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Indian Express
27-05-2025
- Climate
- Indian Express
What is a bow echo, how did it signal Delhi's fierce storm?
Storms may be triggered by moisture influx, winds changing with height, and rapid cooling aloft. But when the winds that drive these storms can become increasingly dangerous, it can be detected by a special radar observed feature known as the 'bow echo'. In the early hours of Sunday (May 25), Delhi-NCR was hit by squalls or sudden storms accompanied by strong winds, with speeds around 100 kmph. Behind the scenes, the IMD Radar imagery clearly showed a chain of thunderstorms with a bulge in the centre — the shape of an archer's bow. A bow echo is a radar signature of a high wind-driven storm front. It forms due to strong winds pushing the centre of the storm line forward and indicates intense straight-line winds. This is often a precursor to more destructive windstorms. The term 'bow echo' comes from the way bands of rain showers or thunderstorms curve outward, or 'bow out,' as strong winds within the storm reach the surface and spread horizontally, as per the National Oceanic and Atmospheric Administration (NOAA). Ted Fujita, a Japanese American meteorologist known for developing the scale to classify tornadoes, coined this term in the 1970s. Like bow echo, the Met Office also monitors other special-radar observed features such as the 'hook echo' — which is generally associated with tornadoes. While not heavily discussed in the Indian meteorological landscape, the bow echo is an important radar feature commonly associated with derechos, fast-moving swaths of widespread windstorms most frequently observed in the Midwestern United States during late spring and summer. How does the wind mechanics work? Behind a bow echo are powerful winds that continuously spread out after downdrafts. Umasankar Das, senior scientist, National Weather Forecasting Centre at the IMD, said, 'A 'bow echo' is a radar signature of a convective system (CS), typically a squall line, that appears bowed or arched when viewed on radar. This bowing shape results from strong winds spreading out from the storm's downdrafts, creating a gust front at the surface. Bow echoes are often associated with severe weather, including damaging straight-line winds.' A bow echo forms when a group of thunderstorms pushes strong, cool winds from the storm down to the ground. This cool air spreads along the surface, pushing the warm, moist air ahead of it upward, creating new thunderstorm cells. As more storms form and rain falls, more cool air builds up behind the storm, strengthening this push forward, called the gust front. This makes the storm line bend or 'bow' outward, like an archer's bow. The cycle keeps going as long as new storms keep forming at the front, helping the system grow and move forward with strong winds. What was its role during the May 25 storm over Delhi-NCR? Sunday's storm was driven by favourable conditions, including the presence of low-pressure zones due to a western disturbance that lies as an upper-air cyclonic circulation over north Punjab and adjoining Jammu and Kashmir, and two more cyclonic circulations over West Rajasthan and North Haryana, as per the IMD. At Delhi's primary weather station, winds reached up to 82 kmph. 'A slightly slow-moving severe storm compared to earlier estimates now attained proper 'Bow Echo' visible on radar imagery…' wrote weatherman Navdeep Dahiya on X on Saturday night, after sharing a Doppler radar image. As the storm progressed from Punjab and Haryana towards Delhi and Noida, the bow formation as part of the radar signature became increasingly evident, indicating that the storm continued with higher intensity. The higher the convexity, the more intense the system is. 'This is nothing but the movement of thunderclouds observed by Doppler radar. The winds at 15,000 to 20,000 feet usually carry or push the thunder clouds in their direction. In this case, the winds were blowing from the Northwest. Thunderclouds moved from Punjab to Haryana and then reached up to Delhi,' said Mahesh Palawat, vice president of Skymet Weather Services. '..Such a squall line was observed during thunderstorm activity in Odisha too, this month', said Rahul Saxena, senior IMD scientist. He added that these have appeared often in India during intense thunderstorms. While not unknown to India, the IMD observed a similar feature during a 100 km/h squall on May 31, 2022, across Delhi and Noida, which was, however, 'short-lived', lasting for an hour and recorded at 100 kmph over Safdarjung, whereas 70 kmph at Palam. Typically, a bow echo of far-destructive nature lasts 1 to 3 hours, depending on factors like moisture availability.
