JACKSONVILLE, Fla. – On Sunday afternoon, nearly the entire area saw thunderstorms, but in Douglas, Georgia a pulse thunderstorm produced a downburst wind that caused damage to area businesses and vehicles. A traffic light was smashed and trees were snapped at their base as the high, damaging winds rushed through.
At 4:50 p.m. on July 9th, a thunderstorm developed a precipitation core that built up heights between 10-20,000 feet. Shortly after, the core began to crash downward towards the surface. Between 4:50 and 5:05p.m. the core crashed down to the ground level, forcing air out from beneath it. This produced winds between 50-70 mph which caused the damage in the photos above.
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According to the National Weather Service, a downburst is a strong downdraft which causes damaging winds on or near the ground. A downdraft is A small-scale column of air that rapidly sinks toward the ground, usually accompanied by precipitation as in a shower or thunderstorm. Downbursts can be classified as a micro burst or a macroburst, based on the scale and size of the downburst. A microburst, is classified by damaging winds extending 2 1/2 miles or less, it will last 5 to 15 minutes and can cause damaging winds as high as 168 MPH. A macroburst is categorized by damaging winds extending more than 2 1/2 miles, a duration lasting 5 to 30 minutes, and damaging winds causing widespread, tornado-like damage, could be as high as 134 MPH.
How does a downburst form? Cold air begins to descend from the middle and upper levels of a thunderstorm (falling at speeds of less than 20 miles an hour) As the colder air strikes the Earth's surface, it begins to "roll" - much like water as a boat moves through it. As the colder air "rolls" out, it is compressed causing winds to increase dramatically - at times even stronger than tornado winds. People often reports damage from a downburst as tornadic damage, but site surveys then determine the damage to be from downburst winds. Downburst differ from tornadoes in several manners. The key difference is in two words - IN and OUT!
IN - all wind flows INTO a tornado. Debris is often laying at angles due to the curving of the inflow winds
OUT - all wind flows OUT from a downburst. Debris is often laying in straight lines (hence the term "straight line winds") parallel to the outward wind flow.
Downbursts are much more frequent than tornadoes - in fact, for every 1 tornado there are approximately 10 downburst damage reports.
When observing damage from a downburst, you may note trees are blown down in a straight line - a very strong indication of a microburst as opposed to a tornado. Tornado damage is noteable becasue of the rotation, trees will be lying in different directions along the tornado path.
Both downbursts and tornadoes can have very damaging winds. Tornado winds range from 40 to over 300 MPH. Downburst winds can exceed 165mph. The both can be accompanied by a loud "roaring" sound- Wind speeds of 75+ MPH will often sound very loud - leading some to believe they heard a tornado when if fact they only heard a straight-line wind. When observing the damage and trees were "twisted" off - does not exclusively mean it must have been a tornado. This is one of the most common mistakes - the fact that trees were "twisted" off doesn't necessarily mean a tornado has gone through. If you could draw a line straight down a tree, you'd see that the tree isn't exactly alike from one side to the other. Differences in limbs and leaves may cause the tree to have more wind resistance on one side than the other. The tree begins to "twist" (much like a stop sign "twists" in strong winds), if wind speeds are high enough the tree will begin to tear apart in a twisting motion -even though the winds are relatively straight. The best way to determine if damage was caused by a tornado or a downburst is to fly over the area and look down on the damage path.
In August, 1983, the strongest microburst recorded at an airport was observed at Andrews Air Force Base in Washington DC. The winds speeds may have exceeded 150 MPH in this microburst. The peak gust was recorded at 2:11p.m. - 7 minutes after Air Force One, with the President on board, landed on the same runway as the microburst was recorded.
Downbursts are extremely dangerous for airplanes, particularly during takeoff and landing. The rapid change in wind speed and/or direction is what poses a very real threat to airplanes during take-off and landing.