Monthly Archives: March 2018

National Drought Update: Early Spring 2018

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The northeastern United States received copious amounts of precipitation from the four nor’easters that blasted the region this month. Much of the rest of the country, however, has been parched.

According to the latest report from the U.S. Drought Monitor, 31% of the nation is dealing with some form of drought. While this number represents a slight improvement for California, the situation in the southern plains and the southwest has been getting worse. Parts of the Texas Panhandle, western Oklahoma and southwestern Kansas are in exceptional drought, the worst possible category.

Drought conditions have also been building in parts of the southeast. In Florida, according to the state’s Forest Service, dry conditions have fueled more than 1000 wildfires across the peninsula since the beginning of the year.

The US Drought Monitor is a weekly publication produced by a partnership of government agencies, including the National Drought Mitigation Center, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration.

Credit: US Drought Monitor

Fourth Nor’easter of the Month Slams NYC

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The calendar says spring, but it felt more like winter in New York City on Wednesday as the fourth nor’easter of the month slammed the region.

According to the NWS, the storm dumped 8.4 inches of heavy, wet snow in Central Park, setting a new daily snowfall record for the date. The previous record of 7.1 inches had been in place since 1958. The city, on average, gets 3.9 inches of snow for the entire month of March.

This storm was the fourth nor’easter to affect the city and region in less than three weeks. The others were on March 2, March 7, and March 13. This one, however, was by far the snowiest. It was also the first time since 1992 that the city saw at least 6 inches of snow from a spring storm.

The reason for the plethora of nor’easters this month involves something called the North Atlantic Oscillation (NAO). Stuck in its negative phase for weeks, it has caused the jet stream to dip south over the eastern US and steer storms toward the northeastern seaboard.

View of the fourth nor’easter to hit the east coast this March. Credit:  RAMMB/CIRA/CSU

Earth Posts 11th Warmest Feb and 5th Warmest Dec-Feb Season on Record

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Our global temperature continued its upward trend last month. February 2018 marked not only the eleventh warmest February on record, but also closed out the planet’s fifth warmest December – February season.

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 55.07°F, which is 1.17°F above the 20th-century average. This February also marked the 398th 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 1.31°F above the 20th century average of 53.8°F. That makes it the fifth warmest such period on record.

While heat dominated most of the planet this season, some places were particularly warm, including Alaska, northern Russia, and parts of the Middle East. Here in the contiguous US, this winter ranked among warmest third of the nation’s 124-year period of record.

These soaring temperatures are largely attributed to the long-term trend of human-caused climate change. In fact, La Niña conditions – the cool counterpart of El Niño – were present in the Pacific during all three months of the season.

Global temperature records date back to 1880.

The Dec 2017- Feb 2018 season was the planet’s 5th warmest on record. Credit: NOAA

First Day of Spring 2018

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Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially begins at 16:15 UTC, which is 12:15 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

How Rainbows Form

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St. Patrick’s Day is a holiday often associated with images of rainbows promising a path to a leprechaun’s pot of gold. For most people, however, just spotting a rainbow is enough to brighten a day.

These amazing displays of nature form when raindrops, which act like prisms, scatter sunlight. To see one, an observer must be facing a moisture source like rain or mist with the sun at their back. The sun also needs to be at a low angle in the sky, less than 42° above the horizon. The lower the sun angle, the more of a rainbow’s arc will be visible.

Refraction and reflection inside a raindrop. Credit: Met Office

Passing from the air into a denser raindrop, the light slows and refracts. Since the different wavelengths of light bend by different amounts, the white light is dispersed into the colors of the visible spectrum: red, orange, yellow, green, blue, indigo, and violet. Red, which has a long wavelength, is refracted the least and is always on the top of a single rainbow. Violet, with a shorter wavelength, is refracted the most and is always on the bottom.

The light also needs to reflect off the back wall of the raindrop towards the viewer at the critical angle of 48° before it refracts again when it re-enters the air. A lesser angle will let the light pass through the raindrop and a larger angle will allow the light to reflect straight back out of the drop.

A double rainbow is seen when the light reflects twice inside the raindrop. Since each reflection weakens the intensity of the light, the second bow appears dimmer. The order of the colors is also reversed, with blue on top and red on the bottom.

Rainbow and faint second rainbow form after a rainstorm in Bermuda. Credit: Melissa Fleming

Why Are We Seeing So Many Nor’easters?

