Alert archive / New York / Mesoscale Discussions in 2021

Mesoscale Discussion 1321

July 20, 20214 states

The Storm Prediction Center issued this mesoscale discussion at Jul 20, 2021, 7:12 PM EDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Jul 20, 2021, 7:12 PM EDT (23:12 UTC)
Expired: Jul 20, 2021, 9:15 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 384

All 40 counties

Berkshire County, MA, Franklin County, MA, Belknap County, NH, Carroll County, NH, Cheshire County, NH, Grafton County, NH, Hillsborough County, NH, Merrimack County, NH, Sullivan County, NH, Albany County, NY, Cayuga County, NY, Chenango County, NY, Cortland County, NY, Essex County, NY, Fulton County, NY, Hamilton County, NY, Herkimer County, NY, Lewis County, NY, Madison County, NY, Montgomery County, NY, Oneida County, NY, Onondaga County, NY, Oswego County, NY, Otsego County, NY, Rensselaer County, NY, Saratoga County, NY, Schenectady County, NY, Schoharie County, NY, Warren County, NY, Washington County, NY, Addison County, VT, Bennington County, VT, Caledonia County, VT, Chittenden County, VT, Lamoille County, VT, Orange County, VT, Rutland County, VT, Washington County, VT, Windham County, VT, Windsor County, VT

The radar

The Burlington radar (KCXX), 113 km from the middle of the area, began a volume at 23:15 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.

The nearest sounding before it

Albany, NY (KALY), launched 12:00Z, 11.2 hours before the alert went out and 97 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: 85 J/kg
Mixed-layer CIN: -145 J/kg
Mixed-layer LCL: 793 m above ground
0-6 km bulk shear: 19 kt
0-1 km storm-relative helicity: 45 m²/s²
0-3 km storm-relative helicity: 95 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

378 
ACUS11 KWNS 202312
SWOMCD
SPC MCD 202312 
NHZ000-MAZ000-VTZ000-NYZ000-210115-

Mesoscale Discussion 1321
NWS Storm Prediction Center Norman OK
0612 PM CDT Tue Jul 20 2021

Areas affected...New York and New England

Concerning...Severe Thunderstorm Watch 384...

Valid 202312Z - 210115Z

The severe weather threat for Severe Thunderstorm Watch 384
continues.

SUMMARY...The wind-damage threat inside WW 384 is expected to
continue for several more hours this evening. As the convection
moves to the eastern edge of WW 384, a new watch may be needed.

DISCUSSION...The latest radar imagery from Albany, New York shows
two small clusters of strong to severe thunderstorms. The first is
located to the east of Lake Ontario with the second in northern New
York near the Vermont state line. These convective clusters are
located in a moist airmass with surface dewpoints in the 60s F. This
is contributing to moderate instability with the RAP estimating
MLCAPE in the 1500 to 2000 J/kg range. In addition, moderate
deep-layer shear is present with 0-6 km shear near 35 kt on the
Albany WSR-88D VWP. Th instability, shear combined with steep
low-level lapse rates will support isolated wind damage with the
stronger multicells. The easternmost cluster of strong storms will
likely move into New Hampshire and southern Maine over the next
couple of hours, where instability is weaker but still could support
strong to severe gusts.

..Broyles/Edwards.. 07/20/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GYX...BOX...BTV...ALY...BGM...BUF...

LAT...LON   44767209 44507120 43807103 42977126 42377200 42297385
            42347585 42807675 43257670 43787570 44727371 44767209

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 20, 3:05 PM EDT	Severe Thunderstorm Watch	SPC	Berkshire	8 hr
Jul 20, 1:03 PM EDT	Mesoscale Discussion	SPC	Clinton, Franklin, Jefferson, Lewis, Monroe, Orleans and 2 more	2 hr
Jul 20, 4:17 PM EDT	Mesoscale Discussion	SPC	Cayuga, Clinton, Essex, Franklin, Hamilton, Herkimer and 7 more	118 min

Nearby

Mesoscale Discussions in New York, 2021 Mesoscale Discussions in Vermont, 2021 Mesoscale Discussions in New Hampshire, 2021 Every mesoscale discussion in 2021

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.