5/29-5/31 always seems to be a tornado bonanza around Albany, NY. The May 31, 1998 tornado outbreak (F3 in Mechanicville) and the May 29, 1995 Great Barrington (F4) tornado are just some of the examples.
On Wednesday at least 2 tornadoes touched down near Albany – both were confirmed by lofted debris on doppler radar.
What is really interesting about both of these tornadoes is that both formed from separate convective modes. The tornado west of Rotterdam in Schenectady County was from a discrete supercell being taken over by a strengthening squall line/QLCS. The tornado in Schoharie County, on the other hand, formed on a QLCS from a non-descending mesocylone.
Both tornadoes exhibited brief, but strong, rotation on doppler radar and both featured pronounced tornado debris signatures. One of the most powerful tools from the dual polarization upgrade of the WSR-88d is being able to discriminate between precipitation and non-meteorological targets such as lofted debris. Knowing a tornado is on the ground causing damage can help beef up warning statements and for a TV meteorologist who can identify the tornado debris signature (TDS) it can be used to really hammer home the message that a tornado is on the ground and it’s the real deal. In situations where radar presentations are marginal (especially in the QLCS case) the TDS can be used to issue a tornado warning with zero lead time – certainly better than negative lead time!
I’ll start with the supercell near Rotterdam that dropped a tornado in rural Schenectady County.
At 2237 UTC you can see the supercell ahead of the developing QLCS. There’s a fairly weak low level mesocyclone near Wellsville, NY near a developing appendage/hook echo. Not shown, but 0.5 base velocity shows a very strong area of low level convergence along that appendage and through the storm there is a fairly deep mesoscyclone through at least 15,000 feet. Also note behind the supercell is a bowing QLCS.
10 minutes later the low level mesocyclone has rapidly strengthened west of Mariaville, NY. Also note the QLCS is virtually on top of the supercell at this point. While the low level mesocyclone is still fairly broad (i.e. not a TS/TVS at the lowest elevation angle) the mesocyclone through the depth of the storm has dramatically strengthened. You can see the appendage has now fully become a hook echo and there’s some evidence of lofted debris with low correlation coefficient and differential reflectivity near 0.
By 2352 UTC as the QLCS has taken over the supercell low level delta V has spiked to 95 knots about 1,000 ft AGL. At 2357 UTC there is a clear debris signal in both Z, CC, and ZDR. The supercell has now morphed, post-merger, into a large QLCS with the tornado near the inflow notch.
By 2302 UTC the low level mesocyclone has weakened as the storm occluded. The debris signal, however, still remains. There is a lag with TDS – they appear after touchdown and they disappear after dissipation. The storm went on to do major wind damage across the Capital District as the developing QLCS bowed out. The resulting QLCS still shows some supercellular characteristics after merger with the mesocyclone persisting near the bow head.
Supercell/QLCS mergers aren’t terribly uncommon and there are several examples in the literature. In this case it appears there may have been a touchdown prior to merger on the Montgomery/Schenectady County line near SR-30 and then again during the QLCS/supercell merger near Mariaville, NY to near or just west of Rotterdam. All of this is based on radar – we’ll know more once the NWS damage survey is done. Thankfully the TDS occurred after the circulation moved over sparsely populated areas.
It’s entirely possible that the outflow and merger from the QLCS helped aid in tornadogenesis and the sudden onset of a severe and damaging bow echo.
The tornado in Schoharie County also was in a sparsely populated area. This tornado was not from a supercell but rather a QLCS. While there was some very weak/broad mid level rotation prior to tornadogenesis this case appears to be from non-descending mesocyclone/QLCS.
Prior to tornadogenesis you can see a pretty sloppy looking QLCS. A relatively unimpressive surge of 40-50 knot inbounds on base velocity north of Stamford and just south of that gold diamond preceded tornadogenesis. A weak bowing signature may be present on reflectivity here at 2252 UTC. Nothing really jumps out at you and looking aloft there’s no mesocyclone that would be of concern.
By 2257 UTC, however, a tornado vortex signature has developed with around 80 knots of gate-to-gate shear near Arabia, Jefferson, and Eminence New York. In addition, the mesocyclone has developed from the bottom up, rapidly strengthening through 11,000 ft AGL in just one volume scan. This seems like a classic QLCS tornado case with vertical vorticity enhanced by boundary layer convergence on the leading edge of the QLCS. In this volume scan you can also see a notable inflow notch that has developed which is characteristic of QLCS tornadoes.
By 2302 UTC you can see a crystal clear tornado debris signal with high Z, low CC, and near 0 ZDR.
By 2307 there is still a semblance of a TDS but the signal has clearly weakened as has the level level rotation. In the northeast I’ve been very impressed by the ability of radar to pick up tornado debris from even weak tornadoes (see Lancaster County PA TDS). The large areas of densely forested land likely helps – as soon as a tornado starts messing with trees parts of twigs and leaves immediately get lofted.
Over the coming years I wouldn’t be surprised to see a noticeable increase in tornadoes that wind up being reported and confirmed in our region. We now know when a tornado has touched down and has started to do damage – even if it was miles from the nearest home or road.
Let’s hope the damage surveys today show that these tornadoes touched down in very rural areas and didn’t impact property.