This page is the compilation of 10 writings on backyard meteorology including: 1. BACKYARD METEOROLOGY: TEMPERATURE 2. BACKYARD METEOROLOGY: MOISTURE 3. BACKYARD METEOROLOGY: INSTABILITY 4. BACKYARD METEOROLOGY: INSTABILITY RELEASE 5. BACKYARD METEOROLOGY: WIND SHEAR 6. BACKYARD METEOROLOGY: FROPA 7. BACKYARD METEOROLOGY: LATENT HEAT 8. BACKYARD METEOROLOGY: PRECIPITATION TYPE 9. BACKYARD METEOROLOGY: PRECIPITATION RATE 10. BACKYARD METEOROLOGY: VARIOUS SIGHTS 1. BACKYARD METEOROLOGY: TEMPERATURE This series of Haby Hints examines meteorology that can be done in the backyard with and without the aid of basic weather observing instrumentation and online weather data. Weather happens outside thus the goal of this series is to expand upon the sensory information that can be gained by directly observing the weather. Unlike computer models, backyard meteorology offers the most direct view and experience of the atmosphere. The first topic that will be focused on is temperature. Temperature is one of the basic components for weather observation. It will influence the comfort level when outside and how a person dresses for the weather. To develop an intuitive sense for the outside temperature, start with standing outside for a couple of minutes and then guessing what the temperature is outside. Then look at a backyard temperature sensor or local temperature from another source and determine how many degrees you were off. Remember to factor in elements that will make the temperature feel cooler or warmer such as direct sunlight, wind chill, humidity and clothing. Attempting these guesses without knowing the observed temperature in a variety of weather will increase the intuitive feel for the actual temperature outside. When first attempting this activity it can be common to miss the temperature by 5 F, 10 F or more degrees. With practice though, you should be able to guess the actual temperature within 3 F when going outside and not knowing what temperature to expect outside. Keep in mind that actual temperature is measured in the shade and is not changed by apparent temperature changes from wind chill or heat index. With practice and experience, sunlight, wind, humidity and clothing will result in less error in your guess at the outside temperature. There are a variety of interesting experiences in the backyard that can be examined when it comes to temperatures. Several include: 1) Feeling the temperature change from a frontal passage such as the rapid cool down from a cold front 2) Feeling the rapid warm-up that often occurs in the morning hours on a sunny day 3) Feeling the temperature drop to the freezing mark, observing water start to freeze 4) Feeling triple digit heat, 100 F or higher 5) Feeling the temperature change that occurs from thunderstorm outflow 6) Observing unusually cold or warm temperatures 7) Recording high and low temperature for the day on a backyard weather station 2. BACKYARD METEOROLOGY: MOISTURE The two main types of moisture measurements are dewpoint and relative humidity. Dewpoint is the temperature the air needs to be cooled in order for saturation to occur. Relative humidity is the percent of moisture in the air relative to the maximum amount of moisture that could be in the air for a certain temperature. Just like with temperature, an intuitive feel can be gained for the dewpoint and relative humidity of the air. It is more difficult to guess than with temperature since small changes in the amount of moisture can result in significant changes in the dewpoint and relative humidity. It can be easier to guess the relative humidity fairly accurately when the air feels very dry or very moist. The dewpoint is easier to guess fairly accurately when the air is very moist. On any given day, the relative humidity is going to vary significantly during the day. The dewpoint will typically be more stable when the air mass stays the same. When precipitation occurs, the dewpoint and relative humidity will increase. If the precipitation is persistent then eventually the dewpoint and relative humidity will reach their maximum values indicating saturated air and 100% relative humidity. Another clue to a high relative humidity is dew or frost on the ground in the morning. When dew or frost occurs, the temperature will be near the dewpoint and the relative humidity will be near 100%. With an intuitive feel for the temperature, the dewpoint and relative humidity can be guessed fairly accurately when there is dew or frost on the ground. The relative humidity tends to decrease rapidly during the morning hours on a typical day. This is because this time of day generally experiences the greatest warming. As temperature increases the relative humidity decreases. When the air has abundant moisture it is easier to feel this moisture in the air, especially at warm temperatures. This is a major factor in the development of the heat index. Warm humid air will feel warmer than dry humid air even when they have the same measured temperature. 