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Weather Questions tagged “tornadoes”(remove tag filter)
Question: I know that when a Hurricane makes landfall it typically spawns tornadoes... and they vary in intensity from EF0 to EF 2 or 3..would it be possible for a Hurricane to spawn a monster EF5? — David
Answer: You're right that the moist, high-wind-shear area in the right front quadrant of a land-falling hurricane often (not always) triggers a swarm of short-lived and usually rather weak tornadoes. It would be overstating things to say a hurricane can never set off a violent EF5 tornado, but the environment around hurricanes is generally characterized by deep moisture and warm air aloft that limits the kind of extreme instability and explosive updrafts that are usually associated with the most intense tornadoes. This is reflected somewhat in the fact that most hurricanes, in spite of being huge convectively-driven storms systems, produce relatively little lightning.
Mar. 4, 2013 | Tags: hurricanes, tornadoes
Question: We're soon to enter tornado weather season in Eastern and Central North Carolina. Are there any statistics on the likelihood that one's home would be in a direct line for a direct hit? I'm relating this to the seemingly high improbability on a direct hit by lightning in any given area of activity. I don't mean to belittle anyone's trauma if they've ever experienced a tornado or lightning strike or cause people not to be cautious. But given the F-1 or lower categories of tornadoes which we normally see around here and their small area of coverage and their time on the ground, I was just curious about statistical probabilities? — T. Sykes
Answer: As you imply in your question, tornadoes fall very much into the category of very high impact, but very low probability for any individual location. When it comes to statistics, rare and sporadic events like tornadoes present a number of difficult questions to those attempting to quantify the risk in a meaningful way, and thus a range of efforts have yielded a range of estimates that depend on the specific techniques and on whether the probabilities relate to the likelihood of striking some part of a county, a city, an individual structure, etc, and in some cases weaker tornadoes that are likely to produce only cosmetic damage are excluded. All that being said, for central NC the estimates from a sampling of studies by personnel from NOAA,DOE and others point to probabilities of striking a particular point in a given year (for any strength tornado) ranged from about .2% to .03%, corresponding to one tornado striking a given property about every 500 to 3300 years. When these studies limit the tornadoes to the more destructive and injurious tornadoes having intensities of F2 and higher, the probabilities drop to .02% to .005%, yielding one strike of that magnitude on a particular site about once every 5000 to 18,000 years.
Feb. 25, 2013 | Tags: past weather, preparedness, tornadoes, weather & health
Question: I live in Dunn NC. According to a website I found, we are rated pretty high on our risk for tornadoes. I was surprised also to learn that there is a term for NC now called 'Carolina Alley' which is like the term 'Tornado Alley'. Does this mean that the tornado threat has shifted more in our direction now than it use to be. This sort of freaks me out. — Shanta Chavis
Answer: There hasn't been a significant shift in the tornado risk area, but there was a study done by a University of Akron student in which he used a gridded map of the United States to assess the frequency of strong to violent, long-track tornadoes (those staying on the ground for 20 miles or more, and having intensities of F3 to F5), and how that frequency varies geographically. He selected four groupings of enhanced tornado frequency relative to surrounding areas that resulted in four "alleys" covering the central and southeastern U.S. - from most active to least active, these were "Dixie Alley" (runs from northeast TX and AR to northwest GA), "Tornado Alley" (the traditional area running from OK north to NE and over into IA and WI), "Hoosier Alley" (centered around IN but also including parts of OH, KY and IL) and "Carolina Alley" (more or less along and between the US 1 and I-95 corridors in NC and northern SC, and having the lowest rate of tornado incidence among the named areas).
Tornadoes have always been possible over any part of our state, but more likely over central and eastern sections of the state than elsewhere, and everyone should be aware of tornado safety rules and responses, as well as alert for their occurrence when we are in potentially severe weather situations. That being said, it is also the case that for any particular location, even in "Carolina Alley," there is no reason to be overly anxious on an ongoing basis, as the great majority of us have never had our home or property struck by a twister (nor have our parents) and most will not in our lifetimes or that of our children. That is not intended to minimize or understate the impact on those places that have been struck and families that have been affected, because it can certainly be devastating, only to emphasize that while a strong or violent tornado strike is a very high-impact event, it is also a very low-likelihood one for any particular spot in our state. You can see a map and poster summarizing the results of the Akron study and outlining the "alleys" at www.uakron.edu/dotAsset/1085452.pdf.
Feb. 22, 2013 | Tags: cool sites, preparedness, severe weather, tornadoes
Question: With most hurricanes in the past, there have been severe thunderstorms and many tornadoes. Why did we not see tornadoes with this with Hurricane Sandy? — Robin H.
Answer: Many but not all hurricanes do produce some typically brief and fairly weak tornadoes as they make landfall, usually in the right front quadrant of the storm (relative to its direction of motion). Most hurricanes making landfall in the U.S. do so in more southerly locations, and also a little earlier in the year, than did Sandy, meaning that sufficiently moist and unstable air is often in place or carried inland with the storm. In the case of Sandy, there were in fact a few severe thunderstorms on the right side of the circulation. These occurred on October 30th over parts of MA and NH, as seen in the storm reports map at www.spc.noaa.gov/climo/reports/121030_rpts.html. Since the strong inflow from the southeast that helped feed these storms was coming across relatively cool shelf water off the northeastern coast of the U.S., the low-level air was probably just a little too stable to support tornadic cells.
