question: Why is the temperature usually less cold when it's snowing?
comment: If it's snowing that means there is cloud cover. Cloud cover acts as a blanket over the land and holds in heat. When there are no clouds the heat from the ground can radiate directly out into space. That's why it tends to be colder with no clouds.
passages: Due to wind, fresh snow does not stay at the surface but is blown into the first few meters of the surface layer. This blowing snow usually sublimates due to the insulation and has a significant meteorological effect . The sublimation of blowing snow leads to a modification of the energy budget and an overall temperature decrease of 0.5 °C combined to an increase of water vapor has been observed. This forms a stable cold and moist layer of air above the snow surface, even if the surrounding air temperature is above freezing point.
   An illustration of how snow quality can be different follows. In an area which experiences fluctuation in temperatures around 0°C - freezing temperature of water, both rain and snowfall are possible. Wet snow or the wet ground can freeze into a slippery sheet of ice. In an area which consistently experiences temperatures below 0°C, snowfall leads to accumulation of snow on the ground. When fresh, this snow is fluffy and powder-like. This type of snow has a lot of air space. Over time, this snow will become more compact, and the lower layers of snow will become more dense than the top layer. Skiers can use this type of information to improve their skiing experience by choosing the appropriate skis, wax, or by choosing to stay home. Search and rescue teams, and backcountry users rely on our understanding of snow to navigate the dangers present in the outdoors.
   Section::::Analysis.
   Daytime exposure to sunlight will rapidly destabilize the upper layers of the snowpack if the sunlight is strong enough to melt the snow, thereby reducing its hardness. During clear nights, the snowpack can re-freeze when ambient air temperatures fall below freezing, through the process of long-wave radiative cooling, or both. Radiative heat loss occurs when the night air is significantly cooler than the snowpack, and the heat stored in the snow is re-radiated into the atmosphere.
  
  Section::::Dynamics.
   Satellite observations record a decrease in snow-covered areas since the 1960s, when satellite observations began. In some regions such as China, a trend of increasing snow cover has been observed (from 1978 to 2006). These changes are attributed to global climate change, which may lead to earlier melting and less aea coverage. However, in some areas there may be an increase in snow depth because of higher temperatures for latitudes north of 40°. For the Northern Hemisphere as a whole the mean monthly snow-cover extent has been decreasing by 1.3% per decade.
   When an area's albedo changes due to snowfall, a snow–temperature feedback results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g., a warm air mass), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback. However, because local weather is dynamic due to the change of seasons, eventually warm air masses and a more direct angle of sunlight (higher insolation) cause melting. When the melted area reveals surfaces with lower albedo, such as grass or soil, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.
   Section::::Ice segregation.
   Cirrus clouds that produced snow were sighted in "Phoenix" imagery. The clouds formed at a level in the atmosphere that was around -65 °C, so the clouds would have to be composed of water-ice, rather than carbon dioxide-ice because the temperature for forming carbon dioxide ice is much lower—less than -120 °C. As a result of the mission, it is now believed that water ice (snow) would have accumulated later in the year at this location.
   Section::::Cultural references.
   The same effect also occurs over bodies of salt water, when it is termed "ocean-effect" or "bay-effect snow". The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation, which deposit at a rate of many inches of snow each hour, often resulting in a large amount of total snowfall.
   There are several energy fluxes involved in the melting of snow. These fluxes can act in opposing directions, that is either delivering heat to or removing heat from the snowpack. Ground heat flux is the energy delivered to the snowpack from the soil below by conduction. Radiation inputs to the snowpack include net shortwave (solar radiation including visible and ultraviolet light) and longwave (infrared) radiation. Net shortwave radiation is the difference in energy received from the sun and that reflected by the snowpack because of the snowpack albedo. Longwave radiation is received by the snowpack from many sources, including ozone, carbon dioxide, and water vapor present in all levels of the atmosphere. Longwave radiation is also emitted by the snowpack in the form near-Black-body radiation, where snow has an emissivity between 0.97 and 1.0. Generally the net longwave radiation term is negative, meaning a net loss of energy from the snowpack. Latent temperature flux is the energy removed from or delivered to the snowpack which accompanies the mass transfers of evaporation, sublimation, or condensation. Sensible heat flux is the heat flux due to convection between the air and snowpack.
   Global climate change models (GCMs) incorporate snow as a factor in their calculations. Some important aspects of snow cover include its albedo (reflectivity of incident radiation, including light) and insulating qualities, which slow the rate of seasonal melting of sea ice. As of 2011, the melt phase of GCM snow models were thought to perform poorly in regions with complex factors that regulate snow melt, such as vegetation cover and terrain. These models typically derive snow water equivalent (SWE) in some manner from satellite observations of snow cover. The "International Classification for Seasonal Snow on the Ground" defines SWE as "the depth of water that would result if the mass of snow melted completely".
   Global climate change models (GCMs) incorporate snow as a factor in their calculations. Some important aspects of snow cover include its albedo (reflectivity of light) and insulating qualities, which slow the rate of seasonal melting of sea ice. As of 2011, the melt phase of GCM snow models were thought to perform poorly in regions with complex factors that regulate snowmelt, such as vegetation cover and terrain. These models compute snow water equivalent (SWE) in some manner, such as:
  
