Why Is the Southeast So Humid?

iStock
iStock

You don’t have to hop on a plane to visit the tropics when you live in the southeastern United States—it can often feel like you’re already there. It gets humid in this corner of the country. Not just regular humid, mind you, but so disgustingly moist that you can almost feel the air slosh across your skin as you walk out the front door. But what is it that makes the Southeast so humid compared to the rest of the country?

Mugginess during the summer is a problem just about everywhere you go in the United States. The corn fields of Iowa can see a higher dew point than a rainforest. But even there the steaminess doesn’t last as long as it does in the Southeast. Much of it has to do with the region’s proximity to the Gulf of Mexico, which usually feels like bathwater on a good day. The water in some parts of the Gulf of Mexico can heat up to 90°F during the peak of the summer, and the water isn’t quick to cool down once cold fronts start sweeping through in the fall and winter. The warmth of the Gulf and the Caribbean Sea to its south keep moisture in plentiful supply.

It’s not just the water itself that contributes to the mugginess. The water vapor over the ocean doesn’t migrate inland on its own—weather patterns drag it inland and keep it locked in place. Strong winds blowing counterclockwise around low-pressure systems often help bring this tropical moisture inland, especially during the cooler months when you expect to shiver rather than sweat. During the summer, though, persistent ridges of high pressure keep the southeast feeling gross with a moist southerly wind. These “heat domes” deflect most weather systems approaching from the west, basically locking the Southeast into a state of sultriness for weeks and even months at a time.

The constant moisture isn’t merely uncomfortable—it can be downright dangerous. The human body is able to cool itself when sweat evaporates from the surface of exposed skin. But sweat has a harder time evaporating when there’s too much moisture in the air, which could cause a person to overheat. This phenomenon is measured with the heat index, and it’s the cause of thousands of heat-related illnesses and deaths every year.

All of that moisture makes both day and night downright miserable. If you’ve ever been to the desert during the warmer months, you know firsthand that even on a day when the high temperature exceeds 100°F, the mercury can plummet once the Sun goes down and get chilly enough to require a light jacket. The wild temperature fluctuations in desert regions are due to the dryness of the air there. Moist air has a higher heat capacity, so it takes a lot longer to warm up and cool off.

Meanwhile, the gross humidity levels in the Southeast on most days keep it from getting excessively hot, but it also keeps the nights from cooling off very much. The lack of nighttime relief compounds the danger posed by heat and humidity.

What Is a Bomb Cyclone?

Maddie Meyer/Getty Images
Maddie Meyer/Getty Images

The phrase bomb cyclone has re-entered the news this week as parts of the central U.S. face severe weather. Mountain and Midwestern states, including Colorado, Nebraska, Wyoming, and South Dakota, all fall in the path of a winter storm expected to deliver tornadoes, hail, heavy snow, flooding, and hurricane-force winds on Wednesday, March 13 into Thursday. It seems appropriate for a storm that strong to have bomb in its name, but the word actually refers to a meteorological phenomenon and not the cyclone's explosive intensity.

According to The Denver Post, the bomb in bomb cyclone stands for bombogenesis. Bombogenesis occurs when a non-tropical storm experiences at least a 24 millibar (the unit used to measure barometric pressure) drop within 24 hours. Low pressure makes for intense storms, so a bomb cyclone is a system that's built up a significant amount strength in a short length of time.

This type of storm usually depends on the ocean or another large body of water for its power. During the winter, the relatively warm air coming off the ocean and the cold air above land can collide to create a sharp drop in atmospheric pressure. Also known as a winter hurricane, this effect has produced some of the worst snowstorms to ever hit the U.S.

The fact that this latest bomb cyclone has formed nowhere near the coast makes it even more remarkable. Rather, a warm, subtropical air mass and a cold, Arctic air mass crossed paths, creating the perfect conditions for a rare bombogenesis over the Rockies and Great Plains states.

Central U.S. residents in the bomb cyclone's path have taken great precautions ahead of the storm. Over 1000 flights have been canceled for Wednesday and schools throughout Colorado have closed.

[h/t The Denver Post]

Watch a Rare ‘Ice Tsunami’ Slam Lake Erie

Clean Lakes Alliance, Flickr // CC BY 2.0
Clean Lakes Alliance, Flickr // CC BY 2.0

A combination of freezing cold temperatures and high winds is creating an unusual phenomenon along Lake Erie. As KDKA reports, ice tsunamis are toppling onto lake shores, and many locals have been asked to stay inside and even evacuate their homes.

On February 24, 2019, the National Weather Service in Buffalo, New York issued a warning about dangerous wind gusts in the Lake Erie area. The service urged citizens to seek shelter indoors and avoid traveling if possible. Winds peaked at 74 mph earlier this week, the level of a Category 1 hurricane, and tore down trees and power lines throughout the region.

People who got close to Lake Erie during the windstorm witnessed a rare event known as an ice tsunami. When wind pushed ice on the lake's surface toward the retaining wall, the sheet broke apart and dumped massive ice chunks on the shore. The video below captures the phenomenon.

In some areas, the ice piles grew so large that roadways had to be closed. Residents of Hamburg, New York's Hoover Beach area were asked to voluntarily evacuate due to the encroaching ice.

Ice tsunamis, or ice shoves, are rare, but in some cases they can be life-threatening. In 2013, waves of ice shards from a Minnesota lake destroyed people's homes.

[h/t KDKA]

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