After an extended stretch of cool and rather gloomy conditions, it is suddenly summer in New York City!
The temperature in Central Park soared to 88°F this afternoon, marking the warmest day the city has seen since last September. Our normal high for this time of year is 73°F.
These warm conditions are expected to stick around through the upcoming Memorial Day weekend – ideal conditions for the unofficial start of the summer season.
Our global temperature continued its upward trend last month with August 2015 not only marking the warmest August on record, but also closing out the warmest meteorological summer ever recorded for the entire planet.
According to a report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for August – over both land and sea surfaces – was 61.68°F, which is 1.58°F above the 20th century average. It surpassed the previous record set just last year by 0.16°F and was the sixth month this year to break a monthly temperature record. It also marked the 366th consecutive month that our global temperature was above its long-term norm.
Rising ocean temperatures compounded by El Niño conditions in the tropical Pacific helped fuel August’s record warmth. The globally averaged sea surface temperature for the month was 1.40°F above the 20th century average, which makes it the highest temperature on record for any month. The previous record was set in July 2015.
The three-month period of June, July and August – known as the meteorological summer in the northern hemisphere – was also a record breaker! NOAA reports that Earth’s combined average temperature for the season – over both land and sea surfaces – was 1.53°F above the 20th century average. That is 0.20°F above the previous record that was set last summer.
While heat dominated most of the planet from June to August, some places were particularly warm, including much of Europe. Austria, France, and Switzerland each experienced their second warmest summer on record and Germany posted its third warmest. Even the southern hemisphere, where it was austral winter, saw warmer than usual conditions. Argentina experienced its warmest winter since national record keeping began there in 1961.
Here in the contiguous US, the summer of 2015 was our 12th warmest on record. While some of the central states saw average to below average temperatures, many of the western states were exceptionally warm. In fact, Oregon and Washington each experienced their warmest summer on record.
Year to date, the first eight months of 2015 were the warmest of any year on record. That puts 2015 on track to becoming Earth’s warmest year ever recorded. Global temperature records date back to 1880.
Credit: NOAA
2015 is well on its way to becoming Earth’s warmest year on record. Credit: NOAA
It was hot in New York City this August. Everyday produced a high temperature above 80°F and eight days saw the mercury climb to 90°F or higher, which is twice the average number for August. Additionally, the month brought the city its first official heat wave in two years. With overnight lows also running mostly above normal, the city’s mean temperature for the month was 79°F, which is 3.8°F above average. This makes August 2015 the city’s 3rd warmest August on record.
On the precipitation side of things, August was very dry in the Big Apple. All told, the city received a mere 2.35 inches of rain in Central Park, which is 2.09 inches below average. On the latest report (8/25) from the US Drought Monitor, the NYC area is listed as “abnormally dry”.
Fueled by drought, wildfires have been blazing across the American West all summer. Sixteen are currently burning in California alone. While hiking in Kings Canyon National Park in the state’s rugged Sierra Nevada Mountains recently, I crossed paths with the “Rough Fire” and saw it produce a billowing pyrocumulus cloud.
Pyrocumulus clouds form when intense heat at the surface – usually from a wildfire or volcanic eruption – causes air to rise rapidly. As it travels upward, water vapor in the air condenses into droplets and forms a cloud. Filled with ash and smoke, the swelling cloud generally appears more grey than white.
Ignited by lightning over three weeks ago, the Rough Fire continues to spread and has even caused parts of Kings Canyon National Park to close. According to the NPS, smoke from the massive fire has also impacted the air quality in and around the park. To date, the fire has charred close to 50,000 acres and is only 17% contained.
Pyrocumulus cloud rising over California’s Rough Fire in Sierra National Forest and Kings Canyon National Park, August 2015. Credit: The Weather Gamut.
It’s official! We’re having a heat wave in New York City.
While we have hit the 90°F mark a few times already this summer, this is the first real heat wave of the season. Actually, it is the first official heat wave in the Big Apple since 2013.
The threshold for what constitutes a heat wave varies by region, but here in the NYC area it is defined as three consecutive days with temperatures reaching 90°F or higher. In Central Park, the temperature reached 92°F on Saturday, 93°F on Sunday, and today it climbed to 95°F – tying the record high for the date.
When factoring in the high levels of humidity these past few days, the heat index felt like it was near 100°F. While these conditions are oppressive, they can also be dangerous. Both a heat advisory and air quality alerts were issued for the city.
For most of the summer, temperatures have been running slightly above average in NYC, but it is interesting to note that there has not been much extreme heat. To date, we have only had ten days with readings at or above 90°F. On average, we typically see fifteen for the season.
For the continental U.S. as a whole, the hottest part of summer arrives in mid to late July. On the regional level, however, there are significant differences in the timing of the hottest part of the season.
Based on historical averages, NOAA’s National Centers for Environmental Information (NCEI) produced a map showing how the warmest days of summer vary across the country. The desert southwest, for example, is an early bloomer in terms of heat. It’s warmest days typically arrive in June. By early July, the North American Monsoon – a seasonal shift in wind direction – kicks in and helps keep the region relatively cool and rainy through September.
