Warm rear flank downdrafts promote tornadoes, while cold rear flank downdrafts discourage them. Markowski department of meteorology, the pennsylvania state university, university park, pennsylvania manuscript received 19 march 2001, in. Other reliable radar observations have been made that suggest that hook echo formation, in at least some cases, appears to result from the descent of a rain curtain in the rear flank downdraft e. The rear flank downdraft of a supercell is a very complex and not yet fully understood feature. Thats the rear flank downdraft and thats the cool air on the backside of the storm that comes crashing around it can help tighten the circle. Large hail within the rear flank downdraft often shows up brightly as a hook on weather radar images, producing the characteristic hook echo, which often. Some air, as it collides into the side of a thunderstorm, is pushed down toward the surface. First, the mesocyclone rotating air, along with the rear flank downdraft rfd, starts moving towards the ground.
For much of its life cycle, the storm structure of mesovortex 2 was similar to that of a supercell. A rear flank downdraft is cold air on the back side of the storm that rushes down towards the ground and when that cold air hits the cloud base associated with the updraft it quickly erodes them leaving a clear slot. Supercell variations classic and hp and the tornado life. The data appear to have resolved a portion of the rear flank downdraft rfd gust front and a portion of the occlusion process. Rearflank downdrafts have a wellestablished association with hook echoes. The rfd of a supercell is believed to play a large part in tornadogenesis by tightening existing rotation within the surface mesocyclone. Evolution of a longtrack violent tornado within a simulated. Firstly, the initial rear flank downdraft is air from aloft transported down to the surface by colliding and mixing with the storm. Multiple circulations attempt to develop on the rfdinflow interface before the entire area is undercut by outflow from the storms forwardflank. We see in this animation the tornado, the wall cloud with the updraft is, but look that rear flank down draft and. Feb 11, 2009 a rear flank downdraft is cold air on the back side of the storm that rushes down towards the ground and when that cold air hits the cloud base associated with the updraft it quickly erodes them leaving a clear slot. Supercell rearflank downdraft rfd surge capron, ok, may 8. An animation of the simulated cloud and precipitation fields also shows features routinely observed, such as periodic rain curtains that wrap around the lowlevel mesocyclonetornado and a tornado that becomes more rain wrapped in time.
Oct 14, 2010 once a tornado has formed, it follows a predictable life cycle. Jun 18, 2017 in the radar image above, the rear flank downdraft rfd is where the core of heavy rain and hail is occurring pink pixels, and the forward flank downdraft ffd is to the east, or right, of the rfd. It appears in the animation that some extreme winds are pushing out the southwest flank of the supercell with a haze near the cloud edge. Convective storm structure and evolution eumetrain. In the radar image above, the rearflank downdraft rfd is where the core of heavy rain and hail is occurring pink pixels, and the forwardflank downdraft ffd is to the east, or right, of the rfd. These winds can sound like a freight train and in some cases they can be strong enough to mimic tornado damage. At such close distance to the radar rear flank downdraft rfd inflow air could be recycled and becomes part of the rear flank downdraft. Early april east coast cyclone satellite liaison blog. It often is visible as a clear slot wrapping around the wall cloud rfd rear flank downdraft. Vortex2 observations of a lowlevel mesocyclone with multiple. Some other complex factors beyond the scope of the course also contribute to the formation of the rfd, but the bottom line is that a separate rearflank downdraft exists in supercells. Mesovortices and their interactions within a quasilinear. Founded in 1974, the magazine has been edited at various locations and by different communities over the course of its existence.
Specifically, you should be able to describe the forward flank downdraft, rear flank downdraft, updraft region, mesocyclone, and tornado if applicable. There are both linear and nonlinear forcings and it is tough to make a general model so often special case scenarios are developed e. Despite the longsurmised importance of the hook echo and rear. Northnortheast of masters and over the riverside reservoir we see a bullseye of high kdp values 3. The rfd even comes with its own gust front, as the leading edge of raincooled air spreads out laterally from the splashdown point of the rfd. Rear flank downdraft meteorology definition,meaning. Rear flank downdraft or rfd a region of dry air subsiding on the back side of, and wrapping around, a mesocyclone. A strong downdraft of air on the upwind side of a thunderstorm, usually a supercell, which is separated from the forward flank outflow regions of the storm. Here is a short clip from 15km north of dubbo where textbook rfd rear flank downdraft winds are being heard and observed. In warren county, an ef1 tornado packing estimated 90 to 95 mph winds touched down 8 miles south of mcminnville, tennessee, and traveled a path of 3 miles.
Specifically, you should be able to describe the forwardflank downdraft, rear flank downdraft, updraft region, mesocyclone, and tornado if applicable. Originally a meteorological term, meaning in a supercell thunderstorm, an area of dry air that wraps around the back end of a mesocyclone. Following the development of the rfd, the simulated storm acquires a horseshoeshaped updraft prior to tornadogenesis similar to observations lemon and doswell 1979. The rear flank downdraft air tends to be dry and warm since the air warms by adiabatic compression as it sinks to the surface. Sep 25, 2017 rear flank downdraft meaning rear flank downdra. Once the severe thunderstorms began to form across western oklahoma after 18. A lot of times it will create sort of a horse shoe shape in the updraft base. The rearflank downdraft rfd gust front is indicated by a dashed blue line labeled rfdgf in fig. These areas of descending air are thought to be essential in the.
