Station Information
Last updated 4/14/07

Location

Sandy Ridge Weather Station began operating in late February 2002, and is located in Howard County, Maryland, in the town of Elkridge.   The station coordinates are 39^o 12' 29" north latitude, 76^o 46' 8" west longitude, with an elevation of approximately 350 feet above sea level.  Click here to see maps showing the station's location.

Weather Sensors

Sandy Ridge weather data are collected with a Davis Vantage Pro wireless weather station (model 6150).  The Vantage Pro integrated sensor suite includes temperature and humidity sensors, an anemometer for wind speed and direction and a self-emptying ("tipping bucket" type) rain collector.  The temperature and humidity sensors are enclosed in a radiation shield to ensure accuracy in direct sunlight.  The sensor suite is solar powered, but also contains a lithium battery as a back-up power source.  The transmitter and battery are housed beneath the radiation shield.  Data are transmitted via radio signal to the Vantage Pro's indoor display console.  The display console employs a digital format liquid crystal display (LCD), powered by an AC adapter or standard C-size batteries.  The console enables real-time display of all variables, plus recall of daily, monthly and annual maximum and minimum values, and time of occurrence.   The atmospheric pressure sensor is built into the console. 

Installation

The Vantage Pro anemometer is detachable from the rest of the sensor suite.  The anemometer is mounted on a tripod atop the roof of our house at a height of slightly more than 30 feet (10 meters) above ground.   The core of the sensor suite, including the temperature and  humidity sensors, rain collector and transmitter are mounted on the side of the deck in our backyard at a height of approximately 6 feet (2 meters), above grass.   Our house is situated close to the crest of a hill at one of the highest points in our development, providing nearly unobstructed exposure to the wind on three sides.   Several tall trees along the property line behind our house will obstruct the wind under certain conditions (see below).

Subjective Assessment of Data Quality

The data from this site are unofficial and are intended for personal interest use only.  

-  The temperature, humidity and wind direction readings agree well with the official readings at Baltimore-Washington International Airport (KBWI), which is located approximately 5 miles to the east-southeast of Sandy Ridge.  

-  The wind speeds are also quite comparable with the official ones, but may exhibit a slight low bias in some conditions.  The low bias appears to be most noticeable with north to northeast winds during summer, due to several tall deciduous trees just beyond the property line in back of our house.   

-  The rain collector has good exposure, and is periodically calibrated against a graduated cylinder-type rain collector placed nearby.  The tall trees along the back of the property line may have a "shadowing" effect which produces a low bias under northeasterly flow conditions during summer.  The rain collector contains a thermally controlled heater for measuring the liquid equivalent of frozen precipitation.  The heater works well in general, although evaporation from the heated surface of the collector appears to produce lower than expected liquid values in some conditions.  The Davis Rain Collector Heater was purchased separately.

-  The atmospheric pressure is corrected to sea level for display purposes and appears to be quite accurate.   

-  Derived quantities, such as the wind chill and heat index, are computed at the Vantage Pro console or by the graphical display package (see below) using standard formulae and also appear to be quite accurate.

Data Logging and PC/Internet Connection

Collection, analysis and graphical display of the data on a PC (including Internet capability) require additional purchase of the Davis WeatherLink graphical software package.  The heart of the package is the WeatherLink data logger, which provides the data storage capability and transfer connection between the Vantage Pro console and the PC.   While WeatherLink provides adequate PC and Internet display capability, I use Ambient Software's Virtual Weather Station (VWS)  graphics package to enhance this capability (the WeatherLink data logger is still required to transfer the data to the PC).   Both WeatherLink and VWS have built in ftp capability for uploading and downloading data, graphical images, etc. to the web site.  The PC has a Pentium III processor with 256 Mbytes of memory and runs Windows XP, although this is far more computing power than is required to run either WeatherLink or VWS.  The Internet connection is via cable modem, which greatly facilitates transfer of data to the web site.

Web Page Content

The Sandy Ridge web site was established in March 2002.  Real-time data, including the 24-hr and 7-day history graphs, are updated every 15 minutes.  Pages with live data, such as the Current Conditions, Local Area weather, etc., refresh automatically every 2½ minutes.  The Avg Wind Speed on the Current Conditions page is the average wind speed during the 10 minutes (10-minute average) preceding the latest update time.  The climatological summaries are updated daily, just before midnight each day.  The yearly rain is the accumulated rainfall since January 1st of the current year.  The weather icon on the Current Conditions page shows the current weather conditions based on information from both Sandy Ridge Weather Station and the latest METAR report from BWI Airport.  Retrieval (download) and display of the METAR reports and daily climatological data (e.g., the normal and record high/low temperatures at area airports shown on the Extremes page) are built-in capabilities of the VWS graphics package.   Unless otherwise indicated, the radar, satellite and forecast information are obtained from the National Weather Service (NWS) and the National Oceanic and Atmospheric Administration (NOAA) (see Acknowledgments, below).