Weather Page Information

Weather data is recorded live at Newtown Square, PA which is 15 miles west of Philadelphia. The data on the main page is updated every 10 minutes at 0, 10, 20, 30, 40, and 50 minutes past the hour.

Description of weather conditions graph

  1. Temperature - Sampled once per minute. The graph shows the average for the previous 10 minutes.

  2. Barometer - Sampled once per minute. The graph shows the average for the previous 10 minutes.

  3. Relative Humidity - Sampled once every 10 minutes.

  4. Dew Point - Calculated every 10 minutes using the most recent temperature and relative humidity values.

  5. Wind Direction - Sampled every 2.25 seconds. The graph shows the average direction during the previous 10 minutes (266 samples). The readings are lumped into 22.5 degree wide groups centered on the 16 standard compass points (N, NNE, NE, ENE, etc.) The graph line extend slightly above and below the upper and lower SOUTH limits. There is an area of 45 degree overlap above and below the upper and lower SOUTH limits. The graph line may extend into these areas when the wind is shifting between SE and SW. This is an attempt to try to keep the graph from bouncing excessively between the two south limits when winds are from the south. It does not work perfectly under all conditions but it helps most of the time.

  6. Wind Speed - Measured continuously over 2.25 seconds sample periods. The speed line is the average speed for the previous 10 minutes (266 samples). The gust points are the the maximum wind speed that was read during the same 10 minute period.

  7. Rainfall - Counted in 1/100 inch increments as they occur. The line represents total cumulative rainfall in inches since the beginning of the graph period. For this line, the RAINFALL scale at the left is read directly in inches and will be automatically scaled depending on the total rainfall being reported on the graph.
    The NEW RAINFALL points represent the 1/100 inch measurements counted during the previous 10 minutes. For these points, the RAINFALL scale at the left is read as 5/100 of an inch per division.. so a dot at the first division indicates 5/100 inch counted during that 10 minute interval. These dots help make very small rainfall events more visible on the graph.

Current Conditions and High/Low readings

The current temperature, barometer, and wind readings should correspond to the right most points on the graph above them.

The barometer indicator (R/F/S) is determined by comparing the average of the 6 readings for the most recent hour to the average of the 6 readings for the hour before.

The two numbers for current wind are the average and the max gust speeds recorded over the past 10 minutes.

If the temperature is 40 degrees or lower and the average wind is above 4 MPH, a wind chill index is also displayed. A wind chill index is displayed for both the average wind speed and the max gust wind speed.

If the temperature is 85 degrees or above, the heat index is displayed. Heat index is the apparent temperature (what it feel like) accounting for relative humidity.

Description of the weather station hardware

Temperature and Barometer

Outdoor temperature and barometer readings are obtained from a CONEX   WJ-10 Weather Jack temperature and barometer sensor.

The temperature sensor is located outside a window on the northeast side of my house to minimize exposure to direct sunlight. The sensor is about 5 feet above the ground. A very simple yet effective sun shield is located near the sensor to block direct sunlight during the early morning hours during the summer. From mid-morning on, the house blocks the sun from hitting the sensor. This location receives no direct sun at all from early-September to late-March.

The Weather Jack comes with Windows9x software, however I am using my own custom software allowing it to be used with my Linux server. The Weather Jack is polled by the server via a standard serial interface once per minute for a temperature and barometer reading. After 10 readings (10 minutes), the readings are averaged and saved to a file to be used for the graph.

Relative Humidity

Outdoor relative humidity readings are obtained from a Radio Shack 63-1030 Wireless Thermo-Hygrometer. The outside sensor it mounted next to the weather station temperature sensor. The inside unit is mounted inside a constant illuminated box with a small SuperCircuits PC60XS B&W TV camera aimed at the LCD display. The camera is connected to a Hauppauge WinTV-GO Model 190 TV interface board. The camera captures an analog image of the hygrometer LCD readout which is then converted into a digital image which is processed to essentially "read" the humidity digits. The humidity data is merged with the other data weather data and stored for display.

This method for obtaining the humidly reading may seem a bit awkward but actually turned out to be less expensive than first estimated (somewhat because I already had most of the video hardware). This method also provides a second outside temperature reading (currently not being used) and has the potential to also provide inside temperature and humidity data in the future.

Wind Speed and Direction

Wind speed and direction data is obtained from a Davis Instruments   Standard Anemometer.

