Preparing For the Worst

Wind Direction And Impacts On Precipitation Type For The Northeast US

A winter storm is approaching your area. The winds are picking up and the air certainly looks cold enough for snow. The weatherman on the television gives you three storm tracks, each with a different impact. So why is the storm track so important when snow fall totals come into play? Here is why. The track of a low pressure system combined with the position of a high pressure system to the north and west determines the wind direction for an area. Now, certain wind directions support frozen precipitation events while others do not.

When the low pressure system tracks close to the coast, while high pressure may be to the north of a storm, the track of the low pressure system will produce a strong easterly wind. Why is an easterly wind bad for frozen precipitation? Ocean temperatures. The air mass over the ocean in this situation is almost always above freezing, even in the heart of winter. An east or southeasterly wind brings this warmer air into the coastal plain, which leads to temperatures rising above freezing and a change in precipitation to rain. Precipitation may start out as snow and may even change slowly to sleet and freezing rain, however the end result will always be a change to plain cold rain.

When the low pressure system takes what meteorologist call the "bench mark" for winter storms, very heavy snow can be the result. In this track, the low pressure system is roughly 150 miles off the coast, which produces a northeasterly wind at the height of the storm. The trajectory of the wind is extremely important because instead of the Atlantic, the air mass is coming from New England, which supports a vastly cold air mass. As such, while warm, moist air will move into the higher parts of the atmosphere, the cold air mass will remain at the surface producing snow or in some cases a mix of snow, sleet, and freezing rain. In this situation above, the difference between the warm air aloft and the cold air at the surface produce a strong area of ​​rising air, which leads to heavy snow over the coastal plain. This set up has lead to some of the heaviest snowfall totals recorded in the region.

The difference in wind direction for your location may mean the difference between 10 inches of snow or 1 inch of rain. So this winter, if you observe the winds coming from the east you can more times than not put away the snow shovel and get the rain coast.

Source by Steven Dimartino

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