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The 1998 Eastern Tornado Outbreak of June 2, 1998 was one of the most significant tornado outbreaks in recent history over the east-central United States. This severe weather event spawned a total of 47 tornadoes over 9 states from New York to South Carolina and caused an estimated $42 million in damage, 80 injuries and 2 fatalities. For Pennsylvania in particular, it was the second historic and deadly severe weather outbreak in three days, as it immediately followed the Late-May 1998 Tornado Outbreak and Derecho on May 30–31, 1998, which spawned 41 tornadoes over NY, NJ, PA and Vermont, caused an estimated $83 million in damage, 109 injuries and 1 fatality. Hardest hit areas from the June 2 tornado outbreak included Pennsylvania, which reported 22 tornadoes on June 2 (and a total of 45 tornadoes from May 31 - June 2), western Maryland, where 5 tornadoes occurred, and West Virginia, where some counties in the Potomac Highlands reported their first tornado in recent history. Tornadoes were also observed in New York, Virginia, Ohio, Tennessee, North Carolina and South Carolina. The most damaging tornado hit Carnegie, part of the Pittsburgh metropolitan area in Allegheny County, PA, at 5:55 PM (EDT ). There, 50 injuries and $13 million in damage were reported. The deadliest tornado, an F3 on the Fujita Scale, hit near Meshoppen, PA, in Wyoming County, around 10:30 PM EDT. This tornado caused 2 fatalities, 15 injuries and $2.2 million in damage. The most violent tornado hit Frostburg, MD, in Allegany County, at 9:43 PM EDT. 5 persons were injured, and $5 million in property damage was reported. With winds up to 210 mph, it was the first F4 tornado to have hit the state of Maryland since the National Weather Service began keeping records in 1950. The Frostburg Tornado had moved southeast from Somerset County, PA, where it was rated F3. The 1998 Eastern Tornado Outbreak stands out, because it spawned an unusually high number of supercell thunderstorms, occurrences of damaging winds and hail, and tornadoes, in the central Appalachian Mountain area, where most residents were unaccustomed to experiencing such violent thunderstorms that are commonly believed to only occur in Tornado Alley in the central part of the United States. ==Meteorological synopsis== June 2, 1998 began with very stable atmospheric conditions in the areas later affected by severe weather. Fair skies and near-record low temperatures were noted in the east-central U.S., with minimum temperatures reaching the 40s in many areas, and upper 30s in portions of northern Pennsylvania and New York State. Dew points were in the 30s and 40s. However, a potent upstream disturbance approaching the region quickly destabilized the atmosphere, placing the region in a moderate risk for severe weather. A moderate risk is unusual for this portion of the U.S. Significant surface heating (temperatures quickly reached the 80s and even 90s in some areas), a significant influx of moisture (pushing dewpoints well into the 60s in many areas), a rapid increase in atmospheric shear, steep adiabatic lapse rates, rapidly lowering lifted indices, and a major surge in CAPE set the stage for a major severe weather outbreak during the afternoon and evening hours of June 2. File:03 June 1998 00z IAD Skew-T.jpg Skew-T log-P diagram plot of atmospheric profile at 00z, June 3, 1998 at IAD (Dulles Airport). Courtesy of the National Weather Service (NWS) Sterling, Virginia. The above atmospheric profile indicates several unusually favorable factors for development of severe weather, including tornadoes. One is these is significant vertical wind shear. The wind barbs on the right indicate significant speed and directional shear with height in the lower 500 mb of the atmosphere. Winds veer significantly, from SW at the surface to NW at 500 mb, and also increase from 8 kts at the surface to 46 kts at 500 mb, leading to a vertical shear value of 44 s −1. This exceeds the "high potential" severe weather threshold of 40 s −1. Veering winds with height indicate warm air advection; this, coupled with strong surface heating, contribute significantly to destabilization of the atmosphere. The second favorable feature on the plot is the steep vertical temperature gradient in the lower atmosphere up to the Lifted condensation level (LCL) - from 26.4 C at the surface (989 mb) to about −5 C at the LCL, which is about 600 mb. While the 600 mb height is unknown, it is likely that the atmospheric lapse rate is close to or exceeds the threshold for (absolute instability ), strongly driving convection. Air is therefore forced to rise rapidly, leading to a significant latent heat release (LHR), providing further energy for severe thunderstorms. Other strongly favorable conditions for severe weather are a highly negative (-6.1) lifted index (which exceeds the threshold of −6 for "high potential" of severe weather) and a CAPE value that peaked at 3.8 kJ, well over the threshold of 2.5 kJ for a high potential of severe weather. Vertical velocity at the surface is 13.6 m s −1, indicating strong rising motion. Severe supercell thunderstorms developed rapidly during the afternoon and evening hours. The first tornadic supercell developed over southeastern Ohio and spawned the first tornado at 2:50 EDT near Gallipolis, where many trees were downed and large hail accumulated. This supercell crossed the Ohio River into West Virginia, where tornado damage continued. The second tornadic supercell dropped its first tornado in extreme western Pennsylvania near Shippingport. This storm later caused major damage and 50 injuries in the Pittsburgh metro area before moving southeast through Somerset County, where many residents were still without power after the deadly May 31 (Salisbury tornado ). The majority of the June 2 tornadoes formed between 5:30 pm and 11 pm EDT. All of Pennsylvania's 22 tornadoes occurred between 5:30 and 10:40 local time, 14 of them from 7 to 10 pm. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「1998 Eastern tornado outbreak」の詳細全文を読む スポンサード リンク
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