On May 27, 2014 a violent microburst with winds up to 100 mph felled trees across New Milford, Bridgewater, Southbury, Newtown, and Roxbury. Power was knocked out to large portion of the aforementioned towns with widespread tree and power line damage.
Weak synoptic scale forcing was present with slight height falls over southern New England on the afternoon of the 27th.
That said, a powerful backdoor cold front was racing in from the northeast with a fairly dramatic theta-e gradient. Modest instability and deep-layer shear were present in western Connecticut and adjacent portions of eastern New York. Here’s the 22 UTC RAP Sounding for Poughkeepsie, NY which is fairly representative of the environment along the CT/NY state line.
0-6km bulk shear was on the order of 35 knots and in addition there is some modest low level speed/directional shear. While mixed layer CAPE is approaching 1000 j/kg there’s not much 0-3km or 0-1km CAPE and LCL heights are fairly high (on the order of 1.3km). Here’s the METAR from Danbury prior to the storm.
METAR KDXR 272153Z 22010KT 10SM CLR 28/15 A2977 RMK AO2 SLP075 T02830150
You can see the actual boundary environment was a bit drier than the RAP analysis (15C vs 17C dew point) which would point to even higher LCL levels and less CAPE. At the same time, that relatively dry boundary layer. The relatively high LCL levels and the somewhat dry boundary layer may be important clues why the storm produced damaging winds but did not drop a tornado.
On radar the storm became fairly intense when entering New Milford. A fairly strong level mesocyclone was present, and reached peak strength, during the onset of damaging winds in New Milford.
62 knots of gate-to-gate Delta-V was present at 4500 ft AGL which is a fairly impressive for Connecticut. As the storm moved south the low level rotation slowly weakened but a rear flank downdraft produced wind gusts greater than 50 knots over a fairly widespread area. Pockets of even greater wind speeds were found as well.
There is a clear damaging wind signal on radar as the storm entered Southbury/Bridgewater with many pixels of 50-60 knots of inbound radial velocity observed around 3500 ft AGL. Prior to the clear surge of strong RFD winds the strong low level mesocyclone over New Milford was an impressive signature and enough to grab anyone’s attention. The relatively high LCL values argue for no tornado in this case even in the presence of impressive rotation. Indeed, no tornado damage was found. The bulk of the damage was located west of the path of the low level mesocyclone.
The relatively dry boundary layer also likely contributed to the downburst potential in this case. A dry boundary layer promotes negative buoyancy via evaporation/sublimation of rain and hail falling from a cloud base.
One additional note here regarding the warnings that were (and weren’t) issued by the National Weather Service. The New York NWS office issued a warning for Fairfield and New Haven Counties while the storm was doing damage in Litchfield County. The Albany NWS office issued no warning. Another example of confusing mixed-messages sent by disparate NWS offices in a state (and TV market) that falls under the jurisdiction of 3 different National Weather Service offices. In this case, local TV meteorologists had to effectively “issue their own warning” for the people in New Milford and Bridgewater to get the necessary information out.