  SWE = [ –ln( 1 – "f" )] / "D"
  
  where:
  
  BULLET::::- "f" = fractional coverage of snow
   BULLET::::- "M" = melt coefficient
  
  BULLET::::- "T" = air temperature
  
  BULLET::::- "T" = snowpack temperature
  
  More recent models use an energy balance approach that take into account the following factors to compute the energy available for melt ("Q") as:
  
  "Q" = "Q" +"Q" + "Q" + "Q" + "Q" – "Q"
  
  where:
  
  BULLET::::- "Q" = net radiation
  
  BULLET::::- "Q" = convective transfer of sensible heat between snowpack and airmass
  
  BULLET::::- "Q" = latent heat lost through evaporation from or condensation onto the snowpack
  
  BULLET::::- "Q" = conduction of heat from the ground into the snowpack
   Satellite observations record a decrease in snow-covered areas since the 1960s, when satellite observations began. In some regions such as China, a trend of increasing snow cover was observed from 1978 to 2006. These changes are attributed to global climate change, which may lead to earlier melting and less coverage area. However, in some areas there may be an increase in snow depth because of higher temperatures for latitudes north of 40°. For the Northern Hemisphere as a whole the mean monthly snow-cover extent has been decreasing by 1.3% per decade.
   In the United States, wintry mix generally refers to a mixture of freezing rain, ice pellets, and snow. In contrast to the usage in the United Kingdom, in the United States it is usually used when air and ground temperatures are below . Additionally, it is generally used when some accumulation of ice and snow is expected to occur. During winter, a wide area can be affected by the multiple precipitation types typical of a wintry mix during a single winter storm, as counter-clockwise winds around a storm system bring warm air northwards ahead of the system, and then bring cold air back southwards behind it. Most often, it is the region ahead of the approaching storm system which sees the wintry mix, as warm air moves northward and above retreating cold air, causing snow to change to ice pellets, freezing rain and finally rain. The reverse transition can occur behind the departing low pressure system, though it is more common for precipitation to change directly from rain to snow, or for it to stop before a transition back.
   Orographic or relief snowfall is caused when masses of air pushed by wind are forced up the side of elevated land formations, such as large mountains. The lifting of air up the side of a mountain or range results in adiabatic cooling, and ultimately condensation and precipitation. Moisture is removed by orographic lift, leaving drier, warmer air on the descending, leeward side. The resulting enhanced productivity of snow fall and the decrease in temperature with elevation means that snow depth and seasonal persistence of snowpack increases with elevation in snow-prone areas.
  