Yahoo
24-04-2025
- Climate
- Yahoo
Microbursts set wind records in Texas and Indiana this week
Twice this week, a phenomenon known as a microburst has caused wind gusts at an airport to approach or exceed its all-time records. Microbursts, which occur during thunderstorms, are much more common than tornadoes. What are microbursts? Air cooled inside a thunderstorm can fall suddenly to the ground, spreading out in a circle around the storm and causing wind gusts over 100 mph, doing as much or more damage than lower-end tornadoes. This phenomenon is called a downburst, and when the wind area is less than 2.5 miles across, it is called a microburst, a term coined by tornado researcher Dr. Ted Fujita, inventor of the Fujita Scale. Wet downbursts carry rain with the wind, while dry downbursts can be invisible. An infamous plane crash at New York's Kennedy Airport on June 24, 1975, killed 113 people and was blamed on a downburst. The aviation industry used Fujita's research to protect the industry from future crashes caused by the phenomenon. An 84-mph wind gust at Indianapolis Early Saturday morning, the Indianapolis Airport reported an 84-mph wind gust, likely due to a microburst. Several planes slid 6 inches, the NWS said. The NWS confirmed the gust and told AccuWeather it was the second-highest on record at the airport, tying the same reading in 1984 and only 1 mph lower than the all-time record of 85 mph in 2006. Midland airport clocks a 111-mph wind gust A similar event took place Tuesday when wind at the Midland, Texas, airport gusted to 111 mph from a dry microburst. If confirmed, the record would shatter the previous all-time record for the airport, 93 mph, set on June 27, 2007. Power poles were knocked down and a tractor trailer was tipped over 17 miles to the southwest of the airport near Odessa, Texas, but no injuries were reported with either incident.
Yahoo
23-04-2025
- Climate
- Yahoo
The science behind the EF scale: How we measure tornado strength
BUFFALO, N.Y. (WIVB) — When a tornado tears through an area, the main question after the fact is, 'How strong was it?' That's where the Enhanced Fujita Scale, more commonly known as the EF scale, comes into play. The EF scale is the scale that meteorologists use to survey damage and estimate a tornado's maximum wind speeds. Created by Dr. Ted Fujita in 1971, the original Fujita (F) scale was implemented to estimate wind speeds based on observed damage, with no specific criteria as to what constitutes damage levels. To this day, the maximum speed reached by a tornado is an estimate, never an observed number. The Fujita scale ranged from F0 having max gusts of <73 mph, F1 of 73-112 mph, F2 with 113-157 mph, F3 with 158-206 mph, F4 with 207-260 mph, and finally, F5, indicating speeds of up to 261-318 mph. The original Fujita scale overestimated the wind necessary to create the amount of damage observed because there were no levels of destruction used within the system. This is where an upgrade came along almost 40 years later. The Enhanced Fujita (EF) scale launched on February 1, 2007, to get more precise wind speed estimates by incorporating 28 damage indicators and eight degrees of damage. The damage indicators range from damage to hard or softwood trees, to high rises, to automobile showrooms to take into account different structures that hold up differently in strong wind events. The degrees of damage range from barely visible, extremely minor damage to complete destruction. The EF scale includes EF-0 (weak, 65-85 mph), EF-1 (weak, 86-110 mph), EF-2 (strong, 111-135 mph), EF-3 (strong, 136-165 mph), EF-4 (violent, 166-200 mph), and EF-5 (violent, >200 mph). For comparison, an F-3 tornado was 158-206 mph before enhancement, and the higher end of that would reach an EF-5 in today's scale. Here in Western New York, we see lower-end, weaker tornadoes every once in a while, including the four that touched down last summer. Those ranged from EF-0s to EF-2s. The strongest recorded tornado in WNY was an F-4, which would be an EF-5 in today's scale. It occurred on May 31, 1985. It entered Chautauqua County from the PA border and passed just south of the town of Clymer. The tornado had winds in excess of 200 mph and traveled 28 miles before dissipating. We've covered four tornado warnings in our viewing region so far this year, the first three being in our Pennsylvania counties. More could pop up from now through summer. Sara Stierly is a meteorologist who joined the 4 Warn Weather team in February 2025. See more of her work, here. Copyright 2025 Nexstar Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
Yahoo
04-04-2025
- Climate
- Yahoo
How do tornadoes get their ratings and why hasn't Arkansas seen an E(F)-5 since 1929?