Estimates of rearflank downdraft buoyancy as a predictor of tornadogenesis. The above animation shows the evolution of a mesolow on the southwest flank of a supercelllike thunderstorm, which becomes the new surface low pressure. The rear flank downdraft rfd represents relatively warm and dry air which is forced down from the midlevels of the atmosphere. A condensation funnel is made up of water droplets and extends downward from the base of the thunderstorm. Direct surface thermodynamic observations within the rear. The rear flank downdraft is this part over here, so you can see the downdraft over here. In this paper, in situ surface observations within hook echoes and rfds are analyzed. A strong downdraft of air on the upwind side of a thunderstorm, usually a supercell, which is separated from the forward flank regions of the storm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes. Estimates of rear flank downdraft buoyancy as a predictor of tornadogenesis. Hook echoes are known to be associated with a commonly observed region of subsiding air in supercells, called the rearflank downdraft. Labels show rear flank downdraft descent, counterrotating vortices, and storm inflow. The rear flank downdraft or rfd is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. The storm had a persistent mesovortex similar to a mesocyclone, and it developed a hook echo, inflow notch, and a reflectivity core.
Cold air downbursts impinging upon the tornado as it approached davidson county would have caused the tornado funnel to tilt increasingly from the vertical, becoming a funnel cloud as it lifted above the ground and possibly dissipating over davidson. The rfd even comes with its own gust front, as the leading edge of raincooled air. Secondly, hook echoes form through advection of precipitation from the rear of the main echo around the region of strong updraft. If it is in contact with the ground it is a tornado. The hybrid method estimates high frequency turbulence regeneration in an actual severe storm that has complex thermal conditions in order to alleviate the problem of high frequency component dissipation in meteorological models and generate appropriate. Perhaps the bestrecognized radar feature in a horizontal depiction associated with supercells is the extension of lowlevel echo on the rightrear flank of these storms, called the hook echo.
Vorticity increases and the pressure falls mb in 3 hours. Markowski department of meteorology, the pennsylvania state university, university park, pennsylvania. Jan 15, 2010 rear flank downdrafts have a wellestablished association with hook echoes. Mar 03, 2005 vertical pressure gradient fields of supercells get very complex, particularly for nonideal shear profiles. Some other complex factors beyond the scope of the course also contribute to the formation of the rfd, but the bottom line is that a separate rear flank downdraft exists in supercells. The rear flank downdraft rfd is a key ingredient in tornado formation in supercell thunderstorms. Time lapse video 8x speed of the tornadic supercell west of syracuse, ks on 71516. Nrot on gr2 radar was going crazy on the backside of the texas storm. Direct surface thermodynamic observations within the rearflank downdrafts of nontornadic and tornadic supercells paul m. Streamtubes are driven by a wind field parameter in a computational scientific model of the deadly 2011 joplin, missouri tornado.
The rear flank downdraft is air from aloft that is transported down to the surface from colliding with the storm. The forward flank downdraft is the outflow from the raincooled air of the storms downdraft. The inflection point between the rear and forwardflank downdraft boundaries was a focal point for the. You should also be able to describe the cloud formation a wall cloud thats often a precursor to a funnel cloud or tornado formation, and identify the location on radar reflectivity where a. Rfds mainly occur within classic and hp supercells although rfds have been observed within lp supercells. At such close distance to the radar modelengineering les method was used to analyze a tornado and nearground turbulence under realistic conditions. A country journal for gay men everywhere is a readerwritten magazine focused on gay countryliving and alternative lifestyles. Understanding the three types of supercell thunderstorms. The combination of these parameters suggests the presence of large hail in this region of the rear flank downdraft. Rear flank downdrafts have a wellestablished association with hook echoes. Compare selected click up to three compare checkboxes for sidebyside product comparisons. Viking rear downdrafts work quietly behind cooktops and rangetops to eliminate smoke and odors, then conveniently hide away when the job is done. Once a tornado has formed, it follows a predictable life cycle. Super tornado cadens visualization enabling discovery.
Large hail within the rear flank downdraft shows up brightly as a hook on weather radar images, producing the characteristic hook echo, which indicates the. The rear flank downdraft is the motion in the storm that causes the hook echo feature on radar. Secondly, hook echoes form through advection of precipitation. Jul 25, 2016 time lapse video 8x speed of the tornadic supercell west of syracuse, ks on 71516. This supercell drifted eastward very slowly, and was nearly stationary at times. Rear flank downdraft how is rear flank downdraft abbreviated. The rfd also may wrap around a rotating supercell storm, especially is the storm is tornadic. These geometric features are key elements in the formation of tornadoes. Derived from data, blue streamers falling toward the ground indicate the tornados rear flank downdraft, while the quickly rising orange lines constitute the updraft. Could this be precipitation being pushed out similar to a rearflank downdraft.
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