Nov. 8, 2012 | Tags: hurricanes, tornadoes
Question: Was there a tornado in Snow Camp, NC on 7/24/2012? — Gail
Answer: Thunderstorm winds led to many reports of trees down on that day, including some reports of downed trees in the vicinity of Snow Camp in Alamance and Chatham counties between about 2 and 3 pm. You can see a map and listing of storm reports for that day at www.spc.noaa.gov/climo/reports/120724_rpts.html. The only tornado reported in the country that day occurred in Maine.
Aug. 8, 2012 | Tags: cool sites, past weather, tornadoes
Question: Are tornadoes most likely to happen in the winter? — Sella O.
Answer: For North Carolina, tornadoes are actually least likely to occur during the winter months, although they have been observed to form at any time of year. The months of December, January and February have the lowest average numbers of tornadoes of any months of the year. The greatest numbers of tornadoes here occur during the spring, with March through May being the primary peak season. After a relative lull in the summer, there is a smaller increase in the number of tornadoes, form a secondary peak, in October and November.
Aug. 2, 2012 | Tags: severe weather, tornadoes, winter weather
Question: On July 11, 2012, you indicated that radar had indicated a tornado over Scotland County but it had not been visually verified. What are the definitive features you look for on radar that would indicate a tornado? i.e. rotation, the "hook", etc. Also, is there anyway to know from radar if a tornado has reached the ground? — Lee
Answer: It is typically the case that remote sensing techniques like radar can give strong clues that a tornado may exist, but in most cases it is difficult to confirm in real-time without a visual observation. Using Doppler radar, a meteorologist would generally look for a velocity "couplet" in which strong inbound and outbound velocities are immediately adjacent to one another (indicating strong horizontal shear that is likely produced by rotation at the mesocyclone scale), show some vertical continuity (i.e. the rotational signature is still evident if the radar beam is raised or lowered some) and also shows persistence in time rather than showing up for one sweep and disappearing the next. In terms of radar reflectivity, the development of an inflow notch and/or hook echo on the right rear flank of the storm cell relative to its direction of movement can be a further clue of mesocyclone/supercell formation, as can be a storm motion that is a little to the right of the average of non-supercell storms in the area. A combination of these factors would usually lead to issuance of a tornado warning by the NWS, even though none guarantees that a tornado has formed. More recently, dual-polarization technology has made the confirmation of something called the "tornadic debris signature" possible. When a strong or violent tornado is within a reasonable range of the radar, debris lofted by the tornado can produce a distinctive signature in the differential reflectivity and correlation coefficient plots of the radar that can discriminate between heavy rain in that area and non-meteorological targets like pieces of wood, siding, torn shingles and lofted vegetation. This can serve as a rather strong remote sensing confirmation that a destructive tornado has formed and remains in progress.
Jul. 26, 2012 | Tags: tornadoes, weather radar
Question: Have their ever been any recorded tornadoes in either Alaska or Hawaii? — David
Answer: In both cases, the answer is yes, although the numbers are quite small compared to most other states. Depending on the time frame covered, Hawaii ranks in the lowest 5 or so states in terms of numbers of tornadoes, and records indicate no tornadoes there have rated higher than EF-2 on the intensity scale. Alaska has very few recorded tornadoes, and when averaged over the years the rounded off number is zero per year. However, there have been a very few observed there, and the size of the state combined with a very low population density and limited radar coverage means that there have probably been a number of others there that were simply not observed or detected.
Jul. 22, 2012 | Tags: past weather, tornadoes
Question: What is the purpose of a tornado? — Anton
Answer: It's hard to say that they have any specific purpose. Rather, they form as something of a side effect or sub-component of the process of heat and moisture redistribution that we know as thunderstorms. Thunderstorms are one way in which the atmosphere maintains or restores a balance of heat, moisture and density when the lower atmosphere becomes especially warm and moist relative to higher levels, or vice versa. Under certain conditions, the storms become organized in a way that makes it possible for air flowing into and out of the storm to create and properly orient elongated areas of rotation that can be stretched and intensified into the form of a tornado.
Jun. 4, 2012 | Tags: general meteorology, thunderstorms, tornadoes
Question: What is a Gustnado? What is its difference from a tornado? — Siena
Answer: The term gustnado is a non-technical way to refer to a swirl of air that may spin up into a moderate-intensity, short-lived vortex near the outflow boundary from a thunderstorm. Gustnadoes form when the air flowing outward from a thunderstorm downdraft lifts and stretches air just outside the downdraft. If that air has a pre-existing shear or weak rotation, that may be intensified by the vertical stretching into something along the lines of a very strong dust devil or whirlwind. These are sometimes made visible by dust and debris lifted by the winds, and on occasion can do some minor damage. They differ from classic tornadoes, which are generated most commonly by rotating thunderstorms called supercells. These vortices are directly connected to the base of the thunderstorm and can in some cases become much stronger and more long-lived than a gustnado.
May. 20, 2012 | Tags: tornadoes
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