The Science Behind the Spring Equinox

Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially begins at 11:49 PM 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. During the spring 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 winter solstice in December, the arc of the sun’s apparent daily passage across the sky has been getting higher 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.

The vernal equinox normally takes place on March 20 or 21, but this year it is arriving a day early. The main reasons for this involve complicated calendar issues related to leap year and daylight savings time. Happy Spring!

Earth’s solstices and equinoxes. Image Credit: NASA

March: In Like a Lion and Out Like a Lamb

“March comes in like a lion, and goes out like a lamb”. This old proverb refers to March’s famously changeable weather.

As a month where we transition from winter to spring, March can often start off cold and blustery, but end warm and calm. From the beginning to the end of the month, the average daily temperature increases by 10°F. Exact conditions, of course, vary from year to year.

Although the precise origins of this popular phrase are unknown, many believe it is based on the constellations. At the beginning of March, Leo (lion) is highest in the midnight sky, while Aries (ram) begins to rise toward the end of the month.

Credit: The New Yorker

Spring Nor’easter Brings Unseasonably Cold, Wet Weather to NYC

A late season nor’easter soaked the northeastern United States on Monday. Heavy rain triggered flood alerts and advisories from Virginia to Connecticut, and areas further north reported snow.

Here in New York City, 0.70 inches of rain fell in Central Park. This came on the heels of the 1.32 inches that fell the day before when a separate storm system moved through the area. To date this May, the city has received 3.70 inches of rain and it is only the middle of the month. May, on average, brings the city a total of 4.19 inches of rain.

The storm also ushered in unseasonably cool temperatures, making it feel more like March than May. The high in NYC only made it to 48°F on Monday, setting a new record for the coldest high temperature for the date. The old record of 49°F was set in 1914. The normal high for this time of year is 70°F.

This storm was the result of a deep dip in the jet stream that moved over the region, which, in turn, helped generate an area of low pressure off the coast. Producing gusty northeasterly winds, it was categorized as a nor’easter. While this type of storm is more common during the fall and winter months, they can develop any time of the year.

A late spring nor’easter soaked the northeastern US. Credit: weather.com

Spring is Heating Up

Spring is a transitional season. It is a time when the chill of winter fades away and the warmth of summer gradually returns. But, as our climate changes, the season is heating up.

Across the contiguous United States, spring temperatures have increased an average of more than 2°F over the past fifty years, according to Climate Central. The southwest part of the country has seen the fastest seasonal increase, with Las Vegas, NV and Tucson, AZ warming more than 6°F since 1970.

Warming temperatures mean more frost-free days. While this may lengthen the growing season for some crops, it also extends the allergy season and allows pests like mosquitos and ticks to live and thrive longer.

Looking ahead, if greenhouse gas emissions continue to rise, scientists say spring could arrive at least two weeks earlier by 2050 compared to recent years.

April 2019: Eighth Warmest April on Record for NYC

April 2019 was unusually warm in New York City. It produced 18 days with above average readings, including one day where the temperature reached a summer-like 80°F. Overnight lows were also mostly warmer than normal.  In fact, on April 14, the mercury only fell to 60°F, setting a new record warm low temperature for the date. In the end, the city’s mean temperature for the month was 55.5°F, which is 2.5°F above average. That means April 2019 is now tied with April 1985 as the city’s eighth warmest April on record. The city saw its warmest April in 2010, when the average temperature for the month was 57.9°F.

This April was also above average in terms of precipitation, with 18 out of 30 days producing measurable rainfall. In all, 4.55 inches of rain was measured in Central Park. Of that total, 1.03 inches fell on a single day. The city, on average, gets 4.50 inches of rain for the entire month.

April 2019 was NYC’s 8th warmest April on record. Credit: The Weather Gamut

Do April Showers Really Bring May Flowers?

The phrase, “April showers bring May flowers “ has been around for centuries. It is derived from a poem written in the 1500s by Thomas Tusser – an English poet and farmer. This old adage, however, does not hold true in the northeastern United States.

Coming on the heels of the snowy months of winter, April typically produces more rain than snow. Many people, therefore, consider it a rainy month. Since water is necessary for the overall survival of plants, they also associate it with the bloom of flowers in May. Nevertheless, according to botanists, perennials – the plants that go dormant in winter and re-grow in the spring – are more dependent on the soil moisture derived from winter snowmelt and the long-term local precipitation pattern.

