Imagine that it’s late in the evening, the sun has set, and you’re a meteorologist or the National Weather Service (NWS) exhausted from working a 13–hour day providing forecasts and warnings for a significant severe weather event that moved through your forecast area. Although the powerful storm system has exited the region, the event is not completely over. As severe weather reports filter into the office, it becomes evident that the storms caused significant damage and you’ll be heading out to conduct a damage survey first thing in the morning. Get some rest…another long day lies ahead.
This is a common occurrence for meteorologists in the National Weather Service, particularly during severe weather season. In order to increase our understanding of severe weather, scientists at the NWS often survey the storm damage, in particular the damage caused by tornadoes. Since tornadic winds are rarely measured by instruments at the surface, forecasters use the Enhanced Fujita (EF) scale to estimate the wind speed and rate the tornado between EF0 (weakest) and EF5 (strongest).
Trying to determine the strength of the tornado is a lot like forensic meteorology – you have to piece together clues from the damage scene in order to determine how strong the winds were that caused it. You have to analyze not only the extent of the damage, but also the structural integrity of the object (tree, power lines, house, barn, etc) that was involved. For example, complete destruction of building may not be caused by EF4 winds (>165 mph) or EF5 winds (>200 mph) if the building was poorly built. Forecasters must keep this in mind as they look at countless damage indicators along the path of the tornado, and eventually rate the tornado based on the worst damage that occurred.
Another key component of the damage survey process is interacting with the people who were affected by the tornado, which many meteorologists consider one of the most difficult and humbling experiences they have on the job. Gary Woodall, the Warning Coordination Meteorologist at the National Weather Service in Memphis, Tennessee, had this to say about his interactions with people: “In the vast majority of cases people want to share their story. It’s encouraging to hear accounts of people who followed the tornado safety tips and survived. It’s especially rewarding when they talk about getting advanced warning with the NOAA Weather Radio and sirens and they want to thank you.”
One thing that has changed considerably over the past 30 years is the technology used to conduct a damage survey. Brian Smith, Warning Coordination Meteorologist at the National Weather Service Office in Omaha, Nebraska, remember years ago using maps, pencil, pens, and an odometer as a guide.” Advancements with digital cameras and GPS help make the survey process more accurate. Within the past few years, a new software developed by the National Weather Service, called the Damage Assessment Toolkit (DAT), harnesses the power of smartphones and tablets. Using these devices, with just a few finger taps, forecasters can now take pictures of the damage, rate the damage using the EF scale, and upload the information to a server that can be viewed instantaneously back at the local NWS office. All the images are geocoded and can be easily mapped out to calculate the exact track of the tornado. At times, aerial surveys are also done to get a scope of the damage track. High-resolution satellite imagery is another tool that can be requested to help forecasters determine the exact track of the tornado by looking at vegetation scars. Brian hopes in the future that drones may also be used to gather information from a bird’s eye view.
So….how is this information from the damage survey used, and what benefits does it have? Documenting the intensity of storms helps create a severe weather climatology, assists researchers by providing them with more ground truth information that they can compare to the radar and other meteorological parameters, and aids in preparedness campaigns. Another important benefit, according to Gary Woodall, is
“for internal training of forecasters to compare the near storm environment and radar signatures to the damage.” By studying the climatology of severe weather through damage surveys and comparing it to past weather conditions from that day, meteorologists are able to better understand the atmospheric conditions in place prior to significant severe weather outbreaks. In addition, computer models continue to improve and make more accurate predictions of when these conditions are expected to occur. The combination of better understanding and better predictions of the atmosphere leads to improved severe weather forecasts. These improvements would not be possible without the information gathered from damage surveys.
Just over a week ago, the town of Mechanicville experienced localized damage that many residents first assumed was a tornado. However, the following day, a team from the National Weather Service traveled half an hour north from Albany to conduct a storm survey and determined that the damage was caused by a microburst. A microburst is a thunderstorm downdraft with an affected outflow area of less than two and a half miles wide and peak winds lasting less than five minutes; these typically result in tree and property damage. Meteorologists are able to distinguish microbursts from tornadic winds because they produce straight-line winds, which are not associated with rotation.
Wind speeds in microbursts can reach up to 100 mph, or even higher, which is equivalent to an EF-1 tornado! Winds this high can cause major damage to homes and other structures and level hundreds of trees. Thus, it is very important that you take Severe Thunderstorm Warnings just as seriously as Tornado Warnings! Fortunately, no injuries or deaths were reported in Mechanicville, but dozens of hardwood trees were uprooted or snaps, and a few of those fell on homes and cars. Some power poles were snapped, resulting in power outages, and a little league dugout was destroyed by the strong wind. We are confident that these storm surveys have several benefits (including the ones mentioned above), but also provide clarity to the community and future advancements to continue building a Weather-Ready Nation as well!
Note: Much of this article have been adapted from a WRN Article originally published in 2016.