Often seen on days with many varieties of wintry precipitation, these soft, round pellets of snow may just appear on your windshield. It’s a very odd looking form of winter precipitation. With their cloudy, circular appearance, these white pellets take on a form resembling styrofoam or “Dippin Dots” ice cream. It goes by its most common name snow Pellets, but to meteorologists, it is known as graupel.
How are Different Cloud Types Named and Defined?
For anyone who has ever gazed up into the vast blue pool that encompasses the Earth, horizon to horizon, they will have noticed on more than one occasion the different cloud shapes dotting the sky. Some may note them as appearing like fluffy bunnies, others may see dragons, others denote them as simply describing the mood of the sky, while another may discern them to be bumpy or wispy. But what is it that is common amongst these descriptions? Reviewing them, all have to do with a physical appearance of the cloud. Describing the physical appearance of a cloud is actually one of two parts in how the different types are defined from one another. The second part of differentiating one type of cloud from another has to do with altitude in the atmosphere at which that cloud exists, and sometimes the ability of that cloud to precipitate. So what are those fluffy looking clouds called anyways, and what does their name indicate about the cloud?
There are five main categories of cloud name roots that help describe a cloud. These roots are cirro-, alto-, cumulo-, nimbo-, and strato-. All are latin in origin and define the height, appearance, and the precipitation ability of a cloud. The roots are combined to name the specific cloud. Starting with cirro-, this root means “a lock of hair” or “curl-like fringe” and describes clouds that have a wispy, hair-like appearance. The root indicates that it is a high-level cloud, existing at about 6,000m and above in altitude. Situated so high in the atmosphere, they are composed of millions of ice crystals that give them their characteristic hairy, or wispy appearance. Some may even describe them as smudged.
The root alto- means “middle”and describes clouds that exist at middle altitudes in the atmosphere, around 4,000m. As you might imagine, the roots cirro- and alto- cannot be combined to describe a cloud seeing as they both partially indicate the height at which a cloud exists.
In contrast to the previous two roots, strato- does not indicate a cloud’s height whatsoever, and can be found at all levels in the atmosphere. Strato- means layer, such as something that is stratiform, or stratified. As such, stratus clouds are those with a layered look, like sheets covering the sky. Fog is actually a type of stratus cloud! The root can be combined with any one of the other roots to name a cloud. For example, a cirrostratus cloud indicates a cloud that is high level, composed of ice crystals, but in layered form. An altostratus cloud describes a mid-level cloud that appears in sheets or bands.
Moving on, the root nimbo- actually come from the Latin word “nimbus” which means “cloud” in Latin. This specifies a nimbus that precipitates, and can be combined with a few of the different roots, except for alto- and cirro-, seeing as these clouds exist above the freezing point in the atmosphere and cannot precipitate since they are composed of ice. Nimbus clouds are low-level clouds, existing from about 2,000m and below, that often precipitate, be it rain, snow, hail, or sleet.
Finally there is cumulo-, meaning “heap or pile.” Cumulus clouds are interesting in that they occur at all levels of the atmosphere and can be combined with any of the roots listed above. At a low level these clouds are the ones people often make out to be fluffy bunnies or cotton balls thanks to their heaped and bulging appearance. Cirrocumulus appear to be round but raggedy white spots that repeat throughout the sky, while altocumulus are a bit softer and larger in appearance. Stratocumulus tend to occur in waves or lines, and often look as though they are connected, hence where the stratiform appearance comes into play. Finally, the largest and most dramatic of the cumulo- family is the cumulonimbus, a massive cloud that can reach the tallest heights of cloud existence in the atmosphere, up to the troposphere, and sometimes beyond into the stratosphere if they have what is called an “overshooting top.” These clouds are those that produce isolated thunderstorms and are often responsible for large hail storms. Reaching all heights within the atmosphere, these clouds tower, and appear ominous with their dark, bulging bases, and icy tops.
