Tag Archives: explainer

Omega Blocking Pattern Brings a Stretch of Warm Weather to Northeast

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After a chilly start to April, warm weather has returned to the northeastern US and it is expected to stick around for the next several days. For this, we can thank an atmospheric phenomenon known as blocking, or more specifically in this case, an omega block.

Atmospheric blocking causes the stagnation of a particular type of weather pattern. In other words, the same type of weather, be it hot, cold, wet or dry, will remain in place over a specific region for an extended period of time.

Flowing from west to east, the jet stream moves weather systems across the country and marks the boundary of cold air to its north and warm air to its south. When flowing in a zonal pattern – a fairly straight line – we generally see seasonal temperatures. But, there are times when it meanders in a more north/south pattern forming large troughs and ridges. When this type of meridional flow develops, warm air can reach farther north than normal and cold air can spill deeper into the south. It also means that weather systems get “blocked” from their typical eastward flow and therefore move more slowly.

The omega block is named after the Greek letter (Ω) that it resembles and is characterized by a high-pressure ridge sandwiched between two low-pressure troughs. Areas under the ridge experience a prolonged period of warm and dry weather, while areas under the troughs see persistent wet and cold conditions.

This current blocking event, centered over the eastern US, is letting the Northeast as well as parts of both the Midwest and West Coast to bask in unseasonable warmth. States in the central plains, on the other hand, are dealing with repetitive rounds of heavy precipitation and the risk of flooding.

Omega Blocking Pattern over US, April 2016. Credit: CBS

Omega Blocking Pattern over US, April 2016. Credit: CBS

Vernal Equinox 2016

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Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially began at 4:30 UTC, which is 12:30 AM Eastern Daylight Time.

Our astronomical seasons are a product of the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. Today, as spring begins, the Earth’s axis is tilted neither toward nor away from the sun. This position distributes the sun’s energy equally between the northern and southern hemispheres.

Since the winter solstice in December, the arc of the sun’s apparent daily passage across the sky has been moving northward and daylight hours have been increasing. Today, the sun appears directly overhead at the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.

As a transitional season, spring is a time when the chill of winter fades away and the warmth of summer gradually returns.  The most noticeable increases in average daily temperature, however, usually lag the equinox by a few weeks.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

What is a Blizzard?

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A blizzard is expected to blast a large part of the northeastern United States, including NYC, this weekend. Different than a typical winter storm, a blizzard is characterized more by its winds than the amount of snow it produces.

According to the NWS,  the three key factors in a blizzard are wind, visibility, and time. More specifically, they are:

  • Wind – Sustained winds or frequent gusts of 35mph or higher.
  • Visibility – Falling and/or blowing snow that reduces visibility to ¼ mile or less.
  • Time – Wind and reduced visibility conditions must prevail for at least 3 hours.

These conditions heighten the risk for power outages and often produce whiteout conditions on roadways, making travel extremely dangerous.  Stay Safe!

Earth’s Perihelion 2016

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The Earth will reach its Perihelion today at 22:49 UTC, which is 5:49 PM Eastern Standard Time. This is the point in the planet’s orbit where it comes closest to the Sun.

This annual event is due to the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path. The exact date of the Perihelion differs from year to year, but it’s usually in early January – winter in the northern hemisphere. The Earth will be furthest from the Sun in July.

While the planet’s distance from the Sun is not responsible for the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, the Earth is 147.1 million kilometers (91.4 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) closer than it will be in early July. This position allows the planet to speed up by about one-kilometer/second. As a result, winter in the northern hemisphere is about five days shorter than summer.

The word, perihelion, is Greek for “near sun”.

Earth's Perihelion and Aphelion. Credit: Time and Date.com

Earth’s Perihelion and Aphelion. Credit: TimeandDate.com

Winter Solstice 2015

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The December solstice – the first day of winter in the northern hemisphere – is upon us. The new season officially begins at 04:48 UTC on December 22nd, which is 11:48 PM EST tonight.

The astronomical seasons are produced by the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. During the winter months, the northern half of the Earth is tilted away from the sun. This position means the northern hemisphere receives the sun’s energy at a less direct angle and brings us our coolest temperatures of the year.

Since the summer solstice in June, the arc of the sun’s apparent daily passage across the sky has been dropping toward the southern horizon and daylight hours have been decreasing. Today, it will reach its southern most position at the Tropic of Capricorn (23.5° south latitude) marking the shortest day of the year. This observable stop is where today’s event takes its name.  Solstice is derived from the Latin words “sol” for sun and “sisto” for stop.

