Radar
The GRCA has implemented an automated system to download, import, display and archive rainfall data collected by the NEXRAD radar system operated by the US National Oceanic and Atmospheric Administration (NOAA) and delivered by the National Climatic Data Center.
The NEXRAD parameter collected is the Digital Accumulation Array (DAA#170) which represents the precipitation accumulation for the running past 60 minutes. DAA information is downloaded from Buffalo (KBUF) and Detroit (KDTX) stations every hour. The radar file closest to the top of the hour (this could be +/- 6 minutes) is processed. Data is limited to a sub-region of the radar coverage, resampled, and converted to millimetres. Hourly accumulation summaries are calculated for intervals up to 7 days.
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.
