Unusually Intense El Nino May Lie Ahead, Scientists Say

by Andrew Freedman, Mashable, March 19, 2014

Since climate forecasters declared an "El Niño Watch" on March 6, the odds of such an event in the tropical Pacific Ocean have increased, and based on recent developments, some scientists think this event may even rival the record El Niño event of 1997-1998. If that does happen, then 2015 would almost be guaranteed to set a record for the warmest year on Earth, depending on the timing of the El Niño conditions.

El Niño and La Niña events refer to fluctuations in air and ocean conditions in the tropical Pacific. El Niño events are characterized by warmer than average sea surface temperatures in the central and eastern equatorial Pacific, and they add heat to the atmosphere, thereby warming global average temperatures. They typically occur once every 3 to 7 years and can also alter weather patterns around the world, causing droughts and floods from the West Coast of the U.S. to Papua New Guinea.

El Niño events tend to dampen hurricane activity in the North Atlantic, and some research has even linked El Niño events to civil conflicts in Africa.

When combined with global warming from greenhouse gas emissions and other sources, El Niño events greatly increase the odds that a given year will set a new global temperature record, as occurred in 1998.

SEE ALSO: Scientists: El Nino (May Be) A-Comin'

Tony Barnston, the chief forecaster at Columbia University’s International Research Institute for Climate and Society (IRI), told Mashable that the odds of an El Niño event developing during the next six months have increased to about 60%, which is up from just over 50% on March 6.

Global sea surface temperature anomalies, showing milder than average conditions in parts of the tropical Pacific. IMAGE: NOAA.

The Pacific Ocean exists in a constant state of unease, like an ocean badly in need of a mood stabilizer. Trade winds blow along and to the north of the equator from east to west, piling up warm ocean waters in the western Pacific, and causing sea levels to be higher in the west than they are in the east. Like a tipping bathtub, this setup can quickly be reversed with a reversal in trade winds and a sloshing of the warm sea surface temperatures from the western Pacific to the east, first at depth in a series of undersea waves known as Kelvin waves, and next toward the surface as the warm waters rise off the west coast of South America.

This complex chain of events, in which the atmosphere and the ocean act in concert to set up El Niño conditions, is well under way now. Starting in January of this year, there have been a series of strong bursts of winds coming out of the west in the equatorial tropical Pacific, and these have essentially replaced the typical easterly trade winds.

Partly as a result of these wind bursts, ocean buoys and satellites have detected the movement of unusually warm ocean waters from the western Pacific to the east. Ocean surface currents, which normally move westward across the Pacific basin, have reversed as well. El Niño forecasters have taken this as a further sign of a developing El Niño, and these conditions were a key reason why an El Niño Watch was issued on March 6.

Eric Blake, a hurricane specialist at NOAA’s National Hurricane Center in Miami, said conditions are changing rapidly in the Pacific, going from 50/50 odds of an El Niño, to a setup that eerily resembles the circumstances that preceded the monster El Niño of ‘97-'98.

“It’s something we haven’t really seen since the '97 El Niño,” Blake said of the westerly wind bursts and ocean observations. Instead of having trade winds blowing from the east at five to 10 mph, some locations in the western Pacific have had winds from the west blowing at up to 30 miles per hour, Blake says. This is important because it has ripple effects on the sea and below the sea surface.

“[It’s] not that we can’t step away from it, but with each passing day [an El Niño event is] becoming more likely,” Blake told Mashable.

Paul Roundy, a meteorology professor at the University at Albany, State University of New York, said that the westerly wind bursts have been extremely strong compared to historical records. Two of these events in particular, Roundy says, “were of similar amplitude to the events that preceded the 1997 El Niño.”

In addition, the warm waters moving eastward under the surface have been measured as much as nine degrees Fahrenheit above average, which is greater than similar waves observed prior to the 1997 El Niño event. “The present event is actually bigger than it was in 1997,” said Roundy.

Roundy cautioned that this doesn’t necessarily mean that the current event will be stronger than 1997-98 was, but it does raise red flags.

Wind patterns in the next two months will help determine whether an El Niño actually forms, and how strong it becomes. For example, even a temporary reversal of trade winds back to more typical conditions could dampen the eastward moving wave of warm water. So far, though, this hasn’t happened.

“Instead of switching to easterly winds there’s been an actual continuation of westerly winds,” Roundy said.

