Thursday, February 7, 2013

Weather Journal: Snowstorm of Uncertainty Nears

ReutersA woman walks with an umbrella through Times Square last month. The latest forecast for the storm expected to arrive Friday sees greater odds of rain than snow near New York City.

The odds of a weekend winter storm in Greater New York inched up on Wednesday but measurable snowfall remains far from a sure bet, at least in areas near New York City.

In fact, the coming storm looks to be as close to a meteorologist’s worst nightmare as can be imagined, and here’s why: Warm air at the coast will stifle snow accumulations, while just a few miles inland the parent storm could produce hefty precipitation totals. The general rule of thumb is that an inch of rain equals 10 inches of snow, so any inconsistencies are greatly magnified.

The result is shaping up to be an extremely tricky storm outlook, especially more than 48 hours in advance — an eternity in weather forecasting. But as the National Weather Service in New York City warns:�”There is the potential for this to be the strongest winter storm of the season”.

StormTeam4NY/NBC News via FacebookThe forecast map from the local NBC News affiliate suggests snowfall of nearly 30 inches by Saturday — but that outcome appears unlikely.

The tough forecast hinges on the interactions between a small system currently near Chicago and another that hasn’t even formed yet off the Carolina coast. Should the storms merge and pool their energy, a rapidly deepening snowstorm could develop on Friday. If they miss each other — even by 50 miles — most of the resulting storm’s energy will be shifted further northward, leaving primarily rain for New York City.

The uncertainty hasn’t stopped certain local media outlets from�spreading the idea�that this weekend’s storm could reach historic proportions in New York City. One weather map being passed around social-media sites like Facebook and Twitter suggests a nearly 30-inch (!) snowfall might materialize, �based mostly on a proprietary weather model. �While that scenario is virtually impossible for New York City, those kinds of totals could materialize in parts of New England in a top-end scenario.

Two more reliable wintertime models (GFS�and�NAM), on the other hand, are showing a vastly different scenario for Greater New York: an almost entirely rain event. The Euro model, which famously �forecast superstorm Sandy’s landfall eight days in advance, is somewhere in the middle.

Crunching all that data together inside my little weather brain, I haven’t seen anything that argues convincingly for more than six inches of snow in the five boroughs. The National Weather Service agrees — see their most recent snow total forecast map�–�although totals could quickly increase further northward into Connecticut. More likely, the city will get two to five inches of slush mixed with rain.

This forecast applies only to the immediate New York City area.�As Weather Journal wrote last week, the big�atmospheric�picture in Big Apple argues that odds are stacked against significant snowfall probably for the rest of this winter — including this weekend.

Central Connecticut and the rest of New England will likely be telling a different story come Saturday morning. Parts of New England are more certain to get hit quite hard, regardless of the exact way the storm evolves. Around midday Wednesday, the National Weather Service predicted about three inches of liquid equivalent to fall in the Boston area. If all of that came as snow, two feet or more could be quite common in parts of Massachusetts. The National Weather Service’s Boston office is warning that “near blizzard conditions will be possible” on Friday night.

Weather Journal will have continuous coverage of the impending storm (or lack thereof, depending on your location) via Twitter @EricHolthaus.

Weather Journal’s Greater New York forecast roundup for Thursday:

  • WSJ Headquarters in Manhattan:
  • Actual High: 31; High feels like: 33
  • Actual Low: 21; Low feels like: 25
  • Weather: Clouds begin to build in advance of Friday’s possible snowstorm
  • Brooklyn: 32/22
  • Queens: 33/24
  • Bronx: 32/22
  • Staten Island: 33/21
  • Poughkeepsie, N.Y.: 26/12
  • Trenton, N.J.: 35/19
  • Islip, Long Island: 31/20
  • New Haven, Conn.: 30/14

Meteorologist Eric Holthaus contributes daily weather reports and analysis on Metropolis. For the latest on conditions in New York and elsewhere, follow his updates (@EricHolthaus) on Twitter.

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