![]() Formed as an organized line or lines of multi-cell storms frequently with a gust.The gust front may extend for several miles ahead of the storm, bringing with it an increase in wind speed and atmospheric pressure, a decrease in temperature, and a shift in wind direction.The cloud becomes divided into updraft and downdraft regions, separated by a gust front.Groups of cells in different stages of development, which have merged into a larger system.These storms are short lived and last for less than an hour after becoming strong enough to produce lightning.Form when the atmosphere is unstable, but there is little or no wind shear.(aircraft identification) EXTREME precipitation two zero miles west of Atlanta V-O-R, two five miles wide, moving east at two zero knots, tops flight level three niner zero.Precipitation area is two five miles in diameter (aircraft identification) EXTREME precipitation between ten o'clock and two o'clock, one five miles.Alert provided by an ATC facility to an aircraft:.Reference the Pilot/Controller Glossary: Precipitation Radar Weather Descriptions.These precipitation intensity areas are described as "light," "moderate," "heavy," and "extreme" Current weather radar systems are able to objectively determine precipitation intensity.However, by understanding severe thunderstorm criteria, i.e., 50 knot winds or 3/4 inch hail, the information is available in the report to know that one is occurring METAR reports do not include a descriptor for severe thunderstorms.Lightning can strike aircraft flying in the clear in the vicinity of a thunderstorm.The probability of lightning strikes occurring to aircraft is greatest when operating at altitudes where temperatures are between minus 5° Celsius and plus 5° Celsius.Then the lower altitudes may be characterized by strong out flowing winds and severe turbulence.This is especially true when the relative humidity is low in any layer between the surface and 15,000'.Turbulence beneath a thunderstorm should not be minimized.NO FLIGHT PATH THROUGH AN AREA OF STRONG OR VERY STRONG RADAR ECHOES SEPARATED BY 20-30 MILES OR LESS MAY BE CONSIDERED FREE OF SEVERE TURBULENCE.The frequency and severity of turbulence generally increases with the radar reflectivity which is closely associated with the areas of highest liquid water content of the storm.Weather radar, airborne or ground based, will normally reflect the areas of moderate to heavy precipitation (radar does not detect turbulence).This distance decreases to about 10 miles in less severe storms.Severe turbulence can be expected up to 20 miles from severe thunderstorms.The visible thunderstorm cloud is only a portion of a turbulent system whose updrafts and downdrafts often extend far beyond the visible storm cloud.There is no useful correlation between the external visual appearance of thunderstorms and the severity or amount of turbulence or hail within them.While there is some evidence that maximum turbulence exists at the middle level of a thunderstorm, recent studies show little variation of turbulence intensity with altitude.Turbulence, hail, rain, snow, lightning, sustained updrafts and downdrafts, icing conditions-all are present in thunderstorms.AFSS/FSS: EXTREME precipitation two zero miles west of Atlanta V-O-R, two five miles wide, moving east at two zero knots, tops flight level three niner zero.".Precipitation area is two five miles in diameter." ATC: " EXTREME precipitation between ten o'clock and two o'clock, one five miles.In the winter months, snowfall can occasionally take place in a thunderstorm.Cumulus clouds often associated with a calm sunny day can quickly build into a threat to pilots who may find themselves entering a growingly convective environment. ![]()
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