NOAA's Efforts to Fix Critical Weather Radar Gaps Are Slow Going

Doppler radar transformed the way we look at the weather. Tornadoes and severe thunderstorms rarely sneak up on us anymore. However, it only works when it can see the right parts of the storm. Central North Carolina has one of the worst weather radar gaps in the United States. Charlotte is the largest city in the country without adequate low-level radar coverage. There are several similar gaps across the country, but none with so many people at a disadvantage. Congress has tried multiple times over the past few years to rectify the problem. Although a renewed effort to look into gaps in radar coverage became law last year, progress is slow going.

Congress doesn't pay much attention to the weather unless there's discussion about a disaster or climate change. There are a few bills in each meeting of Congress to beef-up funding for forecasting and research, but like most proposed legislation, they never see the light of day. The Weather Research and Forecasting Innovation Act of 2017 represented the most attention Congress has paid to weather forecasting in decades. The bill, which the president signed into law in April 2017, was geared toward improving forecasts and creating better and more timely severe weather warnings.

Among other things, the lengthy piece of legislation specifically directs NOAA to conduct research into critical efforts like increasing tornado warning lead time, increase the accuracy of hurricane forecasts, and work toward better weather modelling.

The bill also directs the agency to identify gaps in the country's network of weather radars and propose a plan to fill those gaps. Lawmakers gave NOAA 180 days after the bill became law to submit to the Senate a report on gaps in radar coverage across the country and 90 days after that to formulate a plan to rectify the problems.

It's been exactly 450 days since the enactment of that legislation. The agency has not yet completed a report on radar gaps or a plan to fix them, a spokesperson for the National Weather Service told me on Tuesday.  When I asked when the agency expected to complete the report, the spokesperson added:

NOAA is working diligently to complete the study and report required. We take this requirement very seriously. Congress was made aware during the formulation of this legislation that such a study and report would take much longer than six months.

Gaps in weather radar coverage is an issue I've talked about for years. The first freelance article I ever wrote was about the radar gap in North Carolina. I've lived near Greensboro for the past eight years.  I'm intimately aware of the occasional sketchiness of radar coverage in this state. The stretch of Interstate 85 between Charlotte and Greensboro has minimal low-level radar coverage, a dangerous gamble with the number of severe storms that regularly traverse over so many people.

Why is this such an issue? It starts with the nature of weather radar and the nature of bureaucracy.

Despite Its Flaws, Radar Today Is Still Better Than Ever

Source: National Weather Service/Wikimedia

Weather radar came into operational use in the United States at the end of the 1950s. The network started with installation of the first WSR-57 radar dish at the National Hurricane Center in Miami on June 26, 1959. Dozens more would be installed over the following years, including the WSR-57 radar atop 30 Rockefeller Plaza in New York City (pictured above) that's still there to this day.

Source: NWS

Early weather radar had limited range and could only see the location and, later on, the intensity of precipitation—a far cry from today's capabilities. The above image shows the terminal that displayed radar data from a WSR-57 radar near Cincinnati, Ohio*. The hook echoes on the monitor are supercells producing destructive tornadoes during the Super Outbreak of April 3, 1974.

There were more than 130 densely-packed radar sites across the central and eastern United States before the network was modernized with the rest of the National Weather Service in the 1990s. The Next Generation Radar (NEXRAD) network was developed in the late 1980s and the National Weather Service began retiring the old radar sites and installing Doppler weather radar (WSR-88D) around the country in 1992.

Weather radar sites before modernization (pre-1989) and after modernization in the 1990s. The radar installed in western Washington in 2011 is not shown. (Source: NWS/National Academy Press | Titles added by author)

The current generation of radar uses the Doppler effect to detect the wind speed and direction within a storm, critical in the detection of storms capable of producing severe winds, hail, and tornadoes. The improved technology also gave the new radar devices a larger radius and higher resolution than the older generations, allowing the use of fewer sites that are spread across a greater distance. Recent upgrades added dual-polarization capability to the existing radar network, giving meteorologists the ability to identify rain, hail, wintry precipitation, and tornado debris.

If Only Earth Was Flat...

Source: NWS Jetstream

Doppler weather radar works by sending out strong radio waves from the radar dish at a slight angle—the standard angle for low-level coverage is 0.5°. The energy reflects off of objects in the atmosphere and the radar measures the strength of the returning beam and the time it takes to return in order to determine the location, intensity, speed, direction of movement, size, and shape of the objects in the beam's path. The radar dish then adjusts its angle upward and repeats this process for several minutes until it has a complete scan of the atmosphere.

