Twister

 

Windstorms
(severe extra-tropical cyclones, hurricanes and other severe weather, heat waves etc)

Windstorms are very strong winds that are caused by ether extra-tropical cyclones or high and low pressure systems colliding. Some of the damaging local winds have names, such as the Taku Wind, which is a violent northeasterly wind that howls from time to time in Juneau, Alaska. The Williwaw is another violent north/northeast wind that howls through Anchorage, Alaska from time to time. The Bora is another cold wind that often howls in the winter time and like Williwaw and Taku winds in Alaska can exceed hurricane or near hurricane-force speeds. There is a very strong local wind that effects all of the United States, the chinook (also known as the snow eater). These powerful winds bring welcome warming but they can cause widespread damage. The most powerful chinook winds occur in Utah and in Boulder, Colorado. On January 17th, 1982 powerful chinook winds from the west up to 140 mph raked the eastern foothills of the Colorado Rockies.

In Boulder, utility poles were snapped in half, damage cost was $17 Million. The high winds also raised the temperature from 2 Degrees to 50 Degrees in just one hour. On October 30th 1959, violent chinook winds from the east sustained at 78 mph with gusts to 100 mph caused millions of dollars in damage in Utah. On December 31st, 1996, following the Great Snowstorm of December 26-29th, heavy rain and powerful chinook winds from the east up to 60 to 70 mph, with gusts to 80 mph, pounded Western Washington. Trees were blown onto power lines plunging millions of people into darkness. Some trees were literally snapped off at the ground. This Western Washington Chinook caused several million dollars in damages and it left several thousand without power. Another chinook that struck in December of 2003 had easterly winds sustained at 45 to 50 mph, with gusts to 65 mph, this particular windstorm caused millions of dollars in damage to the foothills of the cascades and the Puget Sound Region and thousands were left without power in another Pacific Northwest Chinook. The setup for strong chinook winds is a high and low-pressure area colliding overhead that's what makes the winds so damaging, because of the tight pressure gradient between the high and the low.

The powerful winds that pound Alaska from time to time require the same setup. A strong center of low-pressure just of the coast and a strong high-pressure area inland for the winds to pick up. Juneau's worst Taku Windstorm on record took place on January 8, 1975, when northeast winds of up to 200 mph lashed the town knocking down power lines, blowing out windows in some parts and causing widespread destruction. This remains the worst Taku Windstorm to ever pound that part of Alaska. A few months earlier Taku Winds from the northeast up to 180 mph caused 1 million dollars in damage in Juneau. No such wind records have been matched since, but Taku Windstorms of 60 mph or more still occur every winter. On April 1, 1980, Wild Williwaw winds from the north/northeast of over 100 mph walloped the east side of Anchorage. Most buildings were badly damaged or destroyed and damage cost was $25 Million. It was the third notable windstorm in Anchorage that winter. What makes these northeasterly or northerly winds so damaging is the same setup, a strong high inland and a strong low-pressure area out at sea, when these two elments come together the Taku and Williwaw Winds howl.

The more common producer of high winds is the extra-tropical low-pressure system, which usually just brings rain to the west coast, but ocassionally these garden variety low-pressure systems become monster storms in their own right. Either coming down from the north and dumping heavy snow or roaring in from the sea and bringing high winds and torrential rains. One of the most powerful storms to ever pound the West was the Columbus Day Storm of 1962. The storm originated from Pacific Typhoon Freda, which was slowly dying out, but Freda merged with a cold front out in the ocean to become an intense mid-latitude cyclone, which raced into the Pacific Northwest. This powerful storm brought hurricane-force winds and heavy rains, which caused several million in damages to Washington, Oregon and British Columbia. South winds reached 78 mph with gusts over 100 mph. Winds gusted to 116 mph on Morrison Bridge in Downtown Portand and the wind reached 160 mph along the coast. This still remains the greatest blowdown in Pacific Northwest History. On December 11th and 12th, 1995 a similar storm brought south winds of up to 65 mph, with gusts to 78 mph to Seattle and Oregon, damage cost was several million and thousands were left without power.

The Saffir Simpson Hurricane Scale

Here is a list of the differents forms of severe weather

Category Wind Speed Storm Surge Damage
1 74 to 95 mph 4-5 feet Trees are blown down or uprooted, moble homes, buildings and structures badly damaged, tree also loose some of their leaves power lines are also blown down
2 96 to 110 mph 6-8 feet Trees are uprooted and blown down, Structures and moble homes severely damaged shingles and chimneys are blown from roofs
3 111 to 130 mph 9-12 feet Leaves are stripped from trees and trees are blown down and uprooted, mobile homes are destroyed, structures and badly damaged, some destroyed
4 131 to 155 mph 13-18 feet Extensive damage to windows, some are blown out, roves are badly damaged or blown off. Extensive flooding flows several miles inland. Very severe damage
5 155 mph or more 18 ft or more Catostraphic damage. All building severely damaged, most are destroyed. Most trees are literally uprooted and blown down, almost everything destroyed

This kind of marquee is called a sliding marquee:
Severe Weather Alert.

The Different Forms of Severe Weather

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