The same complex cluster of thunderstorms that produced the tornadoes in Davie and Rowan Counties weakened slightly as they moved across Davidson and Guilford Counties between around PM and PM. The weak low-level rotation across eastern Guilford County at PM quickly strengthened as the storm moved into northwestern Alamance County at PM when a tornado touched down around 6 miles northwest of Graham.
The tornado moved across northwestern Alamance County with the storm relative velocity imagery becoming very impressive at PM. The tornado remained on the ground for another few minutes before exiting Alamance County at around PM and entering Caswell County. The tornado remained on the ground for another few miles in Caswell County before dissipating. The parent supercell weakened slightly but still maintained a broad area of rotation as it moved across eastern Caswell County.
As the supercell moved into western Person County, the rotation strengthened while the reflectivity structure improved. The tornado remained on the ground for 10 minutes and nearly 10 miles before the storm weakened and moved into Virginia. The thunderstorm intensified as it moved into North Carolina and approached Wadesboro.
The storm then became a supercell as it developed a persistent rotating updraft as it moved into Moore County just after PM. At PM the storm produced a tornado in northeastern Moore County. The storm weakened a bit as it moved through downtown Raleigh before intensifying as it moved across northeastern parts of the city.
The thunderstorm associated with Sanford-Raleigh Tornado weakened somewhat as it moved across Franklin County but it remained strong as it moved through Warren County into southern Halifax County with no confirmed tornado damage.
The storm intensified markedly during the next few minutes and by the next volume scan the storm relative velocity imagery was indicating a new and intensifying area of rotation with an impressive reflectivity pattern. At PM, both the storm relative velocity imagery and the reflectivity imagery had become even more alarming with a strong velocity couplet approaching Roanoke Rapids.
Just a few minutes later, an EF-2 tornado touched down in the city. This thunderstorm was rather strong as it moved northeast across northern and northeastern South Carolina exhibiting periods of strong radar signatures with reports of damaging winds and hail. As the thunderstorm moved into far southern North Carolina near Cheraw at around PM , it began to strengthen. The thunderstorm exhibited broad rotation across central Hoke County at PM with a fairly impressive reflectivity signature.
The first tornado that this supercell would produce touched down near the Wayside and Johnson Mills communities at around PM. The reflectivity image and storm relative velocity image was very impressive and well defined at PM.
The storm maintained an impressive structure as it moved south of interstate 95 in the PM reflectivity image and storm relative velocity image. As the tornado crossed interstate 95 for the second time and approached Smithfield, a secondary area of rotation developed near U. After the tornado went through Smithfield, it abruptly dissipated as a new tornado was forming to the southeast. The Fayetteville-Smithfield, Micro, and Wilson tornadic supercell developed a new updraft just as the first tornado was approaching Smithfield.
The PM radar imagery not only shows a new updraft developing to the northeast of Smithfield but also a new low level circulation developing to the east of the weakening circulation associated with the first tornado.
This is a remarkable image that shows both the weakening circulation from the first tornado and an intensifying circulation associated with the second tornado. The low level circulation weakened a few minutes later and the tornado dissipated after being on the ground for around 3 miles.
Around 10 minutes after the Micro Tornado dissipates, the same supercell featured broad low level rotation and a modest reflectivity pattern. As the supercell approached Wilson, a small but tightening low level circulation developed at PM with a reflectivity appendage.
This thunderstorm intensified after it moved east of Columbia and approached Darlington and Florence. The tornado moved northeast crossing into southwestern Sampson County and weakened slightly. As the storm moved to the north of Clinton, the circulation strengthened while the reflectivity pattern remained impressive.
The circulation subsequently weakened and the tornado dissipated at around PM. The same supercell continued to move northeast across Sampson County and then produced a relatively brief tornado as it moved across northern Duplin County near Faison. As the supercell moved into and across southern Wayne County, the storm relative velocity signature was generally convergent while the reflectivity pattern showed a developing appendage. Just before the storm was about to exit Wayne County, the storm relative velocity and especially the reflectivity pattern became more impressive on radar.
An EF-0 tornado touched down near Parkstown and was on the ground for a mile before exiting Wayne County and moving into Greene County.
The Storm Prediction Center SPC highlighted the possibility of strong storms in longer range outlooks, and they began offering more specified outlooks starting with the Day 3 forecast, issued the preceding Wednesday night. Throughout the week, forecasters knew that if the models were correct in showing all of these mechanisms coming together during the daytime, when heating would likely provide the instability needed for intense storms, a significant outbreak of severe weather was possible.
