December 20, 2018

Look At This Entire Trough

An ambitious butterfly could make it from Orlando to Buffalo in a couple of minutes if it flew high enough on Friday. An incredibly amplified trough entering the eastern United States will bring this week to the same dreary close we saw last week. In addition to lots of heavy rain and dangerous thunderstorms in Florida, the resulting surface low could bring some of the lowest air pressures ever recorded during the month of December in the Mid-Atlantic.

A line of severe thunderstorms was ongoing in Florida at the time of this post. It's a classic wintertime severe weather setup for this part of the country. Warm, moist air ahead of an advancing cold front allowed a line of strong thunderstorms to sweep across the Florida Peninsula. Cooler, drier air will follow soon after the rain stops, bringing comfortable conditions as far south as Cuba and Mexico's Yucatan Peninsula through the weekend.

A slog of steady, heavy rain will coat just about every square inch of the East Coast between now and Saturday. Most areas can expect an inch or two of rain with heavier totals likely in areas that experience thunderstorms. Some of the storms in the Carolinas could be severe on Thursday night, packing the risk for damaging winds and possibly an isolated tornado.

That trough is something else. I mean, look at this thing:
An animated model image of the jet stream. Source: Tropical Tidbits

A sharp trough like that is impressive enough on its own, but the combination of the amplified trough and strong winds of the jet stream within will strengthen the surface low moving over the Carolinas tonight and Friday. The latest forecast from the Weather Prediction Center shows the minimum surface pressure at the center of the low potentially reaching 987 mb on Friday as it moves over western North Carolina and Virginia.
December record low air pressures (adjusted for sea level). Add a 9 to the front of every number for the value, which is rounded to the nearest tenth ("888" in Greensboro is 988.8 mb). Source: WPC

A surface pressure of 987 mb is extremely unusual for this part of the country during this time of the year. Surface pressure records compiled by David Roth at the WPC show the lowest air pressure recorded during the month of December in Greensboro, N.C., was 988.8 mb, and 986.5 mb up the road in Roanoke, VA. It'll be a close one.

The lower air pressure itself won't really have much of a direct effect other than kicking up a stiff breeze and possibly making your joints achier than usual. Other than that, it's just a novelty.

[Top Image: Tropical Tidbits]

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I contribute to The Weather Network as a digital writer, and I've written for Forbes, the Washington Post's Capital Weather Gang, Popular Science, Mental Floss, and Gawker's The Vane. My latest book, The Skies Above, is now available. My first book, The Extreme Weather Survival Manual, arrived in October 2015.