Weather and Climate for Snow Sports, Flying, and Sailing
Snow sports weather themes. The wind chill is not the actual temperature, but rather the apparent temperature, or how cold it feels to a human due to the combined affects of temperature and wind. If you are on the ski hill, at some point flat light will likely become an issue. Flat light is when sunlight is strongly diffused which can make it difficult to see the texture of the snow surface. The half barbs (the shorter ones) are 10 km/h (or 5 kts) each, while the full barbs (the longer ones) are 20 km/h (or 10 kts) each. When triangles or flags appear, beware, they represent 100 km/h each. Valley clouds form when you have moisture condensing in the air within the valley, but above the valley floor. Valley fog , by contrast, forms at the bottom of the valley. This is usually radiation fog. As the air ascends, it cools down adiabatically, meaning for each kilometre it rises, it cools by nearly 10 ° C for dry adiabatic conditions, for wet it cools 6C. If you want to find the temperature use interpolation. The final result is that the air is warmer and drier after crossing the mountain barrier. This process is known as airmass transformation. The lack
of rain and cloud in the lee of a mountain is known as lee shadowing or a rain shadow. Katabatic winds or drainage flow/winds lead to to cold air pooling within mountain valleys. A diurnal slope flow is induced by thermal (temperature) changes over the course of a day, as a result of the sun heating the earth’s surface, and then the earth’s surface cooling after the sun sets. radiative heating is from the ground heating up over the day. flow , or anabatic wind. Low pressure systems, also referred to as cyclones, are associated with bad weather. This is the opposite to a high pressure system. In short, when you’re on an outing in the mountains, high pressure (anti-cylonic) makes things not only more enjoyable, but also safer, in most cases. The most extreme examples of wind-exposed locations are isolated volcanic peaks, because they can rise so far above surrounding terrain. A second reason that winds can be stronger on ridges and mountain tops is something known as the Venturi or Bernoulli effect. This is when it converges to a peak. The rain-snow line is defined as the elevation at which precipitation type transitions from rain to snow. To calculate this you can find the freezing point and subtract 200-300m. Snow density can be defined as the amount or mass of ice and liquid water per volume. Snow density increases with increasing temperature and increasing winds. Right-side-up snow has higher-density snow on top of lower density. This occurs when temperature and/or wind speed decreases during the course of a storm or storm cycle with warm fronts. Upside-down snow can also occur if it gets windy towards the end of a storm with cold fronts. Faceted crystals, or facets, are produced when a strong vertical temperature gradient exists. The water vapour is moving quickly, and crystal growth happens quickly. The rule of thumb is that faceting takes place when the temperature gradient is larger than 1°C per 10 cm depth, or equivalently 10°C per metre. A lot of space between crystals. This process is called Depth hoar. Rounded crystals, or rounds, are produced when temperature gradients are weak, water vapour moves slowly, and crystal growth happens slowly. The hardness levels from softest to hardest are: fist, four fingers, one finger, pencil, and knife. Dangers to skiers are (1) bitterly cold air, and (2) outflow winds (valley outwards) . An Arctic airmass originates from the Arctic. It forms in the Arctic in cold, clear conditions found under a high pressure system. Gap winds usually occur when the large-scale prevailing wind direction is perpendicular to the large mountain range. Pressure at sea level is typically around 100.0 kPa. This decreases with elevation for about 10.0 kPa per KM General characteristics of a coastal or maritime snow climate and snowpack are: Frequent snowfall, with relatively large amounts in each storm, High density newly fallen snow, Relatively warm temperatures, Coastal location, Deep snowpack, Most avalanches occur during or soon after storms, within storm snow layers Infrequent persistent weak layers in the snowpack, Lower avalanche danger. General characteristics of these transitional or intermountain snow climates are: Moderate amounts of snow Moderate density snow, Frequent snowfall, Snowpack of moderate depth, Some storm snow avalanches, Infrequent persistent weak layers, Lower avalanche danger. General characteristics of a continental snow climate and snowpack are: Low snowfall, Low density snow, Cold temperatures, Inland location far from the coast Shallow snowpack, Persistent weak layers, Higher avalanche danger. Loose-snow avalanches, also called sluffs, are made up of surface and/or near-surface snow that is not well-bonded. They begin at a single point, gathering more loosely-bonded snow crystals from the surface of the snowpack as they descend, gradually fanning out. After the fact, you can recognize them by their inverted “V” pattern, starting