A Massive Snowstorm Is Heading to the Northeast

The National Weather Service’s snowfall forecast through 8:00 PM EDT on Wednesday, March 15, 2017. Image Credit: WeatherBELL Models

 
Winter plans to make up for lost time tonight as a major late-season snowstorm promises to deliver one to two feet of snow to just about the entire northeastern United States. The nor’easter will snarl travel for several days during and after the storm, bringing life to a grinding halt until crews can sweep away the frozen reprieve from spring. If current forecasts hold true, some of the heaviest snow could fall around the New York City area, potentially making this one of the biggest winter storms in the city’s history.

A sprawling nor’easter will develop on Monday night and continue through the day on Tuesday, leaving behind formidable amounts of snow from the Appalachian Mountains of North Carolina to the Canadian Maritimes. Precipitation will begin around the Washington D.C. area on Monday night, spreading north through the nighttime hours. The storm will encounter enough cold air that the majority of the precipitation will fall as snow, but ice and rain will mix close to the coast. This presents a major issue for forecasters, as a small change in the track of the storm could have huge implications for tens of millions of people.

Current forecasts from the National Weather Service call for widespread accumulations of a foot or more covering just about everyone from Maryland to Maine, with totals approaching 2 feet in northeastern Pennsylvania and the southern Hudson River Valley. On Monday afternoon, the forecast called for an even 20 inches of snow in New York City proper, with similar amounts to the city’s north and west. Snowfall amounts to New York City’s north and south—including Boston, Massachusetts, and Philadelphia, Pennsylvania—could wind up around a foot, give or take a few inches. The storm will begin with ice and rain farther down Interstate 95 toward Baltimore, Maryland, and Washington, D.C., which are both on track to see about 4 to 8 inches of snow if everything unfolds as currently forecast.

The amount of land expecting heavy snow from this nor’easter is unusual—areas as far west as Buffalo, New York, are expecting a foot or more of snow—largely because a low-pressure system over the Great Lakes will move east tonight and merge with this nor’easter on Tuesday, providing it the extra moisture and lift it needs to grow its reach much farther inland than you would expect from a typical East Coast snowstorm.

A simulated radar image from the HRRR weather model for 4:00 AM EDT Tuesday, March 14, 2017, showing how close the line between rain (green), icy mix (pink), and snow (blue) will track to the big cities along Interstate 95. Image Credit: Tropical Tidbits

 
As with every nor’easter, the huge caveat with snowfall totals is the exact track the storm takes as it moves along the coast. Winter storms that move up the East Coast are a tricky balancing act between warm and cold air at the surface and mid-levels of the atmosphere. Subtle changes in temperature can mean the difference between a memorable snowstorm and a sloppy, icy mess that’s more dangerous than photogenic.

If the nor’easter tracks closer to the coast than current forecasts expect, communities that lie along Interstate 95 could see dramatically lower snowfall totals than anticipated. On the other hand, if the storm tracks 10 or 20 miles farther out to sea than expected, the heaviest snow will follow this eastward movement and deliver an even greater blow to the major cities that make up the megalopolis. If you live in the affected areas, the snowfall totals in your current forecast are what’s most likely based on present information available to meteorologists. You could see less or more depending on the exact track of the storm, which is very hard to know until the storm is already underway.

Regardless of the exact amounts, this will be a far-reaching and highly disruptive snowstorm. Flight and rail cancellations are a given. Highways will likely be slowed to a crawl during and after the snow, while local roads could remain impassable to most vehicles for at least a day or two. Many school districts will likely close for the remainder of the week, even in areas that are usually resilient during winter weather. Moreover, the psychological and societal impact of this storm will be greater than usual because of how abnormally warm it’s been this winter.

On top of the hardship caused by one to two feet of snow, the snow will be accompanied by strong winds that could damage trees and power lines. Blizzard warnings are in effect for coastal counties between Atlantic City, New Jersey, and the border between Connecticut and Rhode Island, including the entire New York City metropolitan area and western half of Long Island. Sustained winds of 30 to 40 mph are likely across areas expecting blizzard conditions, with gusts of 50 to 60 mph possible.