The wind direction sensor is a potentiometer type wind vane configured to produce an output voltage 0-5 volts representing 0-360 degrees.

The wind speed sensor consists of wind cups and a magnetic switch. The speed sensor is factory calibrated for a 2 1/4 second sample period, such that the number of revolutions of the cups in 2 1/4 seconds is equal to the wind speed in MPH. Each cup revolution activates a magnetic switch which is wired to produce a digital signal pulse. These pulses are counted over a 2 1/4 second sample period.

A custom interface circuit for these wind sensors includes an 8-bit counter to count the pulses from the speed sensor and an 8-bit analog-to-digital converter to read the wind vane potentiometer voltage. The data is sent from the interface to the Linux server via a standard serial interface.

The wind sensors are currently located at the 65 foot level of my ham radio antenna tower in my backyard which places them well above any trees within well over 200 feet.


Rainfall data is obtained from a Davis Instruments   Standard Rain collector.

This is a self-emptying tipping-bucket design that measures rainfall in 0.01 inch increments. The rain collector uses a magnetic switch setup which closes briefly each time the measurement bucket tips. Similar to the wind speed sensor, the switch is wired to produce a pulse for each tip which is detected by the interface circuit which counts these pulses and passes the information to the Linux host computer.

The wind sensor and rain collector share parts of the same interface circuit and wind and rain data are sent to the computer together in the same message every 2 1/4 seconds.

The Weather Data Files

Over a 10 minute period, the 266 wind/rain samples collected are averaged and merged with the 10 minute averaged temperature and barometer samples, and relative humidity data and written to one common data file. This raw data is available for download if anyone has any use for it. The README file provides a description of the data file format.

The live raw un-averaged data is also available via an Internet socket connection to allow live real-time display of the data remotely. Additional information about using this connection, as well as a Windows "weather gauges" program to display it (sample display), can be obtained from

Temperature and Barometer data collection began on January 28, 2000.   Wind and Rainfall data collection began on October 23, 2000.   Relative Humidity data collection begin on September 30, 2001.

Live Web Cameras

There are 2 live Web cams.   Both cameras are SuperCircuits   PC67XS color mini-cameras.

Camera1 uses the standard 5.6 mm lens it comes with and is mounted on a tripod and aimed out of a second floor window to show my front yard. It is intended to show ground conditions.

Camera2 has a 12 mm lens and is enclosed inside a custom built weatherproof box mounted near the top of my 70 foot ham radio tower. It has full 360 degree AZ/EL motion. It is normally pointed near the horizon to the east-southeast showing the Philadelphia skyline some 15 miles away. It is intended to show sky conditions, however it can easily be re-aimed at any time by remote control via a special Web page or by local commands, as needed.

Each camera is connected to the server through it's own Hauppauge WinTV-GO Model 190 TV interface board. The 'webcam' program which is part of the xawtv suite of programs is used to capture the video image from the WinTV card and produce a jpeg file. Each time a graph is generated, an image from camera 2 is captured for display. Click on the picture will give you additional Web cam options such as viewing captures of live off-air TV which is also available through the WinTV card.

Known bugs

  1. If the graph for yesterday is requested, the current and min/max readings at the bottom labeled 'Today' and 'Yesterday' are actually for 'Yesterday' and the day before Yesterday.

  2. When requesting data for a single date in the past, the 'Today' data is actually for the date being displayed. The 'Yesterday' data is undefined. This is not really a true bug but it may seem a bit weird.

  3. The barometer trend indicator (R/S/F) is based on comparing the average of the 6 10-minute readings for the previous hour to the 6 readings for the hour before that. It may not always match the overall trend shown on the graph.

  4. Due to a limitation in the wind speed sensor interface hardware, the maximum wind speed that can be measured now is 63 MPH. If the wind is faster, it will "roll over" and 64 MPH would be recorded as 0 MPH, 65 MPH as 1 MPH, etc. This limitation will be fixed .. someday, but so far has not really been a problem.

  5. A problem with the transition from EST to EDT in the spring causes the graphs to loose a day on the day of the switch. The data is plotted OK but the date/time label is wrong. I have made several attempts to fix this but I only get one shot a year to test it. April 2002 was still wrong. As of 2005 I think this has been fixed.

  6. I am sure there are other bugs I have missed. Please let me know if you see anything that does not look right.

Click here for the latest status of the weather station.

Last Updated Fri Feb 9 19:11:20 EST 2007