May 22, 2014 Severe Weather EF3 Tornado and Significant Hail

(Click on any image for a link to a large image)

Overview

A potent shortwave trough moved from the eastern Great Lakes towards upstate New York during the early afternoon hours on Thursday, May 22nd. A complex frontal system moved from west to east during the mid-afternoon hours, with the triple point of where the occluded, cold and warm fronts met situated over the Mohawk Valley. There was a significant temperature gradient along the warm front, between warm and unstable air (low 70s temp, mid 60s dewpt) over the Mohawk Valley and cooler, more stable air (upper 50s/low 60s) over far eastern New York that originated off the western Atlantic Ocean. This warm front was aided by a differential heating boundary that set up across the region with cloud cover to the east of the Mohawk Valley and mostly clear skies to the west. A fairly strong wind field aloft yielded plenty of shear, with 0-6 km bulk shear values around 40 knots. Instability was marginal, with generally 500-1000 J/kg depicted from SPC mesoanalysis, although there were pockets of higher Convective Available Potential Energy (CAPE) in the 1500-2000 J/kg range located along the immediate Mohawk River and Schoharie Creek.

As a result, a large supercell thunderstorm developed along this boundary over the southern Adirondacks and eastern Mohawk Valley and it quickly strengthened as it moved almost due south. It produced very large hail as large as 4 inches in diameter in the Amsterdam area. This hail tied the largest hailstone on record in New York state history (measured in Niagara Falls, NY on September 27, 1998). As this storm continued to strengthen even further and turn right into the Mohawk River Valley, it moved south to southeast towards the Helderbergs and western parts of the Capital Region, where it produced a tornado. The tornado was on the ground for 7 miles and reached EF3 strength with maximum winds of 140 MPH, as it passed through and just to the south of the town of Duanesburg, NY. The tornado also crossed portions of Interstate 88, roughly 5 miles south of Exit 24. The tornado dissipated once it reached western Albany County, and the more stable air in place allowed thunderstorms to rapidly weaken as they reached the Hudson Valley. Aside from one additional report of large hail in the Mid-Hudson Valley, no other thunderstorms reached severe levels and the threat for storms diminished by the evening with the passage of the occluded boundary.

The unique combination of the triple point and moist, unstable boundary layer near the confluence of the Mohawk River and Schoharie Creek may have significantly contributed to the rapid intensification of the initial mesocyclone that produced the record-tying hailstones, and later, tornadogenesis of the EF3 tornado. The 1200 UTC sounding revealed the top of the leftover nocturnal boundary layer located around 950mb coinciding with a relative increase in the static stability profile. The 20 knots of wind at the top of this layer may have been some sort of channeling jet induced at the top of the still-decoupled near-surface frictional layer, which can often times back cyclonically to the S/SE as it flows up the Hudson, especially if these winds were trapped in a ducting layer and unable to mix out to the lee of the Catskills/Helderbergs (which may have been caused due to a 2nd inversion near 850mb in which the winds become westerly and nearly perpendicular to the terrain above it).

The potential temperature inversion around 950mb could have played a big role in promoting low-level moisture pooling as well, which may have enhanced instability especially across portions of the Mohawk Valley where they had a little more sun than points east. The 0000 UTC sounding from that evening suggested a shallow boundary layer depth of only up to ~900mb, which may have limited mixing effects such as dry air entrainment throughout the day.

The orientation of the forward-flank downdraft (FFD)/rear-flank downdraft (RFD) winds relative to the local topography across Montgomery/Schenectady counties could have also aided tornadogenesis. As the storm came from the north and entered the Mohawk River Valley, it may have tapped this moisture pooled air, allowing it to intensify into the impressive storm that it became. With an impressive mesocyclone accompanying this storm, the FFD winds (based off the radar orientation), appeared to come in from the E/SE along the Mohawk River. The RFD winds appeared to do the same coming in from the W/NW, except interacting with a narrow ridge of higher elevation. As these winds converged in the Schoharie Valley near the Montgomery/Schenectady county line, the RFD winds may have descended down the ridge of higher terrain and may have warmed slightly. Combined with the low-level moisture pooling, this slight warming of the RFD winds may have aided tornadogenesis, as warmer RFDs are more favored than cooler ones.

