Alert archive / New York / Severe Thunderstorm Watches in 2017

Severe Thunderstorm Watch 424

July 20, 201720 counties in New York; 11 counties in Pennsylvania

The Storm Prediction Center issued this severe thunderstorm watch at Jul 20, 2017, 1:11 PM EDT for 20 counties in New York; 11 counties in Pennsylvania. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Jul 20, 2017, 1:11 PM EDT (17:11 UTC)
Expired: Jul 20, 2017, 7:04 PM EDT
In force: 6 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

All 31 counties

Allegany County, NY, Broome County, NY, Cayuga County, NY, Chemung County, NY, Chenango County, NY, Cortland County, NY, Delaware County, NY, Livingston County, NY, Madison County, NY, Onondaga County, NY, Ontario County, NY, Otsego County, NY, Schuyler County, NY, Seneca County, NY, Steuben County, NY, Sullivan County, NY, Tioga County, NY, Tompkins County, NY, Wayne County, NY, Yates County, NY, Bradford County, PA, Columbia County, PA, Lackawanna County, PA, Luzerne County, PA, Lycoming County, PA, Pike County, PA, Sullivan County, PA, Susquehanna County, PA, Tioga County, PA, Wayne County, PA, Wyoming County, PA

The radar

The Binghamton radar (KBGM), 81 km from the middle of the area, began a volume at 17:13 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 20%
One or more EF2 to EF5 tornadoes: 2%
Ten or more severe wind reports: 50%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 40%
One or more hailstones of 2 inches or more: 10%
Six or more combined severe hail and wind reports: 70%

Warnings issued inside it

22 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Jul 20, 1:23 PM EDT	Severe Thunderstorm Warning	BUF	Allegany, Cattaraugus, Wyoming	52 min
Jul 20, 1:35 PM EDT	Tornado Warning	BUF	Allegany	40 min
Jul 20, 1:57 PM EDT	Severe Thunderstorm Warning	BGM	Steuben	63 min
Jul 20, 2:07 PM EDT	Severe Thunderstorm Warning	BUF	Allegany, Cattaraugus, Erie, Wyoming	38 min
Jul 20, 2:46 PM EDT	Severe Thunderstorm Warning	BUF	Allegany	59 min
Jul 20, 2:49 PM EDT	Severe Thunderstorm Warning	CTP	Tioga	56 min
Jul 20, 2:57 PM EDT	Severe Thunderstorm Warning	BGM	Chemung, Steuben	33 min
Jul 20, 3:19 PM EDT	Severe Thunderstorm Warning	BGM	Chemung, Schuyler, Tioga, Tompkins	26 min
Jul 20, 3:28 PM EDT	Flash Flood Warning	BGM	Chemung, Schuyler, Steuben, Tioga, Tompkins	3 hr
Jul 20, 3:29 PM EDT	Severe Thunderstorm Warning	BGM	Bradford	61 min
Jul 20, 3:31 PM EDT	Severe Thunderstorm Warning	CTP	Potter, Tioga	59 min
Jul 20, 3:44 PM EDT	Severe Thunderstorm Warning	BGM	Broome, Chemung, Tioga	46 min
Jul 20, 3:51 PM EDT	Flash Flood Warning	BGM	Broome, Chemung, Steuben, Tioga	6 hr
Jul 20, 4:13 PM EDT	Severe Thunderstorm Warning	CTP	Lycoming, Sullivan, Tioga	92 min
Jul 20, 4:16 PM EDT	Severe Thunderstorm Warning	BGM	Bradford	14 min
Jul 20, 4:28 PM EDT	Severe Thunderstorm Warning	BGM	Bradford, Lackawanna, Susquehanna, Wyoming	32 min
Jul 20, 4:47 PM EDT	Severe Thunderstorm Warning	BGM	Luzerne, Wyoming	28 min
Jul 20, 4:59 PM EDT	Severe Thunderstorm Warning	BGM	Lackawanna, Luzerne, Susquehanna, Wayne, Wyoming	46 min
Jul 20, 5:12 PM EDT	Severe Thunderstorm Warning	BGM	Luzerne	48 min
Jul 20, 5:42 PM EDT	Severe Thunderstorm Warning	BGM	Luzerne	63 min
Jul 20, 5:44 PM EDT	Severe Thunderstorm Warning	BGM	Sullivan	46 min
Jul 20, 6:29 PM EDT	Severe Thunderstorm Warning	BGM	Pike	16 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Buffalo Intl Airport, NY (KBUF), launched 12:00Z, 5.2 hours before the alert went out and 157 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 2004 m above ground
0-6 km bulk shear: 52 kt
0-1 km storm-relative helicity: 122 m²/s²
0-3 km storm-relative helicity: 131 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 20, 11:36 AM EDT	Mesoscale Discussion	SPC	Allegany, Cattaraugus, Chautauqua, Chemung, Erie, Genesee and 10 more	114 min
Jul 20, 3:03 PM EDT	Mesoscale Discussion	SPC	Allegany, Broome, Cayuga, Chemung, Chenango, Cortland and 13 more	87 min
Jul 20, 4:33 PM EDT	Mesoscale Discussion	SPC	Bronx, Broome, Columbia, Delaware, Dutchess, Greene and 11 more	87 min
Jul 20, 5:03 PM EDT	Severe Thunderstorm Watch	SPC	Bronx, Kings, Nassau, New York, Orange, Queens and 3 more	5 hr
Jul 20, 7:48 PM EDT	Mesoscale Discussion	SPC	Bronx, Kings, New York, Queens, Richmond, Rockland	87 min
Jul 20, 3:50 PM EDT	Mesoscale Discussion	SPC	Allegheny, Armstrong, Beaver, Butler, Cambria, Cameron and 10 more	2 hr

Nearby

Severe Thunderstorm Watches in New York, 2017 Severe Thunderstorm Watches in Pennsylvania, 2017 Every severe thunderstorm watch in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.