What the Summer Solstice Means

Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially began at 10:07 UTC, which is 6:07 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. During the summer months, the northern half of the Earth is tilted toward the sun. This position allows the northern hemisphere to receive the sun’s energy at a more direct angle and produces our warmest temperatures of the year.

Since the winter solstice in December, the arc of the sun’s daily passage across the sky has been getting higher and daylight hours have been increasing. At noon today, the sun will be directly overhead at the Tropic of Cancer, its northernmost position, marking the “longest day” of the year. This observable stop in the sun’s apparent annual journey is where today’s event takes its name. Solstice is a word derived from Latin and means “the sun stands still”.

While today brings us the greatest number of daylight hours  (15 hours and 5 minutes in NYC), it is not the warmest day of the year.  The hottest part of summer typically lags the solstice by a few weeks. This is because the oceans and continents need time to absorb the sun’s energy and warm up – a phenomenon known as seasonal temperature lag.

Earth’s solstices and equinoxes. Image Credit: NASA

How Hail Forms

The thunderstorms of spring and summer are notorious for their powerful winds and heavy rain. However, when strong enough, they can also produce hail.

Hailstones start off as water vapor that is lifted high into the atmosphere by the updraft of a thunderstorm. Rising into cooler air, it condenses and forms water droplets. Once these liquid droplets reach a level where the temperature is below freezing, they turn into tiny ice crystals. Overtime, they get larger as other water droplets freeze to them on contact, forming layers like an onion.  Once a hailstone gets too heavy for the updraft, it falls to the ground.

The stronger the updraft of a storm, the longer a hailstone remains suspended, and the larger it can grow. For a ball of ice to be considered a hailstone, according to the AMS, it has to measure at least 5mm in diameter.

The largest hailstone ever recorded in the US was found in Vivian, South Dakota on June 23, 2010. It measured 7.9 inches in diameter and weighed 1.94 pounds. The updraft supporting it would have had to exceed 150 mph.

Needless to say, hail can cause serious damage to people and property.

Weather Lingo: June Gloom

For most people in the US, the month of June is associated with warm temperatures and abundant sunshine. For parts of coastal California, however, it is a month known for cloudy and relatively cool conditions. This regional phenomenon called “June Gloom” is the result of the interaction of several natural elements, including geography, ocean currents, and weather patterns.

With the California Current running south along the coast from the Gulf of Alaska, the water in the area is cold. Ocean temperatures in the region usually hover in the upper 50s to low 60s during the summer, cooling the air that flows over it.

Another significant factor is the temperature inversion aloft created by the North Pacific High, a semi-permanent area of high pressure. This is part of a larger planetary circulation of air known as a Hadley cell, a current of high altitude air traveling poleward from the tropics. As the air cools, it descends around 30N latitude. It compresses and warms as it sinks, making the air aloft warmer than the cold, moist air at the surface. Since air temperatures normally decrease with height, this situation acts like a cap on the cool air below and prevents it from rising any higher.

When the air under the inversion layer, known as the marine layer, is cooled to the point where the moisture condenses, an expansive sheet of low level stratus clouds form.  The region’s prevailing westerly winds, as well as the sea-breeze circulation that often develops during the summer months, carries these clouds inland.  While they create overcast conditions and some light drizzle, the clouds do not produce any significant rain. They also tend to dissipate by the afternoon as the land heats up.

The thickness and inland extent of the marine layer clouds depend on the strength of the high-pressure system. A stronger high will thin the clouds and keep them confined to the coast. A weaker high with allow the clouds to thicken and move further inland. Separated by only a few miles, the cloud-covered coast can be significantly cooler than sunny areas further east.

These conditions are most common in June, but are not necessarily limited to the month. They have been known to develop in May and last on and off through August. The monikers for these events include “May Gray”, “No Sky July”, and “Fogust”.  However, high pressure usually builds over southern California in July, decreasing the impact of the marine layer or eliminating it altogether.

“June Gloom” clouds along west coast. Credit: NWS/UCSD

Summer Preview Brings NYC First 80° of the Year

It felt more like June than April in New York City on Friday. The temperature in Central Park soared to 82°F, marking the city’s first 80-degree day of the year.

Topping out at 22°F above average, the day was more than unseasonably warm. However, it was not a record breaker. That honor belongs to April 13, 1977, when the mercury soared to 88°F. The low temperature was 60°F, which ironically is the normal high for the date.

After an extended winter that included four nor’easters in March and a snowy start to April, many New Yorkers took full advantage of this summer preview. The parks and outdoor cafes were packed.

This spring heat was the result of a ridge in the jet-stream that allowed warm southern air to move further north than it normally would at this time of year.  While the balmy conditions are forecast to remain in place through Saturday, temperatures are expected to plummet into the 40s on Sunday. So, enjoy it while it lasts, but get ready for weather whiplash!