This leads to a couple of flaws in radar technology. The first is that large objects like water towers, wind turbines, and mountains can block the beam. A temperature inversion can refract the radar beam back toward the ground and lead to false returns. Radar towers are vulnerable to lightning strikes, wind damage, and aging mechanics, which could render them inoperable at the worst possible time.

Source: NWS Jetstream

Radar is also eventually thwarted by the curvature of the Earth itself. The radar beam grows higher and higher above ground level as it gets farther away from the radar site. This limits a radar site's effectiveness beyond a certain radius when it comes to looking for tornadoes and other severe hazards.

Source: NWS

The beam curving upward with height results in gaps in radar coverage. Most of the largest gaps occur in the Rocky Mountains where the terrain simply blocks the signal from covering some communities, but some of the gaps are due to radar sites being spaced too far apart. The worst gaps east of the Rockies occur over South Dakota, Missouri, parts of the Deep South, and the worst (by number of people affected) is in central North Carolina.

Low-level radar coverage is important because that's where tornadoes form. It's crucial to see rotation within a thunderstorm as close to the ground as possible in order to detect a potential tornado and issue warnings with adequate lead time. 

Central North Carolina Got Overlooked

A radar image of the tornado near Charlotte, N.C. at 2:32 AM on March 3, 2012. The left image shows base reflectivity (precipitation) and the right image shows base velocity (wind). The radar is located to the west near Greenville, S.C.

The urgency surrounding the radar gap in North Carolina surrounds the unease of knowing what can happen without adequate radar coverage in a densely populated area. Charlotte is the largest metropolitan area between Atlanta and Washington D.C. The city and its suburbs are home to more than 2.4 million people, a population greater than that of 15 states.

There's a small Terminal Doppler Weather Radar (TDWR) site at the Charlotte Airport, part of a network of airport-based radars meant to protect arriving and departing flights from dangerous conditions. These radars are different from the WSR-88D in that they have a much shorter range and they're more susceptible to interference.

The lack of low-level coverage in central North Carolina isn't a theoretical game of what-if. An EF-2 tornado touched down a few miles northeast of Charlotte in the middle of the night on March 3, 2012. There was no tornado warning before the storm. The tornado damaged hundreds of homes and injured several people.

The tornado happened quickly and, despite its strength, the rotation was shallow. The beams from nearby Doppler radar sites were far too high to catch the rotation in the storm. The beam from the radar near Greenville, S.C., was 8,200 feet above ground level at the site of the tornado. The radar image above shows the Greenville radar at the time of the tornado. The beam there from the radar in Columbia, S.C., was 9,100 feet high. The tornado signature did show up on Charlotte's TDWR site, but it wasn't particularly strong.

This issue was known long before any new radar sites were built. Years of debate preceded the Weather Service Modernization Act of 1992, which consolidated smaller, more localized offices into the agency we know today.  A subcommittee in the U.S. House of Representatives held a hearing called "Tornado Warnings and Weather Service Modernization" on August 7, 1989, to specifically discuss the proposed closure of the Charlotte weather service office.

The modernization plan divided the Charlotte area between the consolidated NWS offices in Greenville, S.C., Columbia, S.C., and Raleigh, N.C. The new Doppler weather radars sites were co-located with those three offices, leaving Charlotte—a city whose metropolitan area has millions of people—split in thirds with radar coverage to match.

Many of the issues we're dealing with nearly 30 years later came to light in that congressional hearing. The subcommittee heard a variety of opinions on the topic. The head of citizens' emergency preparedness committee at UNC Charlotte pleaded in his testimony not to move city's radar to Columbia for fear of losing low-level radar coverage:

Jack Roper, broadcast meteorologist for WSPA in Greenville, S.C., expressed his concern about the  new radar system's spatial coverage in his part of South Carolina. He characterized the new Doppler network as something that "could be a new Edsel," a reference to Ford's aggressive marketing of a line of cars that failed to meet the ad campaign's lofty expectations and resulted in tremendous financial losses for the company.

The issues were raised again in a letter from Rep. Liz Patterson (D-S.C.) to Sen. Ernest Hollings (D-S.C.) before a June 1991 U.S. Senate hearing on NWS modernization.

Despite all of the concerns voiced in the years leading up to modernization, Charlotte still lost its weather office and its weather radar to smaller cities down the road. Problems with radar gaps were well known when the government started planning the current radar network, especially in central North Carolina, even as the agency said several years after modernization began that there was no lowering of the quality of service in the Charlotte area.