  Section::::Precipitation.:Cloud physics.
   Snow cover has the second-largest areal extent of any component of the cryosphere, with a mean maximum areal extent of approximately 47 million km. Most of the Earth's snow-covered area (SCA) is located in the Northern Hemisphere, and temporal variability is dominated by the seasonal cycle; Northern Hemisphere snow-cover extent ranges from 46.5 million km in January to 3.8 million km in August. North American winter SCA has exhibited an increasing trend over much of this century largely in response to an increase in precipitation. However, the available satellite data show that the hemispheric winter snow cover has exhibited little interannual variability over the 1972–1996 period, with a coefficient of variation (COV=s.d./mean) for January Northern Hemisphere snow cover of < 0.04. According to Groisman "et al." Northern Hemisphere spring snow cover should exhibit a decreasing trend to explain an observed increase in Northern Hemisphere spring air temperatures this century. Preliminary estimates of SCA from historical and reconstructed in situ snow-cover data suggest this is the case for Eurasia, but not for North America, where spring snow cover has remained close to current levels over most of this century. Because of the close relationship observed between hemispheric air temperature and snow-cover extent over the period of satellite data (IPCC 1996), there is considerable interest in monitoring Northern Hemisphere snow-cover extent for detecting and monitoring climate change.
   The production of snow requires low temperatures. The threshold temperature for snowmaking increases as humidity decreases. Wet bulb temperature is used as a metric since it takes air temperature and relative humidity into account. Snowmaking is a relatively expensive process in its energy use, thereby limiting its use.
  
  Section::::History.
   Section::::Snow science.
   In mountainous areas, heavy snowfall accumulates when air is forced to ascend the mountains and squeeze out precipitation along their windward slopes, which in cold conditions, falls in the form of snow. Because of the ruggedness of terrain, forecasting the location of heavy snowfall remains a significant challenge.
  
  Section::::Causes.:Within the tropics.
   Section::::Extraterrestrial snow.
  
  Extraterrestrial "snow" includes water-based precipitation, but also precipitation of other compounds prevalent on other planets and moons in the Solar System. Examples are:
  
  BULLET::::- On Mars, observations of the "Phoenix" Mars lander reveal that water-based snow crystals occur at high latitudes. Additionally, carbon dioxide precipitates from clouds during the Martian winters at the poles and contributes to a seasonal deposit of that compound, which is the principal component of that planet's ice caps.
   This precipitation occurs when the temperature in the lowest part of the atmosphere is slightly above the freezing point of water The depth of low-level warm air (below the freezing level) needed to melt snow falling from above to rain varies from about and depends on the mass of the flakes and the lapse rate of the melting layer. Rain and snow typically mix when the melting layer depth falls between these values.
  
  Section::::"Wintry showers" or "wintry mixes".
   Similarly, when water vapor condenses, heavier water molecules holding O atoms tend to condense and precipitate first. The water vapor gradient heading from the tropics to the poles gradually becomes more and more depleted of O. Snow falling in Canada has much less HO than rain in Florida; similarly, snow falling in the center of ice sheets has a lighter signature than that at its margins, since heavier O precipitates first.
  
  Changes in climate that alter global patterns of evaporation and precipitation therefore change the background ratio.
  
  Section::::Extrapolation of temperature.
   Persistent cold temperatures can either prevent new snow from stabilizing or destabilize the existing snowpack. Cold air temperatures on the snow surface produce a temperature gradient in the snow, because the ground temperature at the base of the snowpack is usually around °C, and the ambient air temperature can be much colder. When a temperature gradient greater than 10 °C change per vertical meter of snow is sustained for more than a day, angular crystals called depth hoar or facets begin forming in the snowpack because of rapid moisture transport along the temperature gradient. These angular crystals, which bond poorly to one another and the surrounding snow, often become a persistent weakness in the snowpack. When a slab lying on top of a persistent weakness is loaded by a force greater than the strength of the slab and persistent weak layer, the persistent weak layer can fail and generate an avalanche.
  