Tag: North Atlantic Oscillation

Climate: UK weather trends toward extremes

An extratropical cyclone
An extratropical cyclone

North Atlantic pressure variations driving variable pattern

Staff Report

FRISCO — Weather patterns affecting the UK are  becoming more volatile, climate researchers concluded in a new study, concluding that the trend is being driven by extreme variations in pressure over the North Atlantic.

The month of December is showing the biggest variation, but contrasting conditions, from very mild, wet and stormy to extremely cold and snowy are a clear sign of less stable weather, University of Sheffield scientists reported in a study published last month in the Journal of Climatology.

Winter weather conditions are commonly defined using the North Atlantic Oscillation, a south-north seesaw of barometric pressure variations over the North Atlantic which determine the strength of the westerly winds that shape North Atlantic weather systems. Continue reading “Climate: UK weather trends toward extremes”


Climate: Last summer’s Greenland ice sheet surface meltdown linked with an unusual kink in the jet stream

July 2012 melt event far surpassed previous record

In the images above, areas classified as “probable melt” (light pink) correspond to sites where at least one satellite detected surface melting. Areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected melting.
In the images above, areas classified as “probable melt” (light pink) correspond to sites where at least one satellite detected surface melting. Areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected melting.

By Summit Voice

SUMMIT COUNTY — Along with an unusual constellation of low clouds, changes the jet stream were also a factor in last summer’s exceptional surface melt of the Greenland Ice Sheet, according to a research team led by the University of Sheffield’s geography professor Edward Hanna.

A NOAA study published in March indicated that a lingering layer of thin, low clouds helped intensify atmospheric conditions leading to the meltdown.

Hanna and his colleagues used a computer model simulation (called SnowModel) and satellite data to confirm that last summer’s meltdown was unprecedented in the past 50 years. About 90 percent of the ice-sheet surface melted July 11, far surpassing the previous known surface melt extent record of 52 percent in 2010. Continue reading “Climate: Last summer’s Greenland ice sheet surface meltdown linked with an unusual kink in the jet stream”

European forecasters look to NAO for climate clues

Seasonal shifts in the North Atlantic Oscillation have a strong effect on European weather.

New study helps track seasonal shifts in North Atlantic storm track

By Summit Voice

FRISCO — Just as weather forecasters in the western U.S. look at El Niño and La Niña to help get a handle on season outlooks, European meteorologists are carefully analyzing the North Atlantic Oscillation for climate clues. The job is easier in some years, according to a new study carried out by the National Oceanography Centre.

The research shwoed that the relationship between our winter weather and the strength of the airflow coming in from the Atlantic – one of the factors used by forecasters to predict the weather – is stronger in some years than others. The results were recently published in the Royal Meteorological Society publication Weather.

“There are two major atmospheric pressure systems centred around Iceland and the Azores that are very influential for the weather in Europe. Air flows between these two systems, bringing mild air from the North Atlantic to Europe,” said co-authors Joël Hirschi and Bablu Sinha from the National Oceanography Centre. Continue reading “European forecasters look to NAO for climate clues”

‘Wavering’ El Niño vexes winter weather outlook

Not much drought relief expected this winter.

NOAA calls for warmer-than-average conditions in the West

By Summit Voice

SUMMIT COUNTY —This year’s wavering El Niño isn’t just vexing Colorado forecasters. Forecasters with the National Oceanic and Atmospheric Administration say that getting a handle on the winter forecast has been tough.

“This is one of the most challenging outlooks we’ve produced in recent years because El Niño decided not to show up as expected,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center. “In fact, it stalled out last month, leaving neutral conditions in place in the tropical Pacific.” Continue reading “‘Wavering’ El Niño vexes winter weather outlook”

Weather: El Niño, or La Niña’s ghost?

El Niño still struggling to develop

Will a negative Pacific Decadal Oscillation influence Colorado’s winter weather? Graphic courtesy NASA.
The three-month precipitation outlook from the Climate Prediction Center.

By Bob Berwyn

SUMMIT COUNTY — Climate experts are still hedging their bets when it comes to an outlook for the coming winter, with the official outlook from NOAA’s Climate Prediction Center showing no strong trend toward above- or below-average precipitation.

A somewhat murky El Niño outlook is clouding the picture, with sea surface temperatures in the equatorial Pacific ranging above average, but cooling down from just a month ago.

“It’s vexing … the models are just not up to the task,” Wolter said. Overall, he said he’s “guardedly optimistic” that Colorado will see at least close to an average snowfall year, which would would be critical to maintaining water supplies in the state’s depleted reservoirs. Continue reading “Weather: El Niño, or La Niña’s ghost?”

Global warming: Harp seal habitat vanishing fast


Sea ice in breeding areas declining by 6 percent per decade; entire age classes are being lost

By Summit Voice

SUMMIT COUNTY — Along with declining habitat for polar bears, harp seal populations in the far north are also taking a big hit from global warming, according to researchers who documented reduced winter sea ice cover in key harp seal breeding grounds.

That decline has resulted in sharply higher death rates among seal pups in recent years, according to a new Duke University-led study. The researchers documented some movement of breeding harp seals to more stable sea ice environments, but thousands are still returning to traditional breeding grounds, where entire generations of seals are being lost.

“The kind of mortality we’re seeing in eastern Canada is dramatic. Entire year-classes may be disappearing from the population in low ice years – essentially all of the pups die,” said David W. Johnston, research scientist at the Duke University Marine Lab. “It calls into question the resilience of the population.” Continue reading “Global warming: Harp seal habitat vanishing fast”

Global warming: New NOAA study suggests winter droughts may become the ‘new normal’ in the Mediterranean region

Warming sea surface temperatures linked with drought cycles

Reds and oranges highlight lands around the Mediterranean that experienced significantly drier winters during 1971-2010 than the comparison period of 1902-2010. GRAPH VIA NOAA.

By Summit Voice

SUMMIT COUNTY — The Mediterranean has long been identified as an area that will feel global warming impacts because of water scarcity in the region, a rapidly increasing population, and climate modeling that projects increased risk of drought.

And now, a new NOAA study shows that wintertime droughts are becming increasingly common in the region, and human-caused climate change is partly responsible. In the last 20 years, the Mediterranean region has experienced 10 of the driest 12 winters on record, according to data compiled by the Cooperative Institute for Research in Environmental Sciences (CIRES).

“The magnitude and frequency of the drying that has occurred is too great to be explained by natural variability alone,” said Martin Hoerling, Ph.D. of NOAA’s Earth System Research Laboratory in Boulder. Hoerling is the lead author of a paper published online in the Journal of Climate this month. Continue reading “Global warming: New NOAA study suggests winter droughts may become the ‘new normal’ in the Mediterranean region”