from a point and spreading out downhill. This type of avalanche does not usually do any major structural damage, but they can certainly bury a person or carry them over a cliff. It’s surprising how quickly a sluff can build up enough to knock you off your feet. In addition to carrying you off of a cliff, sluffs can pose a danger by burying you in a terrain trap. A slab avalanche occurs when a layer in the snowpack slides down the slope as a cohesive, bonded layer. The strong layer can be a result of snowfall from one storm or multiple storms. Slabs that form due to high wind speeds in new snow are referred to as wind slabs. Very destructive and deadly Northerly (and to a lesser extent easterly) aspects are the best aspects to find preserved powder during sunny periods. Your very best bet for finding preserved powder is on high-elevation slopes that are in the shade all or most of the day, so steep east- or north-facing slopes. The downside to those consistently colder snow surface temperatures is that those same spots are where faceting and surface hoar are most likely to be found (and the resulting persistent weak layers). Deposition occurs when a substance undergoes a phase change directly from the gas to the solid phase, without the liquid stage in between. For instance, the deposition of water is when it changes from water vapour (gas) into ice (solid) without passing through the liquid water phase. It literally deposits itself onto the snow surface. Dewpoint temperature is the air temperature at which water vapour starts to condense into liquid droplets, while being cooled. Frostpoint temperature is the dewpoint temperature if the air is below 0°C. Instead of dew, frost forms. Surface hoar or hoarfrost or just frost is essentially the frozen version of dew. Types of snowflakes. Dendrites are star looking flakes. Columns and needles and Capped columns look like needles. Diamond dust are weird shaped, smallest and found in extreme cold weather. When a snow crystal falls through the atmosphere, it can grow by colliding with tiny water droplets that freeze and stick to it. This process is called accretion. The new snow crystals that form are called graupel. A snow crystal can also grow by aggregation. This is when ice crystals stick to other ice crystals, forming irregular shapes referred to as “aggregates”. The snow surface becomes hardpacked when it hasn’t snowed for a few days. Flying weather themes.The fraction of the sky covered by cloud is called sky cover, cloud cover, or cloud amount. It is measured in eights (oktas) according to the World Meteorological Organization (WMO). 0/8=Clear skies, 1-2-Few clouds, 3-4=scattered, 5-7=broken, 8 overcast, unknown=obscured. Ceiling is the height above ground level (AGL) of the lowest cloud base (bottom of the cloud) that is below 20,000 ft (6,000 m) that is covering more than half the sky. Transmissometers shine an incident light beam across a known path length to measure how much dimmer the received light is compared to when the air is clean. Other instruments measure how much light is scattered (bounced off in all directions) from tiny particles (of dust, fog, smoke, etc.) in the air. For busy airports, sometimes these automated visibility sensors are installed close to a runway to measure runway visual range (RVR). Drizzle=, | Rain=dot | Snowflake=star| Showers=upside down triangle | thunderstorms=R arrow| Fog=3 lines. Sandstorm/ Dust storm=S with arrow| Drifting snow/blowing snow=up arrow side arrow| Hail=filled in triangle| Graupel= blank triangle |Ice pellets=triangle with dot| Ice crystals=line with x | Freexing= sideways S. VFR requires more than 3000 AGL ceiling and 5 statue miles. IFR requires 1000 AGL celing or 3 statue miles. Marginal VFR is inbetween. IMC means instrument meteorlogical. Cold fronts Convective clouds or cumuliform clouds (Cu) look like stacks of cotton balls, and are associated with updrafts. Warm fronts Layer clouds or stratiform clouds (St) look like sheets or blankets that can extend hundreds of kilometers horizontally. Clouds in unstable air aloft: castellanus — Look like small castle turrets. Are a clue that the atmosphere is becoming unstable; thunderstorms possible later in the day. Billow (K-H wave) clouds — Indicate wind shear (change of wind speed or direction) and clear-air turbulence (CAT) at aircraft altitudes. Clouds associated with strong winds across mountain: lenticular (mountain-wave) clouds — Indicate vertical wind oscillations and possible mountain-wave turbulence. Sailplanes like the updraft portion of the waves, because they can “surf” the wave and fly very long horizontal distances. Commercial aircraft hate the waves because they often mean a very bumpy ride at all altitudes for the whole time while flying over the mountains. Rotor clouds — Indicate severe or extreme turbulence at low altitudes due to mountain waves. The rotors can break off aircraft wings and cause pilots to lose control of their aircraft during take-off and landing. Banner clouds — Form on downwind side of mountain peak. Indicate strong turbulence touching the downwind side of a tall, isolated