In the end, though, temperature is the most significant factor in determining when a flower will bloom. As soon as the weather becomes more spring-like, flowers will start to blossom, regardless of how much it rained in April or whatever the prior month was. That said, a “false spring” – a warm spell that triggers flowering but is followed by a hard frost – can kill the fragile blooms.

It is also worth noting that April is not typically the wettest month of the year for most places in the US. In New York City, July, on average, takes that honor because of the downpours associated with its strong summer thunderstorms.

Spring Peonies. Credit: Melissa Fleming

Weather Safety: Flooding and the Power of Water

It is no secret that heavy rain can cause flooding. However, it can be surprising to learn how little water is required to create significant impacts.

As anyone who carries a water bottle knows, water is heavy. In fact, just one cubic foot of fresh water weighs 62.4lbs (28.3kg).  Multiplied many times over, raging floodwater can carry away or destroy most things in its path. Moving at just 4-mph, water has enough force to cause structural damage to an average home.

Flowing floodwaters can also pose a danger when hiking or driving. According to NOAA, it only takes six inches of fast moving water to knock a person off their feet. Twelve inches of water can sweep a small car off the road and eighteen to twenty-four inches can float most large vans and SUVs.

Since it is impossible to know how deep water is just by looking at it, it is best to err on the side of caution. As the saying goes, “Turn around, don’t drown!”

Credit: NWS/NOAA

Climate Change is Making Allergy Season Longer

Spring is a season of rebirth. As temperatures warm, plants awaken from winter dormancy, generate pollen, and produce beautiful blooms. For allergy sufferers, however, the season can be a double-edged sword. With climate change extending the growing season, the outlook for people with seasonal allergies is less than rosy.

Across the US, the growing season – the period between the last and first freezes of the year – has lengthened by an average of two weeks since the 1970s, according to Climate Central. That means pollen allergies are staring earlier in the spring and lasting longer into the autumn. Tree pollen comes out in the spring, grass pollen strikes in the summer, and weed pollen is prevalent in the fall.

If global warming continues unchecked, studies show the growing season, and therefore the allergy season, expanding even further.

These changes to the growing season, like other climate change impacts, vary from region to region. The largest increase has been noted in the western states, according to the National Climate Assessment. Here in NYC, the growing season has increased an average of 21 days between 1970 and 2018.

Rising temperatures, however, are not the only factor for worsening allergy conditions. The carbon dioxide (CO2) in the air that causes the atmosphere to warm also plays a more direct role. When plants, particularly ragweed, are exposed to higher levels of CO2, they produce more pollen. Therefore, as concentrations of atmospheric CO2 continue to increase, pollen production will intensify.

A Look at the Science Behind the Spring Equinox

Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially begins at 21:58 UTC, which is 5:58 PM 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. During the spring 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 winter solstice in December, the arc of the sun’s apparent daily passage across the sky has been getting higher 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

May 2018: Earth’s Fourth Warmest May on Record

Our global temperature continued its upward trend last month. May 2018 marked not only the fourth warmest May on record, but also closed out the planet’s fourth warmest March to May season, known as meteorological spring in the northern hemisphere.

According to the State of the Climate report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for May – over both land and sea surfaces – was 60.04°F, which is 1.44°F above the 20th-century average. The years 2014-2018 now rank among the five warmest Mays on record.

This May also marked the 401st consecutive month with a global temperature above its long-term norm. That means the last time any month posted a below average reading was December 1984.

While heat dominated most of the planet this May, some places were particularly warm, including much of Europe and North America. Here in the contiguous US, it was our warmest May ever recorded. The previous record had been in place since 1934.

Globally, the three-month period of March, April, and May was also unusually warm. NOAA reports that Earth’s average temperature for the season was 1.48°F above the 20th century average of 56.7°F. That makes it the fourth warmest such period on record.

These soaring temperatures are largely attributed to the long-term trend of human-caused climate change. ENSO-neutral conditions prevailed in May, which means there was neither an El Niño nor a La Niña in the Pacific to influence global weather patterns.

Year to date, the first five months of 2018 tied 2010 as the fourth warmest such period of any year on record. Global temperature records date back to 1880.

May 2018 was the fourth warmest May ever recorded on Earth. Credit: NOAA