Past Attempts to Fill Radar Gaps

Several congresspeople introduced legislation to improve Doppler weather radar coverage in the years before the 2017 bill became law. The most recent legislative success that directly resulted in a new weather radar came after a push by Sen. Maria Cantwell (D-WA) to secure funding for a new radar site on the Washington coast. The new radar, which went into service in the fall of 2011, was important in monitoring Pacific storms as they approach Washington and Oregon.

Rep. Robert Pittenger (R-NC) and Sen. Richard Burr both introduced the Metropolitan Weather Hazards Protection Act of 2015 in their respective chambers. The bill directed the government to construct new Doppler weather radar sites near big cities in known radar gaps within a year and a half of the bill's passage. The, uh, creative specifications laid out in the bill—"maintain and operate at least one Doppler weather radar site within 55 miles of each city in the United States that has a population of more than 700,000 individuals"—served to limit the scope of the bill to pretty much just Charlotte, North Carolina. The bill passed the Senate by unanimous consent but died after the House took no action.

Rep. Charles Boustany (R-LA) introduced the RADAR Act in 2016, which died without any legislative action. The bill would have required both 1) the operation of at least one Doppler radar site within 55 miles of each state capital and 2) that any future radar sites would be located near at least one county with a population of 130,000+ that doesn't have adequate low-level radar coverage.

The capitals of 13 states, including Boustany's home state of Louisiana, would have been eligible for new radar sites under the proposal. While the bill would have filled in some glaring gaps in coverage, including those in central South Dakota, central Missouri, and southern Louisiana, it essentially told North Carolina that it can wait its turn until the next time around.

All of the radar-related bills introduced in Congress since Cantwell's successful push a decade ago have died in their respective chambers except for the Weather Research and Forecasting Innovation Act of 2017, the effectiveness of which is still pending.

Assuming a similar timeline to the western Washington radar earlier this decade—funding secured in 2009 and the radar made operational in 2011—we likely won't see any new radar sites until the early 2020s.

[Top Image: Pierre cb via Wikimedia Commons]

*I originally said the old WSR-57 radar image was from Wilmington, Ohio. The NWS office is in Wilmington, but the radar is in Covington, Kentucky, near Cincinnati. I've corrected my error.

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How Do Forecasters Know There's a Tornado Without Seeing It? (Science!)

One of the big problems we run into when we talk about the weather is that people underestimate the risk they face when severe storms approach. The "it'll never happen to me" mindset doesn't only apply to heart attacks and car accidents. The odds that any one of us will find ourselves in the path of a tornado is relatively small. But it still could happen.

It's instinctive to want to run outside and look around when a tornado warning is issued. You want to see the tornado to internalize the threat and seek safety—unfortunately, by the time you can see the tornado, it's usually too late. Meteorologists have some fantastic tools available to them to detect a tornado many minutes before it hits a location, and an important part of severe weather safety is training ourselves to overcome our instincts and trust the warning that an unseen danger is on its way.

Tornadoes were such a sensitive topic in the days before weather radar that meteorologists weren't allowed to publicly mention the word "tornado" for fear of setting off mass panic. After all, tornadoes came by surprise without the technology to detect or predict the storms that produce them. The first successful tornado forecast was issued by meteorologists Ernest Fawbush and Robert Miller at Tinker Air Force Base in Oklahoma City back on March 20, 1948. Fawbush and Miller alerted the commanders at the military installation of the threat three hours before a severe thunderstorm swept across the base and dropped a damaging tornado. Their accurate warning 70 years ago opened the door the advances in tornado forecasting from which we benefit today.

Today, tornado watches and warnings are a ubiquitous part of weather forecasting.

• A tornado watch is a short-term forecast that means conditions are favorable for thunderstorms that could produce tornadoes over the next couple of hours.
  
• A tornado warning is issued when meteorologists detect a thunderstorm capable of producing a tornado, or they have evidence that there's a tornado on the ground. 

It’s easy to confuse a watch and a warning. A watch means you should watch for bad storms, and a warning means you need to act immediately. Tornado warnings are based off of spotter confirmation of a tornado or Doppler weather radar showing strong indications that a tornado is possible or occurring.

Most folks see tornado warnings so often—and personally see a tornado so infrequently—that it can become easy to ignore these warnings as just another false alarm. That's a dangerous gamble to make. Meteorologists don't issue tornado warnings for no reason. There's usually good evidence that a tornado is possible or occurring, and it's all thanks to weather radar.

Weather radar came into use during World War II when soldiers tasked with tracking enemy aircraft found that their radar was picking up rain in the distance instead. This technology revolutionized our ability to track the weather, keeping tabs on everything from snow showers to tornadic supercells without requiring eyes on the ground to scour the skies. Weather radars kept tabs over most of the United States by the 1960s and these devices have undergone upgrades every couple of decades to keep up with scientific advances of the time.

