How do downdrafts form in thunderstorms

One may also ask, how do supercell thunderstorms differ from ordinary cell thunderstorms? The updraft in a supercell thunderstorm is longer-lasting and rotates. HP high pressure has extreme downdrafts, flooding, hail while a LP supercell has little precipitation. Ordinary cell thunderstorms form more frequently in the afternoon because after the warm temperatures, the cold air aloft moves over the region.

The cold air makes the atmosphere unstable and parcels push upward. An air-mass thunderstorm , also called an " ordinary ", "single cell", or "garden variety" thunderstorm , is a thunderstorm that is generally weak and usually not severe.

Like all thunderstorms , the mean-layered wind field the storms form within determine motion. Asked by: Giannina Orlow asked in category: General Last Updated: 9th January, How do downdrafts form in ordinary cell thunderstorms? How do downdrafts form in ordinary cell thunderstorms?

The raindrops evaporate from the dry air, now chills it. The air is colder and heavier than the air around it, begins to descend in a downdraft. The cold particles begin to melt, which chills the air and enhances the downdraft. What are the 4 types of thunderstorms? There are four types of thunderstorms: single-cell, multi-cell cluster, multi-cell lines and supercells.

Supercell thunderstorms are the strongest and most severe. How long do supercell thunderstorms last? As the name implies, there is only one cell with this type of thunderstorm. Also called a "pulse" thunderstorm, the ordinary cell consists of a one-time updraft and one-time downdraft. In the towering cumulus stage, the rising updraft will suspend growing raindrops until the point where the weight of the water is greater than what can be supported.

At which point, drag of air from the falling drops begins to diminish the updraft and, in turn, allow more raindrops to fall. In effect, the falling rain turns the updraft into a downdraft. With rain falling back into the updraft, the supply of rising moist air is cut-off and the life of the single cell thunderstorm is short.

They are short lived and while hail and gusty wind can develop, these occurrences are typically not severe. Although there are times when a thunderstorm consists of just one ordinary cell that transitions through its life cycle and dissipates without additional new cell formation, thunderstorms often form in clusters with numerous cells in various stages of development, merging together.

While each individual thunderstorm cell, in a multi-cell cluster, behaves as a single cell, the prevailing atmospheric conditions are such that as the first cell matures, it is carried downstream by the upper level winds with a new cell forming upwind of the previous cell to take its place.

The speed at which the entire cluster of thunderstorms move downstream can make a huge difference in the amount of rain any one place receives. There are many times where the individual cell moves downstream but addition cells forming on the upwind side of the cluster and move directly over the path of the previous cell. The term for this type of pattern when viewed by radar is "training echoes".

Training thunderstorms produce tremendous rainfall over relatively small areas leading to flash flooding. Sometimes the atmospheric conditions are such that new cell growth is quite vigorous. This is something that can be visualized using a skew-T diagram. Favorable types of vertical shear, or the change of winds with height, interact dynamically with thunderstorms to enhance and maintain vertical draft strengths. Therefore, vertical wind shear is an important item for meteorologists to consider when forecasting the possibility of severe thunderstorms.

Thunderstorm squall lines can form in regions where the vertical wind shear is such that the wind speed increases with increasing altitude. This type of wind shear is shown in this two panel diagram of speed shear.

To understand how this works, you need to consider that individual thunderstorms are typically moved or steered along by the winds in the middle troposphere, close to where the air pressure is mb. Thus the right panel shows the wind profile relative to the storm motion or the winds at mb. Since the thunderstorm will move in the same direction as the surface winds, only faster, a steady supply of warm, humid surface air flows into the storm.

Please see this instuctive drawing of a squall line. You are not expected to be able to explain how squall lines form, though you should know that they often produce gust front lines that can produce strong and damaging winds along the ground. Repeating again, the spreading gust front is like a mini cold front as it is the leading edge of cold downdraft air pushing into warm surface air that was needed to get thunderstorms started. Squall lines and mesoscale convective complexes can develop over huge areas if conditions are favorable see Satellite images of a squall line and an MCS.

Organized squall lines often produce rather strong surface winds in association with the gust front. In desert regions, the squall lines can act to create dust storms. Below is a picture of a dust storm along the leading edge of a gust front taken in the Phoenix area on August 2, Dust storms like this are often called haboobs.

The picture below shows some of the features at the base of a thunderstorm. The cold downdraft air spilling out of a thunderstorm hits the ground and begins to move outward from underneath the thunderstorm.

