National Weather Service: No Gap in Coverage During Radar Upgrade

Information provided by the National Weather Service

Beginning today the National Weather Service's Doppler radar station in Chanhassan will undergo an upgrade to incorporate new technology. While the work is being done, radar data will be unavailable.

The radar is scheduled to be unavailable for two weeks during this upgrade. Technicians have recently been completing the upgrade in five to six days, and radar data will become available as soon as the upgrade is complete.

There is an FAA terminal doppler radar near the Twin Cities that will provide some radar coverage around the metro area. Other surrounding radars include: Grand Forks, ND, Duluth, MN, La Crosse, WI, Des Moines, IA, Sioux Falls, SD and Aberdeen, SD.

This upgrade is part of the National Weather Service's vision to build a Weather-Ready Nation to better protect lives and livelihoods. This upgrade will incorporate a new technology called dual-polarization, or dual-pol. This new technology will result in 14 new radar products. This new technology and data will primarily help forecasters identify the type of precipitation that is falling, as well as improve rainfall estimates

Current National Weather Service Doppler radars transmit and receive pulses of radio waves in a horizontal orientation. As a result, the radar only measures the horizontal dimensions of targets (e.g. cloud and precipitation droplets). Dual-polarimetric radar transmits and receives pulses in both a horizontal and vertical orientation. Therefore, the radar measures both the horizontal and vertical dimensions of targets.

Since the radar receives energy from horizontal and vertical pulses, we can obtain better estimates of the size, shape, and variety of targets. It is expected that this will result in significant improvements in the estimation of precipitation rates, the ability to discriminate between precipitation types (e.g. hail vs. rain), and the identification of non-meteorological returns, such as chaff, ground clutter, and smoke plumes from wildfires that are not uncommonly detected by weather radar systems such as WSR-88D.

• Better estimation of total precipitation amounts
• Better estimation of the size distribution of hydrometeors (raindrops, snowflakes, hailstones, drizzle)
• Much improved ability to identify areas of extremely heavy rainfall that are closely linked with flash floods
• Improved detection and mitigation of non-weather related radar echoes (chaff, smoke plumes, ground clutter)
• Easier identification of the melting layer (helpful for identifying snow levels in higher terrain)
• Improved ability to classify precipitation type

The full benefit of dual-pol radar, however, will not be fully realized until NWS forecasters and research meteorologists develop real-time expertise.