For precipitation to form, we need four key ‘ingredients.’ First, we need a lifting mechanism. This will create saturation. There are three commonly known ways to create this uplift.
The most common one is a front, also known as a cyclone. . These are large scale weather patterns that can last from hours to even days. An everyday example of this type of weather pattern is when a warm front moves into a surface cold front. The warm air will try and stay on top creating a ‘lift’ for saturation to form. The next common way is through convection. This happens in deep cumulonimbus clouds and usually only lasts for an hour or two. These will form mostly in the summer, and are known as thunderstorms (like the ones we see in the summertime in Albany, New York.) Lastly, orographic lifting is another way to get lift and saturation. This happens when there is a mountain range, on the windward side of the mountain. The air will rise on the windward side, and, while it rises, it results in adiabatic cooling and condensation. Which is a “condition is which heat does not enter or leave the system.”
Now after we have the lifting part, we need the next few steps: water vapor to condense and grow. We’ll want the air to reach 100% relative humidity, and from here, it depends if it is a clean water particle, or not. If it is a clean water particle, then it will have to find some cloud condensation nuclei to form onto, and then it can grow. Cloud condensation nuclei (or CCN for short) are particles such as sea salt, dirt, aerosols, or minerals and they serve as a base for water droplets to form onto. A clean water droplet will have a hard time forming to another water droplet, unless it has a CCN, which will allow for it to initiate condensation. (If you have a “dirty” water particle, that just means it’s already mixed with a CCN and doesn’t need to find one to form!) Usually, if it is “dirty” air, it will have lots of small cloud droplets (water droplets) within. But if it is “clean” air, then it will have a few large cloud droplets within it. For the droplet to fall, it needs to grow, as they fall dependent on their size and weight. A droplet will collide and coalescence (the joining or merging of two elements) with other droplets as it is falling through the sky growing in size during its fall. The larger the droplet gets, the faster the fall, and the more it will collide with other droplets. This will create a supersaturated cloud and once it has a lifting mechanism, rain will fall.
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© 2019 Weather Forecaster Allison Finch
As September comes to an end and we enter October, many people are excited about the transition into fall and all of the joys that come with this season and its cooler weather. Pumpkin flavored everything has already made its appearance, stores are filled with Halloween-related decorations and costumes, and many people are already longing for the weather to cool down enough for their cozy fall sweaters. One other major fall highlight that many are looking forward to? The spectacular colors brought on by the leaves changing. So why do leaves change colors in the fall and how might variations in the weather alter how they change?
The coloring in leaves is determined by the amount of chlorophyll within the leaf. Chlorophyll is used by the plant to turn the sun’s rays into energy and is what gives leaves their green color. In the fall, leaves produce less chlorophyll as the days get shorter and cooler, causing them to lose that green color and change into the bright orange, red, and yellow leaves that paint fall landscapes. Weather can be used to estimate when the peak “leaf season” will be in various areas since temperatures and rainfall amounts can play a role in when leaves turn and how quickly they will fall from the trees. Drought can cause leaves to turn more quickly and appear less vibrant. On the other hand, too much rain in the summer can also bring about the changing in colors more quickly as excessive rainfall can be a stressor to the trees. Moderately warmer temperatures can cause a delay in the changing colors, however, excessively warm temperatures could cause the leaves to change colors rapidly and fall sooner, causing the beautiful fall colors to disappear more quickly. An overall increase in temperatures could also cause more variability in when the leaves change, making it harder to predict when they will reach their peak colors.
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©2019 Meteorologist Stephanie Edwards
What Kinds of Weather Do Different Cloud Types Indicate?
Looking at the Difference Between Astronomical Seasons and Meteorological Seasons! (Credit: NOAA NCEI)
Discussion: The calendar has just passed the start of astronomical fall, also known as the fall equinox. For meteorologists and climatologists, they identify each season differently. Due to the position of the Earth in relationship to that of the sun, the date for astronomical seasons can vary by a few days; compared to meteorological seasons. Instead, meteorological seasons are based upon the annual temperature cycles of a season.
Meteorologists and Climatologists prefer to distinguish the seasons by the annual temperature cycles of each season. Each season is divided into its respective group by month. Meteorological winter starts with December and ends in February, spring starts in March and ends in May, summer starts in June and ends in August, and Fall starts in September and ends in November. This method allows for more consistent records with each season being approximately 90 days long.