FAYETTEVILLE, Ark. (KNWA/KFTA) — April 10, 1929, was the day the only documented F5 tornado occurred in Arkansas. It stretched from southern Batesville to north of Swifton and southern Alicia. How are tornadoes rated, and why haven't we seen any in Arkansas in such a long time? The Fujita scale, created in 1971 by Dr. Ted Fujita and first used in 1973 by the National Weather Service, was used to classify tornadoes based on wind speeds. Through several years of rating tornadoes, it became clear that tornadoes couldn't be rated on wind speeds alone. For better rating accuracy, they introduced the Enhanced Fujita Scale on February 1, 2007. This takes the damage into account. This method is also better because as you get farther from a radar, the wind speed measured will be higher in the storm. First, someone from the local National Weather Service office will identify the correct Damage Indicator (DI) from a list of 28 indicators based on the damage they see. Once they choose that, they pick one of the 8 Degrees of Damage (DOD) on the scale. The person evaluating the damage will then judge if the damage is within the upper and lower bounds of the wind speeds associated with the DOD. They go around to many structures in the path and then give it an official rating. Damage Indicators NUMBER(with links) DAMAGE INDICATOR ABBREVIATION 1 Small barns, farm outbuildings SBO 2 One- or two-family residences FR12 3 Single-wide mobile home MHSW 4 Double-wide mobile home MHDW 5 Apt, condo, townhouse (3 stories or less) ACT 6 Motel M 7 Masonry apt. or motel MAM 8 Small retail bldg. (fast food) SRB 9 Small professional (doctor office, branch bank) SPB 10 Strip mall SM 11 Large shopping mall LSM 12 Large, isolated ('big box') retail bldg. LIRB 13 Automobile showroom ASR 14 Automotive service building ASB 15 School – 1-story elementary (interior or exterior halls) ES 16 School – jr. or sr. high school JHSH 17 Low-rise (1-4 story) bldg. LRB 18 Mid-rise (5-20 story) bldg. MRB 19 High-rise (over 20 stories) HRB 20 Institutional bldg. (hospital, govt. or university) IB 21 Metal building system MBS 22 Service station canopy SSC 23 Warehouse (tilt-up walls or heavy timber) WHB 24 Transmission line tower TLT 25 Free-standing tower FST 26 Free-standing pole (light, flag, luminary) FSP 27 Tree – hardwood TH 28 Free-standing pole (light, flag, luminary) TS EF Rating 3 Second Gust (mph) 0 65-85 1 86-110 2 111-135 3 136-165 4 166-200 5 Over 200 While the tornado rating is based on the damage it does, the damage indicators correspond to wind speeds given in the table above. Example Rating For example, let's say a tornado hit one of our local high schools. You would go to Damage Indicator No. 16 and read the description to make sure that's the right building. Then you read the DOD description that goes along with what you see. With each of the 11 DODs for this damage indicator, there's a lower and upper bound for possible wind speed and an expected value that corresponds to possible wind speeds. DOD 9, for example, says 'collapse of exterior walls in top floor.' Winds could be anywhere from 121-153 mph, with the expected to be 139 mph. This would likely be EF-3 damage. You then move on to the next structure. Let's take a one and two-family residence (#2). The description for typical construction is: Asphalt shingles, tile, slate, or metal roof covering Flat, gable, hip, mansard or mono-sloped roof or combinations thereof Plywood/OSB or wood plank roof deck Prefabricated wood trusses or wood joist and rafter construction Brick veneer, wood panels, stucco, EIFS, vinyl or metal siding Wood or metal stud walls, concrete blocks or insulating-concrete panels Attached single or double garage To have EF-4 damage, you would need all walls collapsed or, at the very least, all walls except small interior room walls. To have EF-5 damage, the description reads 'destruction of engineered and/or well-constructed residence; slab swept clean.' Basically, nothing can stand from a well-constructed home. Key words are well constructed, because it can come down to the types of nails and how they have been driven into the wood, and that could mean the difference between an EF-4 and EF-5. Typically, they'll bring engineers out to help iron out those kinds of wrinkles, as well has prove that the bolts or screws didnt't fail during EF-4 strength, but only during EF-5 intensity. It's a complicated question to answer. You have to have high amounts of CAPE (t-storm fuel), strong wind shear (change in direction with height), a lot of warm, moist air, and strong lift along a boundary to get tornadic supercells. The formation of most weather systems comes from the east side of the Rockies, known as lee cyclogenesis. All the warm, moist gulf air gets pushed into the south-central plains and meets up with the strong lift from these systems, which is why most tornadoes occur in states like Kansas, Oklahoma, and Texas. Then, as that energy continues to move east into the overnight hours, yes, they may lose some fuel and heating, but the nocturnal low-level jet kicks in and can add an insane amount of spin, which might answer the question of why there are many nocturnal tornadoes in Northwest Arkansas and the River Valley. Other times, we may see many tornadoes in Dixie Alley, which encompasses eastern Arkansas and northern Louisiana and stretches across the southeast United States. This typically happens when you have strong weather systems and intense lift along a boundary like a cold front. These will typically come in the form of lines of storms known as Quasi-Linear Convective Systems or QLCSs. The shorter answer to the question is: It's hard for all the ingredients to come together at the right time and place for any tornado to form, but Arkansas is located in a place that's just a little more difficult for everything to come together. Supercells are typically favored where its flatter, like central and eastern Arkansas, and QLCSs in Northwest Arkansas, but both can occur in either part. There have been several outbreaks and violent tornadoes across Arkansas, including two recent EF-4s in Northeast Arkansas. Below is a map of all the violent (EF-4 and 5) tornadoes in Arkansas and bordering states from 1950 to 2023. That's the only available data range from the Storm Prediction Center. So while it has been a long time since we've seen an E(F) 5 in Arkansas, let's hope it stays that way. Copyright 2025 Nexstar Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
