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Top 5 Weather Events of 2011 across the North Country
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#1 Weather Event: Tropical Storm Irene (Sunday, 28 August 2011)
Tropical Storm Irene produced catastrophic river and flash flooding across Vermont and portions of northern New York on Sunday, 28 August 2011. The flood waters resulted in 3 fatalities in Vermont and 2 others in Clinton County, New York, and a scale of devastation not seen across the region since the epic floods of November 1927. Nearly a dozen Vermont communities were isolated for days due to the loss of numerous roads and bridges. Nearly 2000 road segments were damaged, with 118 sections of state roads and 175 local roads completely washed out. Among nearly 300 damaged bridges, several iconic covered bridges were heavily damaged or completely destroyed in Vermont, including the antique 160-foot Bartonsville Bridge which spanned the Williams River in southern Vermont since 1870 before being swept downstream in the storm. Over 800 homes and businesses, and several rail and major telecommunication lines were damaged or destroyed by fast-moving flood waters.

Damage from Irene resulted in a Major Federal Disaster declaration for all of Vermont except Essex and Grand Isle counties, and much of eastern New York, including Clinton and Essex counties served by WFO Burlington, Vermont. The hardest hit areas were Essex County in New York, and central and southern sections of Vermont. Monetary damages - while still not finalized - were estimated between $175 and $250 million in insured losses and needed repairs to public infrastructure.
Irene began as a strong tropical wave coming off the west coast of Africa on 15 August, but would not become a named storm until nearly reaching the Leeward Islands late on August 20th (Fig. 1, first point at 00 UTC on August 21st). Irene strengthened to a hurricane on August 22nd, and briefly reached major hurricane status (Category 3) late on August 24th as it moved northwestward across portions of the Bahamas. A minimum central pressure of 942 mb was attained east of Florida on August 26th as the storm made a northward turn on the western periphery of the subtropical ridge, though the eyewall structure of the hurricane was never quite as organized once the tropical cyclone moved north of the Bahamas. That said, Irene maintained a very large circulation and hurricane strength until nearly reaching Cape May, New Jersey at 2 am on 28 August. The tropical storm then accelerated northward across New York City and western Massachusetts during the daylight hours on 28 August, and then across the upper Connecticut River Valley during the late evening hours (Fig. 2). The storm then became extratropical as it exited the United States along the border of Vermont and New Hampshire.
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Wind impacts were not particularly significant from Irene, though channeled north flow across Lake Champlain resulted in 50+ knot gusts at Colchester Reef and some minor damage to boats on the lake. Over-land gusts of 58 mph and 51 mph were observed by ASOS at Plattsburgh and Burlington, respectively. Rainfall was copious, with widespread 4-7" amounts over a period of only about 12 hours. Orographic ascent with low-level east and southeast winds in advance of the tropical cyclone center (Fig. 3) contributed to the highest rainfall totals along the eastern slopes of the Green Mountains and Adirondacks with isolated amounts around 8" (Fig. 4). Some of the higher point amounts included 8.15" in South Lincoln, 7.86" in Ludlow, and 7.72" in Groton.
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Click to enlarge
Click to enlarge
While all rivers in Vermont went above flood stage, the most severe and locally record flooding took place across central and southern sections of Vermont where antecedent soil conditions were the wettest (Fig. 5). This allowed a higher percentage of the falling heavy tropical rain to go into runoff, yielding the most severe flooding. Following significant spring flooding in the Champlain and northern Vermont river basins (e.g., see write-ups on the 26 April and 26-27 May flood events), portions of northern Vermont were actually drying out in the weeks preceding Irene, while several thunderstorm episodes maintained the wetter soil conditions across the southern half of the state. This resulted in some north-south disparity in flood impacts despite similar rainfall totals along the Green mountain spine.
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A selection of hydrographs is shown in Figure 6. River gages show steep rises of 14-24 feet over a period of just 6-12 hours from base levels to historically near-record and record crests. Record crests were recorded at the East Branch of the Ausable River at Ausable, NY (Fig. 6a), the Dog River at Northfield Falls, VT, the Otter Creek at Center Rutland, VT (Fig. 6c), and the Bouquet River at Willsboro, VT. A near-record crest was observed along the Mad River at Moretown, VT (Fig. 6b). Power was lost to gage houses in some cases due to the flood waters. However, via high-water marks and other post-event analysis methods, the recovered crest of 28.4 feet at West Hartford (per USGS) (Fig. 6d) is just below the all-time record crest of 29.3 feet set on 4 November 1927.

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Figure 1. Track of tropical cyclone Irene. (from NCEP/National Hurricane Center)
Figure 2. Track of tropical storm Irene across the northeastern United States on 28 August 2011.
Figure 4. Tropical storm Irene storm total rainfall two-pass Barnes horizontal and vertical analysis, including reports for the period 00 UTC on 28 August through 12 UTC on 29 August.
Figure 5. Soil moisture analysis from the Princeton University Land Surface Hydrology Research Group on 25 August 2011. Soil moisture conditions exceeded the 95th percentile across southern Vermont preceding Irene. Contours show a decrease in soil moisture across northern and northwestern Vermont in the week preceding Irene with soil moisture closer to normal.
Figure 6. Hydrographs during Irene for river gages at (a) the East Branch of the Ausable River at Ausable Forks, (b) the Mad River at Moretown, (c) the Otter Creek at Center Rutland, and (d) the White River at West Hartford. Blue dots and lines represent observed stages, with stage categories and record crest shown by horizontal lines on each graph.

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