The current generation of radars began service in the early 1990s. Weather radar up until that point could only see the location and intensity of precipitation. The new technology utilized the Doppler effect to detect the speed and direction of precipitation—by measuring the velocity of raindrops, you can accurately calculate the wind speed within a thunderstorm. This became an enormous help in figuring out which thunderstorms were severe and which storms included rotation that could produce a tornado.

The Johns Island, S.C., Tornado

Let's look at a tornado that struck near Charleston, South Carolina, in the middle of the night on September 25, 2015. The EF-2 tornado damaged dozens of homes in Johns Island, but advanced warning helped all residents safely avoid injury despite the tornado touching down after midnight.

Thunderstorms were in the forecast for the Charleston area that night, but there was no tornado watch in effect and the Storm Prediction Center made no mention of a potential for severe weather the night the tornado touched down. The larger environment wasn't conducive for widespread severe weather. Just the right mix of ingredients came together to allow a thunderstorm coming ashore to turn into a supercell and drop a significant tornado. That tornado would have come as a complete surprise if it weren't for Doppler weather radar.

The above image shows the reflectivity image (precipitation) we're so used to seeing on the news or in a weather app. It is possible to see where a tornado might be located in this image if you're experienced in working with radar imagery, but it's not obvious and could easily be overlooked if you're not expecting tornadoes to develop in that kind of an environment. This is where Doppler technology comes into the picture.

If you look at the winds within the thunderstorm west of Charleston, it paints a much different and much uglier picture of what's going on that night.

The velocity products generated by radar images are usually displayed as shades of red and green. Green colors depict winds moving toward the radar while red colors indicate winds moving away from the radar. Brighter colors indicate stronger winds. When you have bright green and bright red colors very close together, forming what's known as a couplet, it indicates strong rotation within a thunderstorm. A look at the velocity image just west of Charleston shows a strong couplet approaching Johns Island. Meteorologists issued a tornado warning when they saw this couplet appear on radar, as the data indicated strong rotation that could produce a tornado.

The 2010s saw a new radar technology called dual polarization (or "dual-pol") added to our existing network of Doppler weather radars. Radar could already detect the location, intensity, and velocity of precipitation, but adding a second radar beam (hence the "dual" in dual-pol) essentially adds a third dimension to radar data. Now you can see both the size and the shape of objects picked up by the radar. This lets you differentiate between raindrops, hailstones, snowflakes, and other objects like birds, bugs, and tornado debris.

That last one—tornado debris—marked another significant leap in tornado forecasting. Tornadoes can loft so much debris into the air that weather radar picks it up as intense returns, creating what's known as a "debris ball" on radar imagery. Dual-pol technology allows meteorologists to see this debris more clearly, giving them the chance to warn people that there really is a tornado on the way. This confirmation helps people know that it's the real deal and hopefully gives them the chance to take the warning seriously before it's too late.

Debris shows up in dual-pol data with a product called "correlation coefficient" ("CC"), which tells you if the objects on radar are similar in size and shape. Uniformly-shaped objects like raindrops and snowflakes have a correlation coefficient between 90 and 100 percent, while dissimilar objects like a wintry mix of precipitation will have a lower percentage.

Tornado debris—including trees, building debris, and vehicles—will have as low of a correlation coefficient as you can register on radar. The tragic mix of debris flying through the air shows up as a conspicuous dark blue splotch on CC imagery, which, when co-located with rotation in a thunderstorm, can be used to confirm the presence of a tornado. All three of the above radar images were taken at the same time. You can see the beginning of debris showing up on CC imagery west of Charleston as the tornado starts lifting debris thousands of feet into the air.

Nine minutes after the initial tornado warning was issued, an EF-2 tornado with 130 MPH winds had torn through several neighborhoods and damaged nearly 80 homes. When you look at reflectivity (top-left), velocity (top-right), and correlation coefficient (bottom-left) together, it paints a dire picture of what could have otherwise been a disaster without advanced warning. You'd never see the tornado since it's after midnight and rain-wrapped. Tornadoes weren't in the forecast. There's no obvious sign of a tornado just by looking at the reflectivity image if you didn't know what to look for.

Doppler and dual-polarization technology gives meteorologists the tools they need to see a tornado long before you do. When a tornado warning is issued, it's issued for good reason. Don't wait to see a tornado if you're ever under a warning. Trust the warnings and use those precious minutes to get to safety.
 

[Images: Gibson Ridge. | Top Image: A supercell producing an EF-2 tornado in Mobile, AL, on Christmas Day 2012.]

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