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The GRCA has implemented an automated system to download, import, display and archive rainfall data collected by the NEXRAD radar system operated by the United States federal agency National Oceanic and Atmospheric Administration (NOAA) and delivered by the National Climatic Data Center.
The NEXRAD data product being used is called the Digital Precipitation Array (DPA) which represents a moving one hour total of rainfall accumulation. When rain is detected the DPA file is updated every 6 minutes, and 10 minutes when there is no rain detected in the coverage area. The GRCA constantly downloads the DPA data and imports the DPA interval closest to the top of the hour (this could be +/- 3 minutes from the top of the hour). The data is clipped to a sub-region of the radar coverage, projected to UTM and converted to millimetres per hour.
Each hour, accumulation summaries are calculated for intervals up to 7 days. For example a 1 day accumulation summary from 4:00 p.m. represents the rainfall detected since 4:00 p.m. the previous day. The hourly updates are processed and available at approximately 15 minutes past the latest hour, or 4:15 in the example given here. Users of GRCA web-GIS maps should refresh the map at that time to get the most recent data.
Doppler radar detects rain drops by sending out a pulse of electromagnetic energy from the radar station and then measures the energy reflected back from the rain. Light rain, light snow, or drizzle from shallow cloud weather systems are not necessarily detected. Radar is subject to error of both under estimation (most common) and over estimation. Users should be mindful of variations between ground based rain gauge measurements and radar results. The radar data is presently NOT calibrated to ground-based measurements.
The Buffalo (KBUF) and Detroit (KDTX) radar stations may experience occasional outages which will impact the quality of the rainfall radar data presented on our website. Visit the NOAA/NWS Buffalo and Detroit status pages for more information.