Astronomical seasons have two solstices and two equinoxes which are marked by the point at which the earth’s tilt and the sun’s alignment are over the equator. The equinoxes occur when the sun passes directly overhead of the equator. The summer solstice falls on or around June 21st while the Winter Solstice falls on or around December 22nd. The Spring equinox falls on or around March 21st and the fall equinox occurs on or around September 22nd. These dates for the astronomical seasons are similar for both the Northern and Southern Hemispheres, however; the seasons are reversed in the Southern Hemisphere. According to the National Centers for Environmental Information, the length of an astronomical season can vary in length between 89-93 days. Due to this variation, climate information for each season would be hard to compare year-to-year.
Both Meteorologists’ and Climatologists’ methods of determining the seasons are useful and important to many different occupations and fields of interest. The next time an equinox or solstice is coming up, remember that the particular season it is occurring in actually started a little earlier for your fellow meteorologist or climatologist!
Photo Credit: National Weather Service
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© 2019 Meteorologist Shannon Scully
Everyone has at some point been tricked by the optical illusion of water on a road in front of them or the appearance of a lake in the middle of the desert. Known as mirages, these phenomena represent one interesting example of important scientific principles at work. While these features don’t exist, our brain fools us into believing they are. So what’s really happening? Is there a reason our eyes play these tricks on us? Let’s find out.
To understand the physical process behind this illusion, we must start with an understanding of how temperature behaves in the atmosphere. As you move upward from the surface, air temperature decreases with height. Therefore under average atmospheric conditions, the higher above the ground, the colder the air. The rate at which temperature decreases is known as the lapse rate and is a very useful value within meteorology. Lapse rates help us identify how air will move vertically, analyze the potential for thunderstorms, and, in this case, understand how features such as mirages work.
The strength of lapse rates vary greatly throughout different sections of the Earth’s atmosphere. For example, in the stratosphere (the second lowest layer of the atmosphere), the temperature actually increases with height. This situation is called an inversion and is the opposite of what we typically observe in the troposphere (the lowest level of the atmosphere where our weather forms). If the lapse rate is small, meaning that the decrease happens gradually as you move vertically upward, air is not likely to rise and weather conditions are typically much calmer. When the lapse rate is a high value (i.e. the temperature decreases very quickly with height), air rises rapidly and the potential for clouds and precipitation increases. It is important to note that while lapse rates are important, they are only one of several factors that contribute to the potential for active weather.
In the case of a mirage, we have a very high lapse rate really close to the surface. A hot road for example, underneath cooler air directly above it can create an extreme difference in temperature over a very short distance. Since light travels through warm, less dense air more quickly and wants to take the shortest path possible to any particular point, light travelling near the ground will bend upward in a U-shape through the warm air. To a viewer, this makes light from the sun appear as though it traveled in a straight line directly from the surface. We see what appears to be water because water and this large temperature difference bend light in a very similar fashion. Thus our brains misinterpret this bending of light as the presence of water on the ground. While the water itself does not really exist, mirages are interesting optical illusions that truly trick our brains into seeing something that differs from reality!
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©2019 Weather Forecaster Dennis Weaver
Source: USA Today
Since moving out west I’ve started hearing a lot more about some really informal names for weather features from locals, ranging from the dreaded inversion in Salt Lake Valley to the potent chinook winds of the high plains. And for the most part, most of these names make sense; the inversion refers to a shift in vertical temperatures that result in temperatures increasing with height and the chinook is named after the Native American tribe and its legends about the warm winds. And then there’s the haboob. A name with no immediate bearing to dust storms and whose origins don’t appear to be linked to any Native American legends whatsoever.
Haboob is Arabic for the word “blown”, and it refers to a unique type of dust storm that is common in the Mountain West but especially in the Southwest. During the summer monsoon, isolated and scattered thunderstorms dot the desert and arid areas of the West and as these storms release cold air from their bodies, the air accelerates and sinks back down in the form of downdrafts. These winds strike the surface and then spread out in all directions, kicking up dust in the process. If enough of a column is kicked up from these straight-line winds, the end result can be large, potent dust storms that can reach vertical heights of over 1,000 meters and stretch over 150 kilometers in length, blinding large swaths of land for as far as the eye can see.
