Long Island is jutting right out into the storm track that is very active during the cool season months, i.e. October - March where coastal lows tend to develop after upper-atmospheric energy is transferred from the west over the Appalachian Mountains and interacts with the existing temperature gradient (baroclinic zone) that is in place at the coast sandwiched between the cold, continental air over the Eastern U.S. and the warm, moist air over the Western Atlantic Ocean fed by the Gulf Stream.
|North American Storm Tracks (Source: Understanding Weather and Climate, 6th ed. by Aguado & Burt)|
|The ingredients for a mesoscale snowband modified from Novak et al. 2004.|
Frontogenesis, or the formation of fronts, means that the atmosphere is unbalanced. The fact that there is a temperature gradient (that's what a front is) means that the atmosphere is a bit unstable and wants to even out that temperature gradient. How can it create a uniform temperature distribution if it has to fight against the really strong horizontal winds that keep making the temperature gradient stronger? To combat the imbalance, the atmosphere initiates a vertical wind circulation because when you can't go out you go up, right? The atmosphere induces a frontogenetical circulation that causes warm air to rise and cool on the warm side of the front (cooling down the warmer air) and cold air to descend and warm on the cold side of the front (warming up the colder air). This warm, rising air is usually incredibly moist so there's plenty of water vapor to create deep clouds that produce heavy snow and with that the snowband is formed. This circulation is usually very small because the temperature gradient at the front itself is very narrow in width so the snowband is very narrow as well. A summarizing schematic is provided below that shows a horizontal view of the snowband (yellow star) to the northwest of the surface low with the counterclockwise winds in the upper-right corner above a cross section showing the vertical circulation that causes a lot more snow to fall on your buddy's house (yellow star) versus your house (cozy cottage to the west or mansion to the east depending on your preference).
So why doesn't the weather forecaster know exactly where the snowband is going to set up and instead calls for a large amount of snow for the whole region? As you are now aware of, snowbands are very sensitive to particular ingredients with the most tricky being the location of the surface low pressure center. If the low travels a bit farther off of the coast then so will the snowband and the East End of Long Island may get hit a lot worse than NYC. If the low tracks closer to NYC then perhaps NJ will get hit harder. See the pattern? The following image shows the different weather model simulated locations of the surface low with the orange markers corresponding to the position of the low at 7 PM on Tuesday, January 20th from the Weather Prediction Center. There's quite a spread in locations, huh?
|Low tracks from the Weather Prediction Center. Source|
|SBU-WRF comparison simulated reflectivity for 1 AM EST January 22, 2014.|
The model on the right has a snowband over central Long Island (indicated by the star but please don't expect stars to appear on actual radar data) whereas the model on the left doesn't have that feature. The model on the right also has the low pressure center farther northwestward towards the coast which is helpful with getting snowbands closer to the Island. In looking at the model more in-depth, the ingredients are there for snowband formation-- a well-defined low-to-mid-level circulation, deformation north and west of that circulation center and sufficient moisture and instability at times (especially ~11 PM EST). The fact that temperatures will remain quite cold throughout the most important layers of the atmosphere means that the snow will be dry and fluffy and this fact could lead to large accumulations versus if it was wet (see the NWS infographic on snow ratios).
As of 11 PM EST on Monday, January 20th the NWS has issued a Winter Storm Warning for most of the Tri-state area from noon on Tuesday to 6 AM on Wednesday. The heaviest snowfall should occur after 5 PM EST and the amounts can total as much as 14 inches with the snowband expected to affect the eastern portions of Long Island. You can pay attention to the regional doppler radar for narrow swaths of larger values of reflectivity that indicate a snowband and see where one sets up tomorrow night. Remember to stay safe and stay warm but most of all, enjoy the snow!
- For more information about mesoscale snowbands see this webpage: TheWeatherPrediction.com
- For forecasts and warnings please see the local New York Forecast Office of the National Weather Service (and check out their Facebook Page here!): http://www.erh.noaa.gov/okx/
- For information about the formation of snowflakes and how they'll be observed at the ground please see this previous post: http://longislandweatherandclimate.blogspot.com/2013/12/a-snowflakes-journey-is-deciphered-on.html