The leading edge of this outward moving air is called a gust front. Desert residents think of it as a dust front because the gust front winds often stir up a lot of dust.

If you search, you will find lots of dust storm videos posted on the web. Here is a link to a short article, What are haboobs? Amazing pics and videos , which contains pictures and videos.

Hail is a type of precipitation consisting of balls or irregular clumps of ice. Hail formation requires a thunderstorm with strong upward motion of air over a large vertical extent, which must include a large region of below freezing air temperature. All hailstones begin as a seed or nuclues around which the hailstone will grow. The seed is typically a piece of ice, but it can be solid debris carried up by a thunderstorm, such as insects.

If a supercooled droplet of water collides with a piece of frozen material ice crystal or growing hailstone , the supercooled water will rapidly freeze around the outside of the ice. As a growing hailstone moves up and down through the supercooled region of the cloud, it grows by accretion of new ice with each collision see hail formation diagram above. You should be able to understand and explain how hail forms as described and shown in the figure above. Large hail can be quite destructive.

On average hail is responsible for over 1 billion dollars in property damage each year in just the United States alone. To make large hail very strong updrafts are required to hold up the growing hailstone against the force of gravity. The largest hailstone recovered in the U. It weighed 1 lb 15 oz Image. Link to Google Images for large hailstones where many claim to be the largest.

Be careful as several images are faked. A microburst is a small very intense downdraft that descends to the ground, then spreads out along the ground as a strong gust front moving away from the microburst core see diagram above. Microbursts can produce wind speeds of greater than miles per hour and thus are capable of causing significant damage. Microburst winds can be stronger than the winds observed in some hurricanes and tornadoes.

Because microbursts and tornadoes are both associated with severe thunderstorms, it is common for people to mistake microburst wind damage for tornado wind damage. The pattern of the wind damage can be used to distinguish the two since tornadoes produce rotational winds while microburst winds move out linearly straight line wind damage from the microburst core.

The total size of the microburst is typically less than a few miles in diameter and tend to last on the order of a few to ten minutes. Microbursts form in the same way as ordinary downdrafts. However, while downdrafts occur with most thunderstorms, damaging microbursts are relatively rare. When rain falls below cloud base or is mixed with dry air, it begins to evaporate and this evaporation process cools the air. When the evaporatively cooled air becomes colder and more dense than the surrounding air, it accelerates downward.

As this cold air approaches the ground, it spreads out in all directions and this divergence of the wind is the signature of the microburst. Micorbursts are particularly dangerous for air travel as described in the picture above. Lightning discharges take place within a cloud, from cloud-to-cloud, or from cloud-to-ground. Most discharges are within a cloud or from cloud-to-cloud, but the cloud-to-ground discharges are stronger. Lightning frequency is at a maximum in the mature stage.

Lightning sometimes occurs in the cumulus stage, but reaches its greatest frequency at the time the cell reaches maturity and its greatest height. The start of rain beneath the cloud base at the beginning of the mature stage marks the onset of the greatest lightning danger.

Although lightning may occur throughout a thunderstorm cell, the strongest flashes to the earth usually originate in the lower portion of the cell. Many cloud-to-ground lightning strikes reach out laterally for considerable distances from the cloud base. Once lightning has started, it may continue well into the dissipating stage of the cell. Apparently, less cloud height is needed to maintain continuing discharges than to initiate the first.

But as the height of the cell decreases after reaching maturity, the frequency of lightning flashes decreases. However, individual flashes may remain strong. The noise of thunder is due to compression waves resulting from the sudden heating and expansion of the air along the path of the lightning discharge. These compression waves are reflected from inversion layers, mountainsides, and the ground surface so that a rumbling sound is heard, instead of a sharp explosive clap, except when the discharge is very near.

Since light travels so very much faster than sound, it is possible to estimate the distance of a lightning flash using the elapsed time between seeing the flash and hearing the thunder. The distance to a flash is about 1 mile for each 5 seconds of elapsed time. Weather radar , in which portions of transmitted radio signals are reflected back from precipitation areas in clouds and displayed as radar echoes on an indicator, is helpful in locating, tracking, and revealing the intensity of thunderstorms and their associated lightning.

Thunderstorms are usually classified as frontal or air-mass thunderstorms. The frontal type is caused by warm, moist air being forced over a wedge of cold air. This lifting may occur with warm fronts, cold fronts, or occluded fronts.

Warm-front thunderstorms are usually embedded in large stratiform cloud masses. They are likely to be the least severe of frontal thunderstorms because of the shallow slope of the warm-front surface.

