Isolated Damaging Pulse Severe T-Storm Events
Extremely localized violent wind gusts originating from collapsing thunderstorm cores produced extensive damage to several area communities on the 14th and the 15th. The highly localized and brief nature of the severe weather would not ordinarily garner a write up in the WRGB online climate summary. However, the damaging wind events, in this case, occurred over heavily populated and treed areas leading to enhanced damage that affected many people, thus warranting some attention here.
Severe weather parameters on both the 14th and 15th in the region were marginal at best. Very weak winds aloft, very little wind shear, and no readily apparent strong surface convergence boundaries were present in the atmosphere, all necessary ingredients for widespread severe T'storms when the parameters are strong. However, extreme heat and humidity, especially on the 14th when temperatures ranged from 95-100 and dewpoints from 65-70, produced a significant amount of potential instability. The instability is called "Potential" because without a trigger, thunderstorms do not form. But when T'storms do form, in cases of high potential instability, severe weather becomes a threat.
In the case that occurred on the 14th, the T'storm trigger was likely the Catskill mountains. The mountains acted as an elevated heat source which was sufficient to send rising parcels of air through a moderate capping inversion (A layer of elevated warm air) to form scattered T'storms. As the T'storms drifted in the weak mean flow to the northeast through Albany county from 3:30pm to 4:30pm they intensified, feeding on the extreme instability present in the atmosphere. Updraft strength briefly intensified as the multicell storm moved from Voorheesville to Colonie, Guilderland, and Rotterdam. As the T'storm updraft collapsed, the subsequent downburst of air was accelerated by a pool of cold air that developed in the central regions of the thunderstorm through the process of evaporation as rain fell through a moderately dry layer of air that was present. Of course, cold air is very heavy and thus aided the downward momentum of air to reach velocities up to 80 mph. Unfortunately, the heavily populated Lone Pines, Carmen Road, and Lidius street areas of Guilderland were ground zero for the downburst. The force of the wind sent hundreds of huge trees to the ground seriously damaging many homes in the process. A roof was partially blown off the Guilderland highway department building and a snow slide peeled back on at least one home. The radius of extreme tree damage was approximately two to three miles wide with the radius of high wind much wider. A wind gust of 68 mph was recorded at the Albany International airport at 4:25pm. The storm's outflow also produced havoc as it propagated into Albany as tents set up for the International Food Festival went flying into the Empire State Plaza reflecting pond, being tossed by 30 to 40 mph winds. Wind damage was also reported in Colonie and Rotterdam. The severe weather lasted approximately five minutes with a very quick dissipation of the storm after the damage occurred. The image below is a radar picture from the Albany National Weather Service NEXRAD radar of the severe T'storm over Albany county at 4:11pm just before the initial updraft collapse and subsequent severe downburst. The white and pink area in the radar picture shows the highest reflectivity's in the storm and thus the center of the T'storm updraft.
On the 15th a similar T'storm rapidly developed over Albany county again, this time forming due to the differential heating that occurred along the leading edge of a cloud band moving into the region, which produced some convergence of air, supportive of T'storm updraft development. Air temperatures climbed into the low 90's with dewpoint temperatures rising to around 70, again producing significant potential instability in the atmosphere. And again on the 15th, a moderately dry layer of air existed in the mid levels of the atmosphere to create evaporative cooling in the central part of any T'storm that could break through the capping inversion, which would then go on to accelerate the downdraft as the T'storm collapsed. At about 4:45pm a single multicell T'storm broke through the cap and within about twenty minutes of forming collapsed producing wind damage in Colonie near Colonie Center. Shortly after the updraft collapse a second strong updraft formed over Troy, collapsing around 5:20pm producing another downburst that took down trees and power lines the city of Troy near Samaritan hospital. Parts of the roof of a dormitory at RPI was blown off and street flooding from one to one and a half inches of rain in thirty minutes occurred near and on the Troy-Menands bridge. The thunderstorm quickly dissipated by 6pm. Again, severe weather in each of these downburst events lasted on the order of a couple of minutes and was extremely localized. Damage at RPI alone was estimated at $250,000.
Friday August 16, 2002 Moderate Pulse Severe T'Storm
This was day six of the August 2002 heat wave with temperatures again in the low to mid 90's and dewpoint temperatures in the low 70's. Strong solar heating through early afternoon once again produced a great deal of potential instability in the atmosphere. In this case, the remnants of an old cool front lingered over central New York and mid level winds picked up to about 25 knots. Some mid level dry air was also noted in western New York during the morning and moved east into eastern New York during the afternoon. The remnant cool front acted as the convergence boundary to focus T'storm development, the light mid level winds and presence of mid level dry air acted to accelerate T'storm downdrafts, to produce highly localized, but significant downburst severe T'storm straight line winds. A Severe T'storm watch was issued from 2pm until 7pm by the Storm Prediction Center to cover this event.
T'Storms developed in short lines and clusters and were generally of the multicell type. Severe weather with the collapsing downdrafts in the T'storms was again quite brief in duration and very localized in nature. However, the T'storms were more numerous than on the 14th and 15th, therefore, the occurrences of severe weather was greater than on the two preceding days. In all, scattered T'storms affected the region from 2:00pm through midnight, with most of the severe weather producing T'storms from 2pm until 7pm. A final T'storm produced one severe downburst in southern Herkimer county at approximately 10:30pm.
Rainfall was also quite heavy with many of the storms with common amounts of one to two inches falling in less than an hour's time. Hail was quite limited due to the warmth of the atmosphere.
The table below contains a listing of reported severe weather and damage from this event.