Storm/Radar Overview and Analysis

Although there were many severe reports, most only came from 1 storm (except for a report of 1 in. hail near New Paltz, NY). The thunderstorm formed in central Hamilton County and drifted slowly S/SE, immediately to the west of the frontal boundary. This storm initially wasn't strong, but gradually grew in depth as it moved through southern Hamilton County.

As the storm continued to drift to the SE, the thunderstorm became severe as it approached the corner of Fulton/Montgomery/Saratoga counties. The storm was expected to keep moving SE, however, the storm began to back build with a new, stronger updraft upstream of the old updraft. At this stage, the radar resembled more of a multicell appearance, with 2 distinct updraft cores. The upstream updraft quickly became the more dominant of the two and this cell became severe in addition to the downstream updraft. The 1st report of severe hail (2.0 in.) came in at 1830 UTC, and several more hail reports came in to verify both warnings between 1830-1900 UTC. As the severe hail reports came in, reflectivities were well above 60 dBZ on the lowest elevation slice and in the updraft core. The dual pol variables also supported the hail reports coming in. On the 0.5 degree elevation slice, ZDR values dropped to near 0 dB, CC values were below 0.90, and KDP values were between 2-4 deg/km signifying the presence of large, water-covered hailstones. Analyzing the vertical extent of the thunderstorms, both the ZDR and KDP columns extended above the -10C level, indicating that plenty of liquid water was being lofted into the hail growth zone of -10 to -30C. There was also a depressed region of CC in the updraft core (<0.90) indicative that large, mixed phase hydrometeors were present within the updraft.

Reports of hail in the 1.5-2.0" diameter range were being received at this time. The first hailstones reported were of ping pong ball to golf ball-size and came in from near Broadalbin, NY in Fulton County. The subsequent Severe Thunderstorm Warning would include hail from quarter to ping pong ball size to account for the larger hail. By roughly 1900 UTC, an apparent storm merger had taken place, with one distinct updraft now apparent when analyzing the vertical extent of the thunderstorm. The thunderstorm now had a mesocyclone associated with it, further helping to support large hail formation. This mesocyclone could have been a significant factor in the number of extremely large hail reports (baseball size and greater), allowing greater residence time of the hailstones within the updraft core via recycling processes (strong mid-level rotation for hail monsters).

At this point as well, there was an impressive weak echo region (WER) and tight reflectivity gradient along the leading edge of the storm, with a large swath of ZDR near 0 dB in the hail core. In fact, analyzing CC at this time revealed that the values had actually range-folded on themselves and that there were false values of 0.99. This radar artifact was direct proof of extremely large hailstones as Mie scattering processes altered the radar sampling of the storm. Several reports of severe hail came from the Amsterdam area between 1900-1930 UTC.

As the storm continued its S/SE movement, it gradually descended down lower terrain. The storm originally started just south of the foothills in the Adirondacks, and by the time it reached the Amsterdam area, was located in the Mohawk River Valley. This was when the storm strengthened significantly and obtained supercell characteristics that rival that of a classic Plains supercell. The Amsterdam, NY area took the brunt of the hail with some hail stones greater than or equal to 3 inches in diameter.

As the thunderstorm maintained its severity along the Montgomery/Schenectady County border, the storm appeared even more impressive on the 0.5 degree elevation slice. A large WER was now evident with a "hook" shape as well. There was an impressive ZDR arc in the FFD, with a classic "V" shape as well indicating excellent storm-scale divergence (upper tilts of the radar scan showed this nicely) and ventilation. The mesocyclone had strengthened by this point as well, but remained broad in nature. On the lowest elevation slice, there were indications of rotation as well by 1928 UTC, but this too was broad in nature (and was obscured somewhat by purple haze). The low-level rotational velocity (LLVr) value from the V-R shear tool was only 18 kts over 0.5 nm with a shear value below 0.02 s-1 near Scotch Bush/Florida, NY in Montgomery County, where the May 29th, 2013 tornadogenesis started.

