Monthly Archives: August 2014

A Late Summer Warm Up in NYC

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It’s the last week of August and it finally feels like summer in New York City. The high temperature in Central Park has been in the upper 80’s for the past few days and today it soared to 90°F. This is worth noting, because high heat has been something of a rarity in the Big Apple this summer.

This season to date, NYC has only had five days reach 90°F or higher. On average, we typically get fifteen. Looking back, every month this summer brought a noticeable dearth of extreme heat. June had zero days with temperatures at or above 90°F, July had three and August (so far) has only had two.

The most 90-degree days that the city has ever had in one year, according to NWS records, was thirty-nine. That happened in both 1991 and 1993. On the opposite end of the spectrum, 1902 only had one day hit the 90°F mark.  Last summer, we made it to 90°F or higher seventeen times.

Climate Change at Rocky Mountain National Park

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Rocky Mountain National Park (RMNP) protects 415 square miles of spectacular mountain environments in northern Colorado. It is home to a diversity of ecosystems – alpine, subalpine, and montane – that are each uniquely adapted to the climate zone of their elevation. This is why, as I learned during a recent visit,  climate change is a serious issue for the park.

According to the National Park Service, the average annual temperature in RMNP has increased 3.4°F over the past century. A report from a weather station inside the park (Grand Lake), shows that the number of frost-free days has increased from an average of 65 in the mid-20th century to an average of 100 in this past decade.

temperature_graph_1

In the 20th century, the area including Rocky Mountain National Park experienced a warming trend. The five-year rolling average (thick red line) allows the viewer to look beyond annual variability to focus on long-term trends. (Analysis of PRISM data, original source Daly 2008). Credit: NPS

This warming trend, says the NPS, has caused a number of environmental changes in RMNP. The winter snowpack is melting approximately 2 to 3 weeks earlier, resulting in less water being available for people, plants, and animals during the summer. There has been an explosive increase in the number of mountain pine beetles surviving the now warmer winter months, allowing them to devour more trees. The phenology, or the timing of natural events, can also be thrown out of sync when warm spring weather arrives earlier than normal. Wildflowers that bloom before the arrival of butterflies, for example, can leave the insects with a reduced food source. This puts a kink in how the larger food chain fits together.

In the park’s alpine tundra region, the American Pika is at particular risk. According to scientists, this small furry relative of the rabbit can only live at high elevations in cool, rocky environments. They say it cannot survive in temperatures above 75°F for more than a few hours.  While other species adapted to lower elevations can move upslope as average temperatures rise, the pika has nowhere to go.

American Pika on the rocky terrain of RMNP's alpine tundra region. Image Credit: The Weather Gamut.

The American Pika, a native of RMNP, is sensitive to even small changes in climate.  Image Credit: The Weather Gamut.

Another impact of climate change is the spreading of non-native plant species that can thrive in the now warmer environment of RMNP. While Cheatgrass, a native of Eurasia, is found throughout the western US, it used to be limited to lower elevations.  Now, it is found as high as 9,500 feet in parts of RMNP. In addition to crowding out native plants and changing the look of the landscape, this invasive species is highly flammable. Its presence increases the danger of wildfires – something the West certainly does not need.

While these are just a few examples of the observed and expected impacts climate change is and will have on RMNP, scientists are continuing to research how additional increases in temperature will affect this national treasure.

Why Air Temperature Decreases with Height

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While visiting Colorado recently, I had the opportunity to explore Rocky Mountain National Park, and it was largely a vertical experience. Within its borders are 72 named peaks that reach above 12,000 feet in elevation. Traveling from the Beaver Meadow Visitor Center – elevation 7,840 feet – to the Alpine Visitor Center – elevation 11,796 feet – the drop in temperature was anything but subtle.

The reason for air being cooler at higher elevations is twofold. First, the sun’s rays heat the Earth’s surface, which in turn, radiates that warmth into the atmosphere. As you climb in altitude, there is less surface area of land available to heat the air. Second, as air rises, it expands and cools. This is because air density and pressure aloft are lower than at the surface.

The exact rate at which the temperature decreases with height – the environmental lapse rate – varies with location and daily conditions. On average, however, for every 1000 feet gained in elevation, the temperature drops by about 3.6°F.

Image Credit:British Geographer

Image Credit: The British Geographer

Fourth Warmest July on Record for Planet Earth

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This past July was fairly mild in the eastern United States, including here in New York City. For the western states and much of the rest of world, however, it was hotter than normal. In fact, the average temperature for the Earth as a whole soared into the record books yet again.

According to a report released this week by NOAA’s National Climatic Data Center, July 2014 was the fourth warmest July ever recorded for the entire planet. Earth’s combined average temperature for the month – over both land and sea surfaces – was 61.55°F. That is 1.15°F above the 20th century average. July 2014 also marked the 353rd consecutive month that our global temperature was above its long-term norm.

While above average heat dominated most of the planet this July, the Scandinavian countries were particularly warm. With a monthly temperature 7.7°F above normal, Norway marked not only its warmest July on record, but also its all-time highest monthly temperature for any month.   In the western U.S., several states posted a July temperature in their top ten warmest.

While the Earth’s atmosphere is warming overall, July’s temperature anomalies (both above and below average) highlight the fact that climate change is a complex global phenomenon that involves much more than what is happening in our own backyards.

Year to date, according to the report, 2014 is currently tied with 2002 as the Earth’s third warmest year on record. Global temperature records date back to 1880.

NCDC_2014_07

Image Credit: NOAA/NCDC

Opposing Winds Help Shape Great Sand Dunes National Park

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When you think of the Rocky Mountains, sand dunes are probably not the first thing that come to mind. While driving across southern Colorado earlier this month, however, giant white sand dunes glimmered in the distance. No, it was not a mirage; it was Great Sand Dunes National Park and Preserve.

