Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially began at 10:29 UTC, which is 6:29 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 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
Our global temperature continued its upward trend last month with May 2016 marking the warmest May ever recorded on this planet.
According to the State of the Climate report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for the month – over both land and sea surfaces – was 60.17°F. That is 1.57°F above the 20th century average and 0.04°F above the previous record that was set in 2015. Moreover, May marked the 13th consecutive month to break a global temperature record – the longest such streak on NOAA’s books.
The three-month period of March, April, and May – known as meteorological spring in the northern hemisphere – was also a record breaker. NOAA reports that Earth’s average temperature for the season was 1.91°F above the 20th century average of 56.7°F. That is 0.40°F above the previous record that was set just last year.
While heat dominated most of the planet this spring, some places were particularly warm, including large parts of North America. Here in the US, Alaska marked its warmest spring ever recorded while Washington and Oregon posted their second and third warmest, respectively.
These soaring temperatures, scientists say, were fueled by a combination of El Niño, which has now dissipated, and the long-term trend of human-caused climate change. Research by Climate Central’s World Weather Attribution Program shows that while El Niño gives global temperatures a boost, the majority of the temperature increase is due to rising levels of greenhouse gases in the atmosphere. It should also be noted that no other strong El Niño event has produced temperature anomalies as large as the ones seen recently.
Year to date, the first five months of 2016 were the warmest such period on record. This strengthens the likelihood that 2016 will surpass 2015 as the Earth’s warmest year ever recorded. Global temperature records date back to 1880.
May 2016 was the warmest May on record, globally. Image credit: NOAA
2016 is well on track to being the next warmest year on record. Image credit: NOAA
The calendar says mid-May, but it felt more like March in New York City this weekend.
After a warm spring day on Saturday with readings in the 70s, a cold front swept through the region ushering in significantly cooler conditions. The high on Sunday only reached 57°F, which is 13°F below average. This dramatic cool down was also accompanied by strong winds with gusts in excess of 40-mph.
Moving from Sunday into Monday, the over-night low in Central Park fell to a chilly 43°F. That is the coolest May temperature the city has seen in three years. It was also just one degree shy of tying the record low of 42°F set in 1878. Our normal low temperature for this time of year is 54°F.
With Memorial Day – the un-official start of summer – just two weeks away, many New Yorkers will be happy to hear that temperatures are expected to rebound to more seasonable levels later this week.
A massive wildfire is raging in Alberta, Canada. Situated in the heart of that country’s oil-sands region, it is known as the Fort McMurray Fire.
Charring 772 square miles of parched land since it started on May 1st, it is now one of the worst wildfires the area has ever seen. As of Sunday, according to local officials, more than 1,600 structures have been destroyed and more than 88,000 people have been forced to evacuate.
Only a few days after it began, the fire became so large and intense that it started producing its own weather, including pyrocumulus clouds and lightning.
While the exact cause of the fire remains under investigation, unusually warm temperatures, low humidity, and high winds have been helping to fuel the blaze. But, like many other weather-related events this year, El Niño also played a role. It brought the region a dry autumn and winter followed by a warm spring, which created tinderbox conditions that just needed a spark.
This wildfire, according to the Alberta Emergency Management Agency, is still burning and is expected to take months to fully contain.
The Fort McMurray Wildfire rages in Alberta, Canada. Credit: The Star/ CP
April 2016 was a weather rollercoaster in New York City. We had highs that ranged from a balmy 82°F to a chilly 43°F. But, in the end, the cold and warmth averaged each other out. The city’s mean temperature for the month was 53.3°F, which is only 0.3°F above normal.
In terms of precipitation, April’s famous showers were few and far between this year. The city received a mere 1.60 inches of rain in Central Park. On average, NYC typically gets 4.5 inches of rain for the month. With these parched condtions coming on the heels of scant rainfall in March, the city was listed as “abnormally dry” on the latest report (4/28) from the US Drought Monitor.
Credit: The Weather Gamut
Spring is considered severe weather season in the Central US and on Tuesday the power of Mother Nature was on full display across the region. More than 300 severe storm reports were counted and the vast majority included very large hail.
In Kansas and Nebraska, hailstones the size of a grapefruit were reported. Those are balls of ice measuring about four inches in diameter. According to the NWS, once a thunderstorm produces hail with a one inch diameter or more it is considered severe. So, how does hail get that big?
The answer to that question lies with the speed of a storm’s updraft. Basically, the stronger the updraft, the longer the ice remains suspended in the cloud where it can grow larger. Below is a chart that shows approximately how strong an updraft has to be to support different sizes of hail.
The largest hailstone ever recorded fell in Vivian, South Dakota on July 23, 2010 and measured eight inches in diameter – about the size of a volleyball. To support a hailstone that size, the updraft likely exceeded 150mph.
It is only April, but it felt more like mid-June in New York City today.
The temperature in Central Park soared to 82°F, which is a whopping 20°F above average. This was the first 80° reading the city has seen since the end of September last year.
The primary driver of this unseasonable warmth is the omega-blocking pattern centered over the eastern US. A persistent ridge of high pressure over the region is allowing warm air from the south to flow further north than it normally would at this time of year.
While it was unusually warm today, it was not a record for the city. That honor belongs to April 18, 1976 when the mercury hit 96°F. Nonetheless, after a brisk start to April this year, many New Yorkers were out enjoying the summer-like weather.
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
Most people often associate spring with flowers and mild weather. But as a transitional season, it can also produce some serious cold spells. Wearing shorts one day and a parka the next, you start to wonder when the cold will finally fade away.
The answer to that question largely depends on where you live. Below is a map from NOAA that shows the typical final freeze dates across the continental US. While actual weather conditions vary from year to year, the dates shown are based on climatology – a thirty-year average of temperature data.
Here in New York City, our last spring freeze usually comes in mid-April.
With unseasonably warm temperatures causing trees and flowers to bloom early across New York City, it has felt like spring here for more than a few weeks. But now, as April begins, winter has come fighting back for an encore performance.
The high temperature in Central Park on Friday was a balmy 79°F. Today, it was only 45°F and even colder conditions are expected as the week goes on. So, what’s causing this dramatic cool down? The answer lies in the changeable pattern of the jet stream.
A persistent area of high pressure had been sitting off the eastern seaboard recently, creating a ridge in the jet stream and blocking any cold air from moving southward. Now, the pattern has shifted and a trough in the jet stream is allowing cold air to spill out of Canada and across the northeast.
The first wave of chilly air moved through on Sunday and caused powerful winds to whip through the area. The NWS reported winds gusts of 45 mph in Central Park and 64 mph at JFK airport.
Another wave of arctic air is expected tonight. With the temperature projected to plummet into the 20’s, the NWS has issued a freeze warning for the city and surrounding area – bad news for all the early blooming plants and trees. The forecast high for Tuesday is only 39°F. The city’s normal high for this time of year is 57°F and the normal low is 41°F.
As spring is a transitional season, temperature swings between warm and cold are not uncommon. But, after the city’s second warmest winter and fourth warmest March on record, many folks are finding this spring cold snap more than bit jarring.