A mid-level disturbance moving north along the periphery of a upper level area of high pressure in a very warm, unstable airmass led to numerous showers and thunderstorms to develop in the afternoon and evening hours of July 13th. Two thunderstorms brought isolated wind damage to St.
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The episode as NWS BTV wrote it up.
A mid-level disturbance moving north along the periphery of a upper level area of high pressure in a very warm, unstable airmass led to numerous showers and thunderstorms to develop in the afternoon and evening hours of July 13th. Two thunderstorms brought isolated wind damage to St. Lawrence county in the form of downed branches and trees.
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 13, 2:35 PM EST, 4 hours earlier.
Area Forecast Discussion National Weather Service Burlington VT 335 PM EDT Tue Jul 13 2021 .SYNOPSIS... Low clouds and humid conditions will prevail across much of the North Country tonight and Wednesday. A slow-moving upper trough across the central Great Lakes region will bring scattered showers and thunderstorms into the St. Lawrence Valley this evening, with another round of showers and thunderstorms expected across much of the North Country for Wednesday afternoon. A few stronger thunderstorms will produce heavy rain and gusty winds in localized areas. Increasing sunshine will allow for very warm conditions Thursday and Friday, with some valley high temperatures approaching 90 degrees. Another frontal system approaching from the west will interact with the hot and humid air mass to bring another round of showers and thunderstorms late Friday into Friday night. && .NEAR TERM /THROUGH WEDNESDAY NIGHT/... As of 333 PM EDT Tuesday...Tale of two air masses across the North Country for this evening and tonight. Surface ridge along the Maine coast continues to bring recycled marine modified air westward into central/eastern VT and the Champlain Valley. Anticipate low clouds and perhaps some patchy fog overnight given humid conditions, but only a 20-40% chance of showers from the Champlain Valley eastward across VT. Low temperatures generally in the low-mid 60s tonight east of the Green Mtns, and in the upper 60s for the Champlain Valley. Meanwhile, west of the marine modified air mass, seeing surface- based instability axis across w-central NY (SBCAPE values 2500-3500 J/kg per SPC mesoanalysis) extending nwd into srn St. Lawrence County this afternoon. Precipitable water values are near 1.9" east of Lake Ontario with surface dewpoints in the lower 70s. Convective storms thus far have generally not been associated with elevated reflectivity cores across St. Lawrence County, but environment supports heavy rainfall with high PW values and freezing levels near 14 kft. Mid-level lapse rates around 6C/km are not particularly favorable for severe storms into St. Lawrence county, but can't rule out locally gusty winds with a stronger core or two thru early this evening. KMSS has already seen 0.7" of observed rainfall, and localized radar estimates near 1" exist across swrn St. Lawrence County. With continued moist S-SW low-level flow, we'll need to monitor for possible training thunderstorms and additional moderate to heavy rainfall through this evening. Overall coverage and intensity of storms should decrease after sunset. The 6hr flash flood guidance across St. Lawrence and Franklin Counties is generally 2.5 to 3", so overall likelihood of any flash flooding remains low. Overnight lows across nrn NY generally in the mid-upper 60s tonight. For Wednesday, mid-level ridge axis shifts to our east, allowing mid- level trough and cyclonic flow aloft to move ewd into nrn NY and VT during the daylight hours. The 12Z HREF members generally show convective development across the nrn Adirondacks, with a better chance of thunderstorms moving eastward across the Champlain Valley and central/ern VT during the mid-late afternoon hours. High PBL dewpoints in the upper 60s to lower 70s largely drive SBCAPEs of 1000-2000 J/kg, but once again with marginal mid-level lapse rates. Appears heavy rainfall will be the primary threat with any t-storms tomorrow, but did include gusty wind wording. We remain in a Marginal risk of severe storms based on the updated SPC SWODY2. Some partial sunshine results in highs in the upper 70s to lower 80s areawide for Wednesday. Appears any lingering showers and thunderstorms exit east of the CT River valley later Wednesday evening. Not much change in air mass, and partial clearing should result in favorable conditions for fog formation in the favored valleys Wednesday night. Lows mainly in the mid 60s. