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 February 2017 marking not only the second warmest February on record but also closing out the planet’s second warmest meteorological winter.
According to the State of the Climate report by NOAA’s National Centers for Environmental Information, Earth’s combined average temperature for February – over both land and sea surfaces – was 55.66°F, which is 1.76°F above the 20th-century average. Only February 2016 was warmer.
This February also marked the 386th 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.
The three-month period of December, January, and February – meteorological winter in the northern hemisphere – was also unusually warm. NOAA reports that Earth’s average temperature for the season was 1.60°F above the 20th century average of 53.8°F. That makes it the second warmest winter on record, trailing only the 2015-16 season.
While heat dominated most of the planet this winter, some places were particularly warm, including much of North America and Asia. Here in the contiguous US, it was our sixth warmest winter on record.
Coming on the heels of a five-month long La Niña event, which had a modest cooling effect, these soaring temperatures are largely attributed to the long-term trend of human-caused climate change.
Global temperature records date back to 1880.
Winter 2016-17 was Earth’s 2nd warmest winter season on record. Credit: NOAA
According to Irish folklore, a pot of gold can be found at the end of a rainbow. In reality, however, it is impossible to locate the terminus of this optical phenomenon.
For a rainbow to form, rain has to be falling in one part of the sky while the sun is out in another. The water droplets in the air act like prisms that refract and reflect the sunlight, revealing the colors of the visible spectrum. Red is refracted the least and is always on the top of the bow while blue is on the bottom. Since we only see one color from each drop, it takes a countless number to produce a rainbow.
That said, these colorful arcs are not physical entities that can be approached. No matter how close they appear to be, they are always tantalizingly out of reach. Nevertheless, most people consider seeing one to be a treasure with no gold required.
With a little luck, you can spot a rainbow if you face a moisture source – rain or mist from a waterfall – while the sun is at your back.
Happy Saint Patrick’s Day!
Rainbow after a rainstorm in Bermuda. Credit: Melissa Fleming
After a mostly mild winter in the northeast, a late season snowstorm blasted the region on Tuesday. In New York City, the storm was less intense than originally forecast but still packed a punch.
According to the NWS, 7.6 inches of snow was measured in Central Park setting a new daily record. The previous record of 4.1 inches had been in place since 1958. Strong winds were also part of the storm with gusts reported up to 38mph. The criteria for blizzard conditions, however, were not met in the Big Apple.
Developing from two different systems that merged off the southeast coast, this nor’easter intensified as it moved northward. In weather lingo, it underwent bombogenesis. The storm’s central pressure dropped from 1007mb on Monday night to 974mb on Tuesday afternoon.
While the storm’s precipitation was plentiful, it was more of a wintry mix than a full on snow event in NYC and other cities along the I-95 corridor. This was because the storm was an “inside runner”. It tracked west of the 40/70 benchmark and pulled warmer marine air onshore. More specifically, a shallow zone of air with a temperature warmer than 32°F was wedged between zones of subfreezing air around 5000 feet above the surface. This set-up allowed the snow to melt then refreeze as sleet before hitting the ground.
For areas further inland, to the north and west, the storm lived up to its hype. Numerous communities across eight states received more than 20 inches of snow. Hartwick, NY reported an impressive 48.4 inches, the highest snow total from the storm.
NYC went from 70°F to 7.6 inches of snow in just two weeks. Credit: Melissa Fleming
The weather world has some interesting words and phrases. One of these is “bombogenesis”.
Sounding rather ominous, it is a combination of the words cyclogenesis (storm formation) and bomb. It refers to the explosive or rapid intensification of an area of low pressure. More specifically, it means the central pressure of a storm system drops at least 24 millibars in 24 hours.
Air pressure is measured in millibars (mb) and the lower it is, the stronger the storm.
Taking place along steep temperature gradients, bombogenesis is most common along the east coast where cold continental air masses meet the relatively warm waters of the Gulf Stream. Disturbances in the jet stream above this type of temperature contrast help the air to rise and the pressure to drop.
This process can develop any time of the year but is most likely between October and March. When a system “bombs out” – a variation on the original phrase – strong winds, heavy precipitation, and even lightning can be expected. Nor’easters often become “weather bombs” – another popular variation – as they move up the coast.
The biggest snowstorm of the year is expected to blast the northeastern US on Tuesday. In New York City, on top of the significant snow totals that have been forecast, a blizzard warning is in effect.
Different than a typical winter storm, a blizzard is characterized more by wind speeds and reduced visibility than the amount of snow it produces. According to the NWS, the three main factors for blizzard conditions 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 – High winds and reduced visibility must prevail for at least 3 hours.
These conditions heighten the risk of power outages and often produce whiteout conditions on roadways, making travel extremely dangerous. Stay Safe!
A blizzard warning is in effect for NYC. Credit: NWS
February 2017 was the second-warmest February ever recorded in the continental US.
