values. Growing degree-days (GDD) is a measure of temperature condition that is favorable to plant growth. A range of temperatures is defined by entering lower and upper temperature limits. Temperatures lying within these limits are assumed to be conducive for growth of a given plant.
Appendix C. Dew Point C.1 Dew Point Dew point is the temperature at which air saturates, upon cooling, without change in its water content. C.1.1 Method 1. The value of saturation vapor pressure, es (kPa), is calculated using the polynomial in Ta, the air temperature1 es=(a0 + Ta*(a1+Ta*(a2+Ta*(a3+Ta*(a4+Ta*(a5+a6*Ta))))))*0.1; (1) where Ta is the mean hourly temperature and the polynomial coefficients are: a0=6.107799961; a3=2.650648471E-4; a6=6.136820929E-11; a1=4.436518521E-1; a4=3.
Appendix D. Wind Chill D.1 Wind Chill Wind chill is a degree of ‘coldness’ experienced by exposed human skin due to increasing wind speeds at a given ambient temperature. Wind chill temperature drops with increasing wind speeds at a constant air temperature or with decreasing air temperatures at a constant wind speed. The wind chill effect is more pronounced when the wind speed increases and air temperature drops.
Appendix E. Chill Hours E.1 Chill Hours Chill hours represent the number of hours the temperature stayed at or below a certain base (or reference) temperature provided by the user. E.1.1 Method 1. The hourly average temperature value, Ta, is compared to the base temperature. 2. If Ta < = BaseTemp, then the number of chill hours = 1, and If Ta > BaseTemp, then the number of chill hours = 0 3.
Appendix F. Heat Index F.1 Heat Index Heat index is the perceived temperature as influenced by relative humidity. For example, an air temperature of 90°F would feel like 132°F if the RH was 100%. The equation is only useful if air temperature > 80°F (27°C) and relative humidity > 40%. VisualWeather will report the wind chill as N/A if air temperature is < 80°F (27°C) or relative humidity < 40%. F.1.1 Method Heat index equivalent temperature (°F) can be obtained by using the following equation[1]. HI = -42.
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