A Qualitative Analysis of NWS Forecasters’ Use of Phased-Array Radar Data during Severe Hail and Wind Event
Authors: Katie A. Bowden, Pamela L. Heinselman
Journal: Weather and Forecasting
Publication Date: In Print 2/2016
Forecasters using 1-minute radar updates perceived significantly more information than forecasters using 5-minute radar updates and demonstrated improved projections of storm activity in the hail and wind cases worked, owing to earlier perception of severe weather precursor signatures and the ability to more easily observe strengthening and diminishing trends in storms. Such improvements in situational awareness from the use of 1-minute radar updates resulted in superior severe warning lead times and supported correct rejections of unverified threats.
This paper summarizes qualitative findings from the 2013 Phased Array Radar Innovative Sensing Experiment. It builds on results presented in the published Impacts of Phased-Array Radar Data on Forecaster Performance during Severe Hail and Wind Events. This paper demonstrates efforts that are being made to learn about the forecaster warning decision process through the use of social science techniques.
Early online release 1/13/15 Journal:Weather and Forecasting Impacts of Phased Array Radar Data on Forecaster Performance during Severe Hail and Wind Events
Katie A. Bowden, Pamela L. Heinselman, Darrel M. Kingfield, and Rick P. Thomas
Summary: Twelve National Weather Service (NWS) forecasters participated in the Phased Array Innovative Sensing Experiment (PARISE) 2013 and were assigned to either a control (5-min radar data updates) or experimental (1-min radar data updates) group. Each group worked a marginally severe hail event and a severe hail and wind event in simulated real time. While working each event, participants made warning decisions regarding the detection, identification, and re-indentification of severe weather, now known as “the compound warning decision process.”
Important conclusions: The experimental group’s performance exceeded that of the control group’s, as demonstrated through their significantly longer median warning lead time, as well as superior probability of detection and false alarm ratio scores. The experimental group also had a larger proportion of mastery decisions (i.e., confident and correct) than the control group, possibly because of their enhanced ability to observe and track individual storm characteristics through the use of 1-min updates.
Significance: This work furthers efforts that have already been made to understand the impact of higher-temporal resolution radar data, as provided by PAR, on the warning decision process of NWS forecasters. The research questions, methodology, and analysis presented in this paper build upon the findings presented from earlier PARISE work, while also sharing findings that are of a new nature.
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.
During 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.
The Secretary of Commerce has awarded a Gold Medal to the NSSL/CIMMS Radar Research and Development Division for “scientific and engineering excellence in adapting military phased array radar technology to improve U.S. weather radar capabilities.”
NSSL has led the unique federal, private, state and academic partnership to develop and evaluate phased array radar technology since 2003.
Phased array radar has strong potential to provide revolutionary improvements in NOAA National Weather Service tornado, severe storm and flash flood warning lead times and accuracy, reducing false alarms.
“This Gold Medal Award from DOC signifies a huge accomplishment for the NSSL/CIMMS RRDD group led by Doug Forsyth. They are very worthy of this high level of recognition of their accomplishments,” said NSSL Director Steve Koch.
This is NSSL’s fourth Gold Medal Award and is the highest honorary award granted by the Secretary of Commerce. A Gold Medal is defined as distinguished performance characterized by extraordinary, notable, or prestigious contributions that impact the mission of the Department and/or one or more operating units, which reflects favorably on the Department.
Researchers from NSSL and CIMMS have published the first study to combine rapidly-updating phased array radar data with high-resolution lightning data to study lightning behavior in a hail storm. Frequent scans from phased array radar revealed relationships between lightning and storm growth not able to be seen with current radar update rates. Though total lightning flash rates are expected to increase as storm updrafts intensify, in this case a decrease in total lightning flash rate was observed during the simultaneous development of an updraft surge. This finding cautions forecasters in the use of lightning mapping observations alone to diagnose an increase or decrease in updraft intensity and the potential for severe weather.
The study, funded by the National Science Foundation, was published in the June 2011 Monthly Weather Review, an American Meteorological Society journal.
Severe weather in Oklahoma this spring has offered opportunities for collecting data.
On May 24, 2011 NSSL’s dual-polarized X-Band mobile radar captured the early and mature stages of a tornado in northwest Oklahoma. The data will be compared with another X-Band dual-polarized mobile radar for accuracy. This storm produced an EF-3 tornado.
Also on May 24, 2011 the Multi-function Phased Array Radar (MPAR) successfully sampled a tornadic supercell every 1 minute as it evolved and went on to produce devastating EF-5 damage in towns west of Oklahoma City, Okla. A comparison of PAR data with the damage path shows the radar captured rotation in the storm 12 minutes before it touched down. This tornado was on the ground for two hours with a 75-mile long track.
Data was also collected with PAR on four other tornadic supercells and a strong microburst.
The experimental High-Definition Videosonde Particle Imager, designed to capture high-definition images of raindrops and ice particles, was successfully launched into three thunderstorms. Results are being analyzed.