One problem that forecasters encounter when trying to foresee the likelihood and intensity of El Niño events is that there is limited historical data of the vast Pacific Ocean. Observational data only dates back to about 1990, Roundy says.

Making matters more difficult for forecasters is the recent degradation of a crucial buoy network used for El Niño and La Niña monitoring. Budget cuts have led to missing data, with the network known as the Tropical Atmosphere Ocean Project, or TAO array, operating at just 30 to 40% percent of capacity (see figure below).

Map showing the TAO buoys, with buoys reporting recent data colored in yellow and those without recent data in red. IMAGE: NATIONAL DATA BUOY CENTER

Roundy said the chances of an unusually strong El Niño event “Are much higher than average, it’s difficult to put a kind of probability of it … I’ve suggested somewhere around 80%”

“The conditions of the Pacific ocean right now are as favorable for a major event as they were in march of 1997. That’s no major guarantee that a major event develops but clearly it would increase the likelihood of a major event occurring,” Roundy says.

Barnston said any similarities of current conditions in the Pacific to those seen before the 1997-98 El Niño are an insufficient basis for forecasting an intense event. “As for the strength of the event, it is not known. Just seeing similarities with 1997 is not enough to go on," Barnston told Mashable in an email. "Unless we continue to get westerly wind events in the coming weeks, there is no guarantee that it will be a big event, and there is a 40% or so chance we will not get an El Niño at all,” he told Mashable in an email.

Roundy and Blake also urged caution about concluding that an El Niño event is nearly certain to occur, and that it will be intense. Rather, Blake said, the situation bears close watching.

“Anytime you have a non-negligible chance of something extreme happening, and you see it happening in a way that you haven’t seen in 15 to 20 years, it’s interesting,” says Blake.

http://mashable.com/2014/03/19/intense-el-nino-maybe/

Andrew Freedman: It's Been Exactly 29 Years Since Earth Had a Colder-Than-Average Month

A man clears snow from his vehicle on Capitol Hill in Washington, Monday, March 17, 2014. IMAGE: J. SCOTT APPLEWHITE/ASSOCIATED PRESS

by Andrew Freedman, Mashable, March 19, 2014

It's been exactly 29 years — or 348 consecutive months — since the last cooler-than-average month on this planet, according to new data released on Wednesday morning. The data, from the National Oceanic and Atmospheric Administration (NOAA), reflects the warming trend seen around the world during the past century, which scientists blame largely on the increasing amounts of manmade greenhouse gases in the atmosphere.

The last cooler-than-average month (based on a 1961 to 1990 average) on a global level was February of 1985, the year the first version of Microsoft Windows was released and the first Back to the Future film hit theaters.

NOAA announced that February of 2014, however, was not as unusually mild, globally-speaking, as other recent months, coming in as the 21st-warmest February since records began in 1880. When looking only at land surface temperatures, it was the coolest February since 1994, NOAA said.

SEE ALSO: This Winter Wasn't Nearly as Cold as You Think, Feds Say

The majority of the world experienced warmer-than-average monthly temperatures, and parts of the Arctic Ocean, western North Atlantic, and northeastern Pacific Ocean, among other areas, were record warm. Two areas that are normally frigid in February, Far East Russia and northern Scandinavia, had average temperatures of greater than 9 degrees Fahrenheit above average for the month.

Surface temperature anomalies for February 2014.

IMAGE: NOAA.

Parts of Finland, for example, saw February temperatures that averaged up to 16 degrees Fahrenheit above normal, and Germany had its sixth-warmest February on record.

Meanwhile, parts of Central and North America, including portions of thecontinental U.S. east of the Rocky Mountains, along with western Asia had monthly average temperatures that were more than 9 degrees Fahrenheit below their February average, NOAA said.

For meteorological winter, which runs from December through February, the global average temperature was the eighth highest on record, at more than 1 degree Fahrenheit above the 20th century average.

Austria, where records extend back 247 years, had its second-warmest winter on record, and Switzerland, the Netherlands, and Denmark had winters that ranked in their top 5 warmest on record, NOAA said.

The U.S., however, had its 34th coldest winter on record, with a split personality featuring above average temperatures across the West, and much below average temperatures from the Midwest to the East. While there were many winter storms that criss-crossed the U.S. this winter, the country saw nothing like what hit the UK, where 12 major storms struck between December and the end of February, breaking rainfall records and causing extensive damage.

