A west to east oriented line of thunderstorms evolved north of ON-401 through the afternoon hours on August 7. This line eventually evolved into a bit of a bowing segment as it took on a more northeast to southwest orientation during the evening hours while crossing the St.
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The episode as NWS BUF wrote it up.
A west to east oriented line of thunderstorms evolved north of ON-401 through the afternoon hours on August 7. This line eventually evolved into a bit of a bowing segment as it took on a more northeast to southwest orientation during the evening hours while crossing the St. Lawrence Valley. This resulted in downed trees on Grindstone Island.
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 Buffalo, NY wrote its last area forecast discussion before the first event at Aug 7, 1:54 PM EST, 2 hours 51 minutes earlier.
Area Forecast Discussion National Weather Service Buffalo NY 254 PM EDT Sat Aug 7 2021 .SYNOPSIS... A weak trough of low pressure will slowly cross the area through the rest of the weekend, bringing a chance for scattered showers and thunderstorms mainly during the afternoons and evenings. Temperatures and humidity levels will continue to trend upward with above normal temperatures lasting through most of next week. && .NEAR TERM /THROUGH SUNDAY/... A broad upper level trough over the Ohio River Valley will continue to flatten as it slowly drifts towards our area through the weekend. Diurnal instability combined with the increased synoptic forcing is allowing for some scattered convection this afternoon... Primarily along and inland of lake breeze boundaries and across the higher terrain in the Southern Tier. Lake shadows northeast of the Lakes are helping to minimize shower/storm chances, with more breaks in the cloud cover favored in these areas. Better organized or severe storms will still be unlikely as winds through the layer will be light with 0-6km shear weakening through the day. Stronger convection will be found near the St. Lawrence through this afternoon as a stalled frontal boundary sits just north of the area, though these stronger storms are otherwise expected to remain north of Jefferson County. Although widespread heavy rain is not expected, the weak flow and precipitable water values nudging towards 1.5 inches may result in locally heavy rainfall with any slow moving storms. Coverage will remain scattered in nature, with the majority of the day staying rain-free at any given location. High temperatures will generally top out in the low to mid 80s. Upper trough axis moves into western NY this evening. With weakening lake shadows, this feature may actually bring a slightly better chance for a few showers to areas northeast of Lake Erie. Otherwise, lingering showers and storms will gradually taper off through the early overnight, however with the trough still across the area widely isolated activity can't be ruled out during the second half of the night as well. Overnight lows will only fall back into the mid to upper 60s, some low 60s on the higher terrain. A few showers may linger east of Lake Ontario Sunday morning as the trough axis lies on the eastern periphery of the area. The previously mentioned stalled frontal boundary now draped across Lake Ontario could cause some extra shower/thunderstorm activity in the afternoon, mainly in the North Country. A weak mid-level shortwave tracking into lower Great Lakes along with minor low-level convergence could also result in scattered showers and thunderstorms during the afternoon generally from WNY to the Finger Lakes region. Continued weak environmental shear and instability should keep stronger thunderstorm development at bay. Daytime highs will reach the low to mid 80s, though slowly climbing dewpoints will make it feel a bit more humid. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... Water Vapor imagery this afternoon displays a vorticity maximum in the base of a mid level shortwave trough just to the north of Denver. A second mid level trough is seen over the Ohio Valley. These features will shift eastward, such that Sunday Night and Monday we'll be squeezed between the shortwave trough to our west, and lingering mid level trough along the Atlantic seaboard. This should bring a dry period with increased subsidence over our region. Instability Monday along lake breeze boundaries may bring a spot shower or thunderstorm. It will not be until later Tuesday, this as the mid level trough to our west nears our region that showers and thunderstorms will noticeably increase in coverage area. With the influx of deeper moisture, and lift ahead of the mid level trough showers and thunderstorms will blossom. The wind field is not overly impressive for expansive growth to the storms, but a very moist airmass with PWATS 1.75 inches and greater could lead to drenching downpours. As this mid level trough crosses Lake Ontario Tuesday Night, convection could linger deep into the evening hours, especially east of Lake Ontario. Given the very warm and now muggy airmass a spot shower or thunderstorm will remain possible throughout the night across WNY. