Wunderground Meteorologist Shaun Tanner

Update On Nor'easter Set for the Northeast

By: shauntanner, 6:05 AM GMT on October 29, 2011

The meteorologists at the Weather Underground are set to cover the potentially record-breaking Nor'easter this weekend to keep you informed and safe. We will be doing rapid-fire updates via Twitter and Facebook as well as updating this website as well. If there are any questions we can answer for you, we will be browsing the blogs, Twitter, and Facebook.

Various NWS offices have expanded the severe alert coverage to almost the entire New England Coast while also upgrading various Winter Storm Watches to Winter Storm Warnings.

While the overall effects from the storm will not be as brutal as a Nor'easter that occurs in the end of Winter, this storm will have a triple-edge sword to lookout for:

1) Wind: This storm is a Nor'easter. It gets its name because of the strong northeasterly winds that these types of storms often produce due to their track up the eastern seaboard with the center of the storm remaining off the coast. So, it is not surprising that High Wind Watches are in effect from Long Island through Cape Code. This area can expect sustained winds to 35 mph and gusts up to 55 mph. I believe it is safe to say that it will not be a good day at the beach. The strongest of these winds are expected Saturday night so if you have any travel plans for that time period and into Sunday morning, it might be smart to reschedule.

2) Snow: While October snowstorms are far from rare, the very low historical records for various cities show that significant snowfall is infrequent. For instance, the NWS office responsible for Providence, RI sent out a record report for Friday, October 28 stating that the airport received a trace of snowfall, tying a record that was first set in 1934. A trace of snowfall would not be considered a lot of snow, so it will not take a lot of snow to break some records in the major cities of the Northeast. Significant snowfall is what is on tap.

Here are some potential forecast snowfall totals for some of the major cities Saturday through Sunday (sorry if yours isn't on the list):

New York City: 2-5 inches
Philadelphia: 1-2 inches
Albany, NY: 4-8 inches
Baltimore, MD: 2-4 inches
Newark, NJ: 3-7 inches
Providence, RI: 4-6 inches
Bridgeport, CT: 3-7 inches
Portland, ME: 5-10 inches

There are a couple more items with respect to snow I should mention. First, higher elevations in the Catskills could have over a foot of snow by the time the storm starts to wind down. So local accumulations could be higher in the areas above and throughout the Northeast. Second, the snow that will fall will be very wet and heavy. Temperatures have a hard time diving into the frigid territory this early in the snowfall season. As such, the snow that will fall will be quite wet. Something to note.

3) Flooding: All of Delaware and most of New Jersey is under a Coastal Flood Warning on Saturday. The main reason for this warning is due to a high tide that will move through the area Saturday afternoon. While this is not specifically tied to the storm, a strong wind blowing even close to perpendicular to the coastline will enhance the tide and flooding along the coast. In addition, excess precipitation will cause some local flooding on land.

Some quick links for you:
Severe Weather map for Northeast

WunderMap with model map layer turned on

WunderMap with radar layer turned on

Webcam in New York City


Figure 1. Severe weather alerts for the Northeast.

Blizzard Winter Weather Nor'Easter

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Intense Nor-easter Set To Slam Northeast

By: shauntanner, 7:04 PM GMT on October 28, 2011

If you like Winter weather and you live in the Northeast, then you will like this weekend. An early season Nor-easter is set to slam the Northeast with a significant punch of snow. The storm is expected to rapidly intensify off the Mid-Atlantic coast on Saturday before passing southeast of Cape Cod Saturday night.

The storm's minimum low pressure via the European model seems to be around 992 mb Saturday night, which makes it not a particularly strong storm in terms of pressure. Also, temperatures throughout the area will not be incredibly low (Saturday forecast for NY is 43, Boston is 45) so expect mostly rain for many areas until the colder temperatures of night set in. Once this happens, however, expect potentially record-setting October snowfalls to occur.

