Using a dual-pol radar feature to anticipate downburst development

Downbursts—an area of strong winds in a thunderstorm—can damage trees and buildings, disrupt air travel, and cause loss of life. Decades of work by scientists has revealed a lot of information about downbursts including certain features seen on radar, known as precursor signatures, that can help forecasters anticipate when a downburst might develop. However, downbursts are still quite challenging to predict—especially in low-shear, summer-time thunderstorms—perhaps because the downbursts and their precursor signatures can develop quickly and be difficult to observe. 

Therefore, researchers at the University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies with the NOAA National Severe Storms Laboratory decided to look into it further. They studied  a dual-pol radar feature, known as a specific differential phase (KDP) core, because it could provide information about important processes that cause a downdraft to develop and get stronger. Our research shows KDP cores could be a reliable and easily observable downburst precursor signature that can help NOAA National Weather Service forecasters predict where a downburst could develop next. 

Our research began one afternoon in the halls of the National Weather Center in Norman, Oklahoma, when Randy Bowers, a forecaster at the NOAA National Weather Service Norman Forecast Office (OUN) and I (Charles Kuster, a research scientist with the CIMMS working at NSSL), were having an informal discussion about a completely unrelated topic. At the end of our conversation, Randy mentioned seeing a consistent area of high KDP—the KDP core— while issuing severe thunderstorm warnings and wondered if we could do some research on it together. I had been looking for opportunities to work more with forecasters, so this topic sounded like an amazing opportunity. We jumped in and began identifying potential cases, collecting data with a research radar in Norman, and brainstorming how to best study KDP cores.

The KOUN radar with storm clouds behind it.
The NOAA National Severe Storms Laboratory research radar collects data on a downburst-producing thunderstorm in Norman, Oklahoma. (Photo by Charles Kuster, OU CIMMS/NSSL)

Ultimately, we selected 81 downbursts in 10 different states to analyze. I got to work on comparing the size, magnitude, and vertical changes in the KDP cores associated with strong and weak downbursts, while Randy examined atmospheric conditions and possible warning applications. We also began working with Jacob Carlin, a CIMMS research scientist also working at NSSL, who explored model simulations of downdrafts and important microphysical processes—such as melting and evaporation—that can result in a stronger downburst. Another research scientist, Terry Schuur (OU CIMMS/NSSL), also brought microphysics expertise and experience to the team while researchers Jeff Brogden (OU CIMMS/NSSL) and Robert Toomey (OU CIMMS/NSSL) provided extensive support and expertise in radar data analysis software. Andy Dean, a forecaster with the NOAA/NWS Storm Prediction Center, provided data about atmospheric conditions around the downbursts.

Together, we determined KDP cores were a reliable downburst precursor signature in the events we studied. All 81 downbursts were preceded by a KDP core by as much as 30 minutes. The KDP core also reached its maximum intensity, typically about 10–15 minutes before the downburst reached its maximum intensity. In addition, there were very few instances where a KDP core was observed and no downburst occurred (i.e., very few null events).

Anticipating downburst intensity using KDP cores was more challenging because there was overlap between the characteristics of KDP cores associated with strong and weak downbursts, but in general, a stronger KDP core was more likely to be associated with a stronger downburst.

We also found the atmospheric conditions during each event were very important. When atmospheric conditions were less favorable for downburst development, we observed stronger KDP cores, which likely means more melting, precipitation loading, and evaporation are needed for a downburst to develop in such conditions. Ultimately, our work showed KDP cores provide a good signal that a downburst is likely to develop soon, assuming atmospheric conditions are favorable for downburst development, and can help forecasters triage storms to determine which one has the highest chance of producing a downburst.