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... Hot and humid weather will continue Wednesday and Thursday, with deep moisture in place and subtle shortwaves bringing a chance of mainly afternoon and evening showers and thunderstorms. Weak flow and limited shear will limit the severe weather potential to more localized pulse storms. However, there will be a risk of locally heavy rain and flooding from any slow moving or training storms. The most significant feature in the long term will be the passage of a strong cold front, with 12Z model consensus bringing this through on Friday. This stands the best chance to produce widespread convection, along with more wind shear which could increase the potential for severe weather. This bears watching, but still lots of uncertainty this far off. The front should move east of the area by Saturday, with cooler weather and dry conditions for the start of next weekend. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Scattered showers and thunderstorms this afternoon, mainly from the Southern Tier up thorugh the Finger Lakes region inland of the lake breeze boundaries. Lake shadows northeast of the lakes will minimize shower/storm chances. Otherwise, mainly VFR conditions conditions as weak high pressure continues to depart to the east. Areas that do see rain will likely see low VFR CIGS. However, localized IFR/MVFR (VSBY) conditions will be possible in any stronger showers/storms. Activity will wane overnight with mainly VFR conditions expected through tomorrow morning, although some localized valley fog cannot be ruled out once again tonight, especially if skies at least partially clear. Outlook... Sunday...Mainly VFR. A chance of a few isolated showers and thunderstorms. Monday...VFR. Tuesday through Thursday...Mainly VFR with a chance of afternoon showers and thunderstorms. && .MARINE... Generally light winds and negligible waves of less than 1 foot expected through early next week, with a series of weak systems moving across the area. Winds will remain less than 15 knots through Monday. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && SYNOPSIS...PP NEAR TERM...PP SHORT TERM...Thomas LONG TERM...Apffel AVIATION...PP MARINE...Apffel/JM
Hazardous Weather Outlook National Weather Service Buffalo NY 423 AM EDT Sat Aug 7 2021 NYZ001>008-010>014-019>021-085-080830- Niagara-Orleans-Monroe-Wayne-Northern Cayuga-Oswego-Jefferson-Lewis- Northern Erie-Genesee-Wyoming-Livingston-Ontario-Chautauqua- Cattaraugus-Allegany-Southern Erie- 423 AM EDT Sat Aug 7 2021 This Hazardous Weather Outlook is for western and north central New York. .DAY ONE...Today and tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. This product, along with other watches, warnings, advisories, and statements issued by the National Weather Service office in Buffalo can be found on the internet at http://www.weather.gov/buf LEZ020-040-041-LOZ030-042>045-062>065-SLZ022-024-080830- Upper Niagara River and Buffalo Harbor- Lake Erie nearshore waters from Ripley to Dunkirk- Lake Erie nearshore waters from Dunkirk to Buffalo- Lower Niagara River- Lake Ontario nearshore waters from the Niagara River to Hamlin Beach- Lake Ontario nearshore waters from Hamlin Beach to Sodus Bay- Lake Ontario nearshore waters from Sodus Bay to Mexico Bay- Lake Ontario nearshore waters from Mexico Bay to the Saint Lawrence River- Lake Ontario open waters from the Niagara River to Hamlin Beach- Lake Ontario open waters from Hamlin Beach to Sodus Bay- Lake Ontario open waters from Sodus Bay to Mexico Bay- Lake Ontario open waters from Mexico Bay to the Saint Lawrence River- Saint Lawrence River from Cape Vincent to Ogdensburg- Saint Lawrence River from Ogdensburg to Saint Regis- 423 AM EDT Sat Aug 7 2021 This Hazardous Weather Outlook is for the New York waters of Lake Erie, Lake Ontario, and the Saint Lawrence River. .DAY ONE...Today and tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. This product, along with other watches, warnings, advisories, and statements issued by the National Weather Service office in Buffalo can be found on the internet at http://www.weather.gov/buf JLA
The Ft Drum radar (KTYX), 68 km away, was scanning. The volume nearest the first event began at 21:43 UTC.
1 marine thunderstorm wind. Local standard time, as filed.
Media reported trees were downed on Grindstone Island in the middle of the St. Lawrence River.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in St. Lawrence River in 2021Every state in 2021This day in weather history
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: 965357.