On the evening of May 15th a strong line of thunderstorms developed across Western New Hampshire ahead of an approaching cold front. A well developed squall line formed bowing line segments which brought localized destructive wind damage to areas of the state with extensive tree damage in areas.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS GYX wrote it up.
On the evening of May 15th a strong line of thunderstorms developed across Western New Hampshire ahead of an approaching cold front. A well developed squall line formed bowing line segments which brought localized destructive wind damage to areas of the state with extensive tree damage in areas.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Gray, ME wrote its last area forecast discussion before the first event at May 15, 5:52 PM EST, 30 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Gray ME 652 PM EDT Fri May 15 2020 .SYNOPSIS... Low pressure over upstate New York will track across southern New Hampshire and the southern tip of Maine spawning widespread showers and thunderstorms this evening. Along and south of the low track will be the area most likely to see thunderstorms containing large hail, damaging winds and heavy rainfall. The low will race offshore tonight with high pressure and drier air to follow for Saturday and Saturday night. Low pressure will approach from the west late Sunday, before slipping south of the region early next week. && .NEAR TERM /THROUGH TONIGHT/... 655 PM Update... Straight-line wind damage appears to be about to occur in southern NH at the moment. Nice bowing segment is moving east quickly into far southern NH. To the north, we are seeing scattered rain showers. Expecting some lightning/thunder across southern NH and SW ME over the next 1-3 hrs. Minor changes to the forecast database for this update; and will keep with severe wording over southern NH. At 18z a 1008 millibar low was centered over eastern Lake Ontario with a warm front extending eastward through southern and western New England. The trailing cold front extended through the lower lakes and upper midwest. NWS Doppler Radar mosaic showed an area of showers across eastern Ontario and southern Quebec that will cross the mountains through central Maine this evening as that area remains mired in the cooler and more stable air north of the warm front. Further south...an area of blossoming convection was developing across the lower lakes and nearby upstate New York in response to strengthening wind field and increasing instability ahead of shortwave impulse. Through this evening...CAMS brings a broken line of convection into New England by early evening with the best chance for strong and severe convection largely limited to western and southern New Hampshire and perhaps the southern tip of Maine with damaging wind gusts the primary threat. However...a few of the strongest cells could produce some marginal severe hail as well. The HRRR trend over the past several hourly runs has been to shift the strongest convection and best stability a bit further south and west in our CWA. In any event...this will be a short-lived event with most guidance having the bulk of the convection offshore by late evening...with only a few lingering showers across northern and eastern sections overnight. I expect some patchy fog and stratus to develop overnight as well. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... On Saturday, a weak area of high pressure will build in from the north. Partial sunshine is expected along with temperatures slightly above normal with 60s most areas...except for a few low 70s over southern interior New Hampshire. Partly cloudy under the ridge Saturday night with lows in the 40s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Short Term /Through Sat night/...Areas of MVFR developing in SHRA by evening with sct strong to severe TSRA possible along and south of a KLEB to KSFM line through 01z Sat. Overnight... lingering areas of MVFR cigs and isold -SHRA with lcl IFR psb in fog. Becoming VFR throughout aft 12z Sat. Long Term... && .MARINE... Short Term /Through Saturday Night/...Winds and seas expected to remain below SCA thresholds through the period. However...behind the exiting surface low overnight there could be a brief surge of winds with gusts approaching 25 kt. Long Term... && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && NEAR TERM...Schwibs SHORT TERM...Schwibs LONG TERM...Ekster
Hazardous Weather Outlook National Weather Service Gray ME 343 PM EDT Fri May 15 2020 NHZ010-013-014-161945- Strafford-Interior Rockingham-Coastal Rockingham- 343 PM EDT Fri May 15 2020 This Hazardous Weather Outlook is for central New Hampshire and southern New Hampshire. .DAY ONE...This Afternoon and Tonight. Strong thunderstorms will be possible across southeastern NH this evening. Gusty winds, heavy rainfall, and hail will be possible. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed. NHZ003-005-007>009-011-012-015-161945- Northern Grafton-Southern Grafton-Sullivan-Merrimack-Belknap- Cheshire-Eastern Hillsborough-Western And Central Hillsborough- 343 PM EDT Fri May 15 2020 ...TORNADO WATCH 187 IN EFFECT UNTIL 10 PM EDT THIS EVENING... This Hazardous Weather Outlook is for New Hampshire, central New Hampshire, northern New Hampshire and southern New Hampshire. .DAY ONE...This Afternoon and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tornado Watch. Severe thunderstorms will be possible across western and southern NH this evening. Damaging winds, heavy rainfall, and hail will be possible along with a low probability of an isolated tornado. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed. MEZ007>009-012>014-019>022-024>028-033-NHZ001-161945- Northern Oxford-Northern Franklin-Central Somerset-Southern Oxford- Southern Franklin-Southern Somerset-Central Interior Cumberland- Androscoggin-Kennebec-Interior Waldo-Coastal Cumberland-Sagadahoc- Lincoln-Knox-Coastal Waldo-Interior Cumberland Highlands- Northern Coos- 343 PM EDT Fri May 15 2020 This Hazardous Weather Outlook is for Maine, south central Maine, southwest Maine, west central Maine, western Maine and northern New Hampshire. .DAY ONE...This Afternoon and Tonight. A period of heavy rain with embedded thunderstorms is likely this evening. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed. MEZ018-023-NHZ002-004-006-161945- Interior York-Coastal York-Southern Coos-Northern Carroll- Southern Carroll- 343 PM EDT Fri May 15 2020 This Hazardous Weather Outlook is for southwest Maine and northern New Hampshire. .DAY ONE...This Afternoon and Tonight. Strong thunderstorms will be possible this evening. Gusty winds, heavy rainfall, and hail will be possible. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed. ANZ150>154-161945- Coastal Waters from Stonington, ME to Port Clyde, ME out 25 NM- Penobscot Bay- Coastal Waters from Port Clyde, ME to Cape Elizabeth, ME out 25 NM- Casco Bay- Coastal Waters from Cape Elizabeth, ME to Merrimack River, MA out 25 NM- 343 PM EDT Fri May 15 2020 This Hazardous Weather Outlook is for Atlantic coastal waters. .DAY ONE...This Afternoon and Tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed.