When taking a look into the sky, no longer will you simply see cotton balls and bunnies, but perhaps the many individual types, from a cirrostratus, to a cumulonimbus, to a simple cumulus that so makes those fluffy bunnies! All are distinct in their nature and build, and are constructed from a variety of different atmospheric conditions, but there is no denying that each finds common ground in their unique beauty and ability to spark the imagination.
© Weather Forecaster Alexis Clouser
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DISCUSSION: During a typical Summer or Winter morning (or sometimes during the evening to overnight hours), there are often scenarios in which a given region can have a substantial amount of warmer and moistened air flowing in overnight. In such scenarios, it is quite common to find an atmospheric phenomenon such as fog as a result of the increased presence of warmer, moister air into the given region. This process acts to increase the regional dew point temperature which will allow the regional atmospheric environment to get closer to the actual air temperature. When the dew point does indeed reach the actual air temperature, this is the process most commonly known as and referred to as atmospheric saturation. When the atmosphere becomes saturated, this is when fog is most likely to form as the air parcels in a region reach the maximum holding capacity for water molecules that they can at a given air temperature.
It goes without saying that fog can be an incredibly dangerous precedent for any and all forms of ground and air travel. The primary reason for why fog is such a major hazard to general travel is because any type of fog can seriously impact people’s ability to have longer distance visibility when driving or for any pilot’s ability to see sufficiently well when attempting to fly a plane. For example, limited visibility can prevent a pilot or driver from being able to have enough depth perception when it comes to perceiving possible threats or obstacles in the path of a given vehicle or aircraft which can often make a typical trip quite troublesome even on an average day. Therefore, it certainly makes sense for why advisories such as dense fog advisories exist across the National Weather Service network in order to help protect average citizens from placing themselves in the path of danger when it comes to navigating around areas of dense fog when they do indeed occur.
The bottom line here is the message that whenever a major fog event unfolds, it is imperative for anyone and everyone in the path of a current or upcoming fog event to respect the natural power that the atmosphere holds. In addition, whenever there is a threat for an incoming fog threat, is it always best to plan your travel accordingly and avoid doing unnecessary driving through very dense fog since that can sometimes be a life-threatening issue if visibility gets down to 100 feet or less.
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© 2019 Meteorologist Jordan Rabinowitz
DISCUSSION: During any part of the winter season, there is little to no debate that one of the hotter topics when it comes to winter weather has to deal with the track of coastal low-pressure systems. The reason for why this is such a hot button topic during the climatological Winter-time months is the fact that a change in forecast low-pressure center track by a matter of miles will often mean the difference between an all-out classic snowstorm, a slushy mess, or even a flat-out cold rain event. This is often a critical problem for forecasters and the general public alike since many people will often rely on the exact words of their local weather broadcaster to get an idea of what to expect for a given situation. However, when such projections prove to be incorrect, this can often lead to major problems.
Having said that, it is worth noting that there are several legitimate reasons for why such forecast issues arise in the first place. To start, when a local weather forecaster is trying to anticipate the track of a given low-pressure system, a key component has to do with the prevailing photo of the low to mid-levels of the atmosphere as well as how the upper-level atmospheric dynamics will play into how a developing Winter-time extratropical cyclone may travel over some given time-frame. These factors alone create a very transient and fluid situation which can often be very hard to predict of very short timescales and therefore, will often lead to tremendous uncertainty in terms of snowfall forecast cut-off zones for a specified region for any given winter storm scenario.
In addition, another factor which plays into the critical importance of low-pressure track forecasting accuracy is the reality that depending on the strength of the low-level winds in the warm sector of a developing coastal low-pressure system, this will often largely determined how much warm air and to how much of a spatial extent warm air is able to surge northward and impinge on the evolving “freezing line” (i.e., the precipitation line which separates the sectors of rain and snow, respectively). Hence, if there happens to be a stronger low-level surge of warm air closer to the surface of the Earth, this can often lead to a consequential northward nudging of the corresponding freezing line and can quickly cut down on forecast snowfall totals.