This threat was raised to 45 percent by early Friday afternoon. As confidence in a potential major severe weather event increased, WFO Raleigh forecasters offered strongly-worded statements and discussions providing more specifics on the most likely storm threat tornadoes as well as the location and timing of the severe weather.
The first detailed online weather briefing, focused on alerting the public, emergency managers, and other officials , was prepared and posted on our web page the morning of Friday 15, April. Recent advances in NWP and in computational efficiency have resulted in an improvement in and the availability of high resolution model forecasts on the convective scale. An example of the opportunities that high resolution NWP can provide is shown in the image to the right click on the image to enlarge.
A major tornadic outbreak was becoming a near certainty. On Saturday morning, forecasters at WFO Raleigh and SPC issued statements and alerts that emphasized the unique and serious dangers presented by this particular weather pattern. In particular, in the hours before storms developed and moved into central NC, low level instability was increasing rapidly , low level shear was very strong , and lifted condensation levels were low, a little more than one half kilometer which is a condition which research has shown is supportive of the development and maintenance of significant tornadoes.
This sounding combined with other observations and analysis from the early afternoon hours on 16 April confirmed that the environment that was predicted for several days had materialized and that a significant severe weather event would soon be underway. Evolution from a Squall Line to Discrete Supercells The evolution of the convective mode from a long linear structure to multiple discrete supercells on 16 April was unusual.
Often times, convection will grow upscale from individual cells, to multicells, and then into a line of convection or squall line as the convectively induced cold pools merge and interact. This event was rather remarkable in that no discrete supercells developed ahead of the line, rather the squall line fractured into several discrete long lived tornadic supercells. The squall line moved quickly east, advancing off of and out ahead of the slow moving cold front. The outflow behind the squall line was not especially cold; outflow temperature deficits ranged around 5 degrees C, which is common in environments with high relative humidity in the boundary layer.
Anecdotal experience of forecasters at the NWS Raleigh is that some of the most significant tornado events, including those with long track tornadoes, November Raleigh tornado , November tornadoes , and the March tornadoes , occur with rich boundary layer moisture, often at night when the lack of convective mixing keeps the boundary layer moist.
Radar imagery indicated very little trailing stratiform precipitation behind the squall line. This suggests that the support or maintenance of the cold pool was limited, and that the squall line was potentially missing a component to sustaining itself. It is interesting to note that very little if any intense convection developed ahead of the squall line.
The limited amount of convection that did develop ahead of the squall line was weak and dissipated fairly quickly. One thought is that the strong vertical wind shear had a detrimental effect on the developing updrafts and essentially tilted and ripped the immature convection apart.
This helps to explain why the few showers that developed ahead of the line failed to intensify and fell apart. It could be argued that the larger scale forcing at the mid and upper levels and the surface cold front were sufficient to initiate and intensify the convection in a region of potentially hostile shear. Once the convection matured, it was able to race ahead of the cold front and survive in the strongly sheared environment.
It has been shown that the component of the km low-level environmental shear oriented perpendicular to a squall line is one of the most important factors in the line's evolution. Long-lived squall lines can be expected when the wind shear is perpendicular to the line while squall lines with little or no line-normal shear will likely be shorter-lived and promote more discrete cells. The low-level shear vectors during this event were largely parallel to the squall line.
The large vertical wind shear, strongly curved clockwise hodographs, and minimal low-level line-normal shear appeared to strongly favor discrete supercells.
It can be argued that the environmental shear played a significant role in the evolution of the convection. As the squall line pushed east, the line began to fracture and discrete supercells emerged.
The 16 April outbreak was comprised of 30 tornadoes including five EF-3 and eight EF-2 tornadoes and resulted in 24 fatalities. The 28 March Tornado Outbreak is the only precedent during the 20th or 21st century of an event of this size, intensity, destruction, and fatalities. The March tornado outbreak impacted around 20 counties in eastern North Carolina whereas the outbreak impacted 37 counties across central and eastern North Carolina.
The Raleigh tornado which touched down on 28 November was rated an F It was the only tornado that night but it killed 4 people and injured residents. The 5 May tornado outbreak produced only 11 tornadoes, but they were generally more intense, including three F-4 tornadoes and they resulted in 5 fatalities in North Carolina.