Here are just a few daily record snowfall amounts that appear to be in jeopardy for Saturday and Sunday:

Central Park Trace(2002) 0.80(1925)
Boston 1.10(2005) Trace(2000)
Albany 0.40 0.10
Bridgeport (CT) Trace(2008)
Providence Trace(2005) Trace(2000)

As you can see, it is not going to take much to break some of these records, which is why this snowstorm will be of significance. Will it be a storm of epic proportions? No, but several inches of early season snow on the Northeast could cause quite a headache for the residents in the area.

Here are some links you can use to navigate your way around the storm:

New York City Radar. I know what you are saying..."What if I don't live in New York City? No problem, I don't either. Just go to that page, and click on a cross in the map to the right that is associated with your area. You will be taken to a radar page that shows what is going on in your area. This is a good way to keep track of where the precipitation is and when it will hit you.

WunderMap with radar on it. If you are more inclined to watch radar for a wider area, then WunderMap is for you. Just click on that link and you can animate it to watch the storm in real-time. Then click on the Weather Stations checkbox to see what the temperature is like in your area. You can zoom in to see more local areas as well. An important note is that it can be snowing in an area where the temperature is greater than 32 degrees. So keep that in mind when you go out to do your errands this pre-Halloween weekend.

Also, it would be smart to monitor your local city page. For instance, if you go to the city page for Boston, MA, there is a wealth of information there. My favorite is the webcams. Pick a webcam in your area and watch the snowfall accumulate throughout the day. Better yet, grab yourself a warm cup of chocolate Saturday night and watch your favorite webcam.

The most snow is set to fall on the Catskills with over a foot possible. Most other places that will receive snow will get anywhere from a dusting to a few inches.



Figure 1. Severe weather map of the Northeast, showing Winter Storm Watches that will shift over to warnings as the weekend progresses.


Figure 2.

Nor'Easter Blizzard Winter Weather

Updated: 7:05 PM GMT on October 28, 2011

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Lesson 2, part 4: Earth vs. Venus

By: shauntanner, 9:58 PM GMT on October 19, 2011

In the last lesson, you learned about the greenhouse effect and how it is essential for life on Earth. The greenhouse effect is created by greenhouse gases such as carbon dioxide and methane that form a blanket around the surface. This blanket allows the warmth emitted by the surface to remain in the atmosphere, keeping the surface warmer than it would be otherwise.

This lesson, however, will give you a practical application of the greenhouse effect gone wild. It is also a near-Earth warning shot of the direction the Earth could be headed if we continue to pump greenhouse gases into the atmosphere.

Earth vs. Venus

Our solar system is made up of nine planets. True, Pluto was recently relegated to a dwarf planet, but I still call it a planet because that is how I grew up. Old school. Earth is the third planet from the Sun, making it one of the warm planets. Earth's nearest neighbor is Venus, which is the second planet closest to the Sun. Thus, it makes a pretty good comparison when comparing the atmosphere of the two planets.

There are three main factors that determine the surface temperatures of both Earth and Venus.

1. Which planet is closer to the Sun?
2. What planet is more reflective?
3. Which planet has a larger ability to absorb and retain solar energy?

Let's take a look at each of these step-by-step.

Which planet is closer to the Sun?

Since Venus is closer to the Sun, you would obviously expect it to receive more solar radiation than Earth. In fact, sunlight striking Venus is 93% stronger than sunlight striking Earth, thus we would expect Venus to be warmer. 93% is considerably more solar radiation. That is almost double what the Earth receives.

Thus, based only on the distance from the Sun, the average surface temperature of Venus should be much warmer than Earth. Keep in mind, this takes into account that ALL of the solar radiation that strikes the planets is absorbed by the respective surfaces. If this were to happen, the surface temperature of Earth would be 5°C and the surface temperatures of Venus would be 55°C. That is a big difference. However, based on the last lesson when you learned about the greenhouse effect, you know that the average surface temperature of Earth is around 15°C. Thus, something is up.

What planet is more reflective?

