John Homenuk

NWS confirms derecho in New England on October 7

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The National Weather Service has confirmed that a derecho occurred in New England on October 7th, 2020. More than 200 damaging wind reports were received from New York to Massachusetts. The event was officially classified as a derecho after re-analysis confirmed a 320 mile long damage swath and multiple 75+mph wind gusts.

What is a derecho?

NOAA officially defines a derecho (pronounced “deh-REY-cho”) as “a widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms.” They occur most frequently in the summer months, especially in the Midwest where the combination of atmospheric instability and wind shear can lead to fast moving lines of storms. The most recent derecho to make headlines occurred in Iowa this summer, where billions of dollars in damage occurred.

Derechos explained. Source: thetandd.com

Not every line or complex of storms is classified as a derecho. To make things more confusing, the official classification of a derecho is often misinterpreted and poorly reported. NOAA’s official derecho classification requires both of the following to occur:

  1. A damage swath of at least 250 miles
  2. Multiple wind gusts over 60mph throughout the extent of the damage swath

The high-end severe weather event on October 7th, 2020 met both of these criteria. With a path length of 320 miles, widespread damage reports, and multiple wind gusts over 70mph the event easily meets derecho criteria. In fact, it was the most impressive severe thunderstorm event of the year to date in New England.

Derecho’s are uncommon, but not unheard of in the Northeast United States. In June, a derecho impacted parts of Pennsylvania and New Jersey. In 2018, another derecho impacted the Northern Mid Atlantic. A derecho roared from the Ohio Valley through Washington, DC in 2012. For historians or old folks like myself, you’ll remember the Labor Day Derecho from 1998.

Nevertheless, the event on October 7th, 2020 was impressive. Wind gusts to 70mph were observed in parts of New York State, Connecticut and Massachusetts. Perhaps most impressive of all is the fact that the derecho occurred “out of season”. How did such a powerful line of thunderstorms develop in October?

Technical breakdown: How the derecho happened

A few days prior to the event, it became apparent that an anomalous storm system would impact New England. Forecast models were in good agreement that a strong low pressure system would develop in Eastern Canada. More notably, they were also suggesting a powerful mid level jet streak would surge into the Northeast States.

The morning of the event, the NAM model suggested that a 100+kt jet streak would move through New England during the afternoon hours. The powerful winds in the mid levels of the atmosphere were supportive of the potential for strong wind gusts. The downward transfer of momentum could be enhanced by any thunderstorms that formed.

Parameters in place the day of the derecho suggested the potential for strong, damaging winds.

By the late morning hours, a warm front began to lift northward through the Capital Region of New York and towards Vermont. South of this front, atmospheric moisture and instability began to increase. As a disturbance approached the area from the west, the environment in place was characterized by weak instability (CAPE values 250-500j/kg) and high shear (100+kt mid level jet streak).

The presence of three key ingredients for a severe thunderstorm event would occur by the early afternoon:

  1. Lift to help develop storms (via the approaching mid level disturbance)
  2. Instability (weak, but sufficient for storm organization)
  3. Wind shear (very strong mid level jet streak)

Thunderstorms quickly developed in Western New York and began to move quickly eastward. The environment ahead of them remained supportive of storm organization and maintenance. These storms began to mix down the very strong winds which were present a few thousand feet above the surface, and strong wind gust reports began flowing in.

By the mid-afternoon hours, the complex of storms began shifting quickly eastward into New York State, reaching the borders of Vermont, Connecticut and Massachusetts. Multiple 70+mph wind gusts occurred. Albany International Airport reported a wind gust to 69mph.

By evening, the storms continued their trek towards the New England coasts. Gusts over 60mph were still occurring as the storms picked up momentum. Eventually, the complex of storms would clear the coast and head into the waters of the Atlantic.

Assessing the damage

By the time all was said and done, the derecho left a damage swath longer than 300 miles. Multiple wind gusts reached higher than 70 miles per hour. Two tornadoes were confirmed. By all measures, it was an extremely impressive event and likely the most impactful severe thunderstorm event in New England this year.

The Storm Prediction Center received well over 200 reports of damaging wind gusts. Mapping out those reports, we can clearly visualize the path of the derecho beginning in Western New York and ending on the coast of New England.

While not unheard of, a derecho occurring in New England during the month of October is rare. It speaks to the dynamics of this impressive storm system, and serves as a nice reminder that severe weather events can occur at any time of the year if the dynamic setup and atmospheric ingredients allow.