As shown in the idealized forecast graphic attached above (courtesy of NBC Chief Meteorologist Brad Panovich), low-pressure center tracks across the southeastern United States will quite often have a substantial influence on the spatial extent of the accumulating snowfall potential and thus, leaving little to no surprise for why the southeast is often an uncertain forecast when it comes to snowfall forecasts with developing Winter-time coastal low-pressure systems.
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© 2018 Meteorologist Jordan Rabinowitz
Picture this: you’re on vacation in the Florida Keys enjoying the warm, humid weather at the beach, when all of a sudden you notice what looks like a tornado on the water. What you have just witnessed is a phenomenon known as a waterspout. Waterspouts typically occur in the tropics and subtropics, but can also occur in other areas such as the Great Lakes. But what exactly is a waterspout?
A waterspout is a column of spinning air, or a vortex, that occurs over water. There are two different categories of waterspouts: tornadic and non-tornadic. Tornadic waterspouts form in the same way as a tornado that would form over land and are associated with severe thunderstorms. The primary difference between a tornado and a tornadic waterspout is that a tornadic waterspout occurs over water. This can refer either to tornadoes that form over water or tornadoes that form over land and then move over water.
Non-tornadic waterspouts are not formed in severe thunderstorms, and are often referred to as fair-weather waterspouts as they are associated with developing cumulus towers. Non-tornadic waterspouts typically move very slowly, if they move at all, since the clouds they are associated with are developing through vertical convective action rather than through the collision of moving frontal boundaries. Non-tornadic waterspouts go through five stages of development. The first is the appearance of a light-colored disk surrounded by a larger, darker colored area on the water. The second stage of development is characterized by a spiral pattern of light and dark bands outside of the dark spot on the water. A swirling ring of sea spray, called a cascade, then develops around the dark spot. As the waterspout continues to develop, it will form a visible funnel that extends between the water’s surface and the dark flat base of the developing cumulus cloud. The final stage of a waterspout’s life cycle occurs when the inflow of warm air into the vortex of the waterspout weakens causing the waterspout to dissipate.
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©2018 Meteorologist Stephanie Edwards
A Haboob is what a lot of local arid climate residents call a dust storm. “Haboob” is a term derived from the Arabic word “habb” meaning “wind”. This type of dust storm is created from a strong thunderstorm downdraft called a downburst. Starting as a downdraft of cold air descending from a storm, the cold dense air hits the ground at a strong speed and extends outward. The strong outward flowing wind sweeps up dry sand and dirt from the ground as it travels. This doesn’t always happen with every storm. Haboobs are unique and only occur in certain parts of the world. Areas that frequently see weather like this are arid climates, mostly dry with little trees and sandy soil. Places that have these types of climates are Northern Africa: specifically Sudan and the Saharan Desert, The Middle East, Australia, and in North America: such as western Texas, New Mexico and Arizona. These storms will occur more frequently in these areas during the summer and/or Monsoon seasons.
The wind from a Haboob can carry dust long distances and can be rather intense reaching up to 62 miles wide and traveling up to 62 miles per hour. They approach with little to no warning and can recede just as quickly. You can typically see a Haboob before it reaches your area because these dust clouds are thick and brown with tons of sand, dirt, and debris. Just as soon as you see one approaching, it is already starting to affect your area. What makes these storms so dangerous is how quickly they appear and how quickly they reduce visibility down to almost zero. In these conditions, it is important to pull over when driving and wait until the Haboob has passed. High winds can whip small particles like dust and sand, pelting anything that stands in the way. This can be hazardous to a person's respiratory system. Small particles can enter your nose and mouth making breathing difficult, triggering severe irritation to the throat and lungs. Eyes and ears can also be infiltrated by these particles causing painful irritation. Before a Haboob passes your area, It is important to find shelter immediately if you are outside. The high winds of a Haboob also have the ability to blow dust and sand into cracks. It is essential to close all windows, doors and block cracks and vents with rags to prevent dust particles from entering your home or place of shelter.
