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WFO BTV Top 10 Weather Events of 2000 to 2009
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8.) July 18th 2008 Chazy to Plattsburgh to Cambridge (tornado) Severe Weather Outbreak
On July 18th, 2008, several meteorological ingredients came together to produce a significant severe weather outbreak across northern New York and central and northern Vermont. The highest concentration of damage occurred from the Saint Lawrence Valley in northern New York into the northern Champlain Valley, then into central and northern Vermont. This particular severe weather outbreak produced over two dozen severe weather reports, with the primary damage being caused by strong and damaging straight line wind gusts. However, a damage survey and video obtained by the National Weather Service in Burlington, confirmed a brief EF1 tornado touched down several times in the North Cambridge, Vermont area. It was determined by the survey and the damage; winds approached 100 mph with this tornado. In addition, several nickel to quarter size hail reports occurred during this event. The widespread severe thunderstorms resulted in over 20,000 customers losing power across northern New York and Vermont during the event.

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Thunderstorms first developed across the northern Adirondack Mountains near Lyon Mountain on the afternoon of 18 July 2008, then traveled east into Chazy, New York, through Grand Isle County, Vermont, then down the Lamoille River Valley to Waterville, Vermont. A second cluster of storms developed across southern Ontario, Canada and tracked into western and central Saint Lawrence County, New York on 18 July 2008. It should be noted other areas of severe wind and hail damage occurred in Addison County, Vermont and across portions of eastern Vermont during this event.

Click here to view the local storm report of all the severe weather reports, which occurred in the National Weather Service Office Burlington, Vermont forecast area. Figure 8-1 shows a plot of the significant severe weather reports across our forecast area on 18 July 2008.
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The pre-storm environment featured a very strong jet of 70 to 90 knots across the region, along with several embedded areas of enhanced lift from disturbances in the jet stream winds aloft. Figure 8-2 shows a water vapor loop on 18 July 2008, along with the cloud-to-ground lightning activity. Note how quickly the cluster of thunderstorms moves across our forecast area, which suggests very strong jet stream winds aloft. In addition to favorable conditions aloft, the surface featured a boundary draped across northern New York into Vermont, which helped to focus storm development. This boundary separated very warm and moist air to the south to relatively cooler and more stable air to the north.
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Figure 8-3 shows a composite radar reflectivity loop, along with lightning data, on 18 July 2008.
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Image 8-4 shows a Google Map outline of the damage, which occurred in the Cambridge to Waterville, Vermont area. From the map and the survey The National Weather Service determined the damage started on Pond Road in North Cambridge, then continued eastward across Kinsley Road, North Cambridge Road, Route 108, then Route 109 about 1 mile south of Waterville, and finally ended on Plot Road several miles southeast of Waterville. We determined the damage from Pond Road to Kinsley Road was caused by straight-line winds between 70 and 90 mph from the bow echo which also impacted the Grand Isle County area. Meanwhile, as the bow echo interacted with strong southerly winds moving up the North Cambridge Road Valley, and Route 108 Valley, two brief EF0 and EF1 tornadoes touched down. The first touch down on North Cambridge Road is labeled with a "T" in the image below and produced winds up to 80 mph. Meanwhile, the next touch down occurred near a farmstead located on Route 108 and produced winds up to 100 mph according to the amount of damage and is also labeled with a "T" on the image below. The lighter white areas represent winds of 50 to 60 mph with isolated to scattered trees down and minor damage was observed. Meanwhile, the brighter white color in figure 17 below indicates winds between 70 and 90 mph with isolated areas of winds approaching 100 mph based on the damage. The damage path was about 6 to 7 miles long and one third to one half mile wide. According to eyewitnesses the storm occurred between 3:27 PM and 3:35 PM on July 18th. The worst of the damage occurred near North Cambridge Road and Route 108, where 80 to 90 percent of the trees, mostly softwood, were blown over or snapped midway up. There was also significant structural damage which occurred to a farmstead along Route 108.
The Chazy, New York to Isle La Motte, Vermont damage was due to straight line thunderstorm winds of approximately 70 to 80 mph, based upon analysis of damage pictures and video, as well as radar analysis. The damage path was about 10 to 15 miles long. The damage started around 300 PM along Miner Farm Road (Route 191) between Olean and Ridge Roads and Continued east-southeast through Chazy, New York then moved over Lake Champlain, impacting some of the island communities before reaching the eastern shore of the lake and finally affecting the residents between Saint Albans and Georgia between 320 and 325 PM. The hardest hit areas were around Chazy and the town of Isle La Motte, especially along portions of West Shore Road. The open waters of Lake Champlain allowed the winds to accelerate before coming ashore in Isle La Motte and caused damage to dozens of homes and downed hundreds of trees.
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This severe weather outbreak will be remember for producing a rare EF-1 tornado near Cambridge, Vermont and the significant amount of wind damage, which occurred from Chazy, New York to Isle La Motte, Vermont. A complete write up of this significant outbreak can be found at the following link: http://www.erh.noaa.gov/btv/events/18July2008/.


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Figure 8-1: Severe Weather Plot for 18 July 2008 (Green Dots=Severe Hail, Blue Dots=Severe Wind Damage
Figure 8-2: Water Vapor Loop 18 July 2008
Figure 8-3: Composite Radar Loop 18 July 2008
Figure 8-4: Damage Path near Cambridge, Vermont from EF-1 Tornado on 18 July 2008
Figure 8-5: Damage Pictures near Cambridge, Vermont from EF-1 Tornado on 18 July 2008


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