Wednesday, November 17, 2010
Heavy Convective Rain Event/Ghent EF1 Tornado
A strengthening low pressure system racing northeast on a track west of the Appalachians, taking it on a line up through Kentucky, Ohio and west of the St. Lawrence valley from late Tuesday night November 16 through Wednesday November 17, produced heavy rain, isolated severe weather, and regional strong wind gusts on its trek through the Northeast. On average, 1/2" to 1.25" of rain fell, with locally 1.5" to 2" of rain in terrain favored areas (much of this in a two to three hour period early Wednesday morning.) Isolated wind damage and a confirmed EF1 (95 mph wind estimate) tornado in Ghent, Columbia County occurred with the passage of a strong convective line between 4am and 6am Wednesday morning. And in the storm's wake, strong gradient wind gusts up to 45 mph buffeted the region from Wednesday afternoon into the night. With the storm's passage well west of the region, mild air with temperatures well into the 50s occurred through the duration.
The rain came in two distinct installments with the first largely a light rain or drizzle from the mid afternoon on Tuesday November 16 through approximately 10pm. An average of .15" to .35" of rain fell with the first round. The second round of rain, tied closely to a strong surface front and powerful upper air disturbance transiting the region was much more intense and included a narrow and fast moving convective line of torrential rain embedded within a broader area of moderate rainfall. This intense convective line moved from west to east across the region between 4am and 6am Wednesday morning accompanied by strong gusty wind in some areas. A t-storm developed within the line which went on to produce small pockets of significant wind damage to trees in the Claverack area and a confirmed (NWS storm survey) EF1 tornado in Ghent (winds estimated to 95 mph) The occurrence of the wind damage and brief tornado, although not common in November, is not unprecedented as strong storms with intense and highly sheared wind fields (ingredients favorable for severe weather) often transit the region at that time of the year. What is typically lacking is sufficient instability for severe weather to develop. In this case, a strong and highly sheared wind field existed, with very strong winds residing only about 3000' off the deck. Just enough instability developed, with temperatures in the low 50s and dewpoints near 50° in the mid Hudson valley coupled with cooling temperatures aloft, for a tall enough updraft to form which effectively tapped into the high momentum air aloft and then mixing that air down to the ground in brief damaging downbursts. The high shear supported the brief tornado spin up in Ghent.
Storm Report from the Albany National Weather Service Damage Survey
Rain tapered to scattered downpours through Wednesday morning, then tapered further to widely scattered sprinkles and light showers through the afternoon and evening. A tight pressure gradient around the departing storm coupled with increasing instability in the atmosphere due to the air cooling aloft more quickly than at the surface worked in tandem to increase the gradient winds across eastern New York and western New England through the afternoon and evening. Westerly winds ranged from 15-30 mph with gusts occasionally ranging from 40-45 mph.
WeatherNet Storm Total Rainfall Reports for the November 16-17, 2010 Event
|Photographer: WeatherNet 6 spotter Jim Meehan. Wednesday November 17, 2010. Straight line wind and tornado damage in Ghent, NY, Columbia County|
|Albany Nexrad (ENX) Base Reflectivity image of the convective line a minute before 5am, just prior to the downburst in Claverack and brief tornado in Ghent, Wednesday, November 17, 2010|