A summer preview for NYC. Credit: The Weather Gamut

NYC Monthly Summary: August 2017

August was unusually mild in New York City this year. Of the month’s thirty-one days, nineteen posted below average readings, including an unseasonably cool 68°F on August 29. Furthermore, the month typically produces four days with readings in the 90s, but this year we only had one. In the end, the city’s mean temperature for the month was 74°F, which is 1.2°F below average.

In terms of precipitation, August was mostly dry. Overall, 3.34 inches was recorded in Central Park, marking the fourth month this year and second in a row to deliver below average rainfall. The city usually gets 4.44 inches of rain for the month.

August 2017 was unusually mild in NYC. Credit: The Weather Gamut

NYC Monthly Summary: July 2017

July was a month of extremes in New York City. It delivered five days with temperatures in the 90s and the city’s third heat wave of the season. However, it also produced a few unseasonably cool days. On July 14, the high only reached 73°F, tying the record low maximum temperature for the date that was set in 1963. The average high for the date is 84°F. Nonetheless, the heat and the chill balanced each other out in the end. The city’s mean temperature for the month was 76.8°F which is only 0.3°F above average.

July is usually the city’s wettest month, but this year precipitation was slightly below normal. Only eight of thirty-one days produced measurable rainfall. Overall, 4.19 inches was recorded in Central Park. Of this total, 1.78 inches (42% of the total) fell in a single day. On average, the city gets 4.60 inches for the entire month of July.

Credit: The Weather Gamut

What are the Dog Days of Summer?

The “Dog Days” of summer have arrived. This popular saying refers to what are traditionally the hottest and most oppressive days of the season.

Rooted in astronomy, the phrase is linked to Sirius, the brightest star seen from Earth. As part of the constellation Canis Major, it is known as the Dog Star.  During most of July and August, Sirius rises and sets with our Sun. Ancient Greeks and Romans believed it acted like a second Sun, adding extra heat to summer days. Today, we know that light from this distant star does not affect our weather, but the name has endured.

Varying by latitude around the globe, the so-called “Dog Days” of summer typically run from July 3 to August 11 in the United States.

Sirius, the “Dog Star”.  Credit: EarthSky/Tom Wildoner

Aphelion 2017: Earth Farthest from Sun Today

The Earth will reach its farthest point from the Sun today – an event known as the aphelion. It will officially take place at 20:11 UTC, which is 4:11 PM Eastern Daylight Time.

This annual event is a result of the elliptical shape of the Earth’s orbit and the slightly 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 the sun”.

Earth is farthest from the Sun during summer in the northern hemisphere. Credit: TimeandDate.com

June 2017: A Temperature Roller Coaster in NYC

June 2017 felt like a temperature roller coaster in New York City. Highs ranged from an unseasonably cool 58°F to a balmy 94°F. June also brought the city its second heat wave of the year. In the end, however, the cold and warmth balanced each other out. The city’s mean temperature for the month was 72°F, which is only .06°F above average.

 

In terms of precipitation, the city was wetter than normal. Overall, 4.76 inches of rain was measured in Central Park. Of this total, 84% fell during three separate heavy rain events that each produced over an inch of rain. On average, the Big Apple gets 4.41 inches of rain for the entire month of June.

Credit: The Weather Gamut

Hot Temperatures and Strong Winds Fuel Western Wildfires

Summer is wildfire season in the American West and this year it is off to an explosive start.

As of Wednesday, according to the National Interagency Fire Center, thirty large wildfires – defined as greater than 100 acres – are burning in ten western states.  These include Alaska, Arizona, California, Idaho, New Mexico, Nevada, Oregon, Texas, Utah, and Washington.

The largest is the Brian Head Fire in southern Utah. It has burned approximately 50,000 acres and forced the evacuation of nearly 1500 people. Ignited on June 17, the massive blaze is only 10% contained.

Another hard hit state is Arizona, where six large fires are currently burning. The governor, Doug Ducey, has declared a state of emergency in Yavapai County in response to the Goodwin Fire, which has burned more than 20,000 acres near the Prescott National Forest. Local officials have ordered the full evacuation of the town of Mayer, AZ.

These huge fires are being fueled by extremely hot and dry conditions that have left the region’s vegetation susceptible to any type of spark. Just a few days ago, excessive heat advisories were in effect for a large swath of the area as temperatures soared into the triple digits. Now, high winds are fanning the flames and helping the fires to spread.

Year to date, 2.7 million acres in the US have been charred. The country’s worst wildfire season on record was 2015 when more than ten million acres burned.

Brian Head Fire, UT. Credit: Desert News