Northern Hemisphere snow cover was above average for the winter, and the 17th largest for February since such records began 48 years ago. North America had its ninth largest February snow cover extent on record, while Eurasia had its 21st largest, NOAA said.

According to data from the National Snow and Ice Data Center (NSIDC), the average February Arctic sea ice extent was 5.58 million square miles, which was 350,000 square miles, or 5.9%, below the 1981 to 2010 average of 5.93 million square miles. At times, Arctic sea ice extent flirted with record low levels for February, and the overall February extent was the fourth lowest February Arctic ice extent since satellite records began in 1979.

In contrast, Antarctic sea ice, which covers a smaller area than Arctic sea ice, was well above average, at the fourth largest February ice extent on record.

Climate scientists have found that manmade climate change is very likely causing a decline in Arctic sea ice extent, but that the picture for the South Pole sea ice is more complicated, due to natural climate variability, the loss of the ozone layer in the upper atmosphere, and other causes.

While climate skeptics have seized on the growing Antarctic sea ice extent as evidence that global warming is not, in fact, melting global sea ice, most climate scientists say the sea ice trends are consistent with what is expected from manmade global warming.

http://mashable.com/2014/03/19/29-years-cooler-than-average/

Andrew Freedman: In Much of U.S., Extreme Cold is Becoming More Rare

by Andrew Freedman, Climate Central, January 7, 2014

The deep freeze that continues to affect the U.S. has resulted in numerous daily temperature records, and some all-time cold temperature records. But in general, this Arctic outbreak, courtesy of a huge chunk of the polar vortex that the jet stream temporarily dislodged from the Arctic, is bringing the coldest temperatures in 20 to 30 years to many areas of the Midwest, Ohio Valley, Deep South, and the eastern seaboard.

Trend in frigid nights in St. Louis from the 1970s to the most recent decade. Yellow line indicates linear trend since 1970.
Click to enlarge the image. Credit: Climate Central.

Some of the most severe cold has affected the Midwest, from Minnesota to Illinois and east to Michigan. Chicago set a record for the 7th coldest noontime temperature since 1930, with a temperature of just -14 °F at midday on Monday. But the city did not set any all-time cold records.

While the cold temperatures have been unusual and even deadly, climate data shows that intense cold such as this event is now occurring far less frequently in the continental U.S. than it used to. This is largely related to winter warming trends due to manmade global warming and natural climate variabiility.

Climate Central calculated the number of nights below a specific temperature threshold for dozens of U.S. cities based on the local climatology and current weather conditions. The calculations encompass the entire winter season, and show that overall there is a downward trend in the number of extreme cold nights like we’re currently experiencing – although there are variations in a few cities. This trend is consistent with climate studies showing that overall, winters across the contiguous U.S. have warmed by 0.61 °F per decade since 1970, and every region has warmed at least somewhat over that time.

Trend in frigid nights in Minneapolis-St. Paul from the 1970s to the most recent decade. Yellow line indicates linear trend since 1970. Click to enlarge the image. Credit: Climate Central.

Winters have also warmed over a longer period of record, but the fastest warming has taken place during the past few decades. In addition, the fastest warming has taken place at night, rather than during the day, which is consistent with climate change projections.

For example, in Minneapolis in the 1970s (1969-79), there were an average of 14.7 nights with temperatures below minus 10 °F. But in the past decade (2002-2012), that number has fallen dramatically, to about 3.8. The calculations run from July through June of the following year, so that we wouldn't break up the winter season.

In Detroit in the 1970s, there were an average of 7.9 nights with temperatures below zero degrees. But now, that number is closer to 2 nights. And in Washington, D.C., the number of nights with a low of 20 °F or below was 13.5 in the 1970s, but was closer to 8.3 in the past decade. The overnight low at Reagan National Airport on January 7 was 6 °F.

Trend in frigid nights in Detroit from the 1970s to the most recent decade. Yellow line indicates linear trend since 1970. Click to enlarge the image. Credit: Climate Central.

And in St. Louis, the 1970s featured an average of 3.8 nights with a low of 0 °F or below, yet in the past decade, the average for such frigid nights fell to zero.