mountain peak. Clouds formed by extra heat, updrafts, or turbulence pyrocumulus — Form over forest fires and volcanoes. pileus — Form over fast-growing cumulus clouds. Don’t affect flying, sailing or snow sports. fractus / scud — Form in turbulent humid air near the ground. These scud clouds indicate high humidity Clouds formed by humans fumulus — Water-droplet clouds over cooling towers. Harmless for flying, sailing, or snow sports. contrails — Aircraft condensation trail. Indicate the turbulent wing-tip vortices behind aircraft. Small aircraft can be flipped upside down if they accidently fly into a wing-tip vortex. Military pilots hate contrails, because they reveal the aircraft to the enemy. Fog is a cloud that touches the ground. Most fog is made of tiny liquid water droplets that are falling so slowly through the air that they seem suspended. If the fog is made of supercooled tiny liquid water droplets (unfrozen liquid water at temperatures below freezing), then it is called freezing fog, because the supercooled droplets can freeze instantly when they touch something like an airplane or runway. Ice fog is made of tiny ice crystals (water that is already frozen). Fog is considered to be an “obscuration” that reduces horizontal visibility to 0.5 statute miles or less. Obscurations (and their abbreviations) include: mist [BR; horizontal visibilities ≥ 1 km (i.e. ≥ 5/8 of a statute mile)], fog [FG; visibilities Flights above 13,000 ft. To fly above 13,000 feet and avoid hypoxia, pilots can wear an oxygen mask to breathe from oxygen tanks on the aircraft. Flight above 40,000 ft At about 40,000 ft altitude (12.2 km), even breathing pure oxygen does not put enough oxygen in our lungs for us to survive. Flight above 62,000 ft Above this altitude, a completely different problem happens — your bodily fluids begin to boil. But human body temperature is about 37°C. Thus, moisture in your lungs and saliva in your mouth will begin to boil at your normal body temperature. This altitude is called the Armstrong altitude or the Armstrong limit. Your blood won’t boil yet, because if your heart is pumping then you still have blood pressure that is greater than the ambient environment pressure. Wind shear is the change of wind speed and/or wind direction with altitude. anabatic winds (warm air moving up along mountain slopes that are warmed by the sun during daytime), and katabatic winds (cold air draining down mountain slopes into valleys at nighttime as the mountain slopes cool). Thermals are warm air rising, can create cloud streets. Almost all of our weather occur in the troposphere. Troposphere, Stratosphere, Mesosphere, Thermosphere. Temp increases in stratosphere. Decreases is mesosphere. Increases at thermosphere. Another word for non-turbulent is “laminar”. If S is positive, then it is statically stable, and the air becomes non-turbulent (if no wind shear exists). If S is zero, then it is statically neutral (neither stable nor unstable). If S is negative, then it is statically unstable, and the air becomes turbulent. Clear air turbulence (CAT) can happen at any altitude, but is often the most intense where the winds are strongest, such as near the jet stream. The jet stream is a region of fast winds at roughly 6 – 12 km. Both clear-air buoyant updrafts/downdrafts and wind shear can create turbulence in the bottom 300 m to 4 km of the atmosphere. This layer of the atmosphere is called the atmospheric boundary layer (ABL) or the planetary boundary layer (PBL), and turbulence in this layer is called boundary-layer turbulence. Thunderstorms are convective clouds, which means they are driven by the buoyancy of warm rising air inside the cloud. recommends that pilots get no closer than 20 nautical miles to any severe thunderstorm. Hailstones are irregularly-shaped balls of ice, larger than 0.5 cm in diameter, Hail that is smaller than 0.5 cm is called graupel. Tornadoes are violently rotating columns of air between thunderstorm (cumulonimbus) clouds and the ground. Cloud droplets (condensation funnel cloud), dirt and debris stirred up from the ground (debris cloud), or both, make the tornado funnel visible. Thunderstorm cells: Cumulus consists of only updrafts and no downdrafts. No anvil. Mature consists of both updrafts and downdrafts, anvils and lots of precipitation. Disspating is downdrafts and no updrafts. Raining itself out. Basic storms a. single cell b. multicell c. orographic Mesoscale convective systems d squall line e. bow echo f. mesoscale convective complex g. mesoscale convective vortex (not that dangerous) (MCV) Supercells h. low precipitation (LP) i. classic (CL) j. high precipitation (HP). Clear ice: Larger raindrops take a second or more to freeze when they hit the aircraft, allowing some of the water to flow a short distance along the wing before freezing. Also, droplets in regions of 0 to –5°C air temperature freeze slowly. It is difficult to remove this type of ice. Rime ice: forms when smaller cloud droplets freeze instantly upon hitting the leading edge of the wind and fuselage (body) of the aircraft. Also, droplets in regions of –15 to –20°C air temperature