3. BACKYARD METEOROLOGY: INSTABILITY Instability when present is increased by several factors including warming surface temperature, increasing surface dewpoint and cooling aloft. The characteristics of clouds can be used to assess instability and stable layers (called a cap) that prevents the instability from being released. Many clues for instability and capping can be obtained by looking at the sky. Instability release that develops into thunderstorms often starts from air rising from near the surface. Warm surface temperature and humid surface air help increase instability and increase the chance that instability release (thunderstorms) will occur. In backyard meteorology, it is a good idea to know what wind directions bring certain air masses. For example, a surface southeast wind may tend to bring in more humid air into a specific location while a surface northwest wind may tend to bring in cooler and drier air into a specific location. The temperature often warms during the day thus instability tends to be highest in the afternoon when the greatest amount of cumulative warming has occurred. The feeling of very warm and humid air along with breezy winds can be a good indication that the lower atmosphere is helping build instability. The vertical development of clouds can be used to indicate where in the atmosphere instability release is occurring. In thunderstorm situations it is common to have low level cumulus clouds that have some vertical development but are limited in their vertical development. The limit is provided by a capping inversion that slows and then halts the upward convection. These are the fair weather cumulus that are common in the warm season. They do indicate that if given more instability, the fair weather clouds could then develop into thunderstorms. This can be provided for example by a lifting mechanism, increasing surface temperature or the breaking of the capping inversion. It is difficult to assess the temperature profile above the surface of the atmosphere with only looking at the sky. This is important to know since it is where a cap may be in place. Knowing the temperature profile will also help indicate the amount of instability since cold air aloft will help enhance instability. Examining forecast soundings before observing the sky will help with this information. Once thunderstorms form then instability is released. In this situation the air rises throughout the troposphere and is only capped once the storm rises to the upper reaches of the troposphere. The next writing will expand upon the process of instability release. 4. BACKYARD METEOROLOGY: INSTABILITY RELEASE In the backyard meteorology series, this is the second writing that involves instability. Storm and cloud observations are a popular reason to do backyard weather observing. Instability release involves strong convective vertical motions that develop into thunderstorms. Towering cumulus and storms can make for some of the most amazing photography. While instability is difficult to see physical, instability release is easy to see as evidenced by the towering thunderstorm clouds. The storm is made visible by cloud droplets, rain, hail, ice particles, lightning and sunlight. These can combine together to produce amazing colors and threatening skies. When instability release occurs it is known that the cap is broken. Once one storm forms it can lead the way for more storms to develop since the first storm can provide outflow lifting mechanisms that can aid in the development of more storms. Several storms can sometimes be witnessed, some closer and some in the distance. The top of the storm will show an anvil of frozen ice particles that has a wispy appearance at high elevations above and downwind from the storm. These anvils seen in the distance are evidence that a storm has developed. When observing in the backyard, thoughts will occur if the storm will hit your location or not and if you will get the worst of the storm. Once the storm develops, observe the cloud movements and storm motion to get an idea if it will move to your location. The first experience as a storm approaches will often be a gust front of cooling wind. As the storm gets closer the rain curtain will be seen getting closer and closer to being over head. As the rain curtain moves over then heavy rain can quickly begin. If the storm is severe then severe wind, hail or a tornado will be associated with the storm. Two other dangers from storms are flooding rain and lightning. If a storm is slow moving and overhead it can dump a large volume of rain on one location. Any thunderstorm is capable of producing dangerous lightning thus it is recommended to stay inside during the storm. Once the storm is close or overhead then thunder will be crashing close by. Thunder travels about a mile for every 5 seconds from when the lightning is seen. Thus for example, when lightning is seen and thunder is heard 10 seconds later then the strike was about 2 miles away. 5. BACKYARD METEOROLOGY: WIND SHEAR When observing the wind, two observations that can be made in the backyard are a relative wind speed and the influence of the wind on clouds. Wind