Dual-polarization radar will be pickier on precipitation, more precise on tornadoes.
The most significant addition to the weather forecasting toolbox in nearly two decades is expected to arrive Tuesday at the Twin Cities office of the National Weather Service.
Dual-polarization radar, coming as part of a $50 million radar upgrade for 160 Weather Service offices around the country, promises better tornado detection and more precise predictions of what's about to fall from the sky -- including how much and how fast.
Weather watchers will notice one difference on the Internet immediately. Radar readings from the Chanhassen office will cease temporarily Tuesday, and users will have to use scans of south central Minnesota and western Wisconsin from the Federal Aviation Administration's Woodbury radar tower, as well as from neighboring Weather Service radars in Duluth, La Crosse, Sioux Falls, Des Moines and Aberdeen, S.D. Links to those displays are at www.startribune.com/a1598.
The Chanhassen service will be unavailable for about a week.
The Weather Service radars adjacent to the Twin Cities, except for Des Moines, have been upgraded already. Upgrades, which were scheduled during times when severe weather risks are generally low, are being completed in about half the time originally envisioned.
"From a user standpoint, which is really all we care about, it went very, very smoothly, " said Dan Miller, chief science officer for the Duluth weather service office, where dual-polarization radar is already operating.
The new radar displays won't look any different from those the public is used to, and weather officials said it will take time even for professionals to explore the dual-polarization radar's capabilities. But at the very least the new radar, by looking into clouds horizontally as well as vertically, will be able to determine the size, shape and density of precipitation. Current radar can only determine that precipitation is present.
"Snow? Rain? Hail?" said Tom Hultquist, science officer at the Twin Cities Weather Service office, describing distinctions the new radar is expected to be able to make. "Is it wet snow, dry snow, graupel or a biological target? Is it unknown?"
Dual-polarization radar should also be able to provide accurate readings of precipitation that has fallen over wide areas, which in some cases could help property owners, emergency responders and transportation planners "downstream" prepare for disruptions, Hultquist added.
The new radar also will be able to detect airborne debris, which can be a more accurate sign of a tornado than the "hook echo" radar image of storm clouds. Hook echoes often lead directly to tornado warnings, but may or may not represent actual tornadoes. So there is some hope that the radar upgrade could cut down on false tornado alarms, which most are.
Bill McAuliffe 612-673-7646