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The east coast of the United States has been slammed with three nor’easters in just eleven days – March 2, March 7, and March 13. The reason for this barrage of storms involves something called the North Atlantic Oscillation (NAO).

Based in the North Atlantic Ocean, this weather pattern 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 areas and a robust jet stream that keeps cold air bottled up in the northern latitudes.

Three nor’easters in eleven days. Credit: NOAA

Fluctuating between positive and negative, the strength and duration of these phases vary. Since late February, however, a strong negative phase has been locked in place. With an area of high pressure over Greenland, the jet stream is blocked and therefore dipping southward over the eastern US. As the jet stream is essentially a storm track, this pattern has allowed areas of low pressure to be steered over the warm waters of the Gulf Stream off the eastern seaboard, where they have intensified into nor’easters.

In terms of climate change, the connection between the warming Arctic and the storm track across the mid-latitudes is an active area of research. Sea level rise, however, is clearly amplifying the coastal flooding associated with these powerful storms.

NAO Patterns. Credit: NOAA

Second Nor’easter in Less Than a Week for NYC

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For the second time in less than a week, a nor’easter slammed New York City.

The storm intensified quickly and brought heavy snow, strong winds, and even thundersnow to the area. It downed trees and caused a number of travel disruptions, including nearly 2000 flight cancelations and the temporary suspension of all NYC Ferry service.

While the snow fell quickly, the surface temperature hovered just above freezing and did not allow much to accumulate. Only 3.2 inches of snow was reported in Central Park, according to the NWS. Areas north and west of the city received much higher storm totals.

GOES-16 image of nor’easter on March 7, 2018. Credit: NOAA

Weather Lingo: Venturi Effect

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March, a transitional month between winter and spring, is well known for its winds. In large cities like New York, however, the wind can be accelerated by something called the Venturi Effect.

Tall buildings and straight, grid-like streets essentially create man-made canyons that affect how the wind moves through a city. Funneled through the buildings, the wind is constricted and forced to speed up. The same process is seen when you put your thumb over the mouth of a hose to create a choke point and make the water flow faster.

The Venturi Effect is named for Giovanni Battista Venturi, an 18th-century Italian physicist.

Credit: Currents

Powerful Nor’easter Slams NYC

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A powerful nor’easter slammed the northeastern United States on Friday. Heavy precipitation, strong winds, and coastal flooding were reported across the region.

LGA airport. Credit: Chris Rudnick/Instagram

Here in New York City, 2.24 inches of rain fell in Central Park and wind gusts as high as 67mph were reported at JFK airport. These powerful winds canceled hundreds of flights, knocked down trees, and caused power outages in four of the city’s five boroughs. They also tore off a section of the roof of the American Airlines hangar at La Guardia airport and caused two tractor-trailers to flip over on the Verrazano Bridge.

Starting as an area of low pressure moving in from the west, this storm developed into a nor’easter over the Atlantic and then rapidly intensified. It underwent a process known as bombogenesis, the threshold for which is a drop in pressure of 24mb in 24 hours.This storm dropped 26mb in only 21 hours, producing its damaging winds.

Nor’easter of March 2, 2018. Credit: NOAA

February 2018: Warmest on Record in NYC

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February 2018 was New York City’s warmest February on record. Its mean temperature of 42°F was a staggering 6.7°F above the long-term norm. The previous record of 41.6°F was set just last year in February 2017.

Overall, we had nineteen out of twenty-eight days that were warmer than normal. Five of those produced readings in the 60s and one even hit 78°F, marking the warmest February day ever recorded in NYC. A record warm minimum temperature was also set on February 21 when the city only cooled down to 55°F. The average low for that date is 30°F.

While a few warm days in February are not that uncommon, this extended pattern of sustained warmth was very unusual. Driven largely by a persistent ridge in the jet stream, warm southern air was funneled northward almost continuously throughout the month.

February is usually the city’s snowiest month on the calendar, but Central Park only received 4.9 inches of snow this year. That is 4.3 inches below normal. Of that total, 4.4 inches fell during a single, quick-hitting storm when the air was briefly cold enough to support frozen precipitation.

Rainfall, on the other hand, was abundant with seventeen days posting measurable precipitation. In total, Central Park reported 5.83 inches of rain. That is 2.74 inches above average.

New York City weather records date back to 1869.

February 2018 was the warmest February on record in NYC. Credit: The Weather Gamut