shear is a component that can make thunderstorms severe or more severe. Wind shear can increase the longevity of a thunderstorm, contribute to damaging wind gusts, larger hail, heavier rain, vivid lightning and can help with the generation of a tornado. Wind is reported by a wind direction (direction wind is coming from), a wind speed and wind gusts when applicable. With experience, an intuitive sense can be gained for how strong the winds are and how strong the wind gusts are. Compare the reported wind speed and gust speeds at a nearby observing station or with a local instrument with the wind that is experienced at home. With practice over many days, a good sense of wind speed and gust speed can be developed. Surface wind is important for thunderstorms because the inflow into a storm increases as surface wind increases. A stronger inflow can lead to stronger storms and a higher tornado potential. The movement of clouds will aid in the observation of how the wind changes with height. Ideally, low level, middle level and high clouds will be present. Note how relatively fast the clouds are moving and the direction they are moving. If the clouds are moving at significantly different directions with height then that is a sign of strong directional wind shear. For example, if low clouds are moving from the south and middle/high clouds are moving from the northwest then that is an indication of strong directional shear. Upper level speed shear can be noted by how the wind interacts with towering cumulus clouds. Strong upper level winds will quickly produce a large anvil when convective clouds penetrate into the upper troposphere. Strong speed shear will help tilt a thunderstorm and this helps increase the longevity and severity of a storm. 6. BACKYARD METEOROLOGY: FROPA FROPA stands for FROntal PAssage. Being in the backyard at the moment a frontal passage occurs is an interesting experience. Some fronts are most shallow at their edge thus at frontal passage ground level will experience the frontal passage first. The two distinct changes that occur at the moment of frontal passage are a shift in the wind and a change in temperature. The smell of the air will often change also since the air behind the frontal passage comes from a different region. A cold front separates a cold air mass from a warm air mass. Cold fronts can bring a dramatic change in temperature during the first few minutes to hours of frontal passage. The edge of the cold front can also bring precipitation due to the lifting that takes place at and near the cold front boundary. This precipitation can be heavy rain when the front is lifting warm-humid air. A dryline passage can also be a remarkable experience. The dryline will separate warm and moist air from warm and dry air. During dryline passage, the dewpoint drops dramatically. The relative humidity will drop also. For example, the dewpoint could drop from the 60s to the teens during passage and the relative humidity could drop from 75% to 10%. The dryline passage is sometimes accompanied by gusty winds and lowering visibility due to blowing dust. Typically skies clear and precipitation chances decrease after dryline passage, although strong storms can from near the dryline boundary due to lifting and access to warm-moist air. A warm front passage can also result in a dramatic change in weather. The temperature can quickly rise after frontal passage and skies will often be sunnier. The dewpoint will often increase and winds will blow from warmer latitudes. Below are a variety of backyard experiences associated with FROPA: 1) Note how the temperature changes with time on a backyard thermometer especially during the first few minutes and first hour 2) Note convection and precipitation intensity at the time of frontal passage 3) Note the change in the smell of the air during frontal passage 4) Note how dramatic the wind direction change is during frontal passage 5) Note changes in visibility 6) Note changes in how the air feels (i.e. wind chill, humidity) 7) Note wind gusts behind the front 7. BACKYARD METEOROLOGY: LATENT HEAT Latent heat is energy that is transferred when a substance goes through a phase change. For water, 6 phase changes can occur. 3 go in one direction while the other three go in the opposite direction. The pairs of phase changes are melting and freezing, evaporation and condensation, and sublimation and deposition. These phase change occur while the water is at a constant temperature but the energy transfer results in a warming or cooling of the surrounding environment. The cooling processes are melting, evaporation and sublimation while the warming processes are freezing, condensation and deposition. Many of these processes can be witnessed in the backyard. Examples of each are below: Freezing: When the temperature drops of 32 F, liquid water will begin freezing. It will often start as ice crystals and lines of ice crystals that fan out and gradually freeze all the water. Melting: The thawing of snow, dripping of melting icicles, melting of frost and snow melting as it hits the ground are examples. Evaporation: Evaporation can be seen indirectly as rain, dew or other water on the ground that dries up. Virga is precipitation that evaporates before reaching the ground. This can be seen as streaks of rain in the sky that do not reach ground level. Condensation: Condensation can be witnessed as clouds develop. The moisture in the air becomes visible as it is turned into cloud droplets. Deposition: Deposition is the conversion from vapor to ice. This can be seen when frost develops at temperatures below freezing. Sublimation: Sublimation is the conversion from ice to vapor. This can be seen when frost or any other ice goes from ice to vapor without going through the melting process first. 