Extreme Travel Weather Event Broccoli Snarls Northeast Air And Road Traffic

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The forecast for early Wednesday afternoon, courtesy of NOAA

The forecast for early Wednesday afternoon, before Thanksgiving Thursday. Image courtesy of NOAA

Extreme Travel Weather Event Broccoli, also called winter storm Cato by the Weather Channel, would be only a minor nuisance on any other day of the year. But today is the heaviest travel day that Americans encounter, and Broccoli will slow down air and auto travel from Virginia to Maine.

Broccoli Is Barely A Nor’easter

Atlantic coast storms, locally known as nor’easters because the wind blows mostly from the northeast, derive their energy from the proximity of cold air over the land to warm air over the ocean.

The high potential energy of this configuration is the fuel that feeds the storms. The potential energy turns into kinetic energy of motion (wind); eventually the wind is dissipated by friction with the ground.

The end result is a lower potential energy state of cold air beneath warm.

The contrast of air masses is modest for Broccoli, so the storm will only generate a moderate amount of wind.

Why Does It Snow And Rain In A Nor’easter?

During the process of potential energy turning into wind, warm air is rising and cold air is sinking. It is the former that causes precipitation.

The temperature in the atmosphere decreases with height. The amount of water vapor that air can hold is directly proportional to the temperature — the higher the temperature, the more water vapor the air can hold. As the warm air rises and cools, moisture is squeezed out and precipitation falls.

The greatest temperature contrast occurs near the coast. Temperatures will be in the thirties over the land. The water temperature is in the 40s in New England, ranging to the 60s off the Carolinas. As the warm air from the ocean tries to displace the colder, denser air over the land surface, the warm air is forced to rise.

Where Will It Snow And Where Will It Rain?

This is the question that confounds meteorologists in many nor’easters. The distribution of snow and rain depends critically on the path of the low pressure center and the trajectories of the air parcels. Just a few miles can separate places that receive mostly rain from ones that get many inches of snow. And, as it happens, the major cities of Washington, Philadelphia, New York, and Boston lie along the line that often separates rain and snow. In addition, the route of Interstate 95 runs through these cities.

If the low pressure center hugs the coast, the wind is more easterly and the air is warmed by its passage over the water — so the rain pushes farther inland.

If the storm stays a little farther offshore, the wind is more northeast or north, and the rain/snow line moves towards, or even off, the coast.

If the storm’s path is too far offshore, the precipitation will fall mostly over the ocean.

Broccoli’s Rain And Snow

Broccoli is tracking near the coast, so the major cities of the northeast will be spared from the heaviest snow:

  • Washington will be on the rainy side of Broccoli — there will be little or no snow at the Washington or Baltimore-Washington airports. However, Dulles Airport, about 30 miles west of the city, could get several inches of snow.
  • Philadelphia is right on the snow/rain line. There could be an inch  or two at the airport.
  • New York is served by three major airports: LaGuardia and Kennedy are on Long Island, close to the 50 degree water, and will probably get all rain; Newark, about ten miles west, could have a few inches of snow. Note: Some flights out of New York have been canceled in order to facilitate the smooth operation of the remaining flights.
  • Boston‘s weather is the hardest to predict. The water is colder, but the airport is right on the harbor. Most likely, runway maintenance crews in Boston will have to shovel a few inches of snow. At Worcester Airport, 30 miles west of Boston, there could be a foot of snow.
  • Interstate Route I-95 south of New York will be wet but not snowy. North of New York there is an increasing likelihood of snow, especially where the road leaves the shoreline and cuts through central Rhode Island. With temperatures in the mid- to upper thirties, most of the snow will melt on contact with the warm road surface.

Broccoli’s Belt Of Heavy Snow

Away from the megalopolis, there will be a band of heavy snow from central and western Virginia through central Pennsylvania and New York state, and through inland areas of New England. Up to a foot of snow will make driving hazardous in this band, which includes the cities of Charlottesville, Virginia; Harrisburg, Pennsylvania; Albany, New York; Hartford, Connecticut; and Springfield, Massachusetts.

How Can It Snow If The Temperature Is Above Freezing?

Since the temperature decreases with height in the atmosphere, precipitation normally begins as snow in the clouds. When the layer of air above freezing at the surface is shallow enough, the frozen precipitation can reach the ground. Normally it will melt quickly.

Count This Among The Blessings: No Ice

The conditions that lead to freezing rain do not exist with Broccoli. Snow will be falling into above-freezing air. An ice storm occurs when rain falls into sub-freezing air.

Another Blessing: Broccoli Is Moving Fast

The whole system that is causing Extreme Travel Weather Event Broccoli is racing northeastward and will clear New England by Thanksgiving morning. The rest of the weekend should be nice across the northeast, with no travel delays as people return home on Sunday.

Weather In The Rest Of The United States

The jet stream on Saturday should bring settled weather to all of the US except the west coast. Forecast courtesy of NOAA

The jet stream on Saturday should bring settled weather to all of the US except the west coast. Forecast courtesy of NOAA

Much of the United States will be dry for the rest of the week, with temperatures near normal. The exception is the northwest, Cascades, and northern Rockies, which will be affected by Pacific Ocean storms moving east.

The jet stream pattern is changing, at lest temporarily, and storms will push increasingly farther south on the west coast as the week progresses. There could even be some beneficial rain in southern California by late in the weekend.

Residents of the parched areas of the Golden State would certainly be thankful for that.

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