Severe Hail Storms, Monday June 15, 2009
Surface conditions, seemingly, were not particularly favorable for the development of severe convection with maximum temperatures ranging through the upper 60s to low 70s and dewpoints in the mid 50s. However, the coldness of the air aloft was more than sufficient to compensate for the lack of significant heating and surface moisture to yield significant instability (Convective Available Potential Energy ranging from 1500 to 2000 Joules/kg). The combination of the high instability, which created significant buoyancy to the air, which when combined with the large scale ascent caused by the passing jet core and upper level short wave trough, allowed strong updrafts to develop yielding intense thunderstorm development.
Rather weak wind fields existed in the low and mid levels of the atmosphere which precluded significant organization of the thunderstorms and also partially explains the lack of damaging wind in the event. Fairly moist conditions also existed through a reasonably deep layer in the atmosphere which reduced the amount of evaporational cooling that could occur aloft, which reduced the rate at which downdraft air flowed out of the thunderstorms, limiting the strength of the ground level winds. A few of the strongest cores did produce ground level winds ranging from 40-45 mph due largely to frictional effects of the hail and torrential rain dragging that air down to the ground. Therefore, large hail was the main severe weather mode for the event as the cold mid level environment was quite favorable for the formation and maintenance of hail as it fell, allowing lots of it to make it to the ground. The weak steering flow in the atmosphere also explains the slow forward motion/propagation of the storms (15 mph on average) which created a situation where long duration hail falls occurred in some locations with hail falling for up to fifteen minutes or more, leaving accumulations of one to two inches on the ground. The slow motion also meant terrain played an important role in where storms initially developed and how they behaved. This was especially the case with the first round of storms as significant back building occurred over Bennington County Vermont in essence creating a situation of almost stationary torrential hail producing thunderstorms sitting over the same locations for one to two hours. Flash flooding was reported in Vermont, especially in downtown Bennington and across northern Warren and Washington counties as a result of terrain induced back building of the storms. Flash flooding also occurred in and around Pittsfield, MA due to slow moving back building storms dumping torrential rains in short periods of time.
The event began with scattered thunderstorms during the mid to late morning forming over the Adirondacks and higher elevations in western New England as what appeared to be a lead upper level impulse triggered development. A second upper level impulse caused additional thunderstorms to develop during the mid to late afternoon and evening which eventually supported the particularly intense multi-cell cluster which blasted parts of eastern Schenectady, southern Saratoga, and northeast Albany counties with torrential rain and accumulating hail between 5pm and 7pm. The Capital Region storm briefly developed some weak mid level rotation, due to storm based motions, with a wall cloud observed over Albany and rotation observed by National Weather Service meteorologists at the Albany NWS office on Fuller road. Brief rotation was noted as this storm cluster tracked southeast into western Rensselaer County before weakening slightly on its trek through Columbia and southern Berkshire County, then out of the region after 9pm.
This radar image is of the storm cluster over northeast Albany County at 6:28pm. Hail ranging in size from 1/2" to 1" diameter, on average was falling from the slow moving storm at this time throughout the region shaded in light purple. (The light purple color indicates an area of high reflectivity on the radar showing the most likely region for hail)
Saratoga Springs was hit twice by two small in size, but intense hail storms, the first between 2pm and 2:30pm with the primary hail core tracking right over SPAC. Hail up to the size of 3/4" and a twenty degree temperature drop were recorded through WeatherNet 6 spotter Gary Burton. Shovels were reportedly necessary to clear hail in and around Saratoga Springs with this storm. The second hail storm, taking almost the identical track, moved over Saratoga Springs and SPAC between 4:30pm and 5:00pm.
Most of the hail throughout the region ranged in size from 1/2" to 3/4" with some reports of hail the size of golf balls (1.75" in diameter) The larger hail stones were more the exception than the rule, however. The skew towards smaller hail explains the few reports of car, window, siding, and roof damage from the event. Many occurrences of decimated foliage and gardens, however did occur.
The tale below lists the severe weather reports collected by the Albany and Binghamton National Weather Service offices for the purpose of verifying the severe thunderstorm warnings that were issued. The listing is a sampling of what occurred across the region and is therefore not a complete list of all the hail that occurred from the event, only what was reported.
Storm Reports for the Tuesday June 15, 2009 Event