Alert archive / New York / Mesoscale Discussions in 2021
Mesoscale Discussion 1320
The Storm Prediction Center issued this mesoscale discussion at Jul 20, 2021, 4:17 PM EDT for 13 counties in New York; Grand Isle County, Vermont. It was in force for 118 min.
The area
The outline as issued.
The facts
- Issued
- Jul 20, 2021, 4:17 PM EDT (20:17 UTC)
- Expired
- Jul 20, 2021, 6:15 PM EDT
- In force
- 118 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 384
Counties Cayuga County, NY, Clinton County, NY, Essex County, NY, Franklin County, NY, Hamilton County, NY, Herkimer County, NY, Jefferson County, NY, Lewis County, NY, Oneida County, NY, Onondaga County, NY, Oswego County, NY, St. Lawrence County, NY, Wayne County, NY, Grand Isle County, VT
The radar
The Ft Drum radar (KTYX), 27 km from the middle of the area, began a volume at 20:20 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, 8.3 hours before the alert went out and 213 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.
- 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
The text
As transmitted.
940
ACUS11 KWNS 202017
SWOMCD
SPC MCD 202017
VTZ000-NYZ000-202215-
Mesoscale Discussion 1320
NWS Storm Prediction Center Norman OK
0317 PM CDT Tue Jul 20 2021
Areas affected...Parts of western through much of northern New York
State and adjacent northern Vermont
Concerning...Severe Thunderstorm Watch 384...
Valid 202017Z - 202215Z
The severe weather threat for Severe Thunderstorm Watch 384
continues.
SUMMARY...An organized cluster of thunderstorms will spread across
the St. Lawrence River through much of the Adirondacks vicinity,
along with continuing development across and southeast of Lake
Ontario by 5-7 PM EDT, accompanied by the risk for potentially
damaging wind gusts.
DISCUSSION...Moderate southeasterly low-level inflow of moist air
characterized by CAPE in excess of 1000 J/kg is maintaining vigorous
thunderstorm development along the leading edge of an
east-southeastward advancing, convectively driven surface cold pool.
This continues to be aided by large-scale forcing for ascent
associated with a 30-50 kt westerly mid/upper jet streak, and will
overspread the upper St. Lawrence Valley through much of the
Adirondacks region by 22-23Z. As the temperature gradient across
the gust front increases at least a bit further, potential for
damaging wind gusts probably will also continue to increase during
the next hour or two.
Farther to the southwest, thunderstorms which initiated along the
trailing outflow boundary, and preceding lake breezes across the
Lake Ontario vicinity, may also begin to consolidate while spreading
into the unstable environment to the southeast of the lake. This
too may gradually pose increasing risk for damaging wind gusts
near/north of the Finger Lakes region through the Mohawk Valley by
early evening.
..Kerr.. 07/20/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BTV...ALY...BGM...BUF...
LAT...LON 43997686 44397609 44977514 45277421 44887322 43647392
43047508 42957641 43187737 43627813 43997686SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 20, 1:03 PM EDT | Mesoscale Discussion | SPC | Clinton, Franklin, Jefferson, Lewis, Monroe, Orleans and 2 more | 2 hr |
| Jul 20, 3:05 PM EDT | Severe Thunderstorm Watch | SPC | Albany, Broome, Cayuga, Chemung, Chenango, Clinton and 38 more | 8 hr |
| Jul 20, 7:12 PM EDT | Mesoscale Discussion | SPC | Albany, Cayuga, Chenango, Cortland, Essex, Fulton and 15 more | 2 hr |
Nearby
Mesoscale Discussions in New York, 2021Mesoscale Discussions in Vermont, 2021Every 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.