A healthy upper level trough and frontal boundary moved from Ontario into VT during the overnight hours of July 20th. Ahead of this system, a vigorous squall line of thunderstorms that developed in Ontario during the early afternoon hours moved across northern NY from mid-afternoon into the evening hours and evening hours across VT with numerous reports of damaging winds.
Every event with a place to put it. Tap one for its entry below.
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 BTV wrote it up.
A healthy upper level trough and frontal boundary moved from Ontario into VT during the overnight hours of July 20th. Ahead of this system, a vigorous squall line of thunderstorms that developed in Ontario during the early afternoon hours moved across northern NY from mid-afternoon into the evening hours and evening hours across VT with numerous reports of damaging winds.
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 Burlington, VT wrote its last area forecast discussion before the first event at Jul 20, 5:31 PM EST, 24 minutes earlier.
Area Forecast Discussion National Weather Service Burlington VT 631 PM EDT Tue Jul 20 2021 .SYNOPSIS... Strong to severe thunderstorms capable of producing damaging wind, large hail, heavy rain, and frequent lightning will move from west to east this evening, beginning in the Saint Lawrence Valley. Storms will reach Vermont between 7 and 8 PM and continue through midnight tonight. Scattered showers and a few rumbles of thunder will continue overnight into Wednesday morning but improving conditions are expected for the second half of Wednesday. Quieter weather is expected for the second half of the work weak with temperatures remaining a few degrees below normal values. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 631 PM EDT Tuesday...Quick update to time hourly PoPs in close relation to ongoing QLCS moving across the area early this evening. Minor tweaks also to hourly temperatures, dewpoints and sky cover also. Have a good evening. Prior discussion... A Severe Thunderstorm Watch is in effect for all of northern New York and all of Vermont until 11 PM tonight. Radar currently shows a strong line of thunderstorms quickly advancing into the Saint Lawrence Valley which is producing damaging winds, heavy rainfall, and frequent lightning. These storms may also produce large hail. Heavy rain and strong to severe thunderstorms will continue to track eastward through the evening, reaching Vermont between 7 to 8 PM. Storms are then expected to die down between 11 PM and midnight. The greatest potential for severe storms exists across northern New York with lesser chances across the Northeast Kingdom where lingering clouds have limited destabilization. Still, scattered strong to severe storms are still possible across Vermont late this evening as a cold front pushes across the region. Chances for thunder will wane after midnight, though rain showers are likely to continue across Vermont overnight and into Wednesday as an upper-level trough moves. The aforementioned cold front will continue its southeastward trek, though rather slowly. A drastic change in temperatures is not expected in the wake of the front, given the ongoing rain showers and cloudiness through the overnight and early morning hours. Lows will be in the upper 50s to low 60s. Wednesday will see a continuation of rain showers, especially across Vermont with the upper trough slow to depart eastward. A slight chance for thunderstorms exists across southern Vermont Wednesday afternoon, ahead of a secondary cold front. However, very little instability will be available given the lingering rain and clouds across this area early on Wednesday. High temperatures on Wednesday will be in the upper 60s to low 70s. Rain will come to and end late Wednesday night as weak ridging moves into the region. Cloud cover will decrease as well and overnight fog development is likely. Overnight low temperatures Wednesday into Thursday will be in the 50s. && .SHORT TERM /THURSDAY THROUGH FRIDAY/... As of 349 PM EDT Tuesday...Mainly quiet weather expected for Thursday into Thursday night. We remain on the back side of a departing upper trough, but surface high pressure will keep lower levels dry. There could plausibly be a widely scattered shower or two across far northeastern VT on Thursday, but most areas will remain dry. On Friday another weak feature will cross the area embedded within the northwesterly flow aloft. This could spark a slightly better chance for a few showers across the northeastern half of the forecast area. Temperatures remain seasonal during these periods with highs mainly in the 70s and lows in the 50s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 349 PM EDT Tuesday...Not much change to overall thinking for the extended portions of the forecast from next weekend onward into early next week. The Northeast will remain in west to northwest flow aloft on the eastern side of a pronounced western US ridge and features embedded within that flow will be our main weather producers. Decent consensus remains among model solutions this morning showing the most pronounced of those features will affect our area beginning later Saturday night, and then area wide Sunday into Sunday night with scattered to numerous showers and perhaps a few storms. Drier wx then looks to return by later Monday into next Tuesday. Temperatures remain largely seasonal with daily highs from the mid 70s to lower 80s and overnight lows in the 50s to lower 60s. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Through 18Z Wednesday...We continue to see reduced visibilities at most terminals with 4-6SM visibilities due to haze/smoke. The thinking is these conditions will continue, if not deteriorate, through the afternoon hours. Showers and thunderstorms this afternoon may actually help to increase visibilities as the rain helps to remove the smoke particles from the environment with conditions improving after 00Z. We could still see some strong to locally severe thunderstorms this afternoon which could create brief strong wind gusts in excess of 25 knots and IFR visibilities in heavy rain. Thunderstorms will track from west to east between 21z and 03z, with rain showers continuing through the TAF period. After 00z, a trend towards IFR cigs and MVFR/IFR visibility is expected at nearly all terminals with low stratus/fog developing across much of the area. Conditions will improve between 12z and 15z. Outlook... Wednesday Night: VFR. NO SIG WX. Thursday: VFR. NO SIG WX. Thursday Night: VFR. Slight chance SHRA. Friday: VFR. Chance SHRA. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. Chance SHRA. Sunday: Mainly MVFR, with areas VFR possible. Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && SYNOPSIS...Clay NEAR TERM...Hammond/JMG SHORT TERM...JMG LONG TERM...JMG AVIATION...Clay/Hammond
Hazardous Weather Outlook National Weather Service Burlington VT 411 AM EDT Tue Jul 20 2021 NYZ026>031-034-035-087-VTZ001>012-016>019-210815- Northern St. Lawrence-Northern Franklin-Eastern Clinton- Southeastern St. Lawrence-Southern Franklin-Western Clinton- Western Essex-Eastern Essex-Southwestern St. Lawrence-Grand Isle- Western Franklin-Orleans-Essex-Western Chittenden-Lamoille-Caledonia- Washington-Western Addison-Orange-Western Rutland-Windsor- Eastern Franklin-Eastern Chittenden-Eastern Addison-Eastern Rutland- 411 AM EDT Tue Jul 20 2021 This Hazardous Weather Outlook is for northern New York, central Vermont, northeast Vermont, northwest Vermont and southern Vermont. .DAY ONE...Today and tonight. Scattered showers and thunderstorms will be possible this afternoon and evening. Some of these thunderstorms could be strong to locally severe and produce brief heavy rainfall, frequent cloud to ground lightning and wind gusts of 40 mph or higher. In addition to the thunderstorm potential today, we will see reduced visibilities due to smoke and haze from wildfires out west. This could also lead to decreased air quality. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Hazardous weather is not expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BURLINGTON VT
541 PM EDT TUE JUL 20 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0505 PM TSTM WND DMG POTSDAM 44.67N 74.99W
07/20/2021 ST. LAWRENCE NY PUBLIC
NUMEROUS TREES DOWN AND PEA-SIZED HAIL.
&&
EVENT NUMBER BTV2101059
HAMMONDPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BURLINGTON VT
553 PM EDT TUE JUL 20 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0522 PM HAIL 2 SW ST. REGIS 44.98N 74.69W
07/20/2021 E1.00 INCH FRANKLIN NY PUBLIC
QUARTER-SIZED HAIL.
&&
EVENT NUMBER BTV2101060
HAMMONDPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BURLINGTON VT
555 PM EDT TUE JUL 20 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0500 PM TSTM WND DMG 1 WSW SOUTH COLTON 44.50N 74.91W
07/20/2021 ST. LAWRENCE NY TRAINED SPOTTER
ONE LARGE TREE AND NUMEROUS SMALL TREES DOWN.
&&
EVENT NUMBER BTV2101061
HAMMONDPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BURLINGTON VT
602 PM EDT TUE JUL 20 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0435 PM TSTM WND DMG HEUVELTON 44.62N 75.40W
07/20/2021 ST. LAWRENCE NY PUBLIC
TREES DOWN.
&&
EVENT NUMBER BTV2101062
HAMMONDPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BURLINGTON VT
623 PM EDT TUE JUL 20 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0448 PM TSTM WND DMG CANTON 44.60N 75.17W
07/20/2021 ST. LAWRENCE NY BROADCAST MEDIA
LARGE TREE DOWN.
&&
EVENT NUMBER BTV2101063
PSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BURLINGTON VT
635 PM EDT TUE JUL 20 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0625 PM TSTM WND DMG AUSABLE FORKS 44.43N 73.68W
07/20/2021 ESSEX NY 911 CALL CENTER
ARCING POWER LINES DOWN.
&&
EVENT NUMBER BTV2101064
PSThe Burlington radar (KCXX), 53 km away, was scanning. The volume nearest the first event began at 22:53 UTC.
14 thunderstorm wind, 1 flash flood. Local standard time, as filed.
Tree down on power lines on west shore road as well as other tree damage.
Tree and branches down on Hardscrabble and adjacent roads.
Tree down on car at the intersection of Marble and St. Paul streets. No injuries. Other scattered tree damage within the city.
Several reports of trees down in South Burlington, including White Street ,Airport road and Interstate 89 between Exits 12 and 13.
Many branches and a few trees downed by winds.
A few large trees downed by winds in town.
Numerous trees and utility lines downed by thunderstorm winds on Poker Hill road.
Several trees and utility lines downed by thunderstorm winds.
Several trees and power lines across roads.
Several trees and utility lines downed by thunderstorm winds on several roads. Also, some flooding.
Butternut Hill Road washed out gravel road due to heavy rainfall.
Several trees downed by thunderstorm winds.
Many trees uprooted in a straight line in the New Boston area.
Several trees downed by thunderstorm winds.
A couple of Poplar trees down across utility lines.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Vermont in 2021Every state in 2021This day in weather historyWarnings in Vermont, July 2021
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: 962453, 962454, 962458, 962459, 962461, 962462, 962464, 962466, 962467, 962470, 964356, 962472, 962473, 962471, 962474.