It was the great Pollen storm of 2021. Okay, I made that name up, but the blowing plumes of pollen in the Mohawk valley which began around or a little after 3pm in western Montgomery County, reaching Amsterdam a bit before 4pm then into and throughout Schenectady, southern Saratoga, Albany and into Rensselaer counties between 4:00pm and 4:30pm was quite the spectacle dropping the visibility in what was a prolonged period of strong thunderstorm outflow winds that came through well in advance of any rainfall. No measurable rain had fallen in the Capital Region in the fifteen days prior to this event which allowed a huge amount of pollen to build-up and collect everywhere which set the stage for the unusual dust storm like conditions which occurred. Below is the METAR report taken at the Albany airport at 4:11pm which indicated reduced visibility in haze and blowing "dust" and a westerly peak wind gust of 51 mph. This is an extraordinarily rare observation in the Northeast. Wind gusts for a period of up to fifteen minutes ranged from 45-55 mph with a 53 mph gust clocked at the CBS6 weather station just west of Amsterdam at 3:20pm and a 59 mph gust recorded on the MVP building rooftop (100' above ground level) CBS6 weather station in downtown Schenectady at 3:48pm with a 47 mph gust in Troy at the CBS6 weather station at 4:07pm.

 

The outflow boundary, which contained pollen, dust, bugs, and tree and leaf debris, was detected by the Albany (ENX) Doppler radar as a very fine arcing line racing out well in advance of the thunderstorms which generated the cool downdraft wind in the first place. Interestingly, the storms themselves, once locally severe, became what's termed, outflow dominant, which means the warm moist flow of air into them, that initially fired them up, had been cut-off which caused the cells to weaken. By the time they reached the eastern Mohawk valley and Capital Region, roughly 15-30 minutes after the blast of wind, they were down to light showers which dropped only 0.15" of rain or less. New severe t'storms, however, then formed along the outflow boundary, which separated the rain cooled air from hotter more unstable air to the south and east. The new storms fired in Washington and Rensselaer counties which went on to produce pockets of wind damage as they moved through western New England. A cluster of severe t'storms also formed along the boundary in Columbia, eastern Ulster, Dutchess, and southern Berkshire counties which went on to produce wind damage in that part of the area during the early evening.



SEVERE WEATHER SET-UP:
This was the first widespread thunderstorm event for the region of the season, following two very localized events, one on March 26th which produced a few pockets of wind damage in the Adirondacks and a rare tornado in Addison County in VT. The second event was even more unique on April 21 resulting in a tornado in Amenia, Dutchess County, and one in Kent, CT in Litchfield County all while rain was changing to snow in the Capital Region.

So, after a quiet May, in terms of severe weather, a surge of heat and humidity, which resulted in high temperature in the upper 80s to around 90° and dewpoints generally ranging through the lower 60s, coupled with an approaching pre-frontal trough and cold front in conjunction with steep low level lapse rates and strong mainly unidirectional westerly winds aloft ranging from 35-45 mph through a deep layer, set the stage for a widespread afternoon and early evening thunderstorm event, which for the local area was of moderate intensity. Negating a major outbreak was a layer of somewhat warm air aloft due to a lack of any strong upper level disturbance coming in which would have caused cooling aloft and allowed for greater instability. As it was, conditions were adequate for strong storms with surface based CAPE (convective available potential energy) values ranging up to about 1500 j/kg with downdraft CAPE ranging anywhere from 1000-1200/j/kg which is high. (Downdraft CAPE is a unit to gauge the strength and effectiveness of thunderstorm downdrafts to produce damaging surface winds. The higher the downdraft CAPE the greater the likelihood for strong winds to occur at the surface.)

The combination of high heat, which produced steep low level lapse rates when combined with the seasonably cool air aloft for late May, and a layer of mid level dry air, which is another ingredient to enhance downward velocity momentum due to evaporative cooling effects as rain falls into and through that dry layer allowing an elevated cool pool to form, which via gravity, can be accelerated to the ground enhancing a damaging gust potential, were the two key elements that came together to create mainly a damaging wind severe weather event which in the end resulted in 47 severe reports in the Albany National Weather Service forecast area and several hundred overall throughout the Northeast. There was very little hail which was due largely to the warmer air aloft inhibiting updraft strength. Most of the damage was fairly minor and confined to the typical downed trees and power lines with some damage to a metal roof reported in Latham.

Downed tree on Lake Hill Road in Burnt Hills - Wednesday May 26, 2021


The event itself was characterized by an initial line of severe t'storms which had formed along a pre-frontal surface trough over west central New York between noon and 1pm. The line, as it rapidly moved east at 40-45 mph, tilted from NW to SE reaching Herkimer and Hamilton counties around 2pm then moving into Otsego County and into and down the Mohawk valley from 3 to 3:30pm. This was the line that produced the strong to damaging outflow wind which subsequently raced ahead of the rainfall into the Capital region through 4:30pm. Subsequent weakening of the storms occurred with new line segments blowing up east and south of the Capital Region between 5 and 6pm ultimately consolidating into a significant squall line which went across New Hampshire, Massachusetts and northern Connecticut through the evening before dissipating. The series of Albany doppler radar images below show the hourly position of the t'storms between 3 and 7pm.

 

 

NWS Storm Reports for Wednesday May 26, 2021. Note, these reports are used to verify the NWS warnings which were issued for this event and therefore do not necessarily represent an accounting for all of the wind damage which may have occurred.