A screenshot of a graph showing the KDP Core Size Near Melting Layer for all Downbursts.
KDP core size (red line) generally increases in the 30-minute period prior to downburst development. (Photo provided)
A photo montage showing the development of the KDP core.
Example of a KDP core in mid-levels of a thunderstorm (i.e., near the melting layer) and the associated downburst near the ground seen in Doppler velocity data (V). In the velocity images, red colors show air moving away from the radar and green colors show air moving towards the radar. (Photo provided)

We would like to thank everyone who has made this research possible so far and those who continue to help push it forward. Everyone from the CIMMS and NSSL administrative staff, NSSL IT, radar engineers, NOAA National Weather Service Norman Forecast Office, and webinar organizers are very much appreciated. For any questions, please contact or see for more detailed information.

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NSSL/CIMMS researchers to share cutting-edge radar research in Europe

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Researchers from NSSL/CIMMS will share the latest radar research at the 8th European Conference on Radar in Meteorology and Hydrology September 1-5 in Garmisch-Partenkirchen, Germany.

Some of the topics to be presented include:

  • New techniques and algorithms that use output from a high-resolution weather model to predict precipitation types at the ground, and to identify the layer in the atmosphere where melting occurs
  • Observations made by a dual-pol data quality team during and after the dual-pol deployment process including observations of tornado debris, the descent of the snow level in Arizona, a smoke plume, and the interface of shallow and deep water over the ocean.
  • A new technique was demonstrated for WSR-88D and weather Phased Array Radar (PAR) that transmits a few radar pulses into different directions and simultaneously receives returns to shorten update time from 1 minute to 15 seconds
  • Whether super-resolution data produced by range-oversampling techniques help or hurt NEXRAD’s ability to detect tornadoes.
  • A dual-pol product that could aid in the detection of developing and evolving deep moist convection by locating and tracking thunderstorm updrafts
  • A range-based volume coverage pattern algorithm developed to improve vertical spatial resolution without sacrificing scan update times
  • Results from a study that asked a NWS forecaster, who issued warnings for a violent tornado event in central Oklahoma using WSR-88D data, to evaluate the same event using rapid-scanning Phased Array Radar data.  The forecaster found PAR data proved most advantageous in instances of rapid storm organization, sudden mesocyclone intensification, and abrupt, short-term changes in tornado motion.
  • Overview of the NSSL Research to Operations (R2O) process, past scientific and engineering contributions, as well as current R2O activities in signal processing and polarimetric techniques.

The mission of ERAD2014 is to provide a platform for exchange between students, research scientists, radar operators, and end users of weather radar. It also provides an opportunity to transfer knowledge from research into operational use (and vice versa) of weather radar. The first ERAD conference was in Bologna, Italy in 2000.

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Latest weather radar research on display this week

Weather radar research is a key part of NSSL’s mission in support of the NOAA National Weather Service (NWS). This week, NSSL/CIMMS scientists will share the latest in weather radar research at the American Meteorological Society’s 2013 Conference on Radar Meteorology in Breckenridge, Colo.

Phased array radar research presentations include:

  • An overview of the latest improvements to the National Weather Radar Testbed
  • Phased Array Radar (NWRT PAR) capabilities to demonstrate Multi-function
  • Phased Array Radar (MPAR) program weather and aviation requirements
  • How NWS forecasters’ responded to rapid, adaptive phased array radar sampling and if it increased their ability to effectively cope with tough tornado
  • warning cases
  • New techniques to increase the NWRT PAR scan rate and reduce observation
  • times
  • NWRT PAR observations of microburst events
  • A method to detect and characterize storm merges and splits using rapidly updating NWRT PAR observations in thunderstorm models

NSSL/CIMMS researchers also work with current weather radars in operation and will present:

  • A new algorithm that combines output from a forecast model with dual-polarized radar data to more accurately estimate what winter weather is occurring between the lowest scan of the radar and the ground.
  • A study of how NSSL’s products that estimate precipitation amounts improved using dual-polarized radar data
  • Evaluation of existing hail size estimation algorithms
  • Crowdsourced reports precipitation types at the ground using the “meteorological Phenomena Identification Near the Ground” (mPING) smart phone app
  • Development of a database of U.S. flash flood events using NSSL’s Severe Hazards Analysis and Verification Experiment, and mPING reports
  • Improvements in radar wind data quality control

Other presentations include mobile radar observations of a tornadic supercell and rainfall in the Mediterranean region and airborne radar observations of precipitation in the Indian Ocean.