Starting tomorrow, the sun will appear to move northward again and daylight hours will slowly start to increase. Marking this transition from darkness to light, the winter solstice has long been a cause for celebration across many cultures throughout human history.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

UN Climate Change Conference: What the 2°C Goal Means

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The goal of COP 21 – the massive UN Climate Change Conference in Paris – is to limit global warming to 2°C (3.6°F) above pre-industrial levels by reducing greenhouse gas emissions around the world. But why, you may wonder, is 2°C the target and what happens if we pass it?  Below is a short video by Climate Central, a non-profit news organization, that addresses these important questions.

Autumnal Equinox 2015

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Today is the Autumnal Equinox, the first day of fall in the northern hemisphere. The new season officially began at 8:21 UTC, which is 4:21 AM Eastern Daylight Time.

The astronomical seasons are a product of the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. During the autumn months, the Earth’s axis is tilted neither toward nor away from the sun. This position distributes the sun’s energy equally between the northern and southern hemispheres.

Since the summer solstice in June, the arc of the sun’s apparent daily passage across our sky has been moving southward and daylight hours have been decreasing. Today, it crossed the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.

With the sun sitting lower in the sky and daylight hours continuing to shorten, Autumn is a season of falling temperatures.  According to NOAA, the average high temperature in most US cities drops about 10°F between September and October.

Solstices and Equinoxes. Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

Equinox

The Earth’s axis is tilted neither toward nor away from the sun on the Equinox. Image Credit: NASA

Exploring the Urban Heat Island Effect Within City Limits

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During the summer months in New York City, you often hear people talking about plans to escape the city’s heat with trips to the beach or mountains. This is because NYC, like most large cities, is an urban heat island. With miles of paved surfaces that absorb heat, it is generally warmer than surrounding rural areas.

Within city limits, the temperature difference between an asphalt covered street and a nearby park lawn can demonstrate this phenomenon on a smaller scale. Below are some photos of measurements we made around midtown Manhattan at 2:30 PM this afternoon when the air temperature was 95°F.

On the street, the temperature was 122°F in the sun and 101°F in the shade. On the park lawn, only a few feet away, the temperature in the sun was 99°F and a relatively cool 85°F in the shade.  Hands down, the best place to beat the heat – even in the city – is on a grassy surface in the shade.  Stay cool!

Comparing temperatures of surfaces in sun and the shade around midtown Manhattan on July 29th.

Comparing temperatures of surfaces in the sun and the shade around midtown Manhattan on July 29th when the air temperature was 95°F .  Credit: The Weather Gamut.

How Climate Models Work

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Earth’s climate is a complex system with many interacting parts, including the atmosphere, oceans, land surfaces, ice, and the sun. To better understand how it works and to make projections for its future behavior, scientists use computer-based simulations known as climate models.

These models, according to the World Meteorological Organization (WMO), incorporate the physics and chemistry of the climate system’s various components. Using mathematical representations, they aim to answer questions such as when the next El Niño or La Niña event might develop and how the climate will respond to increasing amounts of greenhouse gas concentrations.

Developed from weather forecasting models, climate models look further out in time and involve an extremely large number of calculations. To run, they require very powerful computers. In fact, the WMO says it can take several months to complete a 50-year projection.

Dividing the planet into a three-dimensional grid, a climate model simulates the movement of air, water, and heat energy within each of its grid cells and evaluates interactions between them. All of these processes are based on the laws of physics.  When all the processes from all the grids are linked together over time and space, the model simulates Earth’s climate.

As with weather, there are a number of different climate models in use around the globe. Some, according to the IPCC, perform better than others for particular aspects of the climate system. The variations in predictions that they produce are generally the result of differences in initial conditions, different parameters for interactions between parts of the system, and different estimates of future greenhouse gas emissions. That said, all the climate models included in the IPCC report agree that Earth’s average temperature is rising and expect it to continue to rise in the future.

To see if a climate model will perform well, it is tested against the past. This is a process called Hindcasting. If a model accurately predicts climate trends that have already taken place, it is expected to predict what might happen in the future with a reasonable amount of certainty.  Models can also be refined as new sources of data become available.

Below is a short video by The National Academy of Sciences on the basics of climate modeling. Credit: NAS and YouTube.

Earth’s Aphelion 2015

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The Earth will reach its Aphelion today at 19:41 UTC, which is 3:41 PM Eastern Daylight Time. This is the point in the planet’s orbit where it is farthest from the Sun.

This annual event is a result of the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path. The exact date of the Aphelion differs from year to year, but it’s usually in early July – summer in the northern hemisphere.

While the planet’s distance from the Sun is not responsible for the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, Earth is about 152 million kilometers (94 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) further than during the perihelion in early January. That means the planet will move more slowly along its orbital path than at any other time of the year. As a result, summer is elongated by a few days in the northern hemisphere.

The word, aphelion, is Greek for “away from sun”.

Image Credit: mydarksky.org

Image Credit: mydarksky.org