Winter Outlook for 2012-13

The Climate Prediction Center released its early outlook for the upcoming winter this morning.  Much of the western U.S. will see warmer than normal temperatures while cooler than normal temperatures are expected for the Florida peninsula.  Equal chances of above or below normal temperatures are forecast for much of the East.

Much of the West will be dry particularly in the Pacific Northwest.  The Central Gulf region is expected to be wetter than normal.  This may help ease the drought in Georgia and South Carolina.

Click on either graphic for a larger version or go here for the temperature map and here for the precipitation map.  Image Credit: NOAA\CPC.

Leaves Are Changing, But Later

By Climate Central

If it seems like autumn leaves are taking longer to change color, you’re not imagining things. Over the past 25 years, the onset of autumn has shifted. Fall now arrives two and a half weeks later in Columbia than it did in the early 1980s. This reflects the shift that's happening around the country, where leaves are staying on trees about 10.5 days later across the lower 48 states (see below).

The journal sourced is on the graphic.  Click on the image for a larger view.  Image Credit: Climate Central.

How do we know? Using satellite-based measurements of the Normalized Difference Vegetation Index (NDVI), which gauges leaf cover over wide areas, researchers at the Seoul National University in Korea found that the end of the growing season occurred progressively later over the course of their 26-year study. By noting the time of year changes in color occurred most rapidly, the researchers could track when fall in the lower 48 states started between 1982 and 2008.

The Global Weather Pattern Shifts

The previous post described how changes in the Arctic were causing changes in the weather and climate.  These changes extended down in the mid-latitudes where the impacts included cold, snowy winters.  However, the impacts of a warming earth do not end there.  Research shows that mankind is shifting the entire global atmospheric circulation.

Background

Meteorologists have developed an idealized view of the global atmospheric circulation over the past century.  It has long been recognized that there is too much heat at the equator and too little at the poles.  The atmosphere acts like “the great equalizer “ by transporting heat from the tropics to the poles.  If the earth were not rotating, this would be a simple straight-forward transfer.

The situation is complicated by the fact that the earth does rotate on its axis.  This has given rise to the three-cell global circulation model.  The three cells from the tropics to the poles are named: Hadley, Ferrel, and Polar.  This model is pictured below with the resulting wind patterns.

The three-cell general circulation model of the atmosphere.  This is an idealized model based on observations.  Image credit: NASA.

The Hadley cell (also known as the tropical cell) extends from the equator to 30 degrees latitude.  Many of the world’s major deserts lie at the poleward extent of the Hadley cell where the air descends from upper levels.  This produces a persistent dry climate with little rainfall.  The North American Desert, Sahara, Australian Desert, and Kalahari Desert all are products of this circulation.

The Effects of Losing Arctic Sea Ice

A dramatic loss of Arctic sea ice occurred this year resulting in a record-shattering minimum in mid-September.  The implications were touched upon in a previous post.  However, it is recognized that the loss of Arctic sea ice is changing the ecology, geology, and meteorology of the region.

I will focus on the meteorology in this post.  The Arctic is warming at a rate that is twice that of the mid-latitudes in a phenomenon known as arctic amplification.  This faster warming is reducing the temperature gradient between the high and mid-latitudes which in turn is changing the dynamics of the jet stream.

Image Credit: NOAA.

The jet stream is a river of high velocity winds in the atmosphere.  It meanders generally from west to east around the globe.  The speed of the wind in the jet stream is usually stronger in the winter than in the summer, because the north-south temperature gradient is much stronger in winter.

A cross-section of the atmosphere shows how the lowest layer of the atmosphere, the troposphere, changes from the equator to the pole.  There are three circulation cells in the northern hemisphere and the jet streams are at the upper boundaries of the cells.  The jet stream helps to drive storm systems across the country so that knowledge of its future helps forecast future weather.

How Cold Does It Have To Be?

As we close in on the last quarter of the year (and the end of baseball’s regular season), 2012 is on track to be the country's hottest year ever recorded. But as Yogi Berra says, “It ain't over 'til it's over.”

