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Category Archives: Severe Weather
What is the longest lightning bolt?
Lightning is a huge electrical discharge, or spark, that results from vigorous motions in thunderstorms.
Storms are composed of ice crystals and liquid water droplets. Winds inside the storm cause particles to rub against one another, causing electrons to be stripped off, making the particles either negatively or positively charged. The charges get grouped in the cloud, often negatively charged near the bottom of the cloud and positively charged up high. This is an electric field, and because air is a good insulator, the electric fields become incredibly strong. Eventually a lightning bolt happens, and the flow of electrons neutralizes the electric field. Continue reading
Category: Meteorology, Phenomena, Severe Weather
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What is a heat dome?
“Heat dome” is a term used explain extreme heat conditions across large geographic regions.
The American Meteorological Society maintains a glossary of meteorological terms and defines a heat dome as, “An exceptionally warm air mass at middle latitudes during the warm season that that is associated with a synoptic-scale area of high pressure aloft. This area of high pressure aloft can have a doming effect on the warm air mass below by suppressing rising motion and the development of clouds and precipitation.” This is not the same as a heat wave, which is a spell of 3 or more abnormally hot days. Continue reading
What is a mesoscale convective complex?
Ordinary thunderstorms are a few miles in diameter and exist for less than an hour. The life cycle of an ordinary thunderstorm contains three stages: cumulus, mature and dissipating.
The cumulus stage is the initial stage of a thunderstorm as warm moist air near the ground rises. The mature stage of an ordinary thunderstorm begins when precipitation starts to fall from the cloud. During the mature stage, the thunderstorm produces the most lightning, rain, and can produce even small hail. The dissipating stage of a thunderstorm occurs when the updraft, which provides the required moisture for cloud development, begins to weaken and collapse. During this stage, the downdraft dominates the updraft and the storm begins to disappear. Continue reading
What is a landspout?
According to the American Meteorology Society’s glossary, a landspout is a colloquial name for a small tornado whose vorticity (a vector that measures local rotation in a fluid flow) originates in the boundary layer and has a parent cloud in its growth stage. Landspouts occur when colliding winds at the surface begin to make a vortex and then a developing thunderstorm passes overhead. The updrafts from that thunderstorm draw the rotating vortex upward and give it a tornado-like appearance. While relatively weak compared to traditional tornadoes, landspouts can be strong enough to cause damage and warrant caution.
The term “landspout” was coined by atmospheric scientists in the 1980s to describe a type of vortex associated with thunderstorms that do not possess a strong mid-level mesocyclone. A mesocyclone is a cyclonically rotating vortex, around 2–10 km in diameter, in a convective storm. Strong tornadoes form in mesocyclones.
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Did weather forecasting play a role in D-Day?
Last Friday was the 81st anniversary of the Allied invasion of Europe that began with the landings on the beaches at Normandy. The combined land, air, and sea assault of June 6, 1944 remains the largest such event in history. The success of the invasion was extraordinarily dependent of weather conditions. More than three months before the invasion, a combined British and American forecasting team began rigorous forecast exercises designed to iron out the physical and logistical kinks of such a coordinated effort. As June drew near, the nature of this collaboration was still problematic as the two groups employed vastly different methods in fashioning the requisite 3-5 days forecasts – at the time, absolutely primitive in the underlying science as compared to what is possible at such ranges today. The British were attempting to make such forecasts based upon the understanding of atmospheric dynamics that had grown substantially during the war. The Americans were employing a method based on a statistically- based search through old weather data for historical analogues that could be used to guide the forecast. Continue reading
Category: History, Meteorology, Severe Weather
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