Severe Thunderstorms May 15, 2018

Tornadoes:

Tornado - Saugerties, NY ULSTER/DUTCHESS COUNTIES Date May 15, 2018 Time (Local) 2:29-2:35 pm EF Rating 1 Est. Peak Winds 90 mph Path Length 5 miles Max Width 175 yards Injuries/Deaths 0/0 Summary: The tornado path started along Route 212 between Woodstock and Saugerties and moved east through the western and southern part of Saugerties before crossing the Hudson River and  ending in Tivoli, NY, just south of the Clermont State Historic Site. The majority of the tornado damage was rated EF-0. The storm that produced the tornado also produced at least one microburst with winds up to 90 mph, which sheared and uprooted many large trees  and sheared a few power poles. Most of the damage was indirect, from trees falling on homes, other structures and power lines.  Track Map

Tornado - Winsted, CT LITCHFIELD COUNTY Date May 15, 2018 Time (Local) 3:44-3:46 pm EF Rating 1 Est. Peak Winds 95 mph Path Length 0.7 miles Max Width 175 yards Injuries/Deaths 0/0 Summary: On Tuesday, May 15 there was an EF1 tornado on the northeast side of Winsted, CT. The tornado moved west to east across 8 city blocks, shearing trees, uprooting trees, and producing some minor structural damage to homes. Many homes and power lines were damaged by fallen trees. A member of the local community witnessed the tornado. Track Map

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Macroburst

Macroburst - Dutchess County, NY   Date May 15, 2018 Time (Local) 4:20 pm Est. Peak Winds 105 mph Path Length 8 miles Max Width 3 miles Injuries/Deaths 0/0 Summary: A National Weather Service team determined that a macroburst occurred in southern Dutchess County, NY along the I-84 corridor roughly between Beacon/Wappingers Falls and East Fishkill/Hopewell Junction. The macroburst toppled/uprooted hundreds of trees. Some trees fell on structures. There was limited direct damage from wind to structures with a fallen chimney noted as well as some siding ripped off a few homes. The damage is consistent with wind speeds in the 85 to 105 mph range. For reference... A macroburst is a thunderstorm downdraft affecting an area at least 2.5 miles wide with peak winds lasting 5 to 20 minutes. The macroburst is a straight-line wind phenomena not associated with rotation...used to differentiate from tornadic  winds. Macrobursts can produce as much if not more damage as tornadoes due to the size and scope of a macroburst. Map of Surveyed Damage Swath

Photos & Video:

Damage near Saugerties, NY (NWS Albany damage survey)	Damage near Saugerties, NY (NWS Albany damage survey)	Damage near Saugerties, NY (NWS Albany damage survey)

Damage near Winsted, CT (NWS Albany damage survey)	Damage near Winsted, CT (NWS Albany damage survey)	Damage near Winsted, CT (NWS Albany damage survey)

Radar:

(Loops may take some time to load)

KENX radar loop from approximately 1:40-5:30 pm	KENX radar loop from approximately 1:40-5:30 pm with NWS warnings	2:47 pm image from KENX radar. Reflectivity cross section of a storm that produced baseball sized hail in Columbia County, NY	3:44 pm image from KENX radar of the storm that produced the tornado near Winsted, CT. Reflectivity (left) and storm-relative velocity (right).

Storm Reports

Local Storm Reports

Saugerties, NY Tornado - Public Information Statement

Winsted/Barkhamsted Reservoir, CT Tornadoes - Public Information Statement

Dutchess County, NY Macroburst - Public Information Statement

Links courtesy Iowa Environmental Mesonet

Environment

Fast 500 mb flow existed over the Northeast US on May 15th between a strong upper low over northern Quebec and a high over the Deep South (Fig. 1). While 500 mb height falls were weak, there was a right entrance region of a strong upper jet which enhanced ascent (Fig. 2). At the surface, a NE/SW oriented cold front tracked westward through the day (Fig. 3). There was a bit of an outflow boundary present associated with showers and thunderstorms that tracked through the Mohawk Valley/Capital District earlier in the day, allowing the effective position of the front to sag farther south than originally forecast and spared the I-90 corridor/Schoharie Valley and points north from severe weather potential. To the south, there was plenty of sunshine through the morning and early afternoon which allowed temperatures to soar into the upper 70s (Catskills) to upper 80s (Mid-Hudson Valley) with dewpoints in the low 60s (Catskills) to upper 60s (Mid-Hudson Valley). This allowed a tongue of 1000-2000 J/kg MLCAPE values to surge into the eastern Catskills, Mid-Hudson Valley, and northwestern CT by 18Z (Fig. 4) coincident with a pocket of 6.5-8.0 K/km midlevel lapse rates (Figs. 5, 6). Effective bulk shear values were very impressive at 60-70 kt collocated with the axis of instability (Fig. 7). These factors coming together, along with the continued CAM depiction of several bowing lines of storms, prompted an SPC categorical upgrade to moderate risk with the 1630Z update (Fig. 8). This included probabilities of 10% tornado, 30% hail, and 60% wind.

As a broken line of bowing cells were forming over western/central PA during the early afternoon hours along the cold front, a few supercells formed ahead of the front in the Catskills around 17-1730Z. The lead cell became severe, resulting in an EF1 tornado near Saugerties at around 1830Z, and a swath of large hail in the 2.00-2.75" range in southern Columbia County. This cell eventually would produce two more tornadoes in northwestern CT. A couple of more discrete rotating storms formed with a few hail and wind reports, and then the frontal convection that had formed over western/central PA earlier approached. A portion of this line accelerated across far southern portions of Ulster/Dutchess/Litchfield Counties, producing swaths of widespread wind damage in spots, especially along the I-84 corridor from Beacon to Fishkill, NY. A few tornadoes were confirmed just south of our CWA border in Orange/Putnam/Fairfield Counties in addition to widespread straight-line wind damage. The event was over shortly thereafter for the ALY CWA, with the bulk of the severe reports occurring between 1830-2100Z.

Figure 1: 500 mb analysis, 12Z 15 May 2018	Figure 2: 300 mb analysis, 12Z 15 May 2018	Figure 3: Weather Prediction Center surface analysis valid 18Z 15 May 2018

Figure 4: Storm Prediction Center mesoanalysis of mixed-layer CAPE (J/kg) valid 18Z 15 May 2018	Figure 5: As in Fig. 4 but for 700-500-hPa lapse rates (K/km)	Figure 6: KALB RAOB at 18Z 15 May 2018

Figure 7: As in Fig. 4 but for effective bulk shear (kt).	Figure 8: Storm Prediction Center Day 1 Convective Outlook issued 1630Z 15 May 2018