A Climate Central analysis released in February 2013 found that the states with the coldest winters have been warming the fastest, including states hard hit by the current cold snap. The top 5 fastest-warming states, the analysis found, were Minnesota, North Dakota, Wisconsin, Vermont and South Dakota.

Beyond the U.S., the big picture which shows that global temperatures are on the rise. The rate of warming may have slowed over the last 15 years, but even so, each of those years was warmer than the 20th century average. In fact, it has now been 345 consecutive months and counting where global average temperatures have been above the average for the last century (as of November, that is — numbers for December have not yet been finalized). And there is ongoing research that suggests that rapid Arctic warming, which has been linked to human-caused global warming, may be creating more amplified weather patterns like the one that we are currently seeing, with sharp curves in the jet stream steering weather systems in unusual ways. If that hypothesis is true, we could actually experience more extreme cold snaps, even as the planet continues to warm.

http://www.climatecentral.org/news/extreme-cold-events-in-a-climate-context-16931

Sea Level and Risk of Flooding Rising Rapidly in Mid-Atlantic

by Andrew Freedman, Climate Central, December 12, 2013

During the 20th century, sea levels along the highly populated U.S. Mid-Atlantic coastline between New York and Virginia rose faster than in any other century during the past 4,300 years, according to a new study. And as those sea levels continue to increase as a result of global warming and local land elevation changes, the risks of coastal flooding will dramatically escalate.

The study, by geoscientists at Rutgers and Tufts Universities and published in the new journal “Earth’s Future,” took a comprehensive look at the history of sea level in the Mid-Atlantic, combining sediment records of prehistoric sea level with modern data, which includes readings from tide gauges and satellite instruments. The result is one of the most in-depth examinations of past, present, and future sea level rise of any region in the U.S.

The amusement pier in Seaside Heights, NJ, was heavily damaged by Hurricane Sandy. Credit: Master Sgt. Mark C. Olsen, New Jersey Air National Guard.

The study warns that regional planners will need to factor local rates of sea level rise when making decisions on building any long-lasting infrastructure, from water treatment facilities to Manhattan skyscrapers and Atlantic City casinos.

For example, the study estimated that the New Jersey shore will likely see a sea level rise of about 1.5 feet by 2050, and about 3.5 feet by 2100, at least a foot higher than the average global sea level rise over the rest of the century. Using a middle-range scenario for future sea level rise, the study found that by 2050, flooding caused by a 10-year storm, which has a 10% probability of occurring each year, would exceed all historic storms in Atlantic City.

According to the study, relative sea levels in the Mid-Atlantic region rose at about 0.10 inches per year during the 19th century, and that rate accelerated to 0.15 inches per year during the 20th century. That may not sound like much, but it is already enough to make a major difference when storms strike.

The impact from Hurricane Sandy clearly illustrates that. The study found that a 7.87-inch global sea level rise during the 20th century, which was largely driven by manmade global warming, caused Hurricane Sandy to flood an additional 27 square miles compared to what it would have if the storm had struck in 1880 when sea levels were lower. Using figures from Climate Central’s sea level rise database, the researchers (who were not affiliated with Climate Central) found that sea level rise exposed an additional 83,000 people to coastal flooding, with about 45,000 in New York City and the rest in New Jersey.

While two factors largely control global average sea level — temperature and variations in the volume of the Earth’s ice sheets and mountain glaciers — local rates of relative sea level rise are more complicated.

While the U.N. Intergovernmental Panel on Climate Change (IPCC) projected that global mean sea level rise for 2081-2100 will likely be between 10 and 32 inches, those numbers mean little to local policymakers, who must make decisions based on local sea level rise rates that often differ from the global average. Those differences are the result of several factors, including ocean currents that can cause faster or slower rates of sea level rise in some areas, groundwater depletion, which can result in sinking land, and gradual post-ice age adjustments of the land.

In the Mid-Atlantic region, it turns out, all three of these factors are conspiring to accelerate sea level rise. Every part of the region saw the level rise at a faster rate than the global trend, the study found. In fact, that rate since the early 1900s was nearly double the global average.

Locations that sit atop a coastal plain, such as the Jersey Shore, are seeing the fastest rates of sea level rise compared to those Mid-Atlantic coastal locations that are built on top of bedrock, such as New York City, since the geology of the coastal plain features more settling of the land from groundwater depletion and long-term sediment compaction. Other studies have also identified the Mid-Atlantic as a so-called “hot spot” of sea level rise, but the new research provides more statistical proof that modern sea level rise in this region is outpacing even periods from several thousand years ago. 

