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
Photo Credit: White Squirrel Weather
DISCUSSION: With the autumnal equinox behind us, the days are starting to get shorter and it looks like flannel and pumpkin-spice drinks are all the rage again. And as that fall mood sets in, so too does the Halloween spirit. Several horror-movies and TV-shows come to mind this time of year, including the classic Nightmare on Elm Street or the latest season of American Horror Story on FX. While watching one of those shows, the scientist in me started noticing that a lot of horror-scenes take place in foggy night-time settings. This begged the question “Why is it that fog seems to happen so frequently late at night"? And that’s exactly what we’ll be discussing in today’s article.
There are many different types of fog, but the focus in this article will be on radiation fog, which usually is the type of fog that’s portrayed in horror movies. After sunset, the surface of the earth immediately loses its biggest source of incident radiation. And with no more solar radiation for the surface to absorb, all of the heat that has been collected over the entire course of the day simply begins escaping freely into the atmosphere in a process that’s referred to as radiational cooling. This process can be slowed down on cloudy nights when radiation is absorbed by low-hanging clouds and emitted back down to the surface but on nights with dense radiation fog, the night sky is crystal-clear more often than not.
Photo Credit: The Weather Network
As the radiation continues to scatter outward in all directions, the temperature of the surface will rapidly decrease while the air immediately above it cools more slowly, causing what’s referred to as a temperature inversion. In other words, the temperature actually increases with height for a small column of air that stretches from the surface to a few feet above the ground. But this situation alone won’t be enough for the eerie October fog to develop.
The next key ingredient is moisture, which can come from many sources, including lakes and rivers, and be carried to the surface by light turbulent mixing. Surface-level moisture will also increase since colder air gets saturated a lot faster than warmer air. If enough moisture is transported to the surface and the temperature manages to drop to what’s known as the dewpoint temperature, then the air will saturate to the point where dew droplets will develop! Once the air just above the ground begins to saturate, more droplets form, only this time the droplets that form are condensing in the air. This is the start of the radiation fog!
Photo Credit: Meteorologist Jeff Haby
As these fog droplets float around and slowly fall to the surface, they absorb and emit the radiation still coming off the ground, slowing the rate of cooling at the ground-level and pushing the area of greatest radiational cooling to the top of the expanding fog layer. The air mass inside this fog layer soon becomes isothermal (same temperature) throughout, making it eerily stable. Anyone caught under it will observe a sharp decrease in visibility and a calm, quiet ambiance that is sure to raise some hairs in the middle of the night. It will then maintain itself for as long as the radiative cooling at the fog-top introduces newly-formed droplets to the rest of the layer. If the fog-top reaches a point where the air is no longer moist or stable enough to continue this process, then it will reach its maximum depth. Walking around this quiet, misty environment in the middle of the night would immediately feel like something out of a horror movie!
By daybreak, solar radiation is reintroduced and immediately begins to warm the entire fog-layer, evaporating the fog droplets. Vertical wind shear introduces drier, windier air down to the surface and dries out the fog top. As the ground continues to heat up, the lower levels of the fog thin out. Any remaining fog droplets eventually settle on the ground as well. And of course, the ghosts, ghouls, and witches all go back into hiding.
The Weather Network: The Science Behind the ‘Classic Fall Storm’
Fog Forecasting: Meteorologist Jeff Haby
White Squirrel Weather, Western Kentucky University: On Air
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©2018 Meteorologist Gerardo Diaz Jr.
September 22nd marks the start of autumn, or autumnal equinox every year. Autumn is known as the third season in the year, the transitional period from summer to winter. Autumn also marks the start of daytime and nighttime temperatures steadily decreasing, which leads to leaves changing colors and falling off of trees. Some people have an aesthetic appreciation for the fall transition, but may wonder the scientific process behind this and how leaves fall off of the trees.
First off, this process begins in the spring and summer months. As trees grow throughout these seasons, chlorophyll (or in other words, the green pigment present in all green plants responsible for the absorption of light to provide energy for photosynthesis) is constantly replaced in the leaves. This process with the leaves converting sunlight into energy is known as photosynthesis. This process makes trees lose a lot of water, to the point when winter arrives, the trees are no longer able to get enough water to replace it. As the nights start to grow shorter in the early fall, the cells near the center of the leaf and stem divide rapidly but do not expand. This process of the cells forming a layer is called the abscission layer, which blocks the transportation of materials from the leaf to the branch, and then from the roots to the leaves. As the chlorophyll is blocked from the leaves, it disappears completely from them. The lack of chlorophyll allows the yellow (xanthophylls) and orange (carotenoids) pigments to become visible. The red and purple pigments (anthocyanins) are created from the sugars that are trapped in the leaf. These pigments in leaves are responsible for the vivid color changes in the fall.