Looking at the 1928 UTC 0.5 degree elevation slice of base reflectivity offered some interesting perspectives. Immediately upstream of the hail core, there was a "V" region of depressed reflectivity values near Minaville, NY in eastern Montgomery County south of Interstate 90. This region, resembling a Rear Inflow Notch (RIN), suggested the presence of potentially strong straight-line winds (also evident by the extremely tight reflectivity gradient). CC values at this time also showed a broad region of very low CC (<0.80) in the inflow region of the updraft, suggesting strong inflow was being ingested into the storm. While rotation was indicated on the lowest elevation slice by 1928 UTC (see the V-R shear discussion in the above paragraph), it was still broad in nature. Also interesting at this time period was a flanking line located W/SW of the updraft core. Given the presence of the midlevel mesocyclone, this radar artifact may have been associated with a RFD signature, which was also supported in FSI by the presence of a descending reflectivity core (DRC).

By 1933 UTC, there was a solid hook-shaped appearance to the storm. There continued to be extremely low CC values in the inflow region of the updraft core. The mesocyclone had tightened a little bit in the mid-levels (although not defined by the Digital Mesocyclone Detection (DMD)), along with a clearly defined circulation on the 0.5 degree elevation slice. The circulation remained broad, however, and the issuance of a Tornado Warning was held off pending the next volume scan. There was shallow vertical continuity (~7-8 kft deep) of storm-scale rotation as well. Also at this time, there continued to be a flanking line signature to the W of the hook, indicating that there continued to be the presence of a RFD. This was also verified by looking at the storm-relative motion (SRM), which now showed a deep convergence zone (DCZ) stretching back westward of the hook, which can often be a good indicator for severe winds. These DCZ's are also common with extremely large hail. LLVr was about 30 kts over 0.5 nm with a shear value increasing to 0.036 s-1, but some range folding and purple haze was also near the couplet despite being in VCP-212.

At 1937 UTC, the SRM now showed moderate-high confidence that there indeed was a circulation near the surface capable of producing a tornado. The circulation tightened, along with the mesocyclone rotation as well. The V-R Shear analysis showed a LLVr of 37 kts with a shear value of 0.0427 s-1 over 0.5 nm. The mesoscyclone was about 14 nm from RDA. The LLVr and shear value fit well in the past research to issue a Tornado Warning. There was now vertical continuity in FSI extending past 10kft, along with the DMD and Tornado Vortex Signature (TVS) being triggered. There also remained the presence of the RFD as well. A Tornado Warning was quickly generated and issued at 1939 UTC.

Looking at a high-resolution topographic image of the Mohawk Valley offers another interesting perspective on the tornadic evolution of this storm. The hook echo and circulation tracked right down the Schoharie Valley, immediately south of where it runs into the Mohawk River. As the RFD interacted with the FFD inflow air (via the low CC values), substantial horizontal vorticity may have been generated beneath the updraft. As the storm entered the Schoharie Valley area, both the RFD (coming in from the W), and FFD (coming in for the E/SE), may have accelerated downwards in this little valley, while at the same time, interacting due to cyclonic frictional convergence caused by the terrain. This interaction may have been what was needed for the horizontal vorticity to be tilted and stretched into the vertical to enable the tornadic vortex to form (possibly from the ground up), as twisting/tilting was induced from the frictional convergence caused within the Schoharie Creek Valley (similar to what happened with the Great Barrington tornado with the influence of the Catskill Creek). Before the tornadic vortex as well, winds may have also been funneled down this valley. This is what can be speculated at this point without quantifying these local flows.

By the next volume scan (1942 UTC), the tornadic circulation strengthened further, with a tightening of the circulation on the 0.5 degree elevation slice (though the LLVr = 33 kts, and shear= 0.037 s-1 were slightly lower over 0.5nm), and a vertical continuity seen extending as high as 15-20 kft AGL. When zooming in on the base reflectivity as well, there was also a tiny decrease in reflectivity heading into the core of the hook echo. This may be the indications of a RFD Internal Surge (RFDIS), which has been shown in recent research to be associated with strong tornadic vortices that are often multi-vortex in nature. This RFDIS signature was also apparent in SRM via a stripe of inbound velocities wrapping into the hook echo.