One of the things that is "up" is albedo. Albedo is the percentage of solar radiation that is reflected back to space. The higher the albedo, the more radiation is reflected. When solar radiation is reflected, it is not absorbed and thus takes no part in warming the surface. Thus, if the albedo of a planet is 100%, then it reflects ALL of the incoming solar radiation and thus SHOULD be a pretty cold place because solar radiation is not warming the surface.

The albedo of the Earth is 30%. This means that nearly a third of the Sun's radiation is bounced back out to space by light-colored things on Earth such as ice, snow, deserts, and clouds. If we wanted to increase the albedo of the Earth, we could cover it in snow. This would cool the planet.

The albedo of Venus is 70%. This means that the atmosphere of Venus reflects a whopping 70% of the solar radiation that hits its atmosphere and TAKES NO PART IN WARMING OF THE PLANET. That is key. Remember that as we move forward.


Figure 1. Venus on June 25 2005. Note the high reflectivity of Venus.


Figure 2. A picture of Earth from space.

Which planet has a larger ability to absorb and retain solar energy?

So what on Venus does all the reflecting? Well, remember, the "stuff" that does the reflecting on Earth are the light-colored things like ice, snow, etc. Well, Venus is quite literally covered with a thick layer of clouds made of sulfuric acid. This acid is very highly reflective and does the majority of the solar radiation reflection.

So, let's re-examine the numbers:

If the amount of solar units hitting Earth is 100 units, then based on the fact that Venus is closer to the Sun, it receives 193 units. Yet Earth absorbs 70% of these units and Venus absorbs 30% of these units.

Earth absorbs:

100 X 0.70 = 70 units

and Venus absorbs:

193 X 0.30 = 58 units

Thus, based on the distance from the Sun AND the albedo of both planets, Venus should be COLDER than Earth because it actually absorbs a lot less solar radiation.

Here's the rub. The average temperature of Earth is 15°C, while the average surface temperature of Venus is........480°C! What is up with that? Something else must be going on.

The answer is in the respective atmospheres. Earth's atmosphere is primarily made up of Nitrogen (78%) and Oxygen (21%). There are also trace amounts of carbon dioxide, water vapor, methane, etc. Venus has a much simpler atmosphere that is made up mostly of carbon dioxide and nitrogen. The thing is, the atmospheric content of carbon dioxide on Venus is 96%. The remaining 4% is nitrogen.

Also, because carbon dioxide is a much heavier gas than oxygen and the other gases in Earth's atmosphere, Venus' atmosphere is much more massive than that of Earth. So much so that the mass of just the carbon dioxide in Venus' atmosphere is almost 100 times greater than the TOTAL mass of the Earth's atmosphere! That is amazing.

Here is where we put it altogether. Carbon dioxide is a greenhouse gas. We learned this in the last lesson. Carbon dioxide is very good at trapping radiation from the surface. The more carbon dioxide in the atmosphere, the more radiation it will trap and the hotter the surface will be. Venus' atmosphere contain around 25,000 times as much greenhouse gases as the Earth's atmosphere. Thus, it is much more efficient at trapping radiation and accounts for the vast difference between Earth's surface temperature and Venus' surface temperature.

Thus, Venus has a much hotter surface that Earth, despite the fact that Venus absorbs much less sunlight that Earth does.

I wanted you to know this because if we wanted to debate what happens when we pump more carbon dioxide into our own atmosphere, we look no further than our nearest celestial neighbor. It has a scientific story to tell. That story is also a warning.

Education

Updated: 1:38 AM GMT on October 20, 2011

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Lesson 2, part 3: Greenhouse Effect

By: shauntanner, 4:56 AM GMT on October 11, 2011

The topic of climate change is loaded with charged words that provoke emotions on both sides of the "argument" (I say "argument" because, in fact, there is no argument at all. 97% of climate scientist acknowledge that anthropogenic climate change is real and current). "Fossil fuels", "natural", and "green energy" are just a few of these words or terms. There is one term, however, that gets caught up in the argument but really should not be.

Greenhouse Effect

The term "greenhouse effect" gets batted around like a tennis ball in the media. As far as the media is concerned, it is a dirty word. Greenhouse effect = death of the planet. This is wrong, for the most part. As you will learn by the end of this part of the lesson, the greenhouse effect is essential for life on Earth.

