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In July 1643 Governor John Winthrop described a sort of wind gust that could have possibly been one of the first recorded tornadoes in history. Winthrop, who was ever conscious of the weather, recorded that there was a sudden gust in northeastern Massachusetts and costal New Hampshire. According to Winthrop this “gust” blew down many trees, filled the air with dust, lifted up a meetinghouse in Newbury, and killed one Indian. Because there was no weather technology in that time period we have no way of knowing whether this “gust” was a true tornado or not.
At this point in time, formation of tornadoes are not fully understood by scientists. They usually form in a giant rotating thunderstorm called a supercell. Supercells form when cold polar air meets warm tropical air. The result is a great instability caused by the rising warm air. A squall line, or narrow zone of cumulonimbus clouds forms, giving life to the tornadoes. Lightning flashes, and heavy rains and hail begin to fall. Soon after, the easiest recognizable part of the tornado, the funnel, seems to descend from the base of the cloud. In actuality, it does not, but rather the pressure within the cloud drops due to the increasing wind speeds. This is known as Bernoulli's principle. As the pressure drops, it causes moisture in the air to condense. This action continues down the spiral, giving the impression that the funnel is descending from the cloud base. In addition to the visible funnel, there is also a hissing sound, which turns into a loud roar when the tornado touches the earth.
Tornado conditions are caused when different temperatures and humidity meet to form thunderclouds. In the United States, warm, wet winds from the Gulf of Mexico move northward in spring and summer, meeting colder, dry Canadian winds moving southward. The place where these two winds meet is called a dry line. High, dry air coming from the north piles on top of low-moving, moist Gulf air at a height of over 10,000 feet. The warm southern winds try to rise, but the cold northern air blocks them. This clash causes the warm, trapped air to rotate horizontally between the two air masses. At the same time, the sun heats the earth below, warming more air that continues to try and rise. Finally, the rising warm wind become strong enough to force itself up through the colder air layer. When this occurs, the cold air on
SANTA ROSA (CBS SF) – A small tornado destroyed a wood and corrugated metal shed at a business in Santa Rosa Friday morning, just hours before the powerful storm prompted a Tornado Warning for San Mateo County and knocked out power to many local PG&E customers.
The National Weather service said Friday that an Enhanced Fujita 1 tornado hit the area shortly before 10 a.m. An EF1 is characterized by a three-second burst of wind between 86 and 110 mph., which is roughly what witnesses describe hitting the Sequoia Landscaping Materials facility.
Another funnel cloud was spotted above Ocean Beach as the same system passed over San Francisco.