Haboobs can sometimes be mistaken for Sandstorms. Sandstorms and Haboobs, although look similar, embody different characteristics. Sandstorms usually occur with and are created by high winds as Haboobs originate from thunderstorms only. Sandstorms tend to be more widespread and near the surface as Haboobs are concentrated in a more localized area. Sandstorms also occur strictly in desert like climates when Haboobs can be frequent in both desert and dry arid steppe climates like dry, grassy plains. Sandstorms tend to carry heavier particles like sand and small rocks, near the surface. Since these particles are heavier they don’t get suspended in the air as easily as smaller dust particles carried by a Haboob. Sandstorm winds are stronger but typically aren't as turbulent as Haboob winds.
A very interesting and unique meteorological term, Haboob has quite a ring to it. It’s certainly something you won’t forget. If this really interested you, stay tuned for the next article in the series of Fascinating Meteorology Terms. We will be turning to a more wintery type of weather to discuss the term “Graupel”. Some of you northerners might recognize it!
© 2018 Meteorologist Alex Maynard
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DISCUSSION: During a given Winter season, there can sometimes be a substantial threat for high-impact winter storms along the East Coast of the United States. This often occurs as a result of there being an offshore to semi-coastal temperature gradient in place which acts to “fuel” the development of coastal low-pressure systems during the Winter-time months. The fundamental component which is most often responsible for the development of such Winter-time low-pressure systems are the climatological development of a weak low-pressure system in the vicinity of the Gulf Coast region of the United States.
As the typical weak low-pressure systems which develop in the vicinity of the Gulf Coast region “skip” across the peninsula of the state of Florida and “ride up” along usually a good portion of the U.S. East Coast, this is around the time at which the classical winter storm stage is set. This is the conventional situation in which a classical Nor’easter is identified most often. As shown in the animated radar imagery above, you can see how this was not quite the scenario described above since this system developed in the vicinity of the southern Great Lakes before travelling eastward. Thus, this is the type of coastal winter storm development which is most often referred to as “coastal secondary low-pressure transfer.” This recent winter storm perfectly exemplified this type of scenario which still ended in a substantial accumulating snowfall event across a good portion of the Northeast.
You can see how with this storm, there was heavy rain, snow, and ice on the east side of the winter storm (i.e., within the warm sector of the low-pressure system). This still led to a good portion of Pennsylvania, New Jersey, New York, Connecticut, Rhode Island, Massachusetts, and beyond receiving a high-impact winter weather event. It just goes to show how it does not necessarily need to be the heart of Winter to experience an all-out winter storm along the East Coast of the United States.
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© 2018 Meteorologist Jordan Rabinowitz
DISCUSSION: As of earlier today, history was made over in the Eastern/Central Pacific Ocean basin. Science researchers from around the world continued to be even more optimistic about the future of atmospheric and climate research. This optimistic and confident sentiment is a direct result of the newest and final position of the GOES-West (formerly GOES-17) satellite imager being declared as having reached its final position in its orbit around planet Earth. This is a truly historic and memorable day in the history of atmospheric science research as well as atmospheric forecasting since this satellite imager now matches up with its sister satellite (i.e., the GOES-East satellite imager) to help monitor and study an even greater portion of North America and beyond the scope of the Eastern Pacific Ocean. This is incredibly meaningful since it allows both forecasters and researchers to get even greater detail than ever before in areas further west than the current GOES-East (or GOES-16) satellite imager viewing window could ever accommodate. Hence, this is a tremendous step forward for the future of advancing science and our ability to better understand both the Earth's atmosphere and the Earth's ever-evolving climate system.