Our dear Mother Earth strives for balance. When she gets thrown a curve ball in terms of climate (a volcano erupts or a meteoroid runs into the surface), Earth takes the consequences of that curve ball and strives for a resulting balance. Thus, we have the idea of radiative equilibrium. Think of equilibrium as balance. Ying = Yang, In = Out, Luke Skywalker = Darth Vader, you get the idea. One aspect the Earth strives for balance in is temperature. To obtain radiative equilibrium, the amount of sunlight the Earth is absorbing has to equal the amount of radiation the Earth is emitting. If the Earth emits more radiation than it was absorbing, then it will cool down. If it absorbs more than it was emitting, it would heat up. The radiative equilibrium temperature of Earth if 0°F. Cold! Now, here comes the curve ball. If you were to take the temperature of every thermometer on the planet for numerous years and average all of these values, you would get 59°F. So, I am telling you that based on the radiation we receive from the Sun, the temperature should be 0°F, yet the ACTUAL average surface temperature is 59°F. What gives?

The answer is blackbodies and selective absorbers.

A blackbody is an object that is a perfect emitter and a perfect absorber. This is a fancy way of saying that all of the radiation that hits a blackbody is absorbed. There are several important blackbodies in the Earth system. The surface, is probably the most important of them all. How do we know that the surface is a blackbody? Well, when it is daylight on one side of the planet, it is night on the other. That is to say, the radiation from the Sun does not pass all the way through the planet. Instead, it is absorbed by the surface and prevented from passing any further. You are also a blackbody, which is why you cast a shadow.

The real reason for the difference between radiative equilibrium (0°F) and actual observed surface temperature (59°F) is due to something called selective absorbers.

A selective absorbers is something that only absorbs certain wavelengths and usually emits at similar wavelengths. For instance, an object may absorb only infrared radiation and will emit only infrared radiation. Since the radiation from the Sun passes right through the atmosphere on its way to being absorbed by the surface, the ATMOSPHERE must be a selective absorber since it does not absorb sunlight very well. The "shortwave radiation" from the Sun passes right through the atmosphere. So what does the atmosphere absorb? It does a very good job of absorbing "longwave radiation" from the surface.

The best way to think of this is a blanket. When you go to bed at night, you pull a blanket over yourself. Why? Well, the natural answer is, "to keep warm." How does the blanket keep you warm? Your body is an engine that generates a lot of heat. Without the blanket covering you, the heat that your body generates would be emitted out into the room and be lost. You would get cold. If you throw a blanket over you, your body heat is emitted and then absorbed by the blanket almost immediately. This will warm the blanket a little and keep you significantly warmer. Thus, you are warmer with that blanket than without it.

Now, let's translate this to the atmosphere. The blanket is the atmosphere and your skin is the surface of the Earth. Sunlight passes through the atmosphere and warms the surface. In turn, the surface emits radiation (like your skin) which is trapped by the atmosphere (the blanket). So, without the atmosphere, the surface of the Earth will be a lot colder (0°F) than it currently is (59°F). Get it? This, ladies and gentlemen, is the greenhouse effect. Without the greenhouse effect, the surface of the planet would be 0°F and too cold for life to have evolved how we know it today. Because of the greenhouse effect, the surface temperature is 59°F, which is pleasant enough for life to have evolved.

For those of you more inclined to learn via a picture, behold Figure 1.


Figure 1. The greenhouse effect as we know it.

Now, here is the problem. As we learned in the very first lesson, the atmosphere is made up of numerous different gases (nitrogen, oxygen, carbon dioxide, water vapor, etc.). Some of these gases are much better at absorbing the "longwave radiation" coming from the surface of the Earth. The more radiation these gases absorb, the warmer the atmosphere and surface. Back to our blanket analogy, it would be the equivalent of throwing another blanket on your bed. The extra blanket would act to trap more of your body heat, thus warming you more. At some point, it would become too hot for you to be comfortable.

