Calibrated Radar Rainfall Data

Overview
We all have heard weather reports indicating how much rainfall occurred on a particular day, but have you ever wondered how rainfall is actually measured? Technical instruments, called rain gauges, are designed to collect and accurately measure rainfall during wet weather events.

However, a rain gauge can provide a specific rainfall measurement only for the particular, very limited geographic area where it is located. The biggest challenge for engineers and planners is accounting for the variability of rainfall across even a small geographic watershed. Unfortunately, it is too costly to place thousands of rain gauges over large geographic areas, such as Allegheny County. Yet, accurate rainfall data is critical for communities dealing with the wet weather sewage overflow issue.

That’s why 3 Rivers Wet Weather created the calibrated radar rainfall system in 2001. Communities in the ALCOSAN service area need accurate rainfall data to analyze and design cost-effective sewer rehabilitation projects and long-term sewer maintenance plans. Through this calibrated system, high-quality rainfall data is available online about two weeks after the end of each month. In 2002, 3RWW expanded the system to cover all 130 Allegheny County municipalities and to provide real-time rainfall data, which is critical for optimizing the operation of wet weather treatment and storage facilities.

3RWW operates and maintains 33 rain gauges throughout Allegheny County, which collect actual rainfall during wet weather events. The primary radar source used for the County is the National Weather Service (KPBZ) NEXRAD radar, located in Moon Township. NEXRAD is the rainfall radar usually seen on TV. The radar data gathered during a wet weather event is calibrated with the rain gauge data collected during the same time period for every one square kilometer in Allegheny County. The data is processed into even time increments and presented in 2,276 1x1 km radar grid cells as shown in the illustration map of Allegheny County.

The major benefit of this program is that it allows engineers and planners to potentially save millions of dollars through more accurate design of wet weather solutions that will help to reduce or eliminate sewage overflows and improve stormwater management.

To login to the calibrated radar rainfall system, click here.