freeze faster. Also, this rime is relatively brittle and does not have much strength, so it can break off easier. Frontogenesis = birth of a new front; frontolysis = death of an old front; squall line = line of thunderstorms not along a front. Warmfront = line with half circle | Cold front = line with triangle | Stationary = line with circle and triangle on opposite side | occluded = line with circle and triangle on same side | Sailing weather themes. Although the latitudinal circulations (i.e. Hadley, Ferrel, and Polar) are the major global circulations. The longitudinal circulation across the equatorial Pacific is known as the Walker cell or Walker circulation. These trade winds push the cooler water from the eastern Pacific all the way across the equator to the west Pacific, warming as it goes. The warm air over the warmer west Pacific waters rises, losing its moisture as precipitation. The dryer air then travels back towards the eastern Pacific, creating a loop. This cool Pacific air then converges with cool continental air and sinks along the eastern Pacific coast. This air flow creates a similar ocean current. As water is pushed from east to west, the deeper cooler water along the eastern Pacific coast rises to the surface to fill the gap. This is called upwelling. Once the cooler water reaches the surface, it is also blown across the Pacific towards Austral-Asia, warming along the way. The water is forced to sink once it reaches Austral-Asia (known as downwelling). El Nino Southern Oscillation (ENSO) ENSO has three states: El Niño, La Niña, and neutral. The neutral phase is the Walker cell functioning normally, while El Niño is the warmer phase of ENSO and La Niña is the cooler phase. An El Niño phase occurs when the trade winds weaken. When the trade winds weaken, the warm water from the western Pacific surges, or oscillates, back towards the east and the upwelling of cooler water along the eastern Pacific coastline slows or stops entirely. The La Niña phase occurs when trade winds are stronger than normal, causing increased upwelling of cool waters along the eastern Pacific and more cold water being pushed further across the Pacific. La Niñas can result in higher occurrences of fog due to increased upwelling along the coast. There are three main factors that affect wave formation: wind velocity, fetch, and duration. Crest = Highest point of the wave Trough = Lowest point of the wave Wavelength = Distance from one crest/trough to the next Wave Height = Height from trough to crest Wave steepness = ratio of wave height to wavelength Amplitude = distance from the centre of wave to the bottom of the trough Wave Period = time for one full wavelength to pass a given point. Confused sea is when a bunch of different waves vary in lengths and directions. Wave train is when they disperse into groups. Capilary waves are waves that are 1.7 cms or smaller. Gravity waves are huge waves. Swell causes waves to be formed by distant storms. Rogue waves when waves collide together to make huge waves. Destructive interference is when they cancel out constructive interference is when they collide to make huge waves. When the wave steepness (wave height to wavelength ration) exceeds a ratio of 1:7, it becomes unstable and breaks. Spilling waves break long and slow spilling over. Plunging breakers moderate to steep bottoms, falling forward and surfers love. Surging breakers occur when long wave period and low amplitude. Less foam than other two breakers. Onshore winds blow into onshore. Offshore winds blow into offshore. Shallower the water the steeper the wave. Swell refraction is when it hits at an angle. Swell decay how quickly the swell loses energy. Beaufort wind force scale is based on visuals to represent the waves. Trade winds are easterlies. Polar cells occur between about 60° latitude and the poles. The air movements here are much weaker compared to those in the Hadley cells. Jet streams are fast flowing, narrow bands of wind in the upper atmosphere that circle their way around the globe. The jet stream that forms near 60° latitude is called the polar jet stream, while the one that forms at the poleward limit of the Hadley cell is called the subtropical jet stream. The jet streams flow along the top of the troposphere. Surface currents form gyres that rotate clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere. Ekman transport water will turn 90 degrees to the right of direction of wind blowing it. A hurricane, also known as a tropical cyclone or typhoon in other parts of the world, only forms within warm tropical air masses located between the Tropic of Cancer (23.5o N) and the Tropic of Capricorn (23.5o S). They are created by the energy or latent heat that is released as moist, warm air rises. Hurricanes start as storms (usually in a band), and as warm air converges and lifts over the low pressure centre, more energy is brought into the storm and it can gradually progress into a hurricane. The first level of progression is a tropical depression, which has winds of 37-63 km/hr. A tropical depression then becomes a tropical storm as winds continue to build to 64-118 