In parts of the south central states, a persistent area of high pressure typically builds over the region in August. This limits cloud formation and dries out the soil, which helps to send temperatures skyrocketing.
On the other far end of the spectrum, temperatures along the west coast do not peak until September. This lag is the result of hot air rising over interior deserts and cool Pacific air flowing in-land. By September, this upper-level wind pattern usually weakens and allows warm air to flow toward the coast.
While the NCEI map is derived from long-term climate averages, it is important to note that short-term variability can cause the date of peak temperatures to vary in any given year.
Credit: NOAA/NCEI
Thunderstorms can illuminate the sky with a number of different types of lightning. The most threatening to us at the surface, however, is the cloud to ground variety. Interestingly, it comes in two forms: positive and negative.
While not completely understood, lightning – an intense electrical discharge – is believed to form as a result of the separation of charges in a cumulonimbus cloud. Within these towering clouds, both negatively charged hailstones and positively charged ice-crystals exist at the same time. As the storm’s updraft moves through the cloud, the lighter ice-crystals are carried upward, leaving the denser hailstones to fall to the bottom.
As the negative charge builds at the base of the cloud, it induces a strong positive charge on the ground, especially in tall objects such as buildings and trees. When the charge separation becomes large enough, a negatively charged stepped leader, a channel of ionized air, initiates a lightning strike from the base of the cloud. Moving down toward the ground, it meets a channel of rising positive charges known as a streamer. When they connect, they form negative cloud to ground lightning (-CG), which is the most common type.
Positively charged lightning (+CG), on the other hand, originates in the upper section or anvil of a cumulonimbus cloud. In this case, the descending stepped leader carries a positive charge and travels horizontally as it makes its way toward an area with negatively charged particles on the ground. It can travel more than 10 miles – a distance where thunder from the parent storm cannot be heard – to areas with relatively clear skies. For this reason, positive lightning is often called a “bolt from the blue”. It is most often associated with super cell thunderstorms and is considered rare. According to NOAA, it makes up less than 5% of all lightning strikes.
While uncommon, positive lightning is extremely powerful. Originating at a higher level of a storm cloud, it has to travel through more air to reach the ground, intensifying its electrical field. Its peak charge can be 10 times greater than that of a negative strike. This immense power combined with a lack of warning makes positive cloud to ground lightning particularly dangerous. It is also believed to be responsible for a large percentage of wildfires.
To visually identify positive and negative cloud to ground lightning, look at the shape of the bolt. Negative lightning will have a downward branching pattern and positive lightning will generally display a single bright stroke without branches.
Regardless of these differences in charge and shape, it is important to remember that all lightning is dangerous. Stay safe!
Negative Cloud to Ground Lightning. Credit: NOAA
Positive Lightning. Credit: MD Weather
July is normally the warmest month on the calendar for New York City, and this year was no exception. Despite getting off to a relatively cool start, the month brought us five days with temperatures in the 90s. These hot days helped bring the city’s mean temperature for the month up to 78.8°F, which is 2.3°F above average.
While we had a few stretches of very warm and humid days, including some where the heat index reached the triple digits, it is interesting to note that we did not technically have a single heat wave all month. In this part of the US, a heat wave is defined as three consecutive days with temperatures reaching 90°F or higher.
On the precipitation side of things, NYC was mostly dry. In all, we received 3.98 inches of rain in Central Park, which is 0.62 inches below average. Of this total, 1.95 inches fell in a single day as a cold front moved through the area triggering thunderstorms and intense downpours. July is typically the wettest month of the year in the Big Apple.
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 the sun and the shade around midtown Manhattan on July 29th when the air temperature was 95°F . Credit: The Weather Gamut.
Summer is wildfire season in the American West, and it is off to a raging start.
So far this year, according to the National Interagency Fire Center, wildfires have burned 5.5 million acres across the US. That is an area roughly the size of the state of New Jersey. It is also the second highest total (as of this date) in the last 25 years.
As of Monday, 22 large wildfires – defined as greater than 100 acres – are burning in 5 states. In California’s Napa Valley region, the Wragg Fire has scorched 7,000 acres and forced many residents to evacuate. In Montana, a massive blaze has burned approximately 5 square miles of Glacier National Park since it began last week. The majority of the acres burned, however, have been in Alaska. They have seen nearly 4.7 million acres charred, which is about 85% of the national total to date.
High temperatures and prolonged drought in the West have turned forests and brush areas into tinderboxes that are susceptible to any type of spark. While summer is usually hot and dry in California, the state is enduring its fourth year of drought. Alaska has also been unusually warm and dry. In fact, according to NOAA, they are in the middle of their second warmest year on record, year to date. These warm temperatures helped produce a dearth of winter snowfall, which has lead to drier than normal conditions across a large area of the state.
Overall, wildfires in the US seem to be getting worse. In Alaska, 3 of the worst wildfires have occurred in the last 12 years. In California, 12 of their 20 largest fires have taken place since 2000. In both states, wildfire records date back to the 1930s.
Nationally, summer 2015 is on track to be one of the worst wildfires seasons on record.
Wildfire rages in Glacier National Park, Montana. Image Credit: CBS