8. BACKYARD METEOROLOGY: PRECIPITATION TYPE One of the primary observations that can be made in backyard meteorology is the precipitation type. Watching the precipitation fall and accumulate can be interesting and mesmerizing. This writing will go over the different types of precipitation, fog, as well as moisture developing on the ground and how they all formed. Knowing the history of the precipitation and moisture makes it all the more interesting. 1. Rain (R, RA)- Rain is liquid precipitation that reaches the surface in the form of drops that are greater than 0.5 millimeters in diameter. The intensity of rain is determined by the accumulation over a given time. Categories of rain are light, moderate and heavy. 2. Snow (SN, SNW, S)- Snow is an aggregate of ice crystals that form into flakes. Snow forms at temperatures below freezing. For snow to reach the earth's surface the entire temperature profile in the troposphere needs to be at or below freezing. It can be slightly above freezing in some layers if the layer is not warm or deep enough to melt the snowflakes much. The intensity of snow is determined by the accumulation over a given time. Categories of snow are light, moderate and heavy. 3. Snow Pellets (GS)- A snow pellet is precipitation that grows by supercooled water accreting on ice crystals or snowflakes. Snow pellets can also occur when a snowflake melts about half way then refreezes as it falls. Snow pellets have characteristics of hail, sleet and snow. With sleet (ice pellets), the snowflake almost completely melts before refreezing thus sleet has a hard ice appearance. Soft hail grows in the same way snow pellets can grow and that is ice crystals and supercooled water accreting on the surface. Snow pellets will crush and break apart when pressed. They can bounce off objects like sleet does. Snow pellets have a whiter appearance than sleet. Snow pellets have small air pockets embedded within their structure and have visual remnants of ice crystals unlike sleet. Snow pellets are typically a couple to several millimeters in size. 4. Snow Grains (SG)- Snow grains are small grains of ice. They do not produce much accumulation and are the solid equivalent to drizzle. 5. Ice Crystals (IC)- Also called diamond dust. They are small ice crystals that float with the wind. 6. Sleet / Ice Pellets (PE, PL, IP, SLT)- Sleet (Ice Pellets) are frozen raindrops that strike the earth's surface. In a sleet situation the precipitation aloft when it is first generated will be snow. The snow falls through a layer that is a little above freezing and the snow partially melts. If the snow completely melts it will be more likely to reach the earth's surface as supercooled water instead of sleet. If the snow partially melts there will still be ice within the falling drop for water to freeze on when the drop falls into a subfreezing layer. The lowest layer of the troposphere will be below freezing in a sleet situation and deep enough to freeze drops completely. The lower boundary layer can be above freezing and sleet occur if the sleet does not have time to melt before reaching the surface. 7. Hail (GR, A)- Hail is dense precipitation ice that is that least 5 millimeters in diameter. It forms due to ice crystals and supercooled water that freeze or stick to the embryo hail stone. Soft hail is whiter and less dense since it has air bubbles. Soft hail occurs when hail grows at a temperature below freezing by ice crystals and small supercooled water and cloud droplets merging onto the hail. Hard hail occurs when liquid water drops freeze on the outer edges of the hailstone after the outer edge is above freezing. The freezing of supercooled water releases latent heat and this can result in the outer edge of the hail stone warming above freezing. Then the water refreezes creating solid ice. Hail will commonly have soft ice and hard ice layers when it is sliced open. 8. Graupel (GS)- Graupel forms in the same way as hail except the diameter is less than 5 millimeters. It usually grows by soft hail processes. 9. Drizzle (DZ, L)- Drizzle is liquid precipitation that reaches the surface in the form of drops that are less than 0.5 millimeters in diameter. 10. Freezing Drizzle (FZDZ, ZL)- Freezing Drizzle is liquid precipitation that reaches the surface in the form of drops that are less than 0.5 millimeters in diameter. The drops then freeze on the earth's surface. 