Surface wind conditions, in the cold air wedge beneath the warm front, may be unaffected by the thunderstorms above. Cold-front thunderstorms are generally more severe and occur in a more-or-less continuous line. Their bases are normally lower than those of other frontal thunderstorms. Thunderstorms occurring along a squall line are similar to those along a cold front, but may be even more severe.

Heavy hail, destructive winds, and tornadoes are usually associated with squall-line thunderstorms. Thunderstorms are often associated with a warm-front type occlusion. In this case, they occur along the upper cold front and are set off by the lifting of the warm, moist air. They are usually more severe than warm-front thunderstorms and less severe than the cold-front type. Air-mass thunderstorms are unaffected by frontal activity.

They are usually scattered or isolated. Air-mass thunderstorms may be further classified as convective or orographic , although these lifting processes often act together. Convective thunderstorms formed by convergence may occur day or night, but they tend to be most active in the afternoon. Those produced by instability resulting from advection of low-level warm air or high-level cold air may also occur day or night. The nocturnal, or nighttime, thunderstorm, which is common in the Midwest during spring and summer, is usually due to low-level warm-air advection and convergence.

These storms are among the most severe found anywhere. Orographic thunderstorms develop when moist, unstable air is forced up mountain slopes. They tend to be more frequent during the afternoon and early evening because heating from below aids in the lifting process. Storm activity is usually scattered along the individual peaks of mountain ranges, but occasionally there will be a long unbroken line of thunderstorms. One type of air-mass thunderstorm, the high-level or dry thunderstorm , deserves special consideration because of its importance in starting wildfires.

The lifting process may be orographic, convergence, cold-air advection aloft, or a combination of these, often aided by surface heating over mountain ranges. High-level thunderstorms occur most frequently in the mountainous West during the summer months. The downdraft and outflow from a high-level thunderstorm is likely to reach the ground even though the precipitation evaporates before reaching the ground. The cold, heavy air is usually guided by the topography into downslope and downcanyon flow, although flow in any direction is possible.

Their distinctive feature is that their cloud bases are so high, often above 15, feet, that precipitation is totally or mostly evaporated before it reaches the ground.

As a result, lightning strikes reaching the ground frequently start fires in the dry fuels. The downdraft and outflow usually reach the ground even though the precipitation does not. The cold, heavy air is generally guided by the topography into downslope and downcanyon patterns, but cross-slope flow may also occur. There are two principal weather patterns which produce high-level storms. One is the inflow of moist air , usually from over the Gulf of Mexico but occasionally from over the eastern subtropical Pacific, at levels of 10, to 18, feet.

Thunderstorms are set off by lifting over mountains, and by heating and upslope thermal winds at higher levels in the mountains, as the moist air spreads northward from New Mexico, Arizona, and southern California.

These storms usually develop in the afternoon and may extend into the evening hours. The second important weather pattern in high-level storms is the cold Low aloft. With this pattern a closed low-pressure system aloft becomes cut off from the main belt of westerlies. The cold air within this closed Low produces instability and causes convective currents to develop. If sufficient moisture is present, thunderstorms will form.

They can develop at any time of the day or night, but are most active in the afternoon when they are assisted by daytime heating.

The movement of a closed upper Low is erratic and very difficult to predict. The Low may move in virtually any direction, may deepen or fill, or may be picked up by a trough moving eastward at a higher latitude. The Far West is a favorite place for closed Lows to develop. They may meander around for several days or a week before finally dissipating or moving on. A tornado is a violently whirling vortex which occurs with a severe thunderstorm.

The rotating tube builds downward from the cumulonimbus cloud. Destruction results from extremely strong wind and low pressure. Tornadoes are violent whirling storms which may occur with severe thunderstorms. They take the form of a funnel or tube building downward from a cumulonimbus cloud. These violently rotating columns of air range in size from a hundred feet to a half mile in diameter. They travel with a speed of 25 to 50 m. The length of the path of a single tornado is usually just a few miles, but some tornadoes have remained active for more than a hundred miles—striking the ground for a few miles, skipping an area, then striking the ground again, and so on.

The great destructiveness of tornadoes is caused by the very strong wind and extremely low pressure. Winds in the rapidly spinning vortex have never been measured, but from the destruction it is estimated that winds may exceed m. The low pressure causes houses and structures to virtually explode when a tornado passes over them. There is a sudden decrease in pressure around the house, while on the inside the pressure changes little.