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2013 NOAA National Weather Radar Testbed Spring Experiments

Lowering west of PAR, 2006During the 2013 central Oklahoma severe weather season, researchers will demonstrate and evaluate new capabilities developed for the NOAA National Weather Radar Testbed Phased Array Radar (NWRT/PAR). The most recent software upgrade, released in March 2013 provides new automated storm detection, tracking and scheduled scanning capabilities for NWRT/PAR.

Researchers will target storms within 120nm of NWRT/PAR to examine the strengths and limitations of storm cluster identification and tracking algorithms, and their usefulness for enhanced rapid sampling of severe storms. They will also use the data to understand how a thunderstorm evolves into a supercell and as it begins to produce a downburst or possible tornado. Researchers will evaluate how useful this information could be for enhanced warning lead-time during severe weather warning operations.

In addition, NSSL will work with 12 National Weather Service forecasters during six weeks in May, June, and July. They will assess how the use of rapid-scan NWRT/PAR helps with situational awareness and warning decisions during simulated severe weather events.

New this year, NSSL’s dual-pol research radar will be used as a proxy for future dual-pol Multi-function Phased Array Radar (MPAR) observations. Researchers will observe rapid changes in dual-pol signatures that occur in cyclic supercells and downbursts.

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NSSL leverages new technologies in winter weather experiment

21Jan 2012
Dual-pol radar data of a winter precipitation event in New York.

NSSL and collaborators will leverage new technology including dual-polarized radar observations and a precipitation reporting mobile device app to improve forecasts of winter weather during February and March.

The experiment will evaluate the performance of new algorithms that use dual-polarized radar data and determine what new tools could be developed to improve detection of precipitation type and amount in winter storms.

The group will assess a new technique that is a “first-guess” of precipitation type using dual-pol data and compare it to observations collected from the Precipitation Identification Near the Ground mobile app and the Severe Hazards Analysis and Verification Experiment phone calls. They plan to identify potential biases and regions of poor performance.

They will also look at quantitative precipitation estimation products that include dual-polarized information and compare them to current products to see if dual-polarized data improves the result.

The experiment is a collaboration between NSSL, the Storm Prediction Center, the Norman Weather Forecast Office, the National Weather Service Warning Decision Training Branch and the Radar Operations Center.

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Spread the word: We need your precipitation reports!

NSSL is now collecting two types of winter weather reports from the public to help evaluate the performance of a new winter weather precipitation algorithm. NOAA National Weather Service (NWS) radars across the U.S. are in the process of being upgraded with dual-polarization technology that can detect the difference between rain, sleet, snow, and hail.  The algorithm sorts dual-polarized radar data into types of liquid or frozen precipitation to help forecasters quickly assess a precipitation event and better forecast how much will fall.

To help evaluate and refine the algorithm, the mostly student-run NSSL/CIMMS Severe Hazards Analysis and Verification Experiment (SHAVE) started collecting winter weather precipitation reports through phone surveys during the week of February 3, 2012.  SHAVE reports, when combined with the voluntary reports collected by the NWS, creates a unique and comprehensive database of winter weather weather events used to evaluate algorithm performance.  SHAVE previously had been a primarily summer project, collecting more than 45,000 reports of hail size, wind damage and flash flooding since it began in 2005.

NSSL’s Precipitation Identification Near the Ground (PING) project requests public precipitation reports at  from any area within 90-miles of a radar upgraded with dual-polarization radar technology. Researchers compare the reports of precipitation with what is detected by the dual-polarized radar data.  Volunteers have submitted more than 5,000 reports of snow, ice pellets, drizzle and rain since the beginning of the project in 2006.

Both projects are ongoing.

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NSSL uses weather radar clutter to help biologists

Dual-polarized weather radar can estimate the number of bats in a swarm similar to the way it can estimate the number of raindrops in a cloud.  This information is valuable to biologists, ecologists and entomologists as they try to understand how populations and behaviors of bats and insects are affected by changes in climate over time.