“The study highlights the importance of geological data when making predictions for coastal inundation during the 21st century and that it is important to take a regional approach,” Simon Engelhardt, a professor at the University of Rhode Island who was not involved in the new study, said in an email.

Comparison of tide gauges along the coast with the Battery in Manhattan, showing sea levels are rising slightly faster along the coastal plain than in Manhattan. (The tide-gauge records are referenced to a synthetic 1900–1920 datum.)  Click image to enlarge. Credit: Miller et al. 2013.

To put recent rates of sea level rise into historical perspective, the study found there is at least a 95% probability that the rate of sea level rise in the Mid-Atlantic during the 20th century was faster than any century in the past 4,300 years, and a 67% probability that it was faster than any century in more than 6,600 years.

“The sea level rise that we’re seeing now is very significant,” including in a “prehistoric context,” said study co-author Ben Horton of Rutgers University, in an interview.

The study projects that lower Manhattan will see about 8.6 inches of sea level rise by 2030, 15.7 inches by 2050, and 38 inches, or just more than 3 feet, by 2100. The 15.7 inches of sea level rise by 2050 would be sufficient to transform what would be considered a moderate 10-year storm today to reach the same flood level as a 100-year storm would. The higher-end scenario considered in the study would bring 5.5 feet of sea level rise to Lower Manhattan by 2100. That would cause a 10-year storm event to bring flooding comparable to Hurricane Sandy, which brought the highest storm tide on record to Lower Manhattan. Every subway tunnel connecting Manhattan with Brooklyn and Queens flooded, along with transit stations in adjacent areas of New Jersey and all three of the city's major airport hubs.

A separate study published in 2012 found that similar increases in storm surge risk would occur at many other coastal locations in the U.S.

Assuming continued groundwater extraction rates at coastal plain locations, those areas would see a greater amount of sea level rise, the study found. The study projected that those areas could be in for a rise of 9.8 inches by 2030, 1.5 feet by 2050, and about 3.5 feet, by 2100.

While the study shows that the main component of future sea level rise will be from global sea level rise, local land elevation changes should be factored into development decisions, since they will influence the rate and extent of relative sea level rise at the local level. The study noted that there are currently limited tools for policymakers to use to factor in sea level rise to the planning process.

Even the Federal Emergency Management Agency’s newest flood elevation data, released this year and used to help determine federal flood insurance requirements, failed to include sea level rise projections. “They are accordingly relevant to insuring against current risks but do not provide appropriate guidance for long-term planning,” the study said.

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Follow the author on Twitter @afreedma or @ClimateCentral. We're also on Facebook & other social networks.

http://www.climatecentral.org/news/sea-level-and-risk-of-flooding-rising-rapidly-in-mid-atlantic-16822

Wavenumber-5 Rossby waves used to predict extreme heat waves

New Method Could Provide Heat Wave Early Warnings

by Andrew Freedman, Climate Central, October 27, 2013

Heat waves pose major health and economic problems in the U.S. and around the world. In 2012, a heat wave baked the U.S., shattering temperature records, causing 82 deaths, and withering crops across the country. Improved forecasts with longer lead times could be an asset to emergency managers, farmers, and others who suffer the worst impacts from heat waves. New research holds some promise of being able to predict them up to 20 day in advance across the U.S. by monitoring weather patterns.

The new research builds on the work of Carl Gustav-Arvid Rossby, a giant in the field of meteorology. In the mid-20th century, Rossby studied the perturbations in the jet stream as air moves from west-to-east above the Northern Hemisphere. A math and physics whiz who landed on the cover of Time Magazine in 1956, his work unlocked the secrets of how the jet stream can become contorted into deep dives, or troughs, and large ridges, and how these waves move slowly around the world.

New research offers the promise of forecasting heat waves in the U.S. up to 20 days in advance. Credit: Wikimedia Commons

Now, using Rossby’s insights and the tools of modern meteorology, a research group has made headway toward an elusive goal: predicting the probability of extreme events (in this case, heat waves) two to three weeks in advance.