The average temperature of the lower 48 states, according to NOAA’s National Centers of Environmental Information, was 41.2°F. That is a whopping 7.3°F above the 20th-century average and only 0.2°F shy of the record that was set in 1954.
From the Rocky Mountains to the East Coast, thirty-nine states were warmer than normal and sixteen were record warm. Cooler conditions prevailed in the west, but no state in the region was record cold.
Across the country, a substantial number of local temperature records were challenged during the month. In all, 11,743 daily warm records were tied or broken compared to only 418 cold records. Experts say if the weather pattern was “normal”, records events would be unlikely. If it were volatile but balanced, a similar number of record highs and lows would be expected. However, February’s pattern was extremely lopsided.
On a day-to-day basis, these remarkable conditions were driven by a persistent ridge in the jet stream over the eastern US and a trough in the west. That said, the bigger picture of global warming cannot be discounted. According to World Weather Attribution, a partnership of international scientists, “the chances of seeing a February as warm as the one experienced across the Lower 48 has increased more than threefold because of human-caused climate change.”
February also closed out the country’s sixth warmest meteorological winter. Weather records for the contiguous United States date back to 1895.
February 2017 was the second warmest February on record for the US. Credit: NOAA
The spring equinox is still a few weeks away, but meteorological winter (December, January, and February) has officially ended and it was the sixth warmest on record in New York City.
The season, with daily highs ranging from 23°F to 70°F, felt like a temperature roller coaster. But in the end, the warmth came out on top. The city’s average temperature for the season, according to the NWS, was 39.3°F. That is an incredible 4.2°F above normal.
In all, fifty-three days posted above average readings and every month was warmer than its long-term norm. In fact, February 2017 was the city’s warmest February on record.
In terms of snowfall, the city received 20.5 inches in Central Park, which is only 0.5 inches below average. Of this total, 9.4 inches fell during February’s single, quick hitting nor’easter when conditions were briefly cold enough to support snow.
This winter’s pattern of prolonged warm spells separated by a few short-lived blasts of cold air was largely driven by the North Atlantic Oscillation’s positive phase occurring more often and lasting longer than its negative phase.
The city’s warmest winter on record was the 2001-2002 season when the average temperature soared to 41.5°F. Central Park weather records date back to 1869.
February 2017 was New York City’s warmest February on record. Its mean temperature of 41.6°F was a staggering 6.3°F above the long-term norm. Moreover, February was the city’s 20th consecutive month with an above-average temperature.
Overall, we had nineteen out of twenty-eight days that were warmer than normal. Seven of those produced readings in the 60s and one even hit 70°F, marking the first time the city has seen that type of heat in February in twenty years. Two record warm minimum temperatures were also set during the month. On February 19th and 24th, the Big Apple only cooled down to 53°F and 58°F respectively. The average low for those dates is 30°F.
While a few warm days in February are not uncommon, this extended pattern of sustained warmth was very unusual. Driven largely by a persistent positive phase of the North Atlantic Oscillation, warm southern air was funneled northward almost continuously throughout the month.
February is usually the city’s snowiest month on the calendar, and this year, despite the unseasonable warmth, it did not disappoint. Central Park received 9.4 inches of snow, which is 0.2 inches above average. All of it fell during a single, quick hitting nor’easter when the air was briefly cold enough to support frozen precipitation.
Rainfall, on the other hand, was not as abundant. Only 2.48 inches was reported, which is 0.61 inches below normal. The city, according to the latest report from the US drought monitor (2/23) remains abnormally dry.
New York City weather records date back to 1869.
Feb 2017 was NYC’s warmest Feb on record and 20th straight month with an above average temperature. Credit: The Weather Gamut.
The weather usually associated with winter in the eastern United States has not really taken hold this year. One of the reasons for this involves something called the North Atlantic Oscillation (NAO).
This is a natural phenomenon that affects the position of the jet stream and weather patterns thousands of miles away. Based in the North Atlantic Ocean, it is driven by the pressure differences between the semi-permanent Icelandic Low and Azores/Bermuda High.
When the pressure difference between these two systems is low, the NAO is said to be in a negative phase. This means the winds of the jet stream are relatively relaxed and cold air from the north can spill down into the eastern US. The positive phase of NAO is characterized by a strong pressure difference between the two systems and a robust jet stream that keeps cold air bottled up in the northern latitudes.
Fluctuating between positive and negative, the strength and duration of these phases vary. This winter, however, the positive phase has been occurring more often and lasting longer than the negative phase. That is why the eastern US has been experiencing prolonged warm spells separated by a few brief blasts of cold air.
Unsurprisingly, this season’s soaring temperatures have sparked many important conversations about global warming. But as weather is extremely variable, no single warm day or week can be linked (at this time) to our changing climate. That said, anomalously warm events are happening more often, which is consistent with the long-term trend of human-caused climate change. 2016, for example, was this planet’s third consecutive warmest year on record.
Typical impacts associated with the positive phase of NAO. Credit: NOAA/NCDC
NAO observations, Nov 2016 to date. Credit: NOAA/CPC