At 1947 UTC, a Tornadic Debris Signature (TDS) was now apparent, lining up almost perfectly with high reflectivities in the hook echo, the impressive SRM couplet (LLVr=43 kts, and a shear value of 0.0483 s-1) low CC (<0.80), and low ZDR (<1 dB) (Bodine et al. 2014). The RFD signature was also still apparent, although the RFDIS signature was harder to see. Based on prior research, the TDS is delayed by 1 volume scan, and using just radar by itself suggests a tornado touchdown as early as 1942 UTC. However, the tornado could have been on the ground longer before that, as the TDS signature requires enough debris to be lofted into the air (siding, shingles, etc.) to be sampled by the radar. This TDS occurred at the time the tornadic vortex was moving up the "ridge" on the east side of the Schoharie Creek.

By 1951 UTC (around the time of the worst damage near Delansen, NY and Duanesburg, NY), an even better TDS signature was evident, with base reflectivity values now above 60 dBZ collocated with the SRM couplet (LLVr= 43 kts with a shear value=0.0510 s-1 across 0.5 nm at range of 10 nm), CC values as low as 0.67, and ZDR values near 0 dB. With ZDR values near 0 dB, this signified that debris was not only lofted into the air by the tornado, but was tumbling as it fell to the ground. Meanwhile, the RFD was now visible on the base reflectivity and SRM images beginning to wrap around the tornadic vortex, helping to tighten and strengthen it even further. This was near the time when the worst damage occurred, with a house destroyed on Route 20 about 2 miles west of Duanesburg, NY (EF3 damage) and a semi-truck flipped over on I-88.

Between 1942 and 1951 UTC, another radar artifact was apparent and may have played a role in intensifying the tornadic vortex. There were 2 fine line signatures, one immediately south of the hook and one oriented SE/NW (roughly along the same line as the FFD orientation). These fine lines may have been gravity waves containing horizontal streamline and crosswise vorticity that can aid in sustaining, generating, or enhancing tornadic vortices. These gravity waves were favored synoptically by sharp upper-level ridging aloft (which was located across portions of the Northeast). Given the presence of the occluded boundary and the sharp instability and theta-e gradient nearby, the tornado formed in a perfect, vorticity-rich location that was enhanced by the local topography. By 2005 UTC, the tornadic circulation had dissipated as it moved into the Altamont/Knox, NY area in western Albany County.

Upstate NY and New England continue to have intriguing severe weather events, and this tornado event ranks up there as an anomalous one, where perhaps the triple point to the synoptic system played a critical role for tornadogenesis coupled with steep mid-level lapse rate air (as indicated upstream at the 12Z KBUF sounding), moderate instability, and a strong short-wave in the water vapor loop that moved across northern NY and northern New England (under-analyzed by the guidance) that helped focus the initial severe convection and where local channeled flows with the topography likely helped strengthen the tornado.

Figures

Meteorology Figures

Above: Soundings at Albany, NY (KALB) and Buffalo, NY (KBUF) valid at 1200 UTC 22 May 2014.

Above: Weather Prediction Center (WPC) surface plot valid at 7am 22 May 2014 (left) and 7am 23 May 2014 (right).

Above: Storm Prediction Center (SPC) upper air plots at 250 hPa (left) and 300 hPa (right) valid at 1200 UTC 22 May 2014.

Above: SPC upper air plots at 500 hPa (left) and 700 hPa (right) valid at 1200 UTC 22 May 2014.

Above: SPC upper air plots at 850 hPa (left) and 925 hPa (right) valid at 1200 UTC 22 May 2014.

Above: Loops of IR (left) and water vapor (right) satellite imagery.

Above: Loops of LAPS SBCAPE (left), visible satellite imagery overlaid with METARS (middle), and LAPS 0-1km EHI (right).

Above: SPC Day 1 Convective Outlook (left), Day 1 Tornado Outlook (2nd from left), Day 1 Hail Outlook (2nd from right), and Day 1 Wind Outlook (right) valid at 1630 UTC 22 May 2014.

Above: SPC mesoanalysis of 0-6km bulk shear (left) and 0-1km bulk shear (right) valid at 1900 UTC 22 May 2014.

Above: SPC mesoanalysis of 0-3km SRH (left) and 0-1km SRH (right) valid at 1900 UTC 22 May 2014.

Above: SPC mesoanalysis of 700-500 hPa mid-level lapse rates (left) and low-level lapse rates (right) valid at 1900 UTC 22 May 2014.

Above: SPC mesoanalysis of SBCAPE (left), MLCAPE (middle), and MUCAPE (right) valid at 1900 UTC 22 May 2014.

