The latest video in the “Bite-Sized Science” series highlights the NOAA Hazardous Weather Testbed 2013 Spring Experiments. The short videos are produced for NSSL and other NOAA Weather Partners in Norman, Okla., to focus on specific activities in each of the NOAA units.
The NOAA HWT Spring Experiments occur each spring during Oklahoma’s severe weather season and are hosted by NSSL, the SPC and the NWS Norman. During the experiments, visiting NWS forecasters and researchers evaluate a variety of new forecast and warning capabilities and techniques being developed at NSSL.
Other videos in the series include the mPING app, Multi-function Phased Array Radar, the NWS Storm Prediction Center and Dual-pol radar technology.
Doppler data processed later revealed first Tornadic Vortex Signature
May 24, 2013, is the 40th anniversary of the Union City, Okla., tornadic storm. Researchers from the NOAA National Severe Storms Laboratory collected data on the Union City storm using experimental Doppler radar. When they were able to process the data, they discovered a unique pattern now known as the Tornadic Vortex Signature (TVS).
“The TVS revolutionized the NWS ability to warn for tornado activity with sufficient lead time to save lives,” said former National Weather Service Director Joe Friday.
What follows is a narrative by NSSL’s research meteorologist Rodger Brown describing the activities that took place on the day of the Union City tornado.
“On May 24, 1973, the darkened National Severe Storms Laboratory (NSSL) radar room was a typical beehive of activity. Meteorologists, aircraft controllers and coordinators, radar technicians and visiting scientists were monitoring several radar scopes, including one from an experimental Doppler radar. Excitement rose in the room when a phone call was received from members of the Tornado Intercept Project (TIP) team reporting that a large tornado was touching down to their northwest.
“They were positioned 5 km south of the small farming community of Union City, 47 km west-northwest of NSSL.
“As word quickly spread throughout NSSL, a number of staff crowded onto the observation platform atop the building. The tornado was visible in the distance next to a dark rain shaft. With time, the tornado became obscured by the rain.
“An hour earlier, the Doppler radar meteorologist, engineer and technician in the nearby Doppler radar building began sampling the storm at 2:46pm.
“When the radar data were processed months later, the data revealed the presence of a vortex about 5km in diameter at heights of 5 to 8km above the ground. By 3:15, there was clear Doppler velocity evidence that a smaller tornado scale vortex was present at mid-levels near the storm’s southwest edge. Researchers compared the data with time-stamped photos and movies. They found at the same time, the NSSL TIP team observed funnel-like protrusions extending beneath the more rapidly rotating lowered cloud base.
“With time, what is now known as the Doppler Tornadic Vortex Signature (TVS) descended to the ground and at the same time, a funnel appeared below the cloud base. From 3:38 to 3:48, while the funnel descended and retracted several times as it moved eastward, a dust cloud continuously was evident on the ground. The TIP team, racing eastward during this development stage, arrived at their final photography site—9km southeast of the tornado—just before the visual funnel made continuous contact with the ground.”
The tornado caused fatalities and extensive damage as it passed through the heart of Union City. The newly commissioned Doppler radar at NSSL observed this tornado, and the Tornado Intercept Project researchers photographed the tornado’s life cycle. The radar, coupled with the photographic evidence of the tornado’s development, revealed previously unknown information about motion inside thunderstorms with a persistent rotating updraft, a type known as supercells.
This event played a major role in the decision to develop and deploy a nationwide network of WSR-88D/NEXRAD radars. The NSSL TIP also proved its scientific worth and paved the way for all the tornado intercept research that goes on today.
The discovery of the TVS and other Doppler velocity signatures led to dramatic improvements in accuracy and lead-time in forecasting severe storms nationwide, and as a result, the ability to save lives and prevent serious storm-related injuries.
The Hazardous Weather Testbed Spring Forecast Experiment was in full operation on May 20, 2013 as the tornado tore through Newcastle and Moore, OK. Visiting forecasters and researchers were working with state-of-the art convection allowing experimental modeling systems. They also issued experimental outlook-type forecasts that included areas and probabilities of severe weather over shorter time periods than current operational products. Forecasts generated by the participants were used in real-time to support decisions made for experimental warning operations. New this year, the UK Met Office was testing their modeling system over the U.S. where there is more severe weather.
NSSL’s Mesoscale Ensemble is an experimental analysis and short-range ensemble forecast system. These forecasts are designed to be used by forecasters as a 3-D hourly analysis of the environment, a very important tool in the severe weather process. Each panel shows ensemble mean 1 hour forecasts valid at 3pm CDT, the time of the tornado. The Significant Tornado Parameter (bottom right) with values > 1 have been shown to discriminate supercells that do and don’t produce significant tornadoes. This field highlighted the storm over Moore more so than the storms further south with values > 1 shaded in red. Composite reflectivity from NSSL’s National Mosaic and Quantitative precipitation estimation (NMQ) is overlayed to show where the storms actually formed.
