News•February 8, 2013

What You Need to See to Understand Blizzard 'Nemo'

The blizzard of 2013, named “Nemo” by weather.com, is unleashing a paralyzing blitz of heavy snow, strong winds, and coastal flooding in the Northeast. These images and videos help explain the dynamics powering the storm, as well as its potential consequences.

This three-day satellite loop from NASA shows how the blizzard grew out of a moisture-charged storm traversing the southern part of the country, and a northern system riding the polar jet stream down from the Midwest. Once those two systems began to “phase,” at the end of the loop, things started to get really dicey from New Jersey to Maine.

NASA satellite image showing the blizzard forming along the East Coast.
Click to enlarge the image. Credit: NASA.

This NASA image also depicts the two storms just before they merged off the coast of Virginia, in a messy storm rendezvous that would go on to produce a violent offspring.

Satellite-derived image showing the blizzard tapping into a tropical moisture connection.
Click to enlarge the image. Credit: NOAA/NESDIS.

The blizzard is also pulling in an extraordinary amount of moisture, which is consistent with recent trends in the Northeast toward more frequent one-day precipitation extremes during the cold season, including snowstorms. The satellite-derived image of total precipitable water shows that the storm has been drawing tropical moisture from the Pacific Ocean, Gulf of Mexico, and the Atlantic Ocean. (H/T to the folks at the Capital Weather Gang for spotting this.)

This graphic shows trends in extreme one-day precipitation amounts in the Northeast during the cold season, from 1911-2012.
Click to enlarge the image. Credit: NOAA/NCDC.

For a longer historic view, this graphic shows trends in extreme one-day precipitation amounts in the Northeast during the cold season, from 1911-2012.

Sea-surface temperature departures from average map, showing warmer-than-average waters in the area of the Gulf Stream Current and the Gulf of Maine.
Click to enlarge the image. Credit: NOAA.

Sea-surface temperatures off the East Coast are running slightly warmer than average for this time of year in some areas, which may be adding more moisture to the storm. However, it's unclear how much of this is due to natural variability, and how much may be the result of manmade global warming. In any case, the sea-surface temperatures are not the dominant driver of this storm. Instead, atmospheric dynamics are.

Computer-model simulation showing two bundles of atmospheric energy (yellow hues), before combining to create one storm.
Click to enlarge the image. Credit: Weatherbell.com.

Computer-model simulation showing one major storm after the two pieces of energy combine, as of Saturday.
Click to enlarge the image. Credit: Weatherbell.com

Speaking of atmospheric dynamics, these two images show how the two pieces of atmospheric energy, as depicted in charts of atmospheric vorticity, or spin, were joining forces.

As Friday wore on, heavy snow, sleet, and rain enveloped New York and Long Island on its way to plastering Connecticut, Rhode Island, and Massachusetts with more than 2 feet of snow, as seen in the screengrab below.

Screenshot from a radar image out of Long Island, showing heavy bands of precipitation moving into New York City, Long Island, and Connecticut on Friday afternoon.
Click to enlarge the image. Credit: RadarScope.

It's not often that you see the National Weather Service produce a probability map showing 100 percent odds that Boston will receive at least a foot of snow (below).

Probability that 12 inches or more of snow will fall from this blizzard in southern New England.
Click to enlarge the image. Credit: NOAA/NWS.

Here is the storm total forecast graphic for the Boston area (below).

Storm total snowfall forecast for Boston and the rest of southern New England.
Click to enlarge the image. Credit: NOAA/NWS.

And here is the coastal flooding threat map for the Boston area (more on this threat here).

Map of coastal flooding threat during the Saturday morning high tide, from the Boston office of the National Weather Service.
Click to enlarge the image. Credit: NOAA/NWS.

(And for even more, watch this Huffington Post Live discussion on the possible climate connections behind this major storm, featuring Climate Central's Andrew Freedman.)