With the change of seasons comes increased risk of severe weather
March 19, 2020
Spring brings the promise of warmer temperatures, blooming flowers, and more people getting outside after being cooped up all winter. Thanks to NOAA satellites, we can see how Earth sheds its winter coat from space this time of year. From melting snow to greening vegetation, signs of spring are becoming apparent.
Satellites also monitor the changing weather patterns that come with the transition from winter to spring. The potential for severe thunderstorms, hail, tornadoes, dangerous lightning, and flooding increases in the spring months. According to NOAA’s 2020 Spring Flood and Climate Outlook, released on March 19, much of the country is looking at above-normal precipitation and an enhanced risk of flooding this spring. GOES-16 (GOES-East) and GOES-17 (GOES-West) are equipped to provide detailed information about the atmosphere and clouds in near real-time to help forecasters provide early warnings of hazardous weather.
In the U.S., thunderstorms are most likely to occur in the spring and summer months and during the afternoon and evening hours, but they can occur year-round and at all hours. A thunderstorm is classified as “severe” when it contains one or more of the following: hail one inch or greater in diameter, winds gusting in excess of 58 miles per hour, or a tornado.
The GOES-16 and GOES-17 Advanced Baseline Imager (ABI) provides three times more information about cloud properties and atmospheric conditions that lead to severe weather than the imager on previous GOES. ABI can also see clouds in much finer detail, revealing the presence of overshooting tops, gravity waves, and above anvil cirrus plumes, which indicate a storm may be severe. ABI also provides frequent updates, scanning a targeted area of severe weather as often as every 30 seconds. This rapid imaging allows forecasters to track meteorological phenomena that change very quickly with time.
The presence of an above anvil cirrus plume (AACP) is a strong indicator that a storm may produce a tornado, large hail, or powerful winds. Researchers have identified hundreds of plumed storms over the U.S. using high-resolution imagery from GOES-16. Identifying the presence of an AACP can add 10-30 minutes of lead-time for storm warnings.
“Analysis of significant historical severe storm outbreaks reveals that AACPs are routinely present atop the most intense storms,” said Kris Bedka, an atmospheric scientist at NASA's Langley Research Center in Hampton, Virginia. “The improved resolution and rapidly-updating imagery from GOES-16 compared to previous-generation GOES allows forecasters to quickly recognize AACP signatures. AACP recognition, in combination with radar-observed severe storm indicators, can increase forecaster confidence that a storm is likely to produce severe weather and can aid warning where radar data is unavailable.”
On June 27, 2019, the National Weather Service (NWS) Weather Forecast Office (WFO) in Juneau, Alaska, issued its first-ever severe thunderstorm warning – based on GOES-17 imagery. There are many challenges to issuing weather forecasts in southeast Alaska, including sparse surface observations, large forecast area, poor/no radar coverage, complex terrain, and until GOES-17 arrived, poor geostationary satellite imagery. On this day, they had one-minute ABI imagery that showed the development of thunderstorms over the far southern end of the Alaska Panhandle. Visible imagery showed the presence of overshooting tops, and infrared imagery indicated very cold cloud tops. The colder the cloud top, the more likely the storm is producing rain and severe weather.
Rapid increases in lightning (in-cloud and cloud-to-ground) activity often precede severe and tornadic thunderstorms. GOES-16 and GOES-17 are equipped with a Geostationary Lightning Mapper (GLM), the first instrument of its kind. GLM data provide critical information to forecasters, allowing them to identify initial thunderstorm development and focus on potentially severe storms before these storms produce damaging winds, hail or even tornadoes.
Most tornadoes in the United States occur in two regions — Florida and the Great Plains. Located in the central United States, conditions in the Great Plains are often ideal for the development of severe thunderstorms. In this area, known as Tornado Alley, storms can develop when dry cold air moving southward from Canada meets warm moist air traveling northward from the Gulf of Mexico. Tornadoes can form at any time of year, but most occur in the spring and summer months along with thunderstorms. May and June are usually the peak months for tornadoes.
Severe thunderstorms developed across central Iowa during the afternoon of July 19, 2018, producing multiple tornadoes. Fortunately, one-minute imagery from GOES-16 was available over the region to aid forecasters during the event. GOES-16 winds data indicated favorable conditions for a supercell to develop. Supercells are storms that contain rotating updrafts. Supercell thunderstorms generate the vast majority of long-lived strong and violent tornadoes, as well as wind damage and large hail. The first tornado was reported around 2:50 p.m. EDT, just as GLM data showed lightning activity rapidly increasing. GOES-16 one-minute imagery showed overshooting tops and an above anvil cirrus plume.
GOES-16 GLM data was critical for the Huntsville, Alabama NWS WFO warning decision-making process during a period of severe weather on January 11, 2020, when radar data were limited. GLM data helped forecasters decide to extend the location of a tornado warning after observing an increase in lightning activity. The first warning including Union Grove, Alabama, was issued 17 minutes before an EF-2 tornado hit Brindlee Mountain Primary School. GLM data also helped the forecasters communicate the urgency of the situation to Marshall County first responders as the Union Grove event unfolded.
Lightning strike hazards
GLM provides new insights on the duration and extent of individual lightning strikes. Lightning can travel hundreds of miles before striking the ground. GLM can show forecasters areas far from the main line of storms where the risk of lightning strikes to the ground presents a public safety hazard. In 2018, GLM captured a lightning flash over the southern United States that sprawled some 44,000 square miles—nearly the area of Ohio.
Lightning is a significant threat to life and property, and particularly hazardous for those working outdoors and participating in outdoor recreational activities and events. Knowing the extent of lightning flashes within a storm can help forecasters and emergency managers determine the public safety threat. In June 2018, forecasters used GOES-16 GLM data to evaluate the threat to 33,000 people attending an outdoor music concert in Cullman, Alabama. A cluster of storms formed on the evening of the concert, but thanks to GLM flash extent data, forecasters were able to determine that lightning would not be a threat to the concert.
Accurate, timely, and reliable information on rainfall is vital for predicting flash floods and responding to flood events. NOAA flood maps use data from the polar-orbiting NOAA-NASA Suomi NPP and NOAA-20 satellites and the geostationary GOES-16 and GOES-17 satellites. These maps, along with aircraft, unmanned drones, and ground assets help determine the impact of a storm – where flooding is happening, what the extent is, as well as how long it will last and what damage has occurred. The flood maps are provided to FEMA, local emergency managers, and first responders to help them quickly determine where to employ limited resources, where to issue evacuations, when it’s safe for people to return to their homes, and where to focus recovery efforts.
Protecting lives and property
Spring brings milder temperatures but also an increased chance of hazardous weather. Severe weather and flooding can strike anywhere, whether or not you are in a high-risk area. GOES-16 and GOES-17 continuously monitor Earth and identify potentially severe weather faster than ever before. New capabilities allow the satellites to see cloud features in much finer detail and monitor lightning activity to identify storms that are likely to become dangerous. The ability to monitor storms in near real-time allows forecasters to track rapidly changing weather conditions and give advance warning of severe thunderstorms, tornadoes, and flooding. Better forecasts and earlier warning of severe weather help keep us safe from spring weather hazards and enable officials to make better decisions about evacuations and other critical public safety matters.