An upper level trough axis moved into western New York during the evening hours. This feature moved into a modestly unstable environment fairly unimpressive precipitable water values of only just slightly over one inch.
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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 BUF wrote it up.
An upper level trough axis moved into western New York during the evening hours. This feature moved into a modestly unstable environment fairly unimpressive precipitable water values of only just slightly over one inch. Further, low level moisture transport was unimpressive. A cluster of storms congealed around northern Livingston and southern Monroe counties. Weak flow and some back-building allowed for torrential rain over the area. A few spots had three inches per hour rainfall rates that lasted up to 55 minutes. This resulted in roads closed with water flowing over them in Monroe County.
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, 4:52 PM EST, 1 hour 10 minutes earlier.
Area Forecast Discussion National Weather Service Buffalo NY 552 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/... 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. A stalled frontal boundary draped across Lake Ontario could cause some extra shower/thunderstorm activity Sunday 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 SATURDAY/... 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 /22Z SATURDAY THROUGH THURSDAY/... VFR weather will dominate the period...although scattered convection early this evening and again on Sunday will support isolated MVFR conditions. There will also be MVFR vsbys in fog across parts of the Srn Tier late tonight. Outlook... 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...RSH MARINE...Apffel/JM/PP
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
Special Weather Statement
National Weather Service Buffalo NY
603 PM EDT Sat Aug 7 2021
NYZ003-004-013-014-072245-
Ontario NY-Livingston NY-Wayne NY-Monroe NY-
603 PM EDT Sat Aug 7 2021
...A strong thunderstorm will impact portions of southwestern Wayne,
northeastern Livingston, southeastern Monroe and northwestern Ontario
Counties through 645 PM EDT...
At 602 PM EDT, Doppler radar was tracking a strong thunderstorm near
Henrietta, or near Chili, moving northeast at 25 mph.
HAZARD...Winds in excess of 40 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
East Rochester, Webster, Fairport, Brighton, Ontario, Henrietta,
Penfield, Marion, Palmyra, Avon, Victor, Honeoye Falls, Lima,
Scottsville, Farmington, Walworth, Mendon and Rush.
This includes the following highways...
Interstate 390 between exits 9 and 12.
Interstate 90 between exits 46 and 43.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4286 7773 4301 7781 4328 7745 4318 7717
4296 7720
TIME...MOT...LOC 2202Z 235DEG 22KT 4303 7766
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH
ThomasThe Buffalo radar (KBUF), 78 km away, was scanning. The volume nearest the first event began at 23:00 UTC.
1 flash flood. Local standard time, as filed.
Water was reported to be flowing over the roadway near South Road and Bowerman Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in New York in 2021Every state in 2021This day in weather historyWarnings in New York, August 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: 982714.