11. Freezing Rain (FZRA, ZR)- Freezing Rain is liquid precipitation that reaches the surface in the form of drops that are greater than 0.5 millimeters in diameter. The drops then freeze on the earth's surface. 12. Freezing Fog (FZFG)- Freezing fog is a fog composed of supercooled water drops. These drops freeze just after they wet the earth's surface. 13. Mixed Precipitation (MXD PCPN)- The combination of two or more winter precipitation types occurring at the same time or over a period of time at the same place. 14. Dew- Dew is liquid moisture that condenses on objects at the Earth’s surface when overnight cooling produces saturated air. 15. White frost- Depositional frost is also known as white frost or hoar frost. It occurs when the dewpoint (now called the frost point) is below freezing. When this frost forms the water vapor goes directly to the solid state. Depositional frost covers the vegetation, cars, etc. with ice crystal patterns (treelike branching pattern). If the depositional frost is thick enough, it resembles a light snowfall. 16. Frozen dew- Frost that forms due to the freezing of liquid water is best referred to as frozen dew. Initially, both the dewpoint and temperature are above freezing when dew forms. Longwave radiational cooling gradually lowers the temperature to at or below freezing during the night. Cold air advection can also do the trick (e.g. Cold front moving through in the middle of the night after dew has formed). Once the temperature falls to freezing, the condensed dew droplets freeze. Frozen dew looks different from white frost. Frozen dew does not have the crystal patterns of white frost. White frost tends to looks whiter while frozen dew tends to look slicker and more difficult to see. 17. Fog- Suspended clouds droplets experienced at ground level (a cloud on the ground). 9. BACKYARD METEOROLOGY: PRECIPITATION RATE One observation that is made when doing backyard meteorology is the precipitation rate. The general categories are light, moderate and heavy. A typical reference for the precipitation rate is the amount that falls in an hour. For example, a snowfall rate of 2 inches per hour and a rain rate of 0.25 inch per hour. A heavy precipitation rate can be mesmerizing. Heavy rain is defined as 0.30 inches or more falling within one hour. Heavy rain will tend to lower visibility and the rain will fall in sheets with large drops being observed. Heavy snow is defined using visibility. If the visibility is a quarter mile or less due to snow then it is reported as heavy snow. Heavy snow can accumulate at a rate of 0.5 inches per hour to several inches per hour depending on factors such as melting, snow density and snow intensity. Large numerous flakes with temperatures below freezing will tend to accumulate at several inches per hour. Below are several observations using precipitation rate: 1) The weather can go from no precipitation to huge heavy drops when a storm first moves in 2) Use a backyard rain gauge to measure rain intensity 3) Use a ruler and measure depth of snow at several locations in yard and find average for the amount of snow. Doing this in hourly intervals can be done to determine hourly accumulation rate. 4) Melt snow in a rain gauge to determine snow to liquid equivalent. For example, 10 inches of snow in gauge could melt down to 1 inch liquid equivalent. The density of the snow will determine the value. Dry fluffy snow will tend to take a greater accumulation to melt down to the same liquid equivalent as compared to wet dense snow. 10. BACKYARD METEOROLOGY: VARIOUS SIGHTS In this final installment in background meteorology we look at various phenomena that have not been mentioned yet that can be seen from the backyard. Here are 10 other sights than can be seen: 1) Rainbow- results from sun being low enough on the horizon and shining through rain in order to produce an arcing spectrum of colors 2) Double Rainbow- a fainter second rainbow can sometimes be seen surrounding the primary rainbow 3) Thundersnow- Thunder that occurs at the same time snow is occurring. Often it is heavy snow when this occurs. Convection added to the lifting aids in thunder occurrence. 4) Sun dog- This can occur when the sun shines through thin cirrus clouds. It looks like a weaker sun located on each side of the real sun 5) Cold Air Funnel- A cold air funnel is a high based weak funnel circulation well above the Earth’s surface that occurs in a cool air mass. 6) Various cloud types- http://www.theweatherprediction.com/clouds/ 7) Mesocyclone- This is the cloud formation that can produce a strong tornado 8) Tornado- a violently rotating column of air in contact with the earth's land surface that originates from a thunderstorm. Shelter should be taken in the case of an approaching tornado or tornado warning. 9) Solar noon- can be approximated using a sun dial which gives a relative time of day and position of sun, solar noon is when sun angle is highest 10) Icicles- Form from freezing rain or water runoff that freezes on shady side of the roof |