About 20 million people are currently under a blizzard warning, and double that under a winter weather advisory, for a storm moving into the Northeast today and tomorrow, with snow falling though Wednesday. Thousands of flights have been cancelled. Wind will be at tropical storm force, and occasionally, hurricane force, and coastal flooding is expected to be epic. The total amounts of snowfall will be over a foot for a very large area, and well over that here and there, though this is very difficult to predict.

This is a strong low pressure system that will gather significant energy from a warm sea surface as it moves into the Atlantic.

This is a system that would normally not produce a lot of snow, but the odd configuration of the jet stream (once again) is moving the low pressure system through a pattern that will create an epic blizzard.

Storms of roughly this magnitude, in this the New York City area, have occurred in 1888, 1947, 1978, 1993, 1996, 2003, 2006, 2010. A similar pattern would emerge if the focal area was Boston. Weather Wunderground lists these snow events for New York City, indicating that half of the heavy events since the mid nineteenth century have occurred in the last 12 years:

1. 26.9" Feb 11-12, 2006

2. 25.8" Dec 26-27, 1947

3. 21.0" Mar 12-14, 1888

4. 20.9" Feb 25-26, 2010

5. 20.2" Jan 7-8, 1996

6. 20.0" Dec 26-27, 2010

7. 19.8" Feb 16-17, 2003

8. 19.0" Jan 26-27, 2011

9. 18.1" Jan 22-24, 1935

9. 18.1" Mar 7-8, 1941

Both the odd jet stream and the warm sea surface temperatures can be pegged as likely effects of anthropogenic global warming (AGW). This added to the clear pattern of more of these storms happening very recently strongly suggest that it is reasonable to characterize this storm as a "global warming amplified storm." This is not unexpected.

I'm not sure if the sea surface temperatures in the region are at a record high, but they are very high. Over time, North Atlantic sea surface temperatures have certainly risen:

(a) Global annual mean sea-surface temperature (SST) anomalies from HadISST for the period 1870–2008 (Ref. 58)(thin black line). (b) Annual mean North Atlantic SST anomalies for the period 1870–2008 (ref. 58; thin black line). (c) The Atlantic multidecadal oscillation (AMO) index for the period 1870–2008. The modern AMO index4 is defined by subtracting the global mean SST anomalies (a) from the North Atlantic SST anomalies (b). Five-year running means are shown by heavy black lines with fill in all panels.

And here is the current sea surface temperature anomaly map for the region, showing current temperatures off New York and New England in the upper range:

There has been an increase in extreme precipitation in the Northeast, with a 71% change in the region:

This is inline with predictions the IPCC has been making for some time now. According to climate scientist Michael Mann, "The U.N. Intergovernmental Panel on Climate Change has found that Nor’easters like this one may grow stronger w/ human-caused climate change, as they are driven by the contrast between cold Arctic air masses and ever-warming ocean surface temperatures. We also know that ocean surface temperatures off the U.S. east coast right now are unusually warm, and there is no doubt that a component of that anomalous warmth is due to human-caused climate change. Those warm ocean temperatures also mean that there is more moisture in the air for this storm to feed on and to produce huge snowfalls inland. Climate change is making these sorts of storms more common, much as it is making Sandy-like Superstorms and unusually intense hurricanes more common. Asking whether these storms were caused by climate change, however, is asking the wrong question. What we *can* say is that they were likely made worse by climate change."

Kevin Trenbeth, of the National Center for Atmospheric Research notes that the main reason there is a big blizzard coming to the northeast is that it is winter, but "it is warm over the oceans and the contrast between the cold continent and the warm Gulf Stream and surrounding waters is increasing. At present sea surface temperatures are more than 2F above normal over huge expanses (1000 miles) off the east coast and water vapor in the atmosphere is about 10% higher as a result. About half of this can be attributed to climate change." I would add that the actual anomolies over large areas of the sea where this low pressure system will track are closer to 4 degrees.

There is a live blog at Weather Underground that you may want to keep an eye on, here. There, we see that current predictions for the region are:

New York City, NY: 18 - 24"

Boston, MA: 20 - 30"

Providence, RI: 20 - 30"

The National Weather Service has a page on the storm here.

And, yes, folks, this is a trend: