Look Out! Heavy Snow and Strong Winds Are Heading to the Northeast

Bigfoot takes on a Boston nor'easter. Image Credit: Kayana Szymczak/Getty Images

A major nor’easter will bring heavy snow and gusty winds to the northeastern megalopolis on Thursday, February 9, dropping at least a half-foot of snow across the most heavily populated region of the United States. The dose of intense winter weather will snarl travel and likely bring daily life to a halt through the beginning of the weekend. The heaviest accumulations are possible between New York City and Boston, where some locations could see a foot or more of snow by sunrise on Friday.

The catalyst behind the classic winter storm is a strong disturbance digging its way east across the country. The same system that will trigger the nor’easter brought snow and subzero temperatures to the Upper Midwest earlier this week; morning lows dropped lower than -20°F in North Dakota and Minnesota on Wednesday morning. The upper-level trough will cause a low-pressure system to develop at the surface in Virginia on Wednesday night. This low will quickly strengthen as it moves over the Atlantic Ocean and tracks parallel to the East Coast. It’s a scene that repeats itself every winter—one that snow lovers and winter haters alike are all too familiar with.

The Weather Prediction Center’s most likely snowfall forecast for the three-day period beginning at 7:00 AM EST on Thursday, February 9, 2017. Image Credit: Dennis Mersereau

The latest forecast from NOAA’s Weather Prediction Center calls for about half a foot of snow between eastern Pennsylvania through southern New England. The greatest chance for heavy snow stretches from northeastern Pennsylvania through eastern Massachusetts, where the most productive snow bands are expected to develop. Precipitation will begin on Thursday morning in the Mid-Atlantic and work its way north through the afternoon hours. The last of the snow should taper off on Friday morning in New England. It’s worth noting that there will be a relatively sharp gradient between having to crack out the shovel and a dusting on the grass—a boundary that’s likely to set up right along the Mason-Dixon Line. Precipitation will fall mostly as snow north of this line, while the storm will start as rain and could end as some snow to its south. It’s likely too warm for the Washington D.C. area to see more than a light coating of snow at the most, but its far northern suburbs could see a few inches from this system.

A weather model simulation of the nor’easter on Thursday morning, showing the heaviest snow bands on the northwest side of the storm. Image Credit: Pivotal Weather

Like so many nor’easters before it, this storm will play tug of war between unusually warm temperatures to the south and bitterly cold Arctic air to the north. The sweet spot for the heaviest snow will be where the cold air intersects with the area that has the highest moisture and the strongest lift, a region called the deformation zone. The deformation zone is almost always on the northwestern side of nor’easters, resulting in a swath of heavy snow that parallels the coast. Sometimes the heaviest snow bands set up far enough inland to miss the big cities, and sometimes they form right over the cities and result in those blockbuster blizzards that people remember for years.

The fact that the heaviest snow falls in such a narrow area makes forecasting nor’easters a tricky business. Warm air is a plague in East Coast winter storms; it can turn a potential snowstorm into an icy disaster or just a cold, miserable rain. A small eastward or westward shift—just one or two dozen miles—can render a snowfall forecast completely useless. This happened just last month during the significant snowstorm in the Carolinas and Virginia. The storm tracked a little farther inland than expected, allowing warm air to chew away at the snow and result in mostly ice around cities like Raleigh, North Carolina, while giving heavier snow to Greensboro, two hours to the west of Raleigh.

Temperatures have been a roller coaster leading up to this snowstorm, and that trend will continue soon after it leaves. It’s been so warm on the East Coast lately that some cities are easily setting daily high temperature records, including Washington D.C’s major airports on Tuesday and every airport around New York City on Wednesday. Temperatures behind the nor’easter will remain frigid during the day on Thursday and Friday as Arctic air drains in with the westerly winds behind the storm, aided by the icebox effect of having snow on the ground. Low temperatures on Thursday night will fall into the teens and single digits in areas with snow on the ground, and high temperatures on Friday will struggle to climb out of the 20s. Highs will quickly climb back above normal on Sunday and last through early next week, helping to melt any snow that falls from this hard-hitting but ultimately fleeting burst of winter.

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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