km/hr, and once winds build beyond 119km/hr, the tropical storm becomes a hurricane. Hurricanes rotate counter clockwise in northern hemisphere. Hurricanes are fueled by warm moist air and will usually dissipate once they move over colder water or land masses. One of the more devastating results of a hurricane is its storm surge. As hurricanes approach land, they push large amounts of water up against the shore, creating what is known as a storm surge. Intertropical Convergence Zone (ITCZ) occurs near the equator where the north easterly and south easterly trade winds meet. Extratropical cyclones are cyclones that form outside of the tropical or mid-latitude zones, typically between 30o and 60o latitude. They can either form independently along frontal zones, or are transformed from hurricanes that are near the end of their life cycle and approaching higher latitudes. Sting jets are a rare phenomenon that can be produced by specific type of extratropical cyclone in which the warm and cold fronts never meet. A waterspout is a spiralling column of air and moisture that develops over water (not a column of water as is commonly believed) beneath a cumuliform or cumulonimbus cloud. Include fair-weather and tornadic. Temperature differences between land and sea create sea and land breezes. The sea and land breezes are more common in the spring in summer when the temperature differences are greatest. Sea breeze is when cold air is blowing towards land. Land breeze is when cold land air moves towards sea. Local land features can create localized wind patterns. The west coast of British Columbia has numerous fjords and inlets reaching from the coast to the interior. These inlets act like highways carrying winds to and from the coast. These winds are known as inflows and outflows. An outflow is a strong wind that is produced when cold air in the interior develops into a mass of high pressure that rushes towards the warmer, low pressure air on the coast. The cold air is funnelled through the channels at high speeds, but tends to dissipate rapidly once they reach the open ocean. Outflows, sometimes referred to as Squamish winds. When sailing, it is important to look at both local and regional wind conditions. Mesoscale refers to weather variables ranging from 2 km to 2000 km in size. Mesoscale cellular convection occurs in the boundary layer between the Earth’s surface and the troposphere. It is most common over the oceans, where colder air from the continents blows out over the warmer ocean air. This process is known as cold-air advection. Open cells have clear centres with clouds formed around the outside, and closed cells have convective clouds in the centre with clear edges. Open cells are commonly found in the tail end of cyclones, while closed cells are associated with anticyclones. The open cells will tend to spiral counter-clockwise following a cyclonic pattern and the closed cells will spiral clockwise following an anticyclonic pattern. Horizontal roll vortices, also known as cloud streets, are another product of cold-air advection and temperature inversion. They are called cloud streets because of the long rows of cumulous clouds that form due to the movement of convective currents below the inversion. Mirages are created when light passes through air of different densities. inferior mirage occurs when you have a dense layer of cold air sitting on top of your line of site, with a layer of less dense warm air beneath it. The light bends as it passes through the denser cold air, creating an inverted image below your line of site. superior mirage is the opposite: a layer of warm air sits above your line of vision with a cool layer beneath it. Image is going to appear higher than what it actually is. When the temperature inversion is not even, you may see a Fata Morgana, rather than a superior mirage. Because of the uneven inversion, light is refracted in strange ways, creating multiple segmented reflections of the original image, with sections towering high above the water. green flash is a rare optical phenomenon that only lasts a few seconds immediately after sunset or before sunrise. Tides are highest and lowest during full and new moons in springs as the moon is closest to the sun. Neaps are the opposite of springs. You will typically see two full tide cycles per day, meaning two high tides and two low tides. The difference between the highest and lowest tide experienced in an area is called its tidal range. The rising or falling of the tides creates currents, known as flood currents for the incoming tide and ebb currents for the outgoing tide. Fog arises when warm, humid air cools beyond its dew point and condenses, forming droplets of water in the air. Sea fog is a type of advective fog. Radiation fog develops over land, usually at night as the ground cools beneath a stream of warm and humid air. Frontal fog forms when a warm front rises over a cold front. Arctic sea smoke acts inversely to the other types of fog. Rather than warm air cooling and condensing, cold air that is already laden with moisture reaches its saturation point when passing through warm and humid air