So what is a blizzard, exactly? A blizzard occurs when sustained winds of 35 mph or stronger create blowing snow that reduces visibility to one-quarter of a mile or less for three consecutive hours. It’s a pretty technical definition that’s hard to meet, but the weather conditions required for a “true blizzard” equate to a disorienting whiteout. Venturing even a few dozen feet from safety during a whiteout can put you at great risk for becoming disoriented and possibly lost, a risk that’s even greater when the heaviest snow and wind occurs at night. As tempting as it is to play in the snow, stay inside during blizzard conditions if you can help it.

This could be one of the most significant winter storms to ever hit the northeastern United States during the month of March, and in some spots it could rank in the top-10 all-time winter storms. If the current NWS forecast of 20 inches of snow comes to pass at the weather observing station in New York City’s Central Park, for instance, it would be the fourth-largest one-day snowfall in the station’s 127-year history, and it could place as number 9 or 10 in the list of top-10 snowstorms. The storm probably won’t break any all-time records in other major cities, but it could easily become one of the largest March snowstorms on record all along the Interstate 95 corridor.

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

Is the Heat Index Real?

MarianVejcik/iStock via Getty Images
MarianVejcik/iStock via Getty Images

Complaining about the humidity is a mainstay of small talk. “It’s not the heat that gets you, it’s the humidity” is a common refrain around the South, just as “it’s a dry heat” is a go-to line in the desert Southwest. The clichés aren’t wrong on this one—a hot and humid day can have a dramatic effect on both your comfort and your health. We can measure this very real impact on your body using the heat index. 

The heat index is the temperature it feels like to your body when you factor in both the actual air temperature and the amount of moisture in the air. If the heat index is 103°F, that means that the combination of heat and humidity has a similar physical impact on your body as it would if the actual air temperature were 103°F. Even though it’s tempting to think of the heat index as an exaggerated temperature that only exists to make the heat sound worse than it really is, scientists came up with the measurements after decades of medical and meteorological research devoted to studying the impact of heat and humidity on the human body. It’s the real deal.

The dew point is an important component of the heat index. The dew point is the temperature at which the air would reach 100 percent relative humidity, or become fully saturated with moisture like on a foggy morning. Since cooler air can’t hold as much moisture as warmer air, lower dew points reflect lower moisture levels and higher dew points indicate higher moisture levels. Dew points below 60°F are comfortable, while readings reaching 70°F and even 80°F range from muggy to downright oppressive.

Measuring humidity on a hot day is important because moisture is how your body naturally cools itself off. Your sweat cools the surface of your skin through a process known as evaporative cooling. If the air is packed with moisture, it takes longer for your sweat to evaporate than it would in more normal conditions, preventing you from cooling off efficiently. The inability to lower your body temperature when it’s hot can quickly lead to medical emergencies like heat exhaustion or heat stroke, which is why the heat index is such an important measurement to pay attention to during the summer months.

The heat index is generally considered “dangerous” once the value climbs above 105°F, and your risk of falling ill increases the higher the heat index climbs.

Dry climates can have the opposite effect on your body, with the distinct lack of moisture in the air making it feel cooler to your body than it really is. Summers get oppressively hot in places like Arizona and Iraq, but the heat doesn’t affect residents as severely because the air is extremely dry. Dew points in desert regions can hover at or below 32°F even when the air temperature is well above 100°F, which is about as dry as it can get in the natural world.  

In 2016, a city in Kuwait measured the all-time highest confirmed temperature ever recorded in the eastern hemisphere, where temperatures climbed to a sweltering 129°F during the day on July 21, 2016. The dew point there at the same time was nearly 100 degrees cooler, leading to a heat index of just 110°F, much lower than the actual air temperature. That’s not necessarily a good thing. Extreme heat combined with extreme aridity can make your sweat evaporate too efficiently, quickly dehydrating you and potentially leading to medical emergencies similar to those you would experience in a much more humid region of the world. 

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This story has been updated for 2019.

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