question: What do metrologists mean by the "feels like" temperature and how is is different than the actual temperature?
comment: Let say it's 25°C in a room. Now turn on a fan. The temperature is same but it feels like colder when the fan in turned on.
passages: Apparent temperature
  
  Apparent temperature is the temperature equivalent perceived by humans, caused by the combined effects of air temperature, relative humidity and wind speed. The measure is most commonly applied to the perceived outdoor temperature. However it also applies to indoor temperatures, especially saunas and when houses and workplaces are not sufficiently heated or cooled.
  
  BULLET::::- The heat index and humidex measure the effect of humidity on the perception of temperatures above . In humid conditions, the air feels much hotter because less perspiration evaporates from the skin.
   Section::::Influencing factors.:Relative humidity.:Interplay of temperature and humidity.
  
  Various types of apparent temperature have been developed to combine air temperature and air humidity. 
  
  For higher temperatures, there are quantitative scales, such as the heat index.
  
  For lower temperatures, a related interplay was identified only qualitatively:
  
  High humidity and low temperatures cause the air to feel chilly.
  
  Cold air with high relative humidity "feels" colder than dry air of the same temperature because high humidity in cold weather increases the conduction of heat from the body.
   The heat index and its counterpart the humidex both take into account only two variables, shade temperature and atmospheric moisture (humidity), thus providing only a limited estimate of thermal comfort. Wind passing over wet or sweaty skin causes evaporation and a wind chill effect that the heat index does not measure. The other major factor is sunshine; standing in direct sunlight can add up to to the apparent heat compared to shade. There have been attempts to create a universal apparent temperature, such as the wet-bulb globe temperature, "relative outdoor temperature", "feels like", or the proprietary "RealFeel".
  
  Section::::Meteorological considerations.
   as possible problems with the reading have since been discovered. One of these was noted as early as 1949 by Dr. Arnold Court, who came to the conclusion that the temperature may have been the result of a sandstorm that occurred at the time. Court stated that "such a storm may have caused superheated surface materials to hit upon the temperature in the shelter." Weather historians such as Christopher C. Burt, and William Taylor Reid have also claimed that the 1913 Death Valley reading is "a myth", and is at least too high. If the 1913 record were to be decertified, the highest recorded air temperature on Earth would be , recorded both in Death Valley on June 20, 2013, and in Mitribah, Kuwait on July 21, 2016. 
   BULLET::::- "T" = air temperature, °C
  
  Section::::Alternative approaches.:North American and United Kingdom wind chill index.
   The apparent temperature (AT), invented in the late 1970s, was designed to measure thermal sensation in indoor conditions. It was extended in the early 1980s to include the effect of sun and wind. The AT index used here is based on a mathematical model of an adult, walking outdoors, in the shade (Steadman 1994). The AT is defined as; the temperature, at the reference humidity level, producing the same amount of discomfort as that experienced under the current ambient temperature and humidity.
  
  The formula is:
  
  where:
  
  BULLET::::- "T" = dry bulb temperature (°C)
  
  BULLET::::- "e" = water vapour pressure (hPa)
   The IPCC Fourth Assessment Report found that the instrumental temperature record for the past century included urban heat island effects but that these were primarily local, having a negligible influence on global temperature trends (less than 0.006 °C per decade over land and zero over the oceans).
  
  Uncertainties in the temperature record, e.g., the urban heat island effect, are discussed further in a later section.
  
  Section::::Warmest periods.
  
  Section::::Warmest periods.:Warmest years.
   BULLET::::- In June 2017, more than 40 airline flights in the United States were grounded, with American Airlines reducing sales on certain flights to prevent the vehicles from being over the maximum weight permitted for safe takeoff and Las Vegas tying its record high at .
  
  BULLET::::- In June 2017 again, a heatwave in Iran broke record high temperature. On 28 June 2017, the city of Jask had a dew point of degrees, which is rare. But the highest temperature in Ahvaz soared to degrees and the humidity creates a heat index of .
   Many formulas exist for wind chill because, unlike temperature, wind chill has no universally agreed upon standard definition or measurement. All the formulas attempt to qualitatively predict the effect of wind on the temperature humans "perceive". Weather services in different countries use standards unique to their country or region; for example, the U.S. and Canadian weather services use a model accepted by the National Weather Service. That model has evolved over time.
   BULLET::::- The wind chill factor measures the effect of wind speed on cooling of the human body below 10 °C (50 °F). As airflow increases over the skin, more heat will be removed. Standard models and conditions are used.
   The table below shows examples for three locations in the city of San Francisco, California. Note the corrected barometer readings are identical, and based on equivalent sea-level pressure. (Assume a temperature of 15 °C.)
   BULLET::::- During June 2016, record heat appeared in Arizona, southern Nevada, and southern California. Burbank, California reached , Phoenix, Arizona reached , Yuma, Arizona reached and Tucson, Arizona reached , its warmest temperature in more than 20 years, on 19 June. Riverside, California reached , Palm Springs, California reached , Las Vegas, Nevada reached , Death Valley reached , Needles, California tied its all-time record high of while Blythe, California set a new all-time record high of on 20