Phoenix, AZ, is no stranger to these dust storms. On July 2011, the city experienced one of the largest haboob events ever to happen within the metropolitan area. Indeed, the entire city shut down as skies darkened and visibility levels tanked to less than a meter, making driving nearly impossible across the entire region.
Bystanders on the streets also experienced negative effects, given that air quality almost immediately becomes hazardous as particles can freely enter sensitive parts of the human body, including your eyes, ears, nose, and mouth. So what do you if you’re caught in one of these events? If you’re a driver, your first priority is to immediately get off the road before your visibility is gone. If you’re on a freeway or a road outside of a major city/town, safely pull off the roads and turn your lights off, and wait it out. The only exception to keeping you lights off is if you’re unable to get off the road, in which case you should immediately slow down and have them on while you sound your horn to alert others that you’re driving by. As for those who are outdoors, immediately seek shelter indoors. If you can’t immediately go indoors, cover your mouth and slowly make your way to an indoor shelter so as to avoid having contaminants enter your body. Indeed, haboobs are just one of many unique weather features in the Western US that may back east don’t experience very often. And despite the silly name, these events should be taken very seriously, as they are some of the most impressive but terrifying meteorological forces in desert regions.
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© 2019 Meteorologist Gerardo Diaz Jr
You can probably smell it right now. It’s almost a tingling electric scent in the air as a storm starts to make its way through. Even after the rain has fallen, this smell transforms into a pleasant musty scent that somehow brings a nostalgic feeling to mind. What you are smelling is the molecular scent of ozone and plant compounds that are released into the air.
As a storm approaches, downdrafts from the storm drop from high into the atmosphere to the surface and spread out from under the storm. This air carries with it the tingling scent you often smell before rain. Ozone is the main cause of this smell. Since a larger concentration of ozone is present in our upper atmosphere, many downdrafts from storms pull it down to the surface. The air from a downdraft can travel for long distances even bringing the smell of rain to areas that have yet to see storm clouds. This is why many of us can predict that it will rain just by smelling the air a couple hours to a day before it actually rains. Lightning additionally, is a contributor to the release of ozone in the air. When lightning strikes, the energy splits oxygen and nitrogen molecules, the oxygen molecules then recombine into ozone. Many people describe the sharp smell of ozone to resemble the smell of chlorine.
After it rains, the smell of ozone mixes with something else, something strongly musky. what you are smelling here is called petrichor. The term petrichor, meaning “relating to rocks”, is defined as the smell that accompanies rain after a long spell of dry weather. Petrichor’s smell originates from small compounds or spores that plants release during dry weather. These compounds are released into the air and then settle on hard surfaces, in between crevices, rocks, and pavement. When it rains, the force of raindrops hitting the surface sends the spores back into the air. You may also recognize this smell if you have ever taken a walk in a moist forest or turned over soil in your garden.
The smell of rain has entered our noses for years alerting us of oncoming showers or relaxing us with nostalgic memories of cozy rainy days indoors. It’s interesting to know that plants and ozone are the makers behind it all. Next time it rains, and you notice the satisfyingly pungent smell, just think how awesome it is that you now know its origins. It’s certainly a fun scientific fact you can share with you friends and family too.
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© 2019 Meteorologist Alex Maynard
Stromberg, Joseph. “What Makes Rain Smell So Good?” Smithsonian.com, Smithsonian Institution, 2 Apr. 2013, https://www.smithsonianmag.com/science-nature/what-makes-rain-smell-so-good-13806085/.
“What Causes The Smell Of Rain?” Farmers' Almanac, 26 Apr. 2019, https://www.farmersalmanac.com/what-causes-smell-of-rain-22059.
Yuhas, Daisy. “Storm Scents: It's True, You Can Smell Oncoming Summer Rain.” Scientific American, 18 July 2012, https://www.scientificamerican.com/article/storm-scents-smell-rain/.
“What Are The Different Types of Rain?” Met Office, https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/rain/types-of-rain.
DISCUSSION: The Model Output Statistics (MOS) is the output from models such as the Global Forecasting Systems (GFS) and the North American Model (NAM). MOS is often used to help with forecasting for elements near the surface such as temperature and wind, which are more applicable to civilians. The MOS in the U.S. is sent out multiple times a day with the Localized Aviation MOS Product (LAMP) going out every hour, the GFS MOS every 6 hours, the NAM MOS and the extended GFS MOS every 12 hours.
