On a clear day, a person could see for nearly a dozen miles all around with no trees or buildings to block the view. Masterson, who maintains electronics for the National Weather Service, didn’t pay much attention to the scenery as he unlocked a hatch in the platform.
On the other side is a big white dome familiar to anyone who has driven north of Mayville on County Road 14.
It feels bigger from the inside, even with a 28-foot wide radar dish dominating the space. The purpose of the radome is to protect the radar from the elements as it scans the skies around the clock for signs of snowstorms, thunderstorms and tornadoes.
When meteorologists in the Red River Valley talk about Doppler radar and point to maps filled with swirling rainbow-hued clouds, this radar by the side of a quiet country road is what they’re talking about. This year, in July, the radar will celebrate its 20th year of operation.
Dan Riddle, a radar specialist in the Weather Service’s Grand Forks office, said the radar an important tool for warning the public about potentially dangerous weather conditions.
It’s especially useful in the summer when tornadoes threaten, he said, but they are also helpful in the winter. In early December, for example, the Weather Service was able to warn drivers of heavy snowfall in a narrow band from Cavalier, N.D., to Cooperstown, N.D., he said.
John Wheeler, a meteorologist at WDAY-TV, said he uses many other tools such as weather satellites and computer models to forecast the weather in the hours or days ahead. Though it has limitations, he said, “radar is the only device that we have that will tell me where is it precipitating right now.”
“It’s a very critical tool because we can’t possibly know what the atmosphere is doing everywhere at once,” he said.
750 microwave ovens
At the base of the metal tower are four shacks housing the equipment that support the radar above. Inside one of them is a cabinet containing a gray metal cylinder the size of a large soup pot.
That’s the klystron, a particle accelerator that generates the microwave pulses the radar uses, Masterson explained, yelling above the din of an air handler. A waveguide, basically an empty tube where microwaves bounce around, connects the klystron to the radar, he said.
A weather radar, like all radars, transmits brief microwave pulses and waits for them to bounce back when they hit something, such as water droplets or ice crystals or even bugs. The length of the wait tells the radar how far away the object is and the way the frequency of the microwaves shifts, called the Doppler effect, tells the radar the object’s relative speed, which is critical for detecting tornadoes.
The radar transmits many times a second but only very briefly while spending most of the time “listening” for the echo; in an hour, it would spend a total of just 7 seconds transmitting and the rest receiving.
Masterson said that’s the only way to detect a signal from many miles away.
The WSR-88D radars that the Weather Service operates uses microwaves in a frequency that’s similar to a microwave oven most people have in their kitchen except the energy transmitted is 750 times greater, he said.
The reason it has to be so powerful is because microwaves lose strength as the beam spreads through the atmosphere and there’s a lot of area for each of Weather Service radars to cover. The nearest one to Mayville is 153 miles away in Aberdeen, S.D.
The radar images the general public is likely to see most is the one with the rainbow-hued clouds because they’re simpler to understand. Cooler hues usually mean little or no precipitation and warmer hues usually mean a lot of it. When the clouds are a fierce shade of magenta, watch out.
Meteorologists use this radar image a little differently. Cooler hues just means weak radar returns and warmer hues stronger returns, which may indicate that there are a lot of large droplets or ice crystals, heavy enough that the wind can’t keep them up in the air any more so they fall to earth. But strong returns could also indicate a flock of birds or wind turbine blades, requiring a bit of interpretation.
The professionals also use many other kinds of radar images. One image uses polarized microwaves — the waves alternate between being horizontal and vertical — to understand the shape of the objects being scanned, if they’re raindrops or snowflakes. Another uses the Doppler effect to see how the wind blows. Red dots indicate objects moving away from the radar and green dots indicate objects moving toward and the brighter the color the faster the object is moving. When a group of bright red objects are next to a group of bright green objects, this suggests they’re moving in opposite directions very quickly, possibly the start of a tornado.
Riddle said Weather Service meteorologists like him use radar images along with ground spotters to determine if they should issue a warning to the public.
The WSR-88D now allows a tornado warning about 14 minutes ahead of the storm, according to the Weather Service. In the early 1990s, when Doppler technology was unavailable, warning time averaged five minutes.
Weather radar is so critical that the one in Mayville has a dedicated Internet connection to the Weather Service office in Grand Forks with a Verizon Wireless antenna as a backup.
“It’s such a valuable tool for remote sensing the atmosphere,” said Ryan Knutsvig, who oversees the radar as head of the Grand Forks Weather Service office. “Think of the numbers of lives saved by radar over the years. It’s quite the advancement in meteorology.”
Seeking ‘ground truth’
But, like any technology, weather radar has its limitations.
Though the maximum range is about 290 miles, there are a lot of reasons why it’s useful range is far short of that. For one, the WSR-88D’s Doppler function, critical for tornado warnings, has a maximum range of 143 miles beyond which its accuracy becomes unacceptable.
For another, microwaves do not follow the curvature of the Earth so the farther they are from the radar the higher up in the atmosphere they tend to be, which can cause them to miss many storms that are closer to the ground.
To compensate, Weather Service radars are built close to major cities and usually have overlapping coverage, which is why the Mayville radar is where it is halfway between the Valley’s two biggest cities and overlapping with five other radars.
The overlap can be imperfect though because radars that overlap at the edge of their effective ranges where the beams are highest above the ground can still overshoot storms closer to the ground. It’s harder to see snowstorms over Alexandria and Thief River Falls for that reason, according to Wheeler.
Because the radar does not provide a perfect picture of the weather, Wheeler and Riddle said meteorologists must still rely on ground sensors, such as the precipitation gauges at airports, and volunteer observers to find out the “ground truth.”
On the horizon
WSR-88Ds were developed in the 1980s with the thought that they would serve about 20 years, which some have already reached. The first non-experimental model started operations in 1992 and the last started in 1997, completing a network of 160 radars nationwide and at overseas military bases.
On the horizon is a technology called “phased-array radar” that’s being tested by the National Severe Storms Laboratory in Norman, Okla., a sister agency to the Weather Service. The old Navy radar was used in the 1970s to track aircraft and missiles.
Most weather radars use one transmitter to scan the skies by turning 360 degrees, raising the dish a few degrees and turning again. To get a complete picture takes a WSR-88D about five minutes.
A phase-array radar doesn’t turn but uses hundreds of transmitters that, by varying the phase of each microwave pulse, can steer the beam electronically. This allows it to scan very quickly getting a complete picture in a minute or two, according to the Weather Service. In one test, the Storms Lab found it could provide a tornado warning 20 minute in advance, six minutes better than average.
And because the phased-array radar is not limited by the mechanical turning action, it can rapidly change scans from one patch of the sky to another. The Storms Lab is investigating whether the phased-array can track storms and aircraft at the same time, which would allow the government to save money on several kinds of radar. That could, for example, allow one radar to replace the Mayville weather radar and an aircraft-tracking radar near Finley, N.D.
But the Weather Service doesn’t expect it’ll be able to field phased-array radars until at least 2030. Until then the WSR-88Ds are getting refurbished and upgraded with better computers to continue service for another decade and a half.
To learn more about the Weather Service radar network, go to www.radar.weather.gov.