Special Weather Statement
National Weather Service Gray ME
653 PM EDT Fri May 15 2020
NHZ003-005-007-008-152330-
Merrimack-Northern Grafton-Southern Grafton-Sullivan-
653 PM EDT Fri May 15 2020
...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SULLIVAN...SOUTHWESTERN
GRAFTON AND WEST CENTRAL MERRIMACK COUNTIES...
At 653 PM EDT, radar indicated strong thunderstorms were located
along a line extending from Roxbury to near Mt. Tabor. Movement was
east at 40 mph.
Wind gusts up to 50 mph and penny size hail are possible with these
storms.
Locations impacted include...
Claremont, Lebanon, New London, Grafton, Hanover, Charlestown,
Haverhill, Enfield, Canaan, Groton, Newport, Piermont, Grantham,
Lyme, Cornish, Goshen, Croydon, Benton, Dorchester and Easton.
This includes Interstate 89 between mile markers 32 and 60.
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
LAT...LON 4349 7238 4352 7240 4357 7238 4360 7234
4370 7230 4377 7220 4386 7219 4397 7209
4399 7212 4408 7203 4412 7205 4412 7182
4329 7202 4332 7240 4336 7239 4338 7242
TIME...MOT...LOC 2253Z 275DEG 35KT 4406 7276 4332 7302
MLEThe Albany radar (KENX), 131 km away, was scanning. The volume nearest the first event began at 23:22 UTC.
15 thunderstorm wind, 2 lightning. Local standard time, as filed.
A severe thunderstorm downed trees and power lines on a vehicle.
A severe thunderstorm downed trees in Hinsdale.
A severe thunderstorm downed trees onto wires east of Claremont.
A severe thunderstorm downed multiple trees onto homes on Mechanic Street in Winchester.
A severe thunderstorm downed multiple trees on Centerview Drive.
A severe thunderstorm downed a tree onto a private residents deck in South Swanzey on Warmac Road.
A strong thunderstorm downed multiple trees on Beech Street in Newport.
A severe thunderstorm caused multiple trees and wires down in Swanzey on State Route NH-32.
A severe thunderstorm downed multiple trees on South Pleasant Street in New London.
Structure fire caused by lightning.
A bowing line segment occurred near Jaffrey. While wind gusts of 50 to 60 mph were |common all along the line of thunderstorms, at the apex of the bow echo wind gusts near Jaffrey likely peaked near 90 mph. Hundreds of mainly softwood and some hardwood trees were either uprooted or snapped along a roughly 1 mile path off Route 124. Some of these included large old growth pine trees snapped at the trunk. The |general unidirectional pattern of treefall along the path of the bow apex indicates that the damage was caused by an enhanced area of straight line, outflow winds.
Severe thunderstorm winds caused multiple trees down on Wheeler Street in Jaffrey.
A strong bow signatures occurred near Wilmot in Merrimack County. |While wind gusts of 50 to 60 mph were common all along the line of thunderstorms, the apex of the bow echo and channeled flow in terrain allowed wind gusts near Wilmot to peak at 80 to 90 mph. Hundreds of softwood and hardwood trees were either uprooted or snapped along a roughly 1 mile path off Route 11 near Wilmot Flat. The general unidirectional pattern of treefall along the path of the bow apex indicates that the damage was caused by an enhanced area of straight line, outflow winds.
Severe thunderstorm winds caused multiple trees and wires down in Antrim. A brush fire was also started due to the downed wires.
Severe Thunderstorm winds caused multiple trees and wires down on Weston Hill Road in Mount Vernon.
House struck by lightning and is on fire.
Severe thunderstorm winds downed trees near Spaulding High School in Rochester.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in New Hampshire in 2020Every state in 2020This day in weather historyWarnings in New Hampshire, May 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 896485, 896486, 896487, 896488, 896489, 896490, 896491, 896492, 896495, 896779, 896496, 896497, 896702, 896499, 896498, 896781, 896500.