The study, published in the journal Nature Geoscience on Sunday, shows that long-lasting, intense heat waves in the U.S. — which are becoming more common and severe due to manmade global warming — tend to be preceded by a particular jet stream configuration. By looking for these patterns, weather forecasters could improve their chances of accurately predicting extreme heat events, which are among Mother Nature’s deadliest weather hazards, beyond the traditional 10-day limit of current weather forecasting techniques.

Time Magazine cover in 1956 featuring Carl Gustav Rossby, a pioneer in the study of the atmosphere.

Credit: Time.com

Extensive research has shown that manmade global warming is already exacerbating extreme heat events. The new study does not contradict this past research since it looked only at the predictability of such events, not the role played by increasing average temperatures that make a typical heat wave today more severe than similar events a half-century ago.

For the study, researchers from the National Center for Atmospheric Research (NCAR) in Boulder, Colo., used a computer model to simulate 12,000 years of summertime weather over the Northern Hemisphere. The study analyzed nearly 6,000 simulated heat waves that met the study's criteria, and found that heat waves were more likely to build over the U.S. when a specific pattern of Rossby waves appeared. Rossby waves are large meanders in high-altitude winds that have a significant influence on the weather.

When a "wavenumber-5" pattern of Rossby waves — the presence of five persistent waves of low-pressure and high-pressure areas in the upper atmosphere around the Northern Hemisphere — appeared, a major summertime heat wave was more likely to build over the U.S. about 15 to 20 days later.

In some cases, the probability of a heat wave was more than quadruple what would be expected by random chance alone.

This distinctive pattern, with a high pressure ridge near the Aleutian Islands of Alaska, a trough over the Western U.S., and another high pressure ridge closer to the East Coast, can favor slow-moving weather features, raising the odds of prolonged heat waves.

During the nearly 3 weeks leading up to a heat wave, the five ridges and five troughs that make up a wavenumber-5 pattern migrated slowly westward around the globe, moving against the west-to-east airflow of the jet stream itself — a behavior that Rossby helped to explain. Eventually, models showed that an area of high pressure at the upper levels of the atmosphere would move from the North Atlantic into the United States, reducing rainfall and increasing temperatures.

Visualizing fluctuations in the jet stream, including Rossby Waves. Credit: NASA.

The researchers found hints that the association between heat waves and this jet stream configuration was true in observations of modern data going back to 1948, but there were too few events meeting the study criteria to draw firm conclusions from the observations, said lead author Haiyan Teng of NCAR.

In identifying this configuration, the researchers acted in a similar way to doctors seeking out specific genetic markers that can indicate that a patient will be more likely to develop a particular disease.

In an interview, Teng called the findings “just a little tiny step” toward the development of an early warning system for heat waves, but said the findings are particularly significant because they show that extreme heat events in the U.S. are not necessarily driven by slowly-evolving conditions in the tropics, like El Niño or La Niña events or the South Asia Monsoon, which other studies have looked to as possible sources of predictability.

Instead, the study found, random variability in midlatitude weather patterns may be responsible for setting up the necessary conditions for extreme heat events.

Stephen Bennett, the president and founder of EarthRisk Technologies in San Diego, a firm that forecasts the long-term risk of extreme temperature events (both hot and cold) for the energy industry, said the new study contains “exciting results” that agree with the company’s own findings.

A blocking pattern in the jet stream set up conditions for a historic U.S. heat wave in March 2012. Credit: NOAA

"Teng’s work is fantastic in that it quantifies some of these relationships using a much larger dataset than observational data will allow,” Bennett said in an email. “While the physical explanation remains elusive… it’s important to note that the atmospheric patterns in-and-of themselves can be used as aids for prediction."

Mingfang Ting, a researcher at Columbia University’s Lamont-Doherty Earth Observatory in New York who was not involved with the new study, said the study is important because it provides a potential way to eliminate a forecasting dead zone that exists between two timescales, the short-term out to ten days, which is handled well by current weather models, and seasonal forecasting that looks more at long-term average temperatures over the course of a few months. “The time scales in between these two prove to be challenging to predict,” she said in an email.

Separate research has suggested that rapid Arctic climate change may be slowing down the jet stream in the northern mid-latitudes, leading to slower-moving Rossby waves, which would favor more frequent stuck weather patterns that can lead to heat waves, droughts, and other extreme weather and climate events. This study did not examine the potential Arctic connection.