Several mobile radars, including NSSL’s dual-polarized mobile radar were used in a project to track swarms of millions of bats as they emerged from their caves each night to feast on insects. The radar images of bats appear as distinct “blooms.”

Usually data from birds, insects or bats are considered “clutter” and are filtered out.  NSSL researchers have reversed the filter to now focus on the bioscatter.  Using calculations of radar backscatter from a single bat in the laboratory, made by the University of Oklahoma, the group is developing the first means to calculate aerial densities of bats as they travel.

NSSL will use the data to enhance algorithms that remove the bioscatter clutter to see the weather more clearly.

“What we see in the dual-polarized fields provided by NSSL’s radar, and soon with WSR-88D dual-polarization, will bring a whole new era in behavioral ecology and conservation as well as radar quality control,” says NSSL’s Ken Howard.

The National Science Foundation sponsored project includes researchers from several Universities, the National Park Service and the USGS.

“The summer night sky is filled with a spectrum of biological life that is in many ways equivalent to what we observe in coral reefs,” says Howard.  The data we collected has brought a new appreciation of the rich diversity of life and that can be seen using radars, and especially dual-polarized radars.”

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NSSL video takes viewers to another dimension

The dual-polarization zoneNSSL’s videographer James Murnan has posted a creative outreach video explaining dual-polarization radar technology on the NOAA Weather Partners YouTube channel:

Part of “That Weather Show” series, the video creatively spoofs popular commercials to talk about the benefits of the planned upgrade to existing National Weather Service weather radars.  Viewers are taken into another dimension called, “The dual-polarization zone.”  Dual-polarization technology will give forecasters more precise information to accurately diagnose severe weather.

The video also addresses questions such as, “What is dual polarization technology?” and “Why should you care?”

Murnan has created 30 videos over the past few years on topics ranging from phased array radar technology to the Coastal and Inland Flooding Observation and Warning project (CI-FLOW) .

NSSL has been a leader and major contributor to the scientific and engineering development of dual-polarized weather radar.  This 25-year history is being rewarded as the NOAA National Weather Service will soon begin a major upgrade to all of their weather radars using this technology.

Check out the video at:

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Tornadoes producing damage on the ground detectible by dual-polarization radar

Dual-polarization technology can help detect debris from a damaging tornado

Recent analysis of data from NOAA NSSL’s prototype dual-polarization radar during a significant tornado outbreak in central Oklahoma this past spring showed debris from a damaging tornado.  This critical information can help a forecaster confirm the presence of a rain-wrapped tornado, or a tornado at night causing damage on the ground.

Current NOAA National Weather Service (NWS) radars send a horizontal electromagnetic wave field into the sky.  When the wave field bounces off an object in its path, it is reflected back to the radar and gives a measurement of the horizontal size of that object.  Dual-polarization radar sends both horizontal and vertical electromagnetic wave fields, giving a forecaster a measure of the size and shape of the object.  Combining and comparing these measurements can categorize rain, hail, snow, birds, insects, and tornado debris.  All NOAA National Weather Service radars will be upgraded with dual-polarization technology beginning in late 2010.

NSSL researchers studying the tornado outbreak confirmed four rotation signatures in the radar velocity data.  Tornado warnings had been issued based on this information.  However, these measurements cannot confirm tornadoes are causing damage on the ground because the radar beam is above ground level.

NSSL research showed dual-polarization radar data identifies debris signatures differently from radar echoes.   Leaves, shingles or insulation are randomly oriented, while precipitation echoes behave fairly predictably.

Tornado debris signatures were identified by researchers in the dual-polarized data from the May 10, 2010 outbreak indicating a rain-wrapped tornado was producing damage on the ground.  This tornado killed two people.

NSSL developed, tested and evaluated dual-polarization technology over the past 25 years, culminating in a demonstration project that convinced the NWS to upgrade all their radars with this technology.

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