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 333 PM EDT Tuesday...On Thursday a weak ridge of high pressure and a pocket of drier air will be over the area much of the day, so expecting sunshine and warm temperatures. With 850 temps getting close to +17 could see highs in the 80s and pushing 90 at BTV. A relatively fast WSW-ENE flow aloft will bring more moisture/clouds gradually late in the day into Thursday night across the north though timing could be a challenge. This is all south of a quasi- stationary frontal boundary stretching from the Great Lakes across southern Canada. With precipitable climbing above 1.50" have an increasing probability of showers Thursday night. There will also be a strengthening pressure gradient to keep south winds blowing and with clouds around we are expecting lows in the mid 60s to lower 70s Thursday night. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 333 PM EDT Tuesday...The WSW-ENE stream of moisture high precipitable water continues Friday into the weekend with a front oscillating through the area. The highest probabilities of showers and thunderstorms will be in the afternoon and evening, but really can't be ruled out at any time. There are some model differences in location of the front and strength of an upper level trof that moves into the region by Sunday, but any way you slice it, it looks like a daily threat of showers and thunderstorms through at least Sunday. The flow aloft turns around more northwesterly then northerly next week as a large ridge pushes north into central Canada. There will be a gradual trend toward drier but warm summery weather. Still can't rule out a shower or thunderstorm but the deep moisture will be pushed off to our south. Temperatures should start out warm Friday especially from the Champlain Valley east and south where highs again in the 80s perhaps pushing 90. Currently going with the front over the region Sat into Sun with highs mainly in the 70s, then rising back to our seasonal norms in the upper 70s to lower 80s next week as the airmass dries out and more sun expected with slightly lower dewpoints. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Through 18Z Wednesday...Thunderstorm potential exists through this evening at MSS/SLK closer to instability axis across w-central NY. May see brief heavy rainfall and brief IFR conditions with any thunderstorms. Further east, seeing abundant ceilings between 2500-4000 ft associated with maritime modified air mass with HIR TRRN OBSCD. Will see VFR conditions trending MVFR overnight for most of the TAF sites. An approaching trough on Wednesday will bring developing showers and thunderstorms, with better potential for scattered t-storms to cross into the Champlain Valley and central/eastern VT during the mid-late afternoon hours. Winds will generally remain south at 10-15kt, except locally SE at KRUT with localized gap flow through the Green Mtns. Outlook... Wednesday Night: VFR. Slight chance SHRA. Thursday: VFR. NO SIG WX. Thursday Night: VFR. Chance SHRA. Friday: VFR. Chance SHRA, Chance TSRA. Friday Night: Mainly VFR, with areas IFR possible. Likely TSRA, Chance SHRA. Saturday: Mainly MVFR, with areas IFR possible. Chance SHRA. Saturday Night: Mainly VFR, with local IFR possible. Chance SHRA. Sunday: MVFR. Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && SYNOPSIS...Banacos NEAR TERM...Banacos SHORT TERM...Sisson LONG TERM...Sisson AVIATION...Banacos
Hazardous Weather Outlook National Weather Service Burlington VT 339 AM EDT Tue Jul 13 2021 NYZ026>031-034-035-087-VTZ001>012-016>019-140745- 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- 339 AM EDT Tue Jul 13 2021 This Hazardous Weather Outlook is for northern New York, central Vermont, northeast Vermont, northwest Vermont and southern Vermont. .DAY ONE...Today and tonight. There will be the potential for strong to locally severe storms this afternoon. Gusty winds and heavy rain will be the main threats with any of the thunderstorms. The most likely area for any stronger storms will be from the northern Adirondacks westward through the St Lawrence Valley. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. On Wednesday there will be the potential for strong to severe storms, especially during the afternoon and evening hours. Gusty winds and heavy downpours will be the main threats with any of the thunderstorms. At this time the most likely area for any stronger storms will be from the northern Adirondacks eastward across the Champlain Valley and remainder of Vermont. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