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Follow the author on Twitter @afreedma or @ClimateCentral. 

http://www.climatecentral.org/news/u.s.-heat-waves-may-be-predictable-20-days-in-advance-study-finds-16663

Andrew Freedman: Drunken [backwards, east to west] weather pattern leads to deadly heat

‘Drunken’ Weather Pattern Leads to Deadly Heat

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by Andrew Freedman, Climate Central, July 18, 2013

The heat wave that has built across the eastern U.S. — roasting cities from Memphis to Washington to Boston in a stifling blanket of heat and humidity — has had one strange characteristic that meteorologists cannot yet explain in a long-term climate context. Rather than moving west to east, as typical weather patterns do in the Northern Hemisphere, weather systems across the country have moved in the opposite direction, like a drunken driver on a dark stretch of highway, drifting from east to west during the past two weeks.

And like drunk driving, the weather pattern is having serious —  even deadly — consequences, with at least one death being blamed on the heat, according to the Associated Press. 

The "Bermuda high" that often pumps warm and humid air into the East Coast during July and August decamped around July 11 from Bermuda and came ashore, eventually migrating all the way to the Midwest by July 15. The summertime high pressure ridge, sometimes referred to as a “heat dome,” has set air pressure records as recorded by weather balloons in Pittsburgh and Virginia, and has been responsible for sending air temperatures rocketing into the mid- to upper-90s, and even the lower triple digits, in some parts of the East.

Animation of 500 mb pressure anomalies from July 12 to July 18, 2013, showing the migration of the heat dome from east to west (in orange and red) and the upper level low toward Texas (blue). Credit: Ryan Maue for Weatherbell.com.

New York’s John F. Kennedy Airport, for example, broke a daily high temperature record on Thursday, with a high of 100°F. The heat index, which is a measure how the temperature feels to the humid body, has reached the dangerous range of 105 to 115°F in some spots. Heat is the No. 1 weather-related cause of death in the U.S. in an average year.

Making the heat even more dangerous is that many areas affected have not been getting overnight relief. In New York’s Central Park, the overnight low on Wednesday night into Thursday morning was 79 °F, tying a record for the highest such temperature for the date. Record-high low temperatures were also set in the Midwest and Mid-Atlantic. Washington, D.C., may challenge a record for the longest number of consecutive hours with air temperatures above 80 °F. 

The National Weather Service issued heat warnings and advisories for nearly two-dozen states on Thursday, with a smaller number to be affected on Friday in the densely populated Mid-Atlantic and Northeast.

While heat waves during July are nothing new, the weather pattern that is creating this one is rare enough for meteorologists to take note. In addition to the Bermuda leaving its more tropical locale and camping out in Michigan, an area of low pressure at the upper levels of the atmosphere has also been roaming the U.S. since July 11, drifting from east to west, traveling from the Mid-Atlantic states to Texas, where it brought some welcome rainfall.

With the jet stream (in blue and green) located far to the north, over Canada, weather systems have drifted from east to west across the U.S. Credit: Weatherbell.com.

The air flow heading in the opposite direction across the U.S. is abnormal, as is the strength of the dome of high pressure. In recent years there have been numerous instances of strong and long-duration high pressure areas that have led to extreme weather events, including the Russian heat wave of 2010. According to NOAA, scientists are scheduled to meet at Oak Ridge National Laboratory in September to explore whether such “monster ridges” of high pressure are becoming more frequent or more intense as the atmosphere warms in response to manmade greenhouse gas emissions.

Jon Gottschalck acting chief of the Operational Prediction Branch at NOAA’s Climate Prediction Center, told Climate Central in an email that it’s not yet clear exactly how unusual the recent weather pattern has been, or what has been driving it. “Yes, the evolution you describe of the upper-level low and high pressure ridge moving east to west is definitely unusual. But it is not easy to quantify really how unusual,” he said.

“It would take considerable time to crunch through the data and utilize a methodology to accurately pick events like this that have occurred in the historical record and quantify [them]. From a climate-forcing perspective, there is no clear climate pattern right now that we can point to as a contributing factor and so we can really only attribute this evolution to natural internal variability, at least at this stage.” [no, you cannot attribute it to anything since no study was done!]

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http://www.climatecentral.org/news/drunken-weather-pattern-leads-to-deadly-heat-16260