The gases responsible for absorbing "longwave radiation" from the surface are known as greenhouse gases. To name a few greenhouse gases:

Carbon dioxide
Methane
Water vapor
CFC


Water vapor is perhaps the most important greenhouse gas. The more water vapor in the atmosphere, the more radiation it traps and the warmer the surface. I guarantee you have direct experience with this. Think about a morning when the sky is covered in clouds. It is completely overcast. Now, think of a morning when the sky is completely clear. Which morning is warmer?

Of course, the answer is the overcast morning. This is because water vapor is a greenhouse gas. Thus, the more of it that is in the atmosphere, the more infrared radiation from the surface it will absorb and the warmer the surface will be. Think of the extra blanket on the bed, again.

Carbon dioxide, of course, gets all the headlines as being the most diabolical greenhouse gas. This is because humans are directly involved in pumping this gas into the atmosphere. The more carbon dioxide, the thicker the blanket on the bed. Problem is, we cannot just roll out of this bed to get away from the heat.

Education Climate Change

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Lesson 2, part 3: Heat Transfer

By: shauntanner, 6:03 AM GMT on October 03, 2011

Sorry I am one day late in getting the next lesson up. Busy weekend compounded with a busy weather week for the West Coast translates to late night educational blogging. But, here we go.

Picture yourself sitting in front of a fireplace on a cold Winter's night, reading your favorite novel. The warmth of the fireplace is keeping you warm, but perhaps you have never thought about how it meets its goal. This, ladies and gentlemen, is the introduction to heat transfer.

In the atmosphere, there are three ways heat can get from one place to another.

Conduction

The first, and perhaps simplest, way heat and energy is transferred is conduction. Take a look at Figure 1. In the figure, a foolish man is holding a metal rod over a lit candle. Common sense will tell us that if that foolish man holds the metal rod over the flame for long enough, he will get burnt. But, have you ever thought about the mechanism that makes this possible? As the foolish man places the rod over the candle, the heat from the flame warms the portion, or molecules, directly over the flame. At that moment, the man does not feel any heat, thus the heat transfer is not instantaneous. But, these warm molecules in the metal rod then warm the molecules next to them, which in turn, warm the molecules next to them, and so on. This process continues until the heat hits the foolish man's hand, and he drops the metal rod while saying, "I'm an idiot."


Figure 1. An example of conduction. Credit: www.universetoday.com.

Thus, conduction is heat transferred between molecules.

There are poor conductor and good conductors. A poor condutor would be a substance that does not pass along its heat very well. There is a very important poor conductor in the Earth system. The atmosphere. The air of the atmosphere is very good at ignoring some of the energy, or heat, it receives. Think about it. If air was a good conductor, the charge of a lightning bolt would not be allowed to build and we would have a lot less strong lightning strikes and a lot more weak lightning strikes.

Metal, of course, is a good conductor. Anything that you can touch and quickly be burned by is probably a good conductor.

Convection

The next form of energy transfer is convection. We have all heard of a convection oven. Heck, you might have one in your house and not know how it works. Convection is energy transfer by gases or liquids. Here is an example:

The Sun's energy reaches the ground in the afternoon and warms the very bottom portion of the atmosphere. Warm air, of course, is less dense than cold air, and therefore this newly-heated warm air will rise up into the atmosphere. By doing this, the heat that was near the surface is then transported high up in the atmosphere. Thus, the heat was transferred.

Convection is a good way of moving heat from one spot to another and the atmosphere does a good job of utilizing this form of heat transfer. In fact, it does such a good job that meteorologists have a special word we use to describe when heat is transferred by moving air masses. Advection is a fancy way of saying that heat was moved from one spot to another. Thus, when we say warm air is advected from Alabama to Tennessee, that simply means warm air danced its way from one state to another. Fancy words = scarier than they really air.

Radiation

I want to save a good chunk of space for the last form of heat, or energy, transfer. Radiation is probably the most important form of energy transfer because without it, nothing else is really possible.

