Two Part Severe T-Storm and Tornado
The events of Monday, July 21 shattered what had been one of the quietest severe weather seasons on record for eastern New York and for western New England. And the end of the 2003 severe weather drought came with a high end, widespread two part severe thunderstorm and major tornado event.
The day began with only marginal parameters in place for severe weather over the region, with one exception. And that exception was the large scale pattern which featured an anomalous deep low pressure trough that was actively digging into the Ohio Valley. The trough created a deep layered and fast southwest flow of air over the Northeast. In fact winds at the jet stream level topped 90 knots, with winds closer to the surface, at about 5000 feet off the ground, as strong as 40 knots. Winds of this strength are more common in April and May, rather than July and represented a considerable amount of wind energy available in the atmosphere that was in place prior to the outbreak, and is quite favorable in supporting severe weather if other parameters are in place. Dewpoint temperatures, representing the moisture content in the low levels of the atmosphere, were sufficiently high to support thunderstorms, in the upper 60's. But a discernable convergence boundary to form storms, the amount of sunshine, and thus the level of instability, were in question early in the day. Without a convergence boundary, or enough instability, thunderstorm development is difficult. The position of the upper level low pressure trough, even though it provided quite a bit of wind energy, was quite far to the west of the region and thus in a somewhat unfavorable position for severe thunderstorms in the local area.
By midday it was becoming more clear that small scale weather features, rather than the large scale features, would be key in triggering and supporting severe weather during the afternoon and again during the evening.
A weak warm front type feature became evident, early in the afternoon, draped across central New York to central New England, which acted as a local lifting mechanism and also acted to increase the low level wind shear. (Wind shear is a change in wind direction and speed.) The more shear available, the greater the chance for severe weather. Sunshine also heated the area for several hours during the morning and the early afternoon allowing temperatures to warm to around 80 degrees, increasing the local instability.
Severe Weather Event Part I:
This was only part one, of what later in the evening would develop into a major severe weather outbreak with the occurrence of a supercell thunderstorm that produced a family of tornadoes.
Severe Weather Event Part II, Tornado
The system followed an east to northeast track crossing the New York, Pennsylvania border very early in the evening, then moving just north of the Capital Region by mid evening, and into New England north of Rutland county, VT early at night. The following two radar images show the progress of the system through the region.
The tightly spinning and intense nature of the "Meso" low created a highly wind sheared low level environment, highly supportive of tornado producing thunderstorms. In fact, the dramatic drops in barometric pressure ahead of the system caused the winds in the Hudson Valley to blow almost due east for a time into the "Meso" low, yielding between seventy and eighty degrees of shear or in other words, turning of the wind. The fast nature of the winds aloft with the very favorable upper level jet stream configuration, and the high surface dewpoints leading to sufficient instability, and the very organized nature to the line of thunderstorms associated with the "Meso" low meant an imminent severe weather outbreak for eastern New York and western New England. The Storm Prediction Center had issued a Severe Thunderstorm Watch during Part I of the event, which remained in effect until 10pm.
The first severe thunderstorm warnings went out for Otsego and Delaware counties at 6:20pm as the lines of storms slammed into those counties with force. The Binghamton Doppler radar indicated a 65 mph rear inflow jet into the line of storms in Delaware county, which helped sustain the widespread damaging wind machine. The Albany Doppler radar, to the east of the line, showed 75 mph winds a couple of thousand feet off the ground along the storm front's leading edge. It was later confirmed in Delaware county that straight line winds of 80 and 90 mph occurred causing widespread damage through the county. Severe thunderstorm warnings then went up for Schoharie and Greene counties at 6:57pm.
The main event then unfolded as the storms in western Greene county merged with other thunderstorms in eastern Greene county. The storm merger and subsequent interaction with the higher dewpoint air and the highly wind sheared environment in the Hudson valley, allowed a supercell thunderstorm (a rotating thunderstorm) to rapidly spin up and produced the first, of what would be a family of tornadoes, in Palenville. A tornado warning was issued for eastern Greene county at 8:06pm. Doppler radar indicated that the circulation formed and intensified very quickly within the supercell. And once formed, maintained its strength for over two hours as it tracked, with increasing speeds, up to 55 mph, to the northeast through northwest Columbia, Rensselaer, and finally Bennington county through 10:00pm. The supercell was imbedded within a larger area of thunderstorms that were simultaneously producing damaging straight line winds though Ulster, Dutchess, Columbia, Rensselaer and Berkshire counties. Lightning within the supercell became almost continuous along it's path and 1.5 to 2.5 inches of rain fell. The supercell exited far northeast Bennington county, VT by 10:15pm, marking the conclusion of the severe weather outbreak.
Tornado Warning Time Table:
8:06pm: Tornado Warning Issued for Greene County
Albany National Weather Service Damage Assessment Results: Tornado Confirmations
Greene County: Palenville, F1
Tornado Confirmed: 73-112 mph winds
Catskill/Kiskatom, F2 Tornado Confirmed: 113-157 mph winds
Greene County: Coxsackie, F0-F1
Tornado Confirmed: 75 mph winds
Rensselaer County: Nassau, F1
Tornado Confirmed: 73-112 mph winds
Columbia County: Kinderhook, F2
Tornado Confirmed: 113-157 mph winds
Columbia County: Stuyvesant, F0
Tornado Confirmed: 40-72 mph winds
Columbia County: Newton Hook,
Town of Stuyvesant, F0 Tornado confirmed, 40-72 mph winds
Bennington County, VT: North
Pownal to Bennington, F0 to F1 Tornado Confirmed, 75 mph winds
Graphic Showing the Path of the Parent Supercell Thunderstorm with confirmed Tornado touchdowns labeled
The following is a listing of other damage reports associated with both the afternoon and evening severe events on July 21, 2003
Photographs of Tornado Damage From WeatherNet 6 weather watcher James Meehan from Chatham, Columbia County
Lines Down along Route 9 in Valatie, Columbia County and Damage to Structures from fallen trees in Niverville, Columbia County
Damage to this hoouse and trees in Niverville, Columbia County
Damage along State Farm Road, Niverville, Columbia County
Photographs of Tornado Damage From WeatherNet 6 weather watcher Steve Meicht from Catskill, Greene County
Damage to a home along Route 32 in Catskill, Greene County Debris Field along Route 32 in Catskill, Greene County
More damage along route 32 in Catskill, Greene County