Seven destructive tornadoes struck Oklahoma on May 24, 2011. The tornadoes were well forecast by the National Weather Service (NWS), and NSSL was in position to capture the storms in several ways.
NSSL’s dual-polarized X-band mobile radar captured the early and mature stages of the first tornado reported near Canton Lake, Okla. The data will be compared with another X-band dual-polarized radar for accuracy. This storm produced an EF-3 tornado.
The phased array radar successfully sampled a tornadic supercell every one minute as it evolved and went on to produce devastating EF-4 damage in towns west of Oklahoma City, Okla. A comparison of PAR data with the damage path shows that the radar captured rotation in the storm 12 minutes before it touched down. This tornado was on the ground for two hours with a 75-mile long track.
Visiting forecasters in the NOAA Hazardous Weather Testbed 2011 Spring Experiment found it interesting to be under the threat of tornadoes and then to be in the forecast path of them. They watched the storms out the window and on the National Weather Radar Testbed Phased Array Radar along with the area Terminal Doppler Weather Radar and the NWS NEXRAD. These radars showed the evolution of two confirmed tornadic debris balls as both storms moved towards Norman, Okla. Participants also reported the NSSL/CIMMS weather-adaptive 3D variational data assimilation system (3DVAR) products all handled the track and evolution of the storms and tornadoes very well.
The American Red Cross of Central Oklahoma began using NSSL’s Warning Decision Support System – Integrated Information (WDSS-II) to map rotation tracks of the storm and deploy their teams by 8 a.m. the next day.
And, several NSSL scientists have been in the field as part of NWS teams to survey the tornado tracks and assign EF-Scale ratings based on the damage they find. The EF-Scale is an estimate of the strength of the tornado based on damage to structures and vegetation. Preliminary results show three tornadoes out of the seven in central Oklahoma were ranked a violent EF-4.
The tornado outbreak forecasted by the NOAA Storm Prediction Center and the National Weather Service Forecast Office in Norman, Oklahoma became a reality as five damage-producing tornadoes struck central Oklahoma between 3 pm and 7 pm CDT May 24, 2011. The longest-track tornado, rated EF3 by the Norman Forecast office, damaged homes and businesses along its 75-mile path that originated just northwest of Binger and moved through the towns of El Reno, Peidmont, and Guthrie (Fig. 1).
The rapid-scan, S-band phased-array radar (PAR), located within the National Weather Radar Testbed in Norman, Oklahoma, sampled this tornadic supercell every 1 minute. Based on PAR data, by 3:30 pm supercell storm formed its first well-defined hook echo and associated tornado vortex signature about 6 miles west of Binger (TVS; Fig. 2). At this time, PAR data show that the TVS had a maximum gate-to-gate velocity difference of 89 mph. A comparison of PAR velocity data with the damage path shows that the tornado formed about 12 minutes later, at 3:40 pm.
The 1-minute updates of the PAR exhibit many important details about the evolution of this supercell and its long-lived tornado. One example is the hard-right turn of the TVS and hook at 4:15 pm that placed El Reno in the tornado’s destructive path (Fig. 3 ~62 km northeast of PAR). About 10 min later (4:25 pm, west-side of El Reno), as cells approaching from the southeast began to merge with the hook and a new circulation developed, the hook’s motion was redirected to the northeast, toward Piedmont. Fig. 3 also shows the likely development of two “debris” signatures in the radar reflectivity, which are compact regions of high reflectivity values due to debris from the tornado.
This example shows the PAR’s capability to provide timely, detailed information about where a tornadic storm is headed, and its intensity. In the future, this PAR capability may give families the few additional minutes they may need to take cover from destructive storms.
As severe weather approaches central Oklahoma this spring, NSSL/Cooperative Institute for Mesoscale Meteorological Studies researchers will be able to study fast-changing storms using a new radar processing technique.
The technique, called “range oversampling,” cuts radar update times in half while increasing the accuracy of the data. Researchers will be looking for subtle features that alert to the potential of severe weather and changes in the thunderstorm wind fields to better understand storm evolution.
Range oversampling was successfully installed and run in real time on the National Weather Radar Testbed (NWRT) phased array radar in the spring of 2010.
Phased array radar has a unique flat panel antenna that collects the same information as current radars, but more than five minutes faster. Range oversampling has decreased the already fast scan time by roughly a factor of two.
Forecasters participating in the 2010 Phased Array Radar Innovative Sensing Experiment (PARISE) tested the usefulness of the rapidly updating data. Preliminary results from one case showed forecasters were able to issue a tornado warning 21 minutes before the tornado touched down. This is a significant increase over the National Weather Service’s current average 14-minute tornado warning lead time.
Range oversampling is now operational in modified scanning strategies that have become the default settings on the NWRT phased array radar.
This significant improvement in radar data processing will help pave the road for an eventual implementation on the WSR-88D radars and benefit NWS forecasters.