The MOS has several advantages compared to other models that are shown graphically. One such advantage is that the MOS is more point-specific to an airport as shown above (KSJC) or at some specific locations including a weather station at Central Park in New York (KNYC) instead of a grid, as is most typical displayed by other models. Another advantage that MOS has compared to other models is that the MOS is able to tell you how low of a cloud ceiling to expect as compared to the model graphics which only shows coverage but not height. Additional advantages are that the MOS is able to give you an indication of the probability of precipitation as well as being able to determine if fog will occur as compared to the model where the graphs are sometimes increasingly difficult to identify both. The output is often used by students and broadcast meteorologists to make forecasts with regards to temperatures, winds, clouds and precipitation.
Let’s look at the elements of the MOScast (MOS Forecast):
DT: Date of the month (in the diagram above: August 19/August 20)
HR: Hour of the specific day in Universal Time Coordinated (UTC) or Greenwich Median Time (GMT) (15)
N/X: Nocturnal minimum temperature and maximum daytime temperature in Fahrenheit (59 77)
TMP: Temperature in Fahrenheit
DPT: Dewpoint in Fahrenheit
CLD: Cloud coverage (no clouds=CL 0 to 2/8 of the sky=FEW 2/8-4/8=SCT 5/8-Almost 8/8=BKN and completely cloudy=OVC)
WDR: Wind Direction at 10 meters above the ground (Multiply by 10 to get direction i.e. 32 is 320°)
WSP: Wind speed in knots (nautical miles per hour) at 10 meters above the ground (1 knot is 1.151 mph)
P06: Probability of Precipitation (percent chance of rain and/or snow) in the 6-hour period ending at that time
P12: Probability of Precipitation in the 12-hour period ending at that time
Q06: The Quantitative Precipitation Forecast (QPF) (amount of precipitation forecasted) in the 6-hour period ending at that time [See Chart below for values]
Q12: The QPF for the 12-hour period ending at that time [See chart below for values]
T06: Probability of thunderstorms the 6-hour period ending at that time
T12: Probability of thunderstorms in the 12-hour period ending at that time
CIG: Cloud ceiling height forecasted (See chart below for values)
VIS: Visibility in miles (See chart below for values)
OBV: Phenomena which would cause obscuration to visibility (See chart below for values).
However, the MOS does have some disadvantages. Among the major disadvantages is that there is a temperature bias most of the time where the MOS is either too warm or too cold and needs to be adjusted. However, the MOS bias can be calculated and adjusted by comparing the temperatures to the METAR (Meteorological Terminal Air Report) temperatures of the specific location which some websites do such as here. In addition, the MOS goes out only 72 hours in the forecast and is not graphic so it is not an effective tool for forecasting for tropical systems as compared to the GFS which goes out for 384 hours and the NAM which goes for 84.
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©2019 Meteorologist JP Kalb
When watching forecasts, the public have become familiar with terms like: high and low pressure systems, cold and warm fronts and the jet stream. Depending on your region, you may hear about Sea Breezes if you live near the ocean, lake breezes, if you live near a lake or even see a map depicting velocity during a severe weather event. One of the most important forecasting tools for explaining a long-term forecast often goes overlooked — this is called Geopotential Height, which can is often styled as a height anomaly. The anomaly describes a departure from average or usual occurrence at this level.
The layer of the atmosphere called the troposphere is where most of the weather occurs on the planet. This layer ends at the tropopause, which is on average 36,000 feet high. The reason this would be an average is because the atmosphere fluctuates based on warm and cold regions and is not actually a steady layer throughout. This case goes back to the general rule of science that heat rises and cold sinks — the best application of this rule is in the atmosphere!
Atmospheric pressure is commonly measured in millibars (mb) in forecast models. Standard pressure at the surface (ground level) is defined as 1013.25mb, but we see this change all the time. For example, a high-pressure system event could bring this value up to 1030mb or a low-pressure system can bring this value below 1000mb. While these values do not account for extremes, they provide example for changes at the surface. The jet stream is another subject that is discussed as a forecasting tool in broadcasting that shows a source region for warm or cold air and how it is expected to flow. This area is found around 250mb, which on average is about 35,000 feet high. Recall that pressure levels in atmospheric sciences refer to different heights in the atmosphere that are used to dictate the activity at the surface.