An outbreak on 15 April produced 18 tornadoes, all of them were F-2 or weaker and there were no deaths in the state. More recently, an outbreak on 7 May produced 20 tornadoes in North Carolina, including one F-4 and one F-3, but the other tornadoes during that event were considerably weaker and short-lived and no fatalities were reported.
Finally, Hurricane Floyd's landfall on 15 September resulted in 17 tornadoes, all of them were F-2 or weaker, and there were no fatalities. Chris Broyles from the Storm Prediction Center put together an image click here to open that shows the years with the longest tornado tracks since The longest track tornadoes in North Carolina during this period are from , , , and On 16 April , two tornadoes were long tracked and were on the ground for more than 55 miles each.
The Sanford-Raleigh Tornado was on the ground for 67 miles and the Fayetteville-Smithfield Tornado was on the ground for nearly 59 miles. A tornado on 22 November tracked from Harnett County to Pasquotank County, a total of miles which set a North Carolina record. The 28 November Raleigh Tornado was on the ground for 84 miles and eventually reached Northampton County.
The 28 March Tornado Outbreak included 4 tornadoes which were on the ground for more than 20 miles, including two tornadoes that were on the ground for 40 miles each. The "High Risk" designation is a very unusual occurrence there have been only 44 "high risk" outlooks issued across the country for the 10 year period of with only 5 "High Risk" outlooks issued in The dates are 28 March , 3 May , 29 March , and 16 April There have been several occasions since March when some portion of the state of North Carolina has been in a high risk, most recently a small part of NC was in a High Risk on the Z November 11, outlook.
Tornado Emergencies were issued for every area in which fatalities occurred in central North Carolina with the exception of Sanford which was the first large tornado of the day. During times of extreme severe weather, normal communication means can be hampered. This was the first significant event in which some of the new communication technologies were used and their utility was apparent.
Many of the reports were first hand observations by trained spotters with additional reports relays of Public Safety transmissions heard on a scanner. NWSChat users provided 14 separate reports of damage or severe weather.
The Public Observation Program POP , which allows the public to call and leave reports of severe weather on a computer system, provided 28 separate reports of hail, funnel clouds, or tornadoes.
CoCoRaHS observers provided 10 real time reports of heavy rain, hail, or tornado debris. The Sanford-Raleigh tornado came within 1. State University. The NWS Raleigh operations area is located on the third floor of a three story building with a large bank of windows looking north. The tornado moved just to the southeast of the office and was not visible out the windows. The threat of a potential tornado strike on the office was noted more than 30 minutes in advance and multiple coordination calls were made with our backup office in Blacksburg Virginia.
As the tornado approached, the staff executed a phased evacuation from the operations area. The Blacksburg office backed up the Raleigh office for around 6 or 7 minutes as Raleigh staff members took shelter in the stairwell tornado shelter.
As the tornado drew closer, the power went out and the staff was huddled in the dark. After a few minutes, the staff returned to the operations area and noted very little damage, the tornado had tracked less than 2 miles to the southeast of the office. Some small branches and debris was noted out the window and the staff noted a strong odor of pine in the air. State University internship opportunities since the late s.
On 16 April, one of the student interns, Carl Barnes, was scheduled to work a shadow extended range forecast shift. Carl's first person summary of the event is available here. The map shows the tornado track density per square mile area during the period using a 5 class quartile classification.
An axis of higher tornado track density extends across the southern Piedmont, eastern Sandhills, and the Coastal Plain.
These results show a similar signal to a study by Michael Frates entitled "Demystifying Colloquial Tornado Alley" which examined the frequency of long-track F-3 to F-5 tornadoes. The results in the Frates study identified and labeled a "Carolina Alley" which extends from the southern Piedmont, across the Sandhills region and northward across the Coastal Plain of North Carolina.
Finally, a study by Dixon et al. The basic process for creating these products is initiated when velocity data from each radar is run through a Linear Least Squares Derivative LLSD filter creating an azimuthal shear field. The satellite images and high density maps in Google Earth often make it possible to determine the location of enhanced rotation down to the neighborhood scale. This simplifies the verification process by reducing the amount of time that is spent searching for reports.
This data has been used for numerous events across central North Carolina during the past few years including the 27 October Tornado Event , the 25 April Tornado Event , the 27 March Tornado Event , and the 15 November Outbreak. The rotational track product for this event from to UTC on 16 April is shown above and to the right click on it to enlarge. The product shows numerous corridors of enhanced rotation across central and eastern North Carolina which are associated with the many supercell thunderstorms that moved across the region that afternoon and evening.