Special Weather Statement National Weather Service Burlington VT 506 PM EDT Tue Jul 13 2021 NYZ087-132200- Southwestern St. Lawrence- 506 PM EDT Tue Jul 13 2021 ...A STRONG THUNDERSTORM WILL AFFECT SOUTHWESTERN ST. LAWRENCE COUNTY... At 505 PM EDT, a strong thunderstorm was located near Gouverneur, moving northeast at 25 mph. Winds in excess of 40 mph are possible with this storm. Locations impacted include... Gouverneur, Canton, De Kalb, Rensselaer Falls, Heuvelton, Richville, Hermon, De Peyster, Rossie, Pyrites, North Russell, De Kalb Junction, North Gouverneur, West Fowler and East De Kalb. Torrential rainfall is also occurring with this storm, and may cause localized flooding. Do not drive your vehicle through flooded roadways. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. LAT...LON 4475 7541 4453 7501 4423 7547 4433 7570 TIME...MOT...LOC 2105Z 221DEG 20KT 4431 7555 SLW
Special Weather Statement National Weather Service Burlington VT 603 PM EDT Tue Jul 13 2021 NYZ026-029-087-132330- Northern St. Lawrence-Southeastern St. Lawrence- Southwestern St. Lawrence- Including the cities of Massena, Star Lake, Ogdensburg, Potsdam, and Gouverneur 603 PM EDT Tue Jul 13 2021 ...POTENTIALLY STRONG TO SEVERE THUNDERSTORMS WILL SOUTHERN SAINT LAWRECE COUNTY AROUND 7 PM... At 600 PM EDT, a cluster of strong to severe thunderstorms was located in the southern Tug Hill Plateau was moving north at 35 mph. These storm should approach Southern Saint Lawrence county around 7 pm. These storms may have winds in excess of 40 to 50 mph along with lightning and very torrential rains. Please plan on the possibility of strong storms this evening and closely monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. LAT...LON 4475 7541 4453 7501 4423 7547 4433 7570 TIME...MOT...LOC 2105Z 221DEG 20KT 4431 7555 slw
Special Weather Statement
National Weather Service Burlington VT
622 PM EDT Tue Jul 13 2021
NYZ026-027-029-030-087-132315-
Northern St. Lawrence-Northern Franklin-Southeastern St.
Lawrence-Southern Franklin-Southwestern St. Lawrence-
622 PM EDT Tue Jul 13 2021
...SHOWERS WITH HEAVY RAIN MAY LEAD TO LOCALIZED PROBLEMS THROUGH 7
PM IN NORTHEAST ST. LAWRENCE AND NORTHWEST FRANKLIN COUNTIES...
At 615 pm...Showers and an embedded thunderstorm from time to time
has brought very heavy rainfall to northeast St. Lawrence and
northwest Franklin counties.
Radar estimated rainfall of 1.5 to 2 inches has fallen with rainfall
rates over an inch per hour at times. These rainfall rates will
likely cause some poor driange flooding, ponding of water on roads
and perhaps minor gravel shoulder washouts. The heaviest activity
should exit by 7 pm.
Do not drive your vehicle through flooded roadways. If camping near
a stream, seek higher ground and monitie conditions.
LAT...LON 4499 7434 4499 7415 4464 7470 4477 7487
4500 7444
TIME...MOT...LOC 2215Z 229DEG 32KT 4500 7436
SLWSpecial Weather Statement
National Weather Service Burlington VT
649 PM EDT Tue Jul 13 2021
NYZ026-087-132345-
Northern St. Lawrence-Southwestern St. Lawrence-
649 PM EDT Tue Jul 13 2021
...A STRONG THUNDERSTORM WILL AFFECT WEST CENTRAL ST. LAWRENCE
COUNTY...
At 649 PM EDT, a strong thunderstorm was located near Redwood, moving
north at 30 mph.
Winds in excess of 40 mph are possible with this storm.
Locations impacted include...
Ogdensburg, Edwardsville, Hammond, Morristown, Jacques Cartier State
Park, Chippewa Bay, South Hammond, Nelson Corner and North Hammond.
Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.
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.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
LAT...LON 4441 7579 4442 7579 4442 7581 4443 7577
4444 7579 4444 7577 4445 7576 4445 7578
4447 7577 4447 7579 4451 7575 4470 7550
4471 7547 4477 7541 4433 7570 4439 7583
4441 7584
TIME...MOT...LOC 2249Z 201DEG 25KT 4430 7587
SLWThe Ft Drum radar (KTYX), 92 km away, was scanning. The volume nearest the first event began at 23:34 UTC.
4 thunderstorm wind. Local standard time, as filed.
Tree, branches and utility lines downed by thunderstorm winds.
Tree, branches and utility lines downed by thunderstorm winds.
Trees and branches on wires.
Tree, branches and utility lines downed by thunderstorm winds.
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, 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: 959650, 959651, 959653, 959652.