Truth Frequency Radio
Nov 26, 2014

By Nick Wiltgen, Weather

Traveling to visit family and friends is turning into a major hassle across much of the East Coast as Winter Storm Cato is poised to spread rain and snow across a highly populated and heavily-traveled region of the country on the day before Thanksgiving.

Some 20 million people are under winter storm warnings in the Northeast as of noon Wednesday.

A cold front that swept through the central and eastern U.S. earlier this week has stalled just off the East Coast. Low pressure spun up along the tail end of the front over the Gulf of Mexico Tuesday afternoon, crossed the Florida Peninsula Tuesday evening, and is now along the coast of the Carolinas as of Wednesday morning.

That low is quickly intensifying as it moves north-northeastward Wednesday, and will most likely stay near or just off the Eastern Seaboard. This is a classic track for a significant East Coast storm.

However, as is often the case, the difference between rain and snow hinges on how far south and east cold air can move into the storm’s precipitation zone — and the small details could make a big difference for your travel plans, especially if you will be driving in the Mid-Atlantic and the Northeast.

Here’s an overview of how the rest of this storm should play out.

Wednesday: Snowfall has expanded its areal footprint dramatically over the Northeast. The rain/snow line has been hovering just north and west of the Interstate 95 corridor much of the day.

The situation has been complicated by the fact that the cold side of this storm system isn’t particularly cold. While it is cold enough for snow over a swath of the interior — from West Virginia through central Pennsylvania, the Catskills of New York and into interior New England — areas closer to Interstate 95 may have ground-level air temperatures a few degrees above freezing.

In this case, heavy snowfall rates caused by fast-rising air associated with the low-pressure system have made the difference between rain and snow. When it snows hard enough, air temperatures have cooled enough for the snow to reach the ground and accumulate quickly. Conversely, in areas where precipitation isn’t as heavy, the air is staying just warm enough to melt the snowflakes before they reach the ground — resulting in a cold rain or a rain/snow mix.

This has been happening along parts of the I-95 corridor. Thundersnow was reported around midday near Baltimore and Philadelphia shortly after rain changed to snow. In many of those areas, the snow changed back to rain as the heavier precipitation moved out.

In any case, while the snow/rain line makes a big difference for drivers, major airports are in bad shape regardless. Either rain or snow, combined with the low clouds and blustery winds accompanying the storm, are causing severe delays at already-crowded airports up and down the Mid-Atlantic and Northeast coast. At some airports, just under half of all flights have been delayed or cancelled, according to Flightaware.com.

Wednesday night: The fast-moving storm will keep booking to the northeast, wrapping cold air southward on its back side. This should allow the rain/snow line to advance southeastward across the Northeast Megalopolis in the evening, but by this point precipitation will be diminishing in intensity.

Snowfall should quickly come to an end from the New York City area southward before midnight.

Farther north, snow will continue over much of New England into the evening, ending from west to east later Wednesday night.

Thanksgiving Day: The last of the snow will wind down in the morning over parts of Maine. In the wake of the storm, highs will be below average across the Northeast. But they should climb far enough above freezing to allow rapid improvement in road conditions.

Snowfall amounts and impacts: The inset map at right shows our latest 48-hour snowfall forecast. Bear in mind the amounts shown are in addition to any snow that has already fallen.

For more snowfall maps with specific highways labeled, along with information on travel impacts, click here for our Winter Storm Cato news and impacts article.

Total snowfall isn’t the only thing to consider, however. Temperatures are close to the 32-degree mark for most of the affected area, so this is a heavy, wet snow. This has led to broken tree limbs and significant power outages in areas where the snow has been heaviest.

But it also means less impact on drivers, especially where amounts are lighter. Roads in many cases have been just slushy or wet. Bear in mind that temperatures were in the 70s on Monday in parts of the Northeast, so ground temperatures are not very cold. But as night falls, snow may stick to roads more easily.

The rate of snowfall is also important. Some areas, especially closest to the rain/snow line, could see snowfall rates of 1 inch per hour or more, especially where thunder accompanies the snow. Road conditions can deteriorate very quickly in snows of that intensity, as the snow can fall faster than road crews can clear it with plows. Even where the soil is warm, heavy rates of snowfall can allow snow to accumulate much faster than the ground can melt it.

Stay with The Weather Channel and weather.com for updates on this high-impact storm system.

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