The left panel shows NSSL’s mid-level rotation tracks derived from WSR-88D radar from 1 to 4 pm. The human-generated experimental forecast for severe weather at 12pm, valid from 1 to 4pm on May 20th is overlayed. They used brown, red, and purple lines to enclose areas that were estimated to have a 5%, 15%, and 30% chance of severe weather within 25 miles of a point during the 3-hour period. The black line outlines an area that was estimated to have a 10% or greater chance of significant severe weather, also within 25 miles of a point.
Along with the same human-generated forecast, the right panel shows areas of significant mid-level rotation valid from 1 to 4pm from three different convection allowing model forecasts. The models are the NSSL WRF-ARW model, a parallel version of this model initialized from the NSSL mesoscale ensemble, and a model provided by the United Kingdom Met Office for the Spring Forecasting Experiment run over the CONUS on a domain with 2.2 km grid spacing.
On both May 19 and May 20, 2013, NSSL researchers collected data on storms that produced tornadoes using both the NWRT Phased Array Radar (PAR), and the mobile dual-polarized radar. The NWRT PAR can scan the sky in less than one minute, five-times faster than current weather radars. Datasets from the rapidly-updating NWRT PAR will help researchers better understand the evolution of rotating thunderstorms and the tornadoes they produce.
May 19, 2013
The NWRT PAR, a retired Navy surveillance radar adapted for weather, scanned a storm from its first radar echoes through its production of a tornado. When this storm moved out of range, the PAR was directed to scan the tornado that formed in Norman, Okla. through the time the tornado moved into Shawnee, Okla., killing two people. Loops of radar imagery are below with still images following.
The Hazardous Weather Testbed Spring Warning Experiment was operating May 20, 2013. Participants used the NSSL On Demand rotation tracks, the experimental Tornado Debris Signature algorithm, and GOES-R Proving Ground products during experimental warning operations.
The March 18, 1925 Tri-State Tornado was unusually severe, killing 695 people while it was on the ground for a record 219 miles crossing parts of Missouri, Illinois and Indiana. Unfortunately, there is only one formal paper regarding the tornado and its meteorological setting.
A team of eight severe storms meteorologists re-analyzed the event using all relevant U.S. Weather Bureau data on the Tri-State Tornado. The results, published in the Electronic Journal of Severe Storms Meteorology, revealed previous analyses of the surface weather conditions were inaccurate and led to misconceptions about where the tornado formed in reference to the existing weather system. The authors include retired NSSL Director Bob Maddox, retired NSSL/CIMMS researchers Chuck Doswell, Don Burgess and Charlie Crisp, retired Storm Prediction Center (SPC) meteorologist Bob Johns and current SPC meteorologist John Hart, and Steve Piltz from the National Weather Service Forecast Office in Tulsa, Okla.
The researchers concluded there was no singular feature in the meteorological setting that would explain the extreme character of the Tri-State tornado. The storms of 18 March were associated with a rapidly moving cyclone that was not unusually intense. The new analyses show a long-lived supercell that developed very near the center of the cyclone produced the tornado, possibly where a warm front and a distinct dryline intersected. The south-to-north temperature gradient was very pronounced due to cooling produced by early morning storms and precipitation. The tornadic supercell tracked at an average speed of 59mph moving farther away from the cyclone center with time. And, the storm remained very close to the surface warm front.
Researchers did find as the supercell and dryline moved rapidly eastward, the northward advance of the warm front kept the tornadic supercell within a very favorable storm environment for several hours. It appears this consistent time and space connection of the supercell, warm front, and dryline was extremely unusual.
With reanalysis beginning 70 years after the tornado, it was impossible to confirm the complete continuity of the damage path along the reported path. Even with extensive field work discovering 2,395 individual damage points, there were 32 gaps of at least one mile in length, but only 7 gaps longer than 2.5 miles in length. All of the longer gaps were in the Missouri portion of the path; within the sparsely-populated Ozark mountain area. Assuming that gaps shorter than 2.5 miles might still represent a continuous tornado, the continuous path was at least 174 miles long. Additional, previously unreported tornadoes were also found before the beginning and after the end of the Tri-State Tornado. The research also allowed for conclusion that the storm was a supercell; classic in its stages and high-precipitation in the later stages. The supercell also produced accompanying hail up to baseball size and non-tornadic damaging winds.
Today, researchers launched the Mesoscale Predictability EXperiment (MPEX) field project to collect data on pre-storm and post-storm environments in an effort to better predict where and when thunderstorms will form. MPEX runs from May 15 – June 15, and is funded by the National Science Foundation.
NSSL researchers will team with Colorado State University and Purdue to launch weather balloons carrying instrument packages called radiosondes. They hope to find out how thunderstorms interact with the atmosphere that surrounds and supports them, and how this affects formation of new thunderstorms. They also hope to ingest the balloon data into computer models to see how the extra data collected during the afternoon can help predict the location and severity of evening storms better.
Researchers with the National Center for Atmospheric Research will use a Gulfstream V aircraft to sample pre-storm jet stream winds, upper–level temperatures and other features across Colorado and nearby states. The aircraft will cruise at 40,000 feet for up to six hours so researchers can thoroughly canvass the region. The data they collect will also be ingested into computer models to show how well the extra data can help predict local and regional weather conditions into the next day.
Additional participants are from the University at Albany, State University of New York and the University of Wisconsin-Milwaukee.
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.