It goes without saying that the assets and the resources which will be provided by GOES-West will quickly become incredible valuable and precious to the global atmospheric science and climate science community as times moves along. The combined resources from the GOES-East and GOES-West satellite imagers will be immensely powerful in the current and future ability of atmospheric forecasters and researchers alike to make even more timely and accurate predictions and projections for various forecast scenarios across the coverage domains of the respective satellite imagers. Thus, the combined capabilities of these respective satellite imagers will continue to forever change the ways and the resolution at which we will now able to observe and track various atmospheric phenomena over an even larger region than atmospheric science previously was able to. Hence, GOES-West is taking the advanced remote sensing era to even higher heights.
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© 2018 Meteorologist Jordan Rabinowitz
DISCUSSION: As we head through Fall and every into every incoming Winter season, many people often continue to ponder and wonder about various things and mysteries pertaining to winter weather. One such thing which people wonder about during Winter is how and why snowfall forms during various types of winter weather events. Attached below is a neat discussion courtesy of the Met Office over in the United Kingdom which describes how and why snowfall forms.
“What is snow?
Snow is defined as 'solid precipitation which occurs in a variety of minute ice crystals at temperatures well below 0 °C but as larger snowflakes at temperatures near 0 °C'. It is one of the UK's most striking weather phenomena causing a transformation of the world around us, but it can also lead to the potential for disruption.
How does snow form?
Snow forms when tiny ice crystals in clouds stick together to become snowflakes. If enough crystals stick together, they'll become heavy enough to fall to the ground.
Snowflakes that descend through moist air that is slightly warmer than 0 °C will melt around the edges and stick together to produce big flakes. Snowflakes that fall through cold, dry air produce powdery snow that does not stick together.
Snow is formed when temperatures are low and there is moisture in the atmosphere in the form of tiny ice crystals.
How cold does it have to be to snow?
Precipitation falls as snow when the air temperature is below 2 °C. It is a myth that it needs to be below zero to snow. In fact, in this country, the heaviest snowfalls tend to occur when the air temperature is between zero and 2 °C. The falling snow does begin to melt as soon as the temperature rises above freezing, but as the melting process begins, the air around the snowflake is cooled.
Snowfall can be defined as 'slight', 'moderate' or 'heavy'. When combined with strong winds, a snowfall can create blizzards and drifts. If the temperature is warmer than 2 °C then the snowflake will melt and fall as sleet rather than snow, and if it's warmer still, it will be rain.”
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© 2018 Meteorologist Jordan Rabinowitz
DISCUSSION: There is no doubt that weather forecasting has evolved quite a bit over the past 40 to 50 years (i.e., since the onset of the remote sensing era). Having said that, it is worth noting that there are still many fundamental things which have not changed all that much in the weather forecasting process and there are many profoundly valuable reasons for these long-term techniques testing the sands of time. One such tool which fits this criterion is the world-famous weather balloon.
The primary reason for why the use of weather balloons has remained to be such a key part of the regional, national, and global forecast process is the fact that weather balloons have the unique ability of measuring local and/or regional vertical profiles of temperature, moisture, wind speed, wind direction, and more pertinent details of the atmosphere. Upon measuring the vertical profiles of these meteorological parameters, they are nearly instantly transmitted back to recording devices back in National Weather Service offices and other locations across the country based on their individual launch locations. Thus, weather balloons allow atmospheric scientists to study the atmosphere to better understand and predict how the lower to middle levels of the atmosphere may influence localized and regional weather conditions over some period of time.
Also, the fundamental premise of a weather balloon is such a versatile and reliable form of atmospheric data because the primary weather balloon measuring device known as a radiosonde will always fall back down to the surface of Earth after every launch with the support of a parachute. Thus, allowing the primary atmospheric measuring device to be reused repeatedly on a routine basis. Moreover, it is one of the few forms of meteorological measurement which has not changed over many decades and will likely not change for quite some time to come. Furthermore, radiosondes (and their close twin known as a dropsonde which is dropped from hurricane reconnaissance aircraft during hurricane research missions) are often used even more often both prior to and during winter storm as well as tropical storm events in different parts of the world. Thus, weather balloons have been, are, and will continue to be a critical part of global forecast process.
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© 2018 Meteorologist Jordan Rabinowitz