Above: SPC mesoanalysis of SFC-3km CAPE overlaid with surface vorticity (left), VGP (middle), and Bulk Richardson Number (right) valid at 1900 UTC 22 May 2014.

Above: SPC mesoanalysis of Supercell Composite (left) and Significant Tornado Parameter across a fixed-layer (right) valid at 1900 UTC 22 May 2014.

 

Storm Scale/Radar Images

Above: 1745 UTC to 2101 UTC KENX 0.5 Base reflectivity (left) loop and 1832 UTC to 2029 UTC SRM (right) loop with severe thunderstorm warning (yellow) and tornado warning (red) polygons overlaid.

Above: 1928 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data with a developing hook echo over southeastern Montgomery County.

Above: 1933 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data with a hook echo and a strong mesocyclone over northwestern Schenectady County. The mesocyclonic couplet had a rotational velocity (Vr) = 30 kts, and a Shear (S) value = 0.036 s-1 over 0.5 nm from gate to gate.

Above: 1937 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data with a hook echo and a strong mesocyclone over northwest/west Schenectady County. The mesocyclonic couplet had a Vr = 37 kts, and S = 0.043 s-1 over 0.5 nm from gate to gate with a range of 14 nm from the RDA. The tornado has touched down at this time.

Above: 1942 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data with an intense hook echo and a strong mesocyclone over western Schenectady County. The mesocyclone had a Vr = 33 kts, and S = 0.037 s-1 over 0.5 nm from gate to gate with a range of 13 nm from the RDA. The tornado continues on the ground at this time.

Above: 1947 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data with the intense hook echo and a strong mesocyclone over western Schenectady County. The mesocyclone had a Vr = 43 kts, and S = 0.048 s-1 over 0.5 nm from gate to gate with a range of 12 nm from the RDA. The tornado was just north of Delanson.

Above: 1951 UTC KENX 0.5 Base reflectivity (left) and SRM (center) and a dual-pol 4 panel (right) of base reflectivity (upper left), differential reflectivity (upper right), hydrometeor classification (lower left), and correlation coefficient (lower right) data with the tornado at its most intense state over extreme western Schenectady County near the border of Albany County. The mesocyclone had a Vr = 43 kts, and S = 0.051 s-1 over 0.5 nm from gate to gate with a range of 10 nm from the RDA. A Tornadic Debris Signature (TDS) was evident in the dual pol data with the correlation coefficient lowering to 0.69 on the lowest radar tilt, and the differential reflectivity value was 0.36 dB. The cursor highlights where the TDS is located in relation to the tornadic couplet in the right image.

Above: 1951 UTC KENX Dual-pol 4 panel of the TDS (zoomed in) of base reflectivity (upper left), SRM (upper right) differential reflectivity (lower left), and correlation coefficient (lower right) data with the tornado at its most intense state over western Schenectady County near the border of northwestern Albany County. The tornado polygon is highlighted in red.

Above: 1956 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data with the hook echo and a fairly strong mesocyclone over extreme northwestern Albany County. The mesocyclone had a Vr = 33 kts, and S = 0.038 s-1 over 0.5 nm from gate to gate between inbound and outbound velocities with a range of 9 nm from the RDA. The tornado was west of Altamont.

Above: 2001 UTC KENX 0.5 Base reflectivity (left) and SRM (right) data indicate the hook echo and a tornadic mesocyclone has occluded and begins to weaken over northwestern Albany County. The mesocyclone had a Vr = 27 kts, and S = 0.031 s-1 over 0.5 nm from gate to gate between inbound and outbound velocities with a range of 8 nm from the RDA. The tornado ran into a much more stable environment and the entire supercell weakened and collapsed over the next few radar scans.

Large Hail Images

Above Images: Large Hail Images of 2.5 to 4 diameter hail from Amsterdam, NY from trained spotters (left), (right). The 2nd image (right) was from 325 pm. The 4 diameter hail stone tied the NY state record set on Sept 27th 1998 in Niagara Falls, NY.

 

Storm Damage Images (taken from NWS Albany storm survey)

Above: EF3 damage to a home near Delanson, NY (left) and tree damage/debris (right).

Above: Tornado damage to a home garage (left) and motel (right).

Above: Official Public Information Statement (PNS) sent for EF3 tornado.