Right between the surface level and the jet stream is the 500mb height (between 16,000 and 20,000 feet in the atmosphere). This area is perfect to provide a look at the source regions of an air mass and can assist in long-term temperature forecasts (7-14 day timeframe). Height anomalies appear in red or blue color shades that determine the intensity. For instance, the darker the red color appears then the higher the height will be. The darker the blue, the lower the height will be. As one could imagine, the red correlates to warmth and the blue correlates to cooling.
Photo: An example of a 500mb height anomaly map from the GFS Forecasting Model depicting areas of colder than average temperatures (in blue) and areas of warmer than average temperatures (in red). (Courtesy of Pivotal Weather)
These maps are best related to temperature probability maps that are provided by the National Weather Service (NWS) depicting an outlook of 6-10 days or an outlook of 8-14 days. While the timeframe can change for specific events like a rain shower, this displays an expectation of which part of the country will see warm or cold temperatures.
Photo: An example showing the 6-10 day temperature outlook for the United States, which depicts the surface conditions with a similar color coding to 500mb height anomaly maps. (Courtesy of the National Weather Service)
Considering that these maps help us track air masses through the atmosphere, we can look at a source region of the air as it approaches your area. This will help distinguish potentially drastic changes. This photo depicts the common air masses found in the United States:
Photo: Air Masses in their common source region with abbreviations over North America. (Photo courtesy of Pennsylvania State University)
For a worldwide view, we can see these source regions globally in this photo:
Photo: Air Masses from their source region across the world. (Image courtesy of Bahrain Weather)
The positioning of multiple air masses can lead to prolonged periods of heat or warmth for a region because of a block. Strong areas of high pressure will keep another air mass ‘blocked’ in to a region where it can’t get out and lead to periods similar-occurring weather patterns for multiple days. These drastic periods can be seen distinctly on a map of 500mb height anomalies that gives a view of where the air mass would be coming from and can aid in determining what is happening at the surface.
Multiple forecasting tools exist and the 500mb height anomaly offers further confirmation of long term possibilities for temperature trends on your area. The usual forecasting topics heard above the surface involve the jet stream, but there are multiple levels between them that can help put the pieces together for a more confident forecast.
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©2019 Meteorologist Jason Maska
DISCUSSION: Year in and year out, millions of people across the Caribbean and the Gulf Coast as well as East Coast of the United States contend with the annual threat of impacts from tropical cyclones. Often times, when tropical cyclones do form across the tropical Atlantic and/or the tropical eastern/central Pacific Ocean basins, the National Hurricane Center located in Miami, Florida produces forecasts for any and all tropical cyclones in these regions. One of the premier forecast products which people often take the most time in looking at is the 3 to 5 day forecast cone of uncertainty.
The forecast cone of uncertainty is a representation of the collective reasoning and estimate of the range of possible directions in which a storm is expected to go over some given period and the time it is expected to take for a given storm to move that given projected distance. However, a major weakness of the forecast cone of uncertainty is not so much in how it is produced, but more so how the general public tends to interpret it. It is important to always understand that the forecast cone of uncertainty represents the approximate projected center-point track path of a given cyclone. The issue lies in the fact that many people will often interpret the highlighted portion of the forecast cone of uncertainty as being the only areas which may experience some sort of impact from a given storm which is a false sense of reality. Thus, it is always critical to keep in mind that on top of the fact that impacts can be and often are felt outside of the forecast cone of uncertainty and especially will happen as changes in the projected forecast track occur over time.
On top of that, it is just as important to consider the fact that when it comes to interpreting the forecast cone of uncertainty out to 3+ days, there can quite often be track distance errors of up to 100-200 miles or so. Thus, whenever you are looking at projected track forecasts for storms such as the current evolving situation with Major Hurricane Dorian, it is imperative to keep these issues in mind as time moves along. So, the next time you are looking at a projected track forecast for Dorian or any other future storms anywhere around the world, you can look at projected track forecasts from a completely new and improved perspective.
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©2019 Meteorologist Jordan Rabinowitz