A thunderstorm makes its way through three distinct stages before dissipating, as shown above, it begins with the cumulus stage in which lifting action of the air begins. If sufficient moisture and instability are present, the clouds continue to increase in vertical height, continuous, strong updrafts prohibit moisture from falling.

The updraft region grows larger than the individual thermals feeding the storm within approximately 15 minutes. The thunderstorm reaches the mature stage, which is the most violent time period of the thunderstorms life cycle.

At this point drops of moisture whether rain or ice are too heavy for the cloud to support and begin falling in the form of rain or hail. This creates a downward motion of the air, warm rising air, cool, precipitation, induced descending air and violent turbulence all exist within and near the cloud below the cloud.

The down rushing air increases, surface winds and decreases the temperature once the vertical motion near the top of the cloud slows down the top of the cloud spreads out and takes on an anvil like shape.

At this point, the storm enters the dissipating stage. This is when the down drafts spread out and replace the updrafts needed to sustain the storm for aviation purposes. A ceiling is the lowest layer of clouds reported as being broken or overcast, or the vertical visibility into an obscure Asian like fog or haze.

Clouds are reported as broken when 5/8 to 7/8 of the sky is covered with clouds. Overcast means the entire sky is covered with clouds. Current ceiling information is reported by the aviation routine weather report METAR and automated weather stations of vary types closely related to cloud cover and reported ceilings is visibility.

Information visibility refers to the greatest horizontal distance at which prominent objects can be viewed with the naked eye. Current visibility is also reported in METAR and other aviation weather reports, as well as by automated weather systems.

Visibility information, as predicted by meteorologists, is available for a pilot. During a pre-flight weather, briefing, precipitation refers to any type of water particles that form in the atmosphere and fall to the ground.

It has a profound impact on flight safety, depending on the form of precipitation. It can reduce visibility, create icing situations and affect landing and takeoff performance of an aircraft precipitation occurs because water or ice particles and clouds grow in size until the atmosphere can no longer support them.

It can occur in several forms as it falls toward the earth, including drizzle rain ice pellets, hail, snow and ice precipitation in any form poses a threat to safety of flight. Often, precipitation is accompanied by low ceilings and reduced visibility.

Aircraft that have ice, snow or frost on their surfaces must be carefully cleaned prior to beginning a flight because of the possible air flow disruption and loss of lift rain can contribute to water in the fuel tanks.

Precipitation can create hazards on the runway, surface itself, making takeoffs and landings difficult, if not impossible, due to snow ice or pooling water and very slick surfaces. Air masses are classified according to the regions where they originate.

They are large bodies of air that take on the characteristics of the surrounding area or source region. A source region is typically an area in which the air remains relatively stagnant for a period of days or longer.

During this time of stagnation, the air mass takes on the temperature and moisture characteristic of the source region. Areas of stagnation can be found in the polar regions, tropical oceans and dry deserts.

Air masses are generally identified as polar or tropical, depending on the temperature characteristics and maritime or continental based on moisture content, as shown above a continental polar airmass forms over a polar region and brings cool dry air with it.

Maritime tropical air masses form over warm tropical waters like the Caribbean Sea and bring warm moist air as an air mass moves across bodies of water and land. It eventually comes in contact with another air mass with different characteristics.

The boundary layer between two types of air masses is known as a front. An approaching front of any type always means changes to the weather are imminent shown above are the four types of fronts which are named according to the temperature of the advancing air relative to the temperature, the air, it is replacing warm cold stationary occluded a warm front Occurs when a warm mass of air advances and replaces a body of colder air, warm fronts move slowly, typically 10 to 25 miles per hour, mph the slope of the advancing front slides over the top of the cooler air and gradually pushes it out of the area.

Warm fronts contain warm air that often have very high humidity, as the warm air is lifted. The temperature drops and condensation occurs. A cold front occurs when a mass of cold, dense and stable air advances and replaces a body of warmer air cold fronts, move more rapidly than warm fronts, progressing at a rate of 25 to 30 miles an hour.

A typical cold front moves in a manner opposite that of a warm front. It is so dense. It stays close to the ground and acts like a snowplow sliding under the warm air and forcing the less dense air aloft.

The rapidly ascending air causes the temperature to decrease suddenly forcing the creation of clouds the friction between the ground and the cold front, retards the movement of the front and creates a steeper frontal surface.

This results in a very narrow band of weather, concentrated along the leading edge of the front. A continuous line of thunderstorms or squall line may form along or ahead of the front squall lines present.

A serious hazard to pilots as squall type thunderstorms are intense and move quickly when the forces of two air masses are relatively equal. The boundary or front that separates them remains stationary and influences the local weather.

For days. This front is called a stationary front. The weather associated with the stationary front is typically a mixture that can be found in both warm and cold fronts. An occluded front occurs when a fast-moving cold front catches up with a slow-moving warm front.

As the occluded front approaches warm front, weather prevails, but is immediately followed by cold front weather, whether can pose serious hazards to flight and a thunderstorm packs. Just about every weather hazard known to aviation into one vicious bundle.

These hazards occur individually or in combinations, and most can be found in a squall line for a thunderstorm to form. The air must have sufficient water, vapor, an unstable lapse rate and an initial lifting action to start the storm process, fronts converging winds and troughs aloft force upward motion spawning these storms, which often form into squall lines.

A squall line is a narrow band of active thunderstorms. Often it develops on or ahead of a cold front in moist, unstable air, but it may develop in unstable air, far removed from any front. It often contains steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

It usually forms rapidly generally reaching maximum intensity. During the late afternoon and the first few hours of darkness, an aircraft entering a tornado vortex is almost certain to suffer structural damage.

Since the vortex extends well into the cloud. Any pilot inadvertently caught on instruments in a severe thunderstorm could encounter a hidden, vortex. Potentially hazardous turbulence is present in all thunderstorms and a severe thunderstorm can destroy an aircraft strongest turbulence within the cloud occurs, with shear between updrafts and downdrafts updrafts in a thunderstorm support abundant liquid water with relatively large droplet sizes.

When carried above the freezing level, the water becomes supercooled supercooled water freezes on impact with an aircraft. Clear icing can occur at any altitude above the freezing level, but at high levels, icing from smaller droplets may be rime or mixed rime and clear ice thunderstorms are not the only area where pilots could encounter icing conditions.

Pilots should be alert for icing any time. The temperature approaches, zero degrees Celsius and visible moisture is present, hail competes with turbulence, as the greatest thunderstorm hazard to aircraft possible hail should be anticipated with any thunderstorm, especially beneath the anvil of a large cumulonimbus.

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