Sprawling across the arid San Luis Valley between the San Jose Mountains to the west and the Sangre de Cristos to the east, the dunes cover 30 square miles and rise as high as 750 feet. They are the tallest dunes in North America and were formed, and continually maintained, by a complex interaction of geology and weather.

Over the millennia, according to the National Park Service, rocks from the surrounding mountains eroded and their sandy sediments were transported by stream to the valley floodplain. Prevailing southwesterly winds then carried the sand grains toward a low curve in the Sangre de Cristo Mountains, where they accumulated in a natural pocket.  On occasion, when the wind direction reverses during storms, the sand is pushed back toward the west. This process causes the dunes to grow vertically.

Two mountain streams, the Medano and Sand Creeks, also border the dunes. They capture sand grains from the eastern side of the dunes and carry them back to the valley floor.  This effectively recycles the sand and re-exposes it to the winds.

While the forces of wind and water are continually reshaping the massive dunes, they essentially remain in the same position.

Sand dunes nestled against the foothills of the Sangre de Cristo Mountains, Great Sand Dunes National Park, CO. Image Credit The Weather Gamut.

Massive sand dunes nestled against the foothills of the Sangre de Cristo Mountains, Great Sand Dunes National Park, CO.  Image Credit: The Weather Gamut.

Swamp Coolers

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Coming from the humid east coast, one of the first things you notice upon arrival in the southwestern United States is how dry the air is. Dew points are often in the 40s while the air temperature soars into the 80s and 90s during the summer. This is why swamp coolers are popular in the region.

A swamp cooler is an evaporative cooling device. It takes hot, dry outside air and blows it across water soaked pads. This allows the process of evaporation – the transition of liquid water to water vapor – to cool the air that is pumped into a building. It also adds some moisture to the inside air, making it more comfortable.

While the U.S. Energy Department says swamp coolers cost about one-half as much to install as central air conditioners and use about one-quarter as much energy, they do not work well everywhere. In hot, muggy climates, for example, the high relative humidity would significantly reduce the rate of evaporation. Moreover, adding extra water vapor to the air would not be considered a bonus in an already uncomfortably humid environment.

For this reason, only 3% of homes nationwide utilize swamp coolers, according to a report from the Energy Information Administration. In the arid Rocky Mountain region, however, they are found in more than 26% of all households.

Sign advertising swamp coolers in Salida, CO. Image Credit: The Weather Gamut

Sign advertising swamp coolers in Salida, CO.   Image Credit: The Weather Gamut.

Record Rainfall Floods Long Island

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Record rainfall swamped New York’s Long Island on Wednesday morning. Flash floods prompted evacuations, submerged cars on major roadways, and even uprooted trees. Local officials have also reported one weather-related death.

One of the hardest hit areas was Islip in Suffolk County, where 13.27 inches of rain fell in less than 24 hours. That is more than the town would normally get for an entire summer season and is nearly double its previous daily record of 6.7 inches set in August 1990. The storm also shattered the record for 24-hour rainfall in New York State. The previous record was 11.6 inches, which was measured in Tannersville, NY during Tropical Storm Irene in August 2011.

The intensity of this rain event, according to the NWS, was caused by a few factors. First, several different weather systems came together over Long Island and were fed by moisture from the Atlantic Ocean. Then, the storm essentially stalled in place for hours.

While Suffolk County bore the brunt of the rain, flash flooding also caused problems in nearby sections of New Jersey and Connecticut. Here in New York City, we were mostly unscathed. JFK airport (in Queens) reported 3.2 inches of rain, but less than an inch was measured in Central Park.

Flood waters strand cars on Sunrise Highway in Valley Stream on Long Island, NY. Credit: wpix11

Flood waters strand cars on Sunrise Highway in Valley Stream on Long Island, NY.                 Image Credit: pix11

Why U.V. Intensity Increases with Elevation

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One of the most important items on the packing list for my trip to Colorado this past week was sun-block. Averaging 300 days of sunshine per year at a mean altitude of 6,800 feet above sea level, the U.V. index in the Centennial state can range from high to extreme during the summer months.

The U.V. index is a scale that measures the intensity of the sun’s ultraviolet radiation. Readings vary from place to place as local factors affect the amount of U.V. light that reaches the ground. These include, the thickness of the ozone layer, latitude, season, cloud cover, and elevation. Developed by the NWS and EPA in the early 1990’s, it informs the public about the daily health risk of unprotected exposure to the sun.

At high elevations, the atmosphere thins and is less able to absorb U.V. radiation. With every 1000-foot increase in height, according to the National Institutes of Health, U.V. levels increase by about 4%.  So, in Denver, “the Mile High City”, U.V. radiation is about 20% stronger than a location at sea level at the same latitude. Heading up into the Rocky Mountains, where peaks can reach above 14,000 feet, the U.V. intensity soars even higher.

Credit: EPA

Credit: EPA

NYC Monthly Summary: July 2014

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July 2014 was fairly mild in New York City with a noticeable lack of extreme heat. On average, July typically brings the Big Apple six days with readings of 90°F or higher. This year, however, there were only three. That includes the first 90° day of the season. In the end, the city’s mean temperature for the month was 76.1°F. That is only 0.1°F above normal.

In terms of precipitation, July is usually NYC’s wettest month and this year it lived up to expectations. In fact, it was the city’s wettest July in five years. We received 5.59 inches of rain in Central Park, which is 0.99 inches above average. Most of this total came down in three significant events associated with heavy thunderstorms.

Credit: The Weather Gamut

Credit: The Weather Gamut

Credit: The Weather Gamut

Credit: The Weather Gamut