Radiation energy travels in waves, like waves on the ocean. Except, you cannot see most of these waves as they are invisible to the naked eye. Furthermore, radiation waves travel at the Universal speed limit of the speed of light. But wait...there's more!! For our purposes, the radiation that drives the Earth system comes from the Sun. The Sun emits an enormous amount of radiation that blasts across the inner Solar System at light speed. The best part is that the energy that represents these waves of radiation does not become relevant until it becomes absorbed. In other words, when you are lying out sunbathing, the energy you feel on your skin was emitted by the Sun and did not waste any of its appetite on anything else other than your skin.

Radiation comes in all shapes, sizes, and names. Some of these names you have heard before but just never connected the dots. Figure 2 shows a slice of these names.

Figure 2. Some of the electromagnetic spectrum.

As you move from right to left on the scale, the wavelengths of the waves of radiation become smaller. The wavelength of a radiation wave is the distance between the peak of one wave and the peak of an adjacent wave. So, if you were surfing these waves, a wavelength is the distance between standing on top of one wave and looking off into the distance and seeing the top of the next wave. Get it?

Here is something very important. The shorter the wavelength, the more energy that type of radiation carries. Radiation waves with short wavelengths are particularly harmful to you and me. Thus, radio waves (at 1000 cm wavelengths) are not too harmful to you. This is good news since there are probably radio waves traveling through you right now. Whew! However, on the opposite end of the spectrum, gamma rays are deadly. There have such a small wavelength that if you ever encounter one, you will most likely die...and quickly.

Interesting note: X-ray radiation is on the end of the spectrum that is harmful to you. This is the reason why you have to wear a lead plate when you get an x-ray taken. The lead plate reflects the x-ray radiation away from your organs. But, you still shouldn't have very many x-rays in the course of any given year.

The middle of this spectrum is the most important. Right in the middle is a type of radiation called visible light. This type of radiation is the only radiation that you can see. So, it is no accident that we've evolved to see this type of radiation since the Sun emits a large amount of it. In fact, it emits more visible light than any other type of radiation (44% of its total radiation comes from visible light).

We can break down visible light even more. Visible light can be summed up with one neat acronym...ROYGBIV.

The various types of visible light are:

R--Red
O--Orange
Y--Yellow
G--Green
B--Blue
I--Indigo
V--Violet

The wavelengths get shorter the farther down this list you go (violet has the shortest wavelength). For this reason, blue and violet lasers are very uncommon (some are used for surgeries because they are so energetic they can cut skin) and red lasers are annoyingly common. Red lasers are not dangerous unless you stare at one too long.

So ROYGBIV represents all of the colors of the rainbow, but it doesn't represent all of the radiation from the Sun. The Sun also emits a bunch of other stuff such as ultraviolet, infrared (IR), x-ray, radio, etc.

This leads me to one last topic for today...the three rules of radiation.

1. Everything with a temperature above absolute zero emits radiation. This is a universal truth. You have a temperature of somewhere around 98.6 degrees right now. Thus, based on our rule, you are emitting radiation. To be more specific, you are emitted infrared (IR) radiation. Note that this type of radiation is on the long wavelength portion of the spectrum, thus your radiation is not too dangerous.

2. Objects with higher temperatures emit shorter wavelengths. No matter what you think about yourself, the Sun is hotter than you. Since it is around 10,500 degrees, based on our rule, it will emit shorter wavelengths than you. In fact, it does emit shorter wavelengths since we know it emits visible light, which has a shorter wavelength than infrared radiation. It's a good thing our Sun is not too hot, or else it would emit wavelengths that are much more dangerous to us.

3. Objects with higher temperatures will emit more total radiation. Again, take the Sun for example. Since it is much hotter than you, it emits not only visible light, but also ultraviolet, infrared, x-ray, microwave, radio, etc. Since you are relatively cool, you only emit infrared. Poor you.

Okay, I think I have confused you enough. Have a good week. Next week are are going to talk about...the greenhouse effect!!

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About shauntanner

Shaun Tanner has been a meteorologist at Weather Underground since 2004.

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