So how cold would it need to be for the rest of the year to miss the record?

Click on the image to see the high resolution version.  Image Credit: Climate Central.

Pretty darn cold. As you can see in the graphic above, based on temperature data from NOAA’s NCDC, if we have normal fall and winter temperatures every month for the rest of the year, we will clearly break the record (yellow line). If it stays warmer than average, we will break the record by even more (orange line). In order to miss breaking the record as the hottest year ever recorded in the United States, the months of September through December would each need to be among the coolest third of those months on record (green line).

Arctic Sea Ice Matters

A record low in the Arctic sea ice extent occurred on September 16, 2012 and it was the lowest in the satellite record which started in 1979. Even more troubling was that this year also saw a record low in sea ice volume.

Click on the image for a high-resolution version. Image Credit: NSIDC.

The previous record minimum extent occurred in 2007.  What was extraordinary about this year was that weather conditions were not as favorable for melting as in 2007.  That year was noted for long periods of sunshine which allowed the ice to melt over much of the Arctic.  This year came on the heels of a cold winter in which the ice extent came close to normal.  There were more clouds and a powerful storm which hit the Arctic in early August which helped to break up more of the thin ice.

Click on the image for a high-resolution version. Image Credit: Climate Central.

The Heat Is On

Image Credit: Climate Central.

The January-August period was the warmest first eight months of any year on record for the contiguous United States. The national temperature of 58.7°F was 4.0°F above the 20th century average, and 1.0°F above the previous record warm January-August of 2006. During the eight-month period, 33 states were record warm and an additional 12 states were top ten warm. Only Washington had statewide temperatures near average for the period.

The statewide ranks of temperatures since 1895 and the top ten warmest January-August periods in South Carolina.  Image Credit: NOAA\NCDC.

Relief In Sight

It is about this time of year after a long hot summer that everyone longs for the heat and humidity to be over.  Meteorological summer is over, but the misery of summer lingers. People are sick and tired of the heat and humidity.

Therefore the first cold fronts of the fall season are a welcome relief.  No need to get out the jackets, but it will be refreshing once a cold front passes through the Midlands Saturday night.  The change is noticeable on the 7-day forecast for Columbia.

The 7-day forecast.  Image Credit: WLTX-TV

An Updated View Of Climate Change

The American Meteorological Society updated their statement on climate change last week while much of the country was preoccupied with Hurricane Isaac.  Research has greatly increased our understanding of the climate system and the body of research continues to expand at a rapid pace.  It overwhelmingly supports the consensus that the earth is warming and it is being caused by the burning of fossil fuels and deforestation.

The full statement can be found here.  This newer version is a better read and accessible to the general public.  It is a conservative document and I am sure does not go far enough for some.  However, it is an important one as it represents the position of the society.  It is based on the science and not someone’s ideology or political orientation.  The previous statement on climate change can be found here.

An important point is summarized at the end in the final remarks:

Isaac's Biggest Threat: Water

Update: 1:35 a.m. EDT August 29,

The eye seems to have stalled off the coast of Grande Isle, LA.  It seems to be doing a loop on radar and this will delay landfall.  Much of southeastern Louisiana will be pounded by high winds, heavy rains, and storm surge for much of Wednesday.

The radar view from Slidell, LA at 1:05 a.m. EDT, August 29, 2012.

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As Isaac makes landfall in southeastern Louisiana it is likely to be a category 1 hurricane.  This may not sound like much, but the winds are still a danger and shelter will be needed.  However, it is the water, both surge and rain, that are the biggest threat.  The storm is expected to slow down as it moves through southeastern Louisiana and could produce rain through Wednesday night.

The forecast for Isaac as of 11 a.m. EDT, August 28, 2012.  Click on the images for a larger view.  Image Credit: NOAA/NHC.

At 11 a.m., Tuesday, Isaac was still a tropical storm; however it was close to becoming a hurricane with maximum sustained winds of 70 mph.  This is strong enough to take out trees and power lines with some minor structural damage to buildings.  The satellite picture below showed the storm getting better organized, but the bulk of the rain was east and south of the center.