As fall continues forward, and leaves start to peak their colors, all good things must come to an end as the leaves will start to fall off the tree. However, the term “fall” is a bit misleading, as this implies that the trees are submissive this time of year when in fact, they are actively pushing the leaves off their branches. The changes in temperature and daylight trigger a hormone that releases a chemical message to each leaf that it is time to prepare for winter. Over the next few weeks, abscission cells form a bumpy line at the place where the leaf stem meets the branch. This process goes at a minuscule pace, as the leaf is pushed from the tree branch. This happens as a means for a tree’s survival.
This process is a gentle but seasonal cycle, however, with changes in global climate variability such as the warming trends that have been noticeable throughout the years will noticeably impact the natural cycles within this process. The peaking of the leaves will start later than it has throughout the past, as well as leaves not becoming as vibrant in color and brittle due to the lack of moisture present and general heating throughout the summer and spring months. Fall is one of nature’s greatest beauties that unfortunately may be impacted throughout the years to come if these trends continue.
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©2018 Weather Forecaster Michael Ames
Now that fall has begun in the Northern Hemisphere, we find ourselves turning our attention to the foliage riot of colors. However, the simple transition from summer’s lush, leafy greens to fall’s bold reds, yellows, and oranges can be impacted in complex ways via weather conditions – temperature, precipitation, and amount of sunlight – as well as climate.
As most of us know, leaves serve a functional purpose for trees, producing energy for the entire plant. Their broad shape makes them perfect for absorbing sunlight, which after absorption, interacts with carbon dioxide and water within the leaves, producing sugars and oxygen in a process known as photosynthesis. The plant molecule responsible for photosynthesis is called chlorophyll – giving leaves their trademark green color. But chlorophyll isn’t the only pigment that resides within leaves! Orange (carotenoids) and yellow (xanthophylls) pigments are also present. However, they remain hidden for most of the year due to chlorophyll’s masking capabilities. Throughout the spring and summer months, chlorophyll is continually depleted by sunlight, only replenished during the growing season. Once chlorophyll levels subside, other pigments are able to shine through.
The most brilliant leaf displays tend to follow a summer filled with warm, sunny days and cool, crisp nights. During this weather cycle, the sunny days allow for leaves to produce an overabundance of sugars, while the cool evenings allow for the narrowing of leaf veins, trapping the majority of the sugars within. An overabundance of sugars and light within the leaves leads to the production of vivid anthocyanin pigments – which produce purple, red, and crimson colors. Soil moisture also plays a crucial role in the timing and brilliance of leaf foliage. The healthiest displays are produced when the soil has been adequately moist throughout the year, teamed with the aforementioned late summer weather. A severe late spring or summer drought can delay the onset of colors. A warm period during the beginning of fall can also decrease the intensity of fall colors by triggering early leaf drop before the colors have had a chance to fully develop.
In the future, these temperatures could potentially increase throughout all seasons due to climate change. However, the effect on fall foliage will depend on just how much the temperatures change. For example, New England is projected to have moderate temperatures – potentially leading to a later emergence of fall colors – while in southern New England, trees may be subjected to heat stress – leading to earlier coloration and faster leaf drop. Future precipitation trends in the Northeast aren’t clear, though there are indications that rain could potentially become more intense in episodic bursts, leaving enough time between these episodes for trees to experience drought stress. These warmer temperatures and droughts could also affect the brilliance of red leaves in the future due to nighttime temperatures – which help stimulate red pigments – potentially rising faster than day time temperatures. Local colors may also shift in the future as tree species migrate upwards in elevation and further north to stay in their preferred temperature range.
While the future remains uncertain, autumn is the one season that allows people to go out and connect with nature, possibly influencing people to pay more attention to climate and weather. In that way, fall foliage is a subtle, kind way to increase environmental awareness.
Curious to see how your local weather will affect the fall foliage in your area? The variability of the conditions involved ensures us that no two fall foliage displays will be identical year to year. However, scientists make predictions about the timing of fall colors, and they even created an app that allows you to view their predictions for your region.
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© 2018 Meteorologist Ash Bray