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When a leaf can topple a mighty oak: A deep dive into how Long Island’s weather affects the electrical grid

By Larry Torres, Manager of Emergency Planning, PSEG Long Island

June 1 marked the start of hurricane season, which is a great time to reflect on how weather affects the electrical grid. It’s more complicated than it might seem. Every weather event, whether it’s a hurricane, a wintertime nor’easter, or a heat storm, is a unique combination of factors that can impact electrical equipment in different ways. PSEG Long Island’s Emergency Planning team considers [more than a dozen] of these factors, along with historical outage data from similar, past storms, in order to plan for the appropriate storm response.

Here are some of the most important things decades of experience have taught our dedicated employees about weather and potential system impacts.

Leaves are like tiny sails

Long Island is blessed with tens of thousands of beautiful trees, and the foliage level on these trees is one of the first things we look at when assessing the potential impact of a storm. Each leaf acts like a tiny sail, absorbing the force of the wind and exerting that force on the trunk and root system of the tree. Enough force and the tree comes down, sometimes bringing lines and poles with it. A windstorm that hits in early April, before the trees are in full leaf, will have little effect, while heavy winds in June or July, when the trees are at their peak, may create a large impact. In winter, when deciduous trees are bare, wind, by itself, is not often a major factor in outages.

Wind duration is just as important as wind speed

Once winds exceed 40 mph during seasons when the leaf canopy is present, the potential increases for downed trees that may result in outages. One important thing to remember, though, is that the duration of the high winds can determine the amount of damage. Big trees that can sustain five minutes of 40 mph winds will not necessarily be able to stand eight or 12 hours of 40 mph winds.

Rain isn’t a big deal — until it is

Rain, by itself, may cause some street flooding, but very few areas on Long Island and the Rockaways actually suffer from overbank flooding, and PSEG Long Island’s flood-vulnerable substations have all had key equipment elevated to prevent flood damage. Water tends to seep into the ground and down into the water table quickly. Rain becomes a factor after an extended rainfall, when the ground is saturated. If high winds occur during this condition, the soil may be too soft to keep tree roots in place, resulting in damage.

If it’s easy to build a snowman with, it’s hard on the lines

Dry, fluffy snow is not a threat to the electric transmission and distribution systems. Wet snow, on the other hand, tends to stick to large trees, weighing down branches until they snap, sometimes landing on lines and causing damage.  Wet snow may have the same effect on electrical lines, poles and other equipment, making them heavier and creating more surface area for winds to act upon.

In heat storms, it’s almost as much about the lines as it is about generation

On a macro level, the challenge created by periods of extreme heat is ensuring there is sufficient electric generation capacity to handle “peak demand” levels. We prepare for this with power purchase agreements that factor in historical trends. On a micro level, the challenge is mostly predictable. We know that peak demand occurs in the late afternoon when people return home and turn up their air conditioners. Sometimes the excess load from extreme heat taxes the equipment.  We monitor the load across the service territory and upgrade the equipment, as needed. We tend to see these effects when the heat persists for several days, in some localized areas where more homes were recently built or where people have rushed out to buy more window-mounted air conditioning units. In these cases, the extreme demand for electricity can cause nearby electrical equipment to operate above rated capacity, which sometimes leads to equipment failure. On high heat days, we plan for possible outages and have additional high voltage workers on the afternoon shifts in case this occurs.

If it’s coming from down south, watch out

Storms that drop out from the Hudson Valley and Connecticut at certain times of the year, particularly during July and August, can do some damage, but they tend not to be as severe as the same size storm coming up directly from the south. Those storms have already been over the water and they’re strong enough to survive the less-hospitable marine environment, so when they hit land, they get even more severe.

‘That thunderstorm didn’t have the toll to cross the bridge’

Long Island’s geographic location offers certain benefits: We’re close to the water, so in the summertime, that afternoon breeze kicks in and brings ocean air to cool us off. That’s why, many times, we’ll see these thunderstorms marching across the mid-Atlantic region, and it looks like we’re going to get hammered. They might even wallop New Jersey and Manhattan, but they’re losing their punch by the time they hit Brooklyn and Queens. The effects of the ocean change the way those thunderstorms are being fed, cutting off their ability to get larger and become more severe. When our storm monitoring shows this pattern, we like to say, “That thunderstorm didn’t have the toll to cross the bridge.”

These are just a few insights that have come from observing local storms, season after season. It’s far from a comprehensive list, but it illustrates how wildly different weather can be from one storm to the next. We draw upon this knowledge of past Long Island weather events to upgrade the system in the hardest hit areas to prepare for future extreme weather events.

And while weather forecasting is not an exact science, we draw upon that same deep, earned knowledge of past weather events to augment the predictive meteorology, influencing what time of day we bring extra lineworkers on shift, where we stage personnel and replacement materials, when to request mutual aid from off-Island, and many more decisions that contribute to an effective storm restoration.

This hurricane season, I hope you and your family stay safe. We will be watching the skies and considering everything nature has taught us in order to bring you the excellent service you deserve.

For more information on storm preparation, and outage information visit:

PSEG Long Island

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