John Homenuk

Severe storm leaves path of damage from PA through Long Island

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A complex of severe thunderstorms tracked from Northeast Pennsylvania into New York City on Thursday evening, producing widespread wind damage. The same complex of storms survived all the way to Montauk, almost 200 miles in total length, while still producing widespread damaging winds.

The storms formed in Northeast Pennsylvania during the middle afternoon hours on Wednesday, and quickly began shifting east/southeast toward New Jersey. The atmosphere ahead of the storms was moderately unstable. More notable was the presence of sufficient wind shear – this wind shear helps to keep strong thunderstorms organized and can also transport strong winds down to the surface.

By the early to mid evening hours, the very same storm complex was now pushing through New Jersey. Wind damage reports became more frequent, and as the storm moved through the NYC Metro Area it produced 58mph wind gusts in Tribeca and the Financial District.

The same complex of storms then tracked eastward through Queens and Brooklyn, while maintaining strength. While instability was lower in these areas, ample wind shear and a strengthening low level jet (winds in the lower levels of the atmosphere) helped it maintain intensity.


Over Long Island, the combination of the mentioned instability and strengthening low level jet stream helped the storm to maintain intensity, and also aided in downward transport of winds. This resulted in widespread wind damage reports across Nassau and Suffolk counties throughout the evening.

The storm caused a wall collapse and widespread tree damage in the area from East Farmingdale through Ronkonkoma including Islip and Brentwood. As of this morning, over 20,000 residents remained without power – likely from trees falling on power lines.

While not unheard of, a complex of storms moving from Northeast PA through the NYC Metro and all the way to Montauk is rare. The swath of wind damage reports with this single storm is quite impressive – arguably the most impressive of the summer so far.

Technical breakdown of atmospheric conditions

This storm existed in an environment that was, at best, moderately favorable for severe weather. Instability was present but not extreme (around 1000j/kg of surface based cape). Wind shear was impressive (40 knots of mid level shear for storm organization). Low level wind fields were not overly favorable during the morning but became more favorable by evening. In the end, the storm took full advantage of its environment, riding along a gradient of favorable conditions well into the early evening.

Much of our region was placed within the right entrance region of an impressive jet stream on Thursday, which helped to enhance vertical motion during the evening. But more notable was likely the gradient of instability and the development of a stronger low level jet. This helped to enhance low level winds significantly and likely contributed to the uptick in wind damage reports on Long Island.

The low level jet is known to kick up after sunset (nocturnal low level jet), and in the Midwest and Plains states can help fuel evening outbreaks of tornadoes. In our area, the increasing low level jet helped foster an enhanced threat for wind damage – essentially giving the storm some extra “juice” to continue its trek eastward all the way to Montauk.

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John Homenuk

NWS confirms microburst in Union County on Tuesday

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The National Weather Service in Upton, NY has confirmed that straight-line wind damage, originating from a microburst, was the cause of significant but localized damage in Union County, NJ on Tuesday Night. A severe thunderstorm moving through the Watchung Mountains and into Union and Essex counties showed signs of rotation and strong winds on terminal doppler radar, but no evidence of a tornado has been found as of yet.

The line of showers and thunderstorms formed over parts of New Jersey on Tuesday evening in association with a frontal boundary, which was approaching the area from the west. A localized area of favorable instability and wind shear allowed the storms to briefly strengthen, despite the overall weakening trend which was being observed as storms were approaching the more stable air near the coastal plain.

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John Homenuk

3 months later, Blizzard of ’16 becomes largest in NYC history

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Three months after the last snowflake from the prolific Blizzard of 2016 fell, it has ascended to become the #1 snowfall in New York City’s recorded history. The storm passes February 12th, 2006 which was the previous record holder. The announcement comes after weather enthusiasts and professionals were left disappointed by a 26.8″ measurement which brought the snowfall total just 0.1″ short of the February 2006 record. But a new publication from the National Weather Service says the total will be changed to a whopping 27.5″, adjusting the total well higher and making the Blizzard of 2016 the largest in the city’s history. 

It wasn’t additional snow that fell a few minutes after a measurement, or a last minute snow band that was added on to the snowfall total. It was, apparently a “miscommunication between the NWS WFO and Central Park Conservancy”. Or, more likely, a disturbing lack of communication between the two offices at all. The report also says that the Central Park Conservancy, which measures snowfall officially for Central Park, provided a worksheet with snowfall totals which was deemed “accurate”. The official worksheet recorded 0.2″ of snow on January 22nd, 27.3″ of snow on January 23rd, and a trace of snow on January 24th. How a snowfall total of 26.8″ was reported on the night of January 23rd, then, becomes a real head scratcher.

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