The northeast storm motion is easy to see as is the longevity of the rotating thunderstorms with some of the tracks extending more than miles km. The two long track tornadoes the Sanford-Raleigh Tornado and the Fayetteville-Smithfield Tornado can be identified in the rotational track product. The image to the right is a zoomed in view of the rotational track product across central and eastern portions of the RAH CWA with the tracks of the tornadoes that occurred in the RAH CWA shown in black click on it to enlarge.
While the tornado tracks show a general northeast motion, the tracks are nonlinear and wobble somewhat as the storm structure evolves and as the tornado vortex interacts with the varied terrain and land uses. Note that the rotational track product uses radar data in the lowest 3km of the atmosphere that is blended from multiple radar sites. Because of this and with fast moving, tilted thunderstorms, the rotational track product will not match the tornado track exactly.
Some of the cell-based hail information has been incorporated into high-resolution gridded products that allow users to diagnose which portions of storms contain large hail. One such product is the "Hail Swath" product which accumulates hail size data over a period of time to provide hail swath maps, estimating both maximum hail size by location, and hail damage potential a combination of hail size and how long the hail has been falling. The track of several hail producing supercells that moved across central and eastern North Carolina is clearly visible.
The color scale on the image indicates the maximum expected hail size during the period with the light blue area indicating hail estimated at around a half inch in diameter, the darker blue area indicating hail greater than an inch in diameter, and the lighter green area indicating hail potentially larger than an inch and a half. In the RAH CWA, the hail swath product highlighted eastern Harnett and Johnston Counties as locations with potentially the largest hail and there were numerous reports of golf ball size hail 1.
The hail swath product also highlighted small portions of Sampson County where 2 inch diameter hail was reported and Wake County where 1. The image above and to the right is a zoomed in view of the hail swath product across central and eastern portions of the RAH CWA with the tracks of the tornadoes that occurred in central North Carolina shown in black click on it to enlarge.
In general, the radar estimated hail swaths were located to the north and west of tornado track which is consistent with a conceptual model of a tornado producing supercell thunderstorm. Ortega, Travis M. Smith, and Gregory J. Regional Radar Loop A regional radar loop of the southeastern United States shows the evolution of the 16 April tornado event.
A fairly large area of showers moved through western portions of central North Carolina just prior to and around the time of daybreak. Additional isolated cells developed in the clear air ahead, but were quickly ingested into the line. Most storms became tornadic. Over time, the squall line fragmented into discrete rotating supercells, bolstering the threat of tornadoes. One of them dropped a powerful tornado in Lee County, N. The storm was moving northeast parallel to Route 1, and had its sights set on Raleigh, 30 miles away.
Mike Maze and Nate Johnson, meteorologists at the station, warned their staff live on the air that the tornado was moving in their direction. Viewers watched live as the rain-wrapped silhouette approached a downtown webcam mounted on a high-rise building. The National Weather Service in Raleigh issued its first-ever tornado emergency, which included the city of Raleigh. The tornado passed just 1. Meteorologists there sought shelter while an alternate office located in Blacksburg, Va.
The Raleigh office lost power, and meteorologists reported smelling a pine scent from the large swath of trees mowed down by the tornado. The threat of severe weather was first mentioned three days ahead of the outbreak. In the Raleigh area, four supercell thunderstorms produced nine tornadoes. Classes were canceled for the rest of the spring semester, and students were graded on work they had already completed. EF1 damage, commensurate with winds of 85 to mph, was observed in downtown Raleigh, but the tornado strengthened again as it passed northeast out of the city.
Sporadic EF2 damage was also noted. Elsewhere across North Carolina, Fayetteville, Jacksonville and Wilson sustained hits from significant tornadoes during the outbreak, while a later tornado in Bertie County, N. It was rated an EF3. Another tornado of equal strength hit Bertie County in August and killed two people ; maximum winds were estimated near mph. The outbreak foreshadowed a catastrophic outbreak that would come just 11 days later, when the infamous April 27, , tornado claimed more than lives in Alabama.
In a four-day span, some tornadoes touched down, including four EF5s. Later that season, the deadliest tornado since would cause deaths in Joplin, Mo. Springfield, Mass. Louis, the western suburbs of Oklahoma City and scores of other major metropolitan areas would be struck by tornadoes as well. It was the deadliest year for tornadoes in the United States since Two politicians from Queens embroiled in complaint over F-bomb-riddled phone call.
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