Alert archive / Maine / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 502
The Storm Prediction Center issued this severe thunderstorm watch at Sep 15, 2021, 1:15 PM EDT for 13 counties in Maine; 10 counties in New Hampshire. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 15, 2021, 1:15 PM EDT (17:15 UTC)
- Expired
- Sep 15, 2021, 7:19 PM EDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 23 counties
Androscoggin County, ME, Cumberland County, ME, Franklin County, ME, Kennebec County, ME, Knox County, ME, Lincoln County, ME, Oxford County, ME, Penobscot County, ME, Piscataquis County, ME, Sagadahoc County, ME, Somerset County, ME, Waldo County, ME, York County, ME, Belknap County, NH, Carroll County, NH, Cheshire County, NH, Coos County, NH, Grafton County, NH, Hillsborough County, NH, Merrimack County, NH, Rockingham County, NH, Strafford County, NH, Sullivan County, NH
The radar
The Portland,ME radar (KGYX), 101 km from the middle of the area, began a volume at 17:18 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
- 5%
- Ten or more severe wind reports
- 60%
- 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
- 20%
- Six or more combined severe hail and wind reports
- 90%
Warnings issued inside it
16 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 15, 2:18 PM EDT | Severe Thunderstorm Warning | GYX | Coos, Grafton | 57 min |
| Sep 15, 2:31 PM EDT | Severe Thunderstorm Warning | GYX | Belknap, Carroll, Coos, Grafton, Merrimack, Sullivan | 59 min |
| Sep 15, 2:33 PM EDT | Severe Thunderstorm Warning | GYX | Franklin, Oxford | 42 min |
| Sep 15, 3:04 PM EDT | Severe Thunderstorm Warning | GYX | Franklin, Oxford | 41 min |
| Sep 15, 3:04 PM EDT | Severe Thunderstorm Warning | GYX | Belknap, Grafton, Merrimack, Sullivan | 56 min |
| Sep 15, 3:22 PM EDT | Severe Thunderstorm Warning | GYX | Belknap, Carroll, Coos, Grafton, Merrimack, Sullivan | 53 min |
| Sep 15, 3:41 PM EDT | Severe Thunderstorm Warning | GYX | Franklin, Oxford, Somerset | 49 min |
| Sep 15, 4:07 PM EDT | Severe Thunderstorm Warning | GYX | Cheshire, Hillsborough, Merrimack, Sullivan | 38 min |
| Sep 15, 4:09 PM EDT | Severe Thunderstorm Warning | GYX | Cumberland, Oxford | 51 min |
| Sep 15, 4:28 PM EDT | Tornado Warning | GYX | Cumberland, Oxford | 32 min |
| Sep 15, 4:44 PM EDT | Severe Thunderstorm Warning | GYX | Cumberland, Oxford, York | 46 min |
| Sep 15, 4:57 PM EDT | Severe Thunderstorm Warning | CAR | Penobscot, Piscataquis | 48 min |
| Sep 15, 4:58 PM EDT | Severe Thunderstorm Warning | GYX | Somerset | 29 min |
| Sep 15, 5:09 PM EDT | Severe Thunderstorm Warning | GYX | Cheshire, Hillsborough, Merrimack | 51 min |
| Sep 15, 5:14 PM EDT | Severe Thunderstorm Warning | GYX | Androscoggin, Cumberland, Kennebec, Oxford, Sagadahoc | 46 min |
| Sep 15, 5:29 PM EDT | Severe Thunderstorm Warning | GYX | Cumberland, Oxford, York | 61 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
Gray, ME (KGYX), launched 12:00Z, 5.3 hours before the alert went out and 101 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
- 101 J/kg
- Mixed-layer CIN
- -167 J/kg
- Mixed-layer LCL
- 468 m above ground
- 0-6 km bulk shear
- 54 kt
- 0-1 km storm-relative helicity
- 299 m²/s²
- 0-3 km storm-relative helicity
- 318 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.3
The text
As transmitted.
600 WWUS20 KWNS 151713 SEL2 SPC WW 151713 MEZ000-NHZ000-160000- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 502 NWS Storm Prediction Center Norman OK 115 PM EDT Wed Sep 15 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Western and central Maine New Hampshire * Effective this Wednesday afternoon and evening from 115 PM until 800 PM EDT. * Primary threats include... Scattered damaging wind gusts to 70 mph likely Scattered large hail events to 1.5 inches in diameter possible A tornado or two possible SUMMARY...Scattered severe storms are expected to develop this afternoon and spread west-to-east across New Hampshire into Maine. The initial storms could be more discrete with some supercell structures possible, though a gradual evolution into line segments is expected. Damaging winds of 60 to 70 mph and isolated large hail of 1 to 1.5 inch diameter will be the most common threats, though a tornado or two may occur with embedded circulations. The severe thunderstorm watch area is approximately along and 65 statute miles north and south of a line from 15 miles west of Lebanon NH to 60 miles north northeast of Augusta ME. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU2). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 501... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 25035. ...Thompson
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 15, 11:59 AM EDT | Mesoscale Discussion | SPC | Androscoggin, Cumberland, Franklin, Kennebec, Lincoln, Oxford and 6 more | 2 hr |
| Sep 15, 4:38 PM EDT | Mesoscale Discussion | SPC | Androscoggin, Cumberland, Kennebec, Oxford, Penobscot, Sagadahoc and 2 more | 67 min |
| Sep 15, 10:33 AM EDT | Mesoscale Discussion | SPC | Addison, Bennington, Chittenden, Orange, Rutland, Washington and 2 more | 2 hr |
| Sep 15, 11:55 AM EDT | Severe Thunderstorm Watch | SPC | Addison, Bennington, Caledonia, Chittenden, Essex, Lamoille and 6 more | 8 hr |
Nearby
Severe Thunderstorm Watches in Maine, 2021Severe Thunderstorm Watches in New Hampshire, 2021Every severe thunderstorm watch 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.