As expected, the National Weather Service has confirmed the 2 tornadoes that radar confirmed on Wednesday, May 29th and one additional tornado in southern Saratoga County. The Schoharie and Saratoga County tornadoes were rated EF-1 while the Montgomery and Schenectady County tornado was rated an EF-2.
The tornadoes occurred in a modestly unstable environment. The 18z 4km NAM by 22 UTC had 1283 j/kg of MLCAPE at KALB but also had an impressively long hodograph that veered with height particularly in the 0-1km layer. A backed boundary layer flow underneath 700mb winds of 50 knots produced impressive shear that aided in storm organization and lead to tornadogenesis.
The 2 tornadoes that produced tornado debris signatures (TDS) on doppler radar give us a useful learning lesson in just how powerful dual polarization technology can be. In the northeast, the presence of heavily forested areas will likely make TDS relatively easy to spot and there may be a larger percentage of tornadoes that produce TDS here than in the plains. I also expect dual polarization to result in an increase in tornado reports since, in many cases, we’ll know exactly where to look for tornado damage even in the case of a tornado moving through a very rural area.
Schoharie County Tornado – EF-1
The tornado that touched down in Schoharie County was on the ground for 2 miles and a total time of 5 minutes according to the National Weather Service storm survey.
The tornado touched down at 6:57 p.m. At that time KENX radar showed a gate-to-gate LLΔV of about 75 knots at about 1500 ft AGL. The TVS was only present for one volume scan at 0.5º base velocity and then the rotation broadened with 75 knots of LLΔV separated by about a mile . By 7:02 p.m. there was a significant debris signature with very low CC, co-located with ZDR near zero, and the remnant circulation.
Within 5 minutes the tornado lofted enough debris to produce a significant TDS. The TDS was still present, though much less impressive, by the 7:07 volume scan.
The debris was picked up by radar within 5 minutes of touchdown and lingered for 5 minutes after the tornado lifted up. The signal was probably even stronger given the close proximity to the radar site. The radar was sampling the storm at only about 1500 ft AGL on its lowest slice.
The TDS was also visible on the 1.4º slice at approximately 3500 ft AGL though it was weaker. The TDS was not visible on the 2.4º slice or ~5500 ft AGL. If this storm was more than about 40 miles from the radar it is certainly possible that the TDS wouldn’t be picked up at all and if it was a bit farther than that the low level mesocyclone on the QLCS would have been overshot as well.
Montgomery/Schenectady County EF-2
The tornado in Montgomery and Schenectady Counties was the only significant tornado of the day with an EF-2 rating. It was a mile wide for most of its life and was on the ground for many miles ending just past the New York State Thruway in Rotterdam. While the Public Information Statement from the NWS says the tornado was on the ground for 17 miles based on the coordinates of its beginning and end location I’m coming up with only 12 miles. I’m not sure what the discrepancy is here.
The National Weather Service storm survey puts the touchdown at 6:47 p.m. which seems too late by about 4 minutes per KENX radar. Radar shows the tornadic circulation over the beginning part of the track at 6:43 p.m. (the warning came out at 6:45 p.m.).
Around the time of touchdown the rotation was fairly broad, though quite strong, with LLΔV of nearly 95 knots spread over 7 radials (about 3/4 mile). By the time the circulation was over Mariaville the gate-to-gate LLΔV was 95 knots. Very impressive.
What’s interesting in this case is that the debris signature doesn’t appear until 6:57 p.m. – more than 10 minutes after touchdown. It took twice as long for the TDS to appear with this tornado than in the weaker and shorter-lived Schoharie County tornado. The 0.5º slice was also sampling this storm at a lower elevation than the Schoharie County storm (900 ft AGL versus 1500 ft AGL). The debris signature was present for 2 volume scans – 6:57 p.m. and 7:02 p.m. before disappearing at 7:07 p.m. Though there is an area of depressed CC and ZDR near the circulation at 7:07 p.m. the values aren’t low enough to classify as a TDS though since the radar isn’t detecting hail in that location chances are there was some small detritus from the tornado being sampled.
After the storm went through Mariaville, NY there was a debris signature as high as 5100 ft AGL on the 3.4º slice.
One possible reason by the debris signature took twice as long to appear on the Schenectady County storm is that in the beginning the tornado was moving through mainly farm land. The Schoharie County storm was in a heavily wooded area and approached a state forest.
Once the storm moved through Mariaville Lake it encountered homes, buildings, and a more wooded landscape. The TDS appears after the tornado moved east of Mariaville Lake.
The ability to detect tornado debris will be a huge help in severe weather coverage. Being able to confirm a tornado around here in real time is so difficult due to hilly terrain and the fact many of our tornadoes are rain wrapped.