On Sunday afternoon, New York City Mayor Bill de Blasio warned residents that "one of the largest snowstorms in the history of this city" could hit early this week.
Here's what he's talking about: The National Weather Service is currently warning of a "crippling and potentially historic blizzard" making its way up the East Coast from Monday to Wednesday, with high winds that could make it dangerous to drive.
The NWS is forecasting somewhere between 1 to 3 feet of snow falling in the area from New York City to Boston. The current snowfall record for a single storm is 26.9 inches in New York and 27.6 inches for Boston:
The NWS has issued a "blizzard warning" for the entire coast from New Jersey up to the Canadian border — an area encompassing some 29 million people:
29 Million people under #Blizzard Warning: http://t.co/Encl3uyc2s | http://t.co/Zqhxk6AFlR pic.twitter.com/1zfP8PP3x6— NWS (@NWS) January 25, 2015
That would be serious. A blizzard occurs whenever there's snow, strong winds of at least 35 miles per hour, and visibility of less than one-quarter of a mile for at least three hours. The snow and wind can combine to create "whiteout" conditions — making it dangerous to drive. Powerful gusts can also knock down trees and power lines.
The blizzard warning for New York goes into effect at 1 pm on Monday (and 7pm for Boston). City officials have already closed after-school programs and are warning people that commuting could become dangerous by nightfall.
"Assume that you don't want to be out in this storm," de Blasio said. "Stay off the roads. Make plans to travel another day and try with everything you have to avoid being in the middle of this storm."
Where did this storm come from?
21z WPC surface analysis shows system crossing OH valley this evening that will evolve into major #winterstorm for NE pic.twitter.com/jIuwJAqfXI— NWS WPC (@NWSWPC) January 25, 2015
It started as an "Alberta clipper," a low-pressure weather system that traveled down from Canada to the Midwest and over the Ohio Valley. That system may bring a small bit of rain and snow to the Washington DC area on Sunday night.
Then things get interesting. A few days ago, forecasters figured this clipper would wander harmlessly out to sea and that would be the end of it. Over the last few days, however, that forecast has changed.
Thanks to a jolt from the jet stream, the system is now expected to strengthen rapidly, transform into a powerful "nor'easter," and travel north, pulling moisture from the Atlantic Ocean and dumping it on cities along the East Coast.
How bad could the storm get?
Here are the most recent National Weather Service forecasts for New York and Boston (as of Sunday afternoon). Keep in mind that things could change as we get closer:
New York: The NWS is saying that a "crippling and potentially historic blizzard" could affect the New York City area. The blizzard warning is in effect starting 1 pm on Monday until midnight Tuesday.
Snow is expected to begin falling Monday morning, with accumulations of up to 1 to 3 inches possible by the evening. The snow will then pick up intensity between Monday night and Tuesday afternoon. All told, the NWS says, some 20 to 30 inches could fall. By contrast, the Weather Channel is expecting less snow, between 12 and 18 inches.
Latest snowfall expected via @NWSNewYorkNY. Blizzard Warning for greater NYC Metro area now through Tuesday night. pic.twitter.com/2KBtltV0G9— Andrew Cuomo (@NYGovCuomo) January 25, 2015
Winds could reach 30 to 40 miles per hour, with gusts of up to 65 miles per hour possible in some regions. Areas near the ocean could also see storm surges and coastal flooding.
The NWS is blunt in its warnings: "Life-threatening conditions and extremely dangerous travel due to heavy snowfall and strong winds... with whiteout conditions. Secondary and tertiary roads may become impassable. Strong winds may down power lines and tree limbs."
In his press conference on Sunday, de Blasio said that New York City schools would stay open Monday, but after-school activities would be canceled. He advised workers to go into the office early or avoid commuting altogether, since travel would be hazardous by nightfall on Monday. (The city is planning to deploy road salt before the snow falls and bring out the plows, though that won't help with whiteout conditions.)
Boston: The NWS issued a similar warning for Boston and the surrounding area, with the blizzard warning in effect starting 7 pm on Monday and lasting until 1 am Wednesday.
The current forecast is for 20 to 30 inches of snow around Boston, with possibly more in surrounding regions, as well as gusts over 35 miles per hour. (Again, the Weather Channel is expecting less, around 18 to 24 inches.)
"Travel will be impossible and life threatening across the entire region," warns the NWS office in Taunton, Massachusetts. "Also snow will be wet enough to result in downed trees and power outages in addition to the hurricane force winds."
Could this snowstorm end up being a bust?
Nothing is ever for certain — and snowstorm forecasts can often fizzle out, since the conditions have to be just right. One wild card, as Linda Lam points out, is whether the the nor'easter will stay close to the coast or push further east. If the latter happens, then some cities (like New York) could end up getting far less snow than expected.
Right now, the betting line is that there will be snow. As Eric Holthaus points out at Slate, the National Weather Service currently estimates there's a 67 percent chance of at least 18 inches in New York City and 75 percent odds of that much snow in Boston.
Will this storm set records?
We'll have to wait and see. Right now, the NWS is calling for 20 to 30 inches of snow in New York City and Boston. But the Weather Channel is only calling for 12 to 18 inches in New York and 18 to 24 inches for Boston.
For reference: The previous record for New York City was 26.9 inches, set in 2006. And the previous record for Boston was 27.6 inches, set in 2003. So the potential is certainly there:
And here are the 5 top biggest snowstorms for #NewYorkCity. Current fcst : 18-24" pic.twitter.com/hLVwDyzRvy— Greg Diamond (@gdimeweather) January 25, 2015
Here's the top 5 snowfall events for #Boston on record. Current @weatherchannel fcst: 27" pic.twitter.com/wllkQsKAUC— Greg Diamond (@gdimeweather) January 25, 2015
By the way, here's a pic of New York City's 1947 blizzard, still second place on the record books — for now:
Times Square NYC amid Blizzard of 1947: #Kauffman pic.twitter.com/PeKKFdR9Jj— Michael Beschloss (@BeschlossDC) January 25, 2015
-- The National Weather Service's Twitter account has frequent updates. You can also follow the regional offices in New York or Boston.
-- Over at Mashable, Andrew Freedman has a very nice explanation of how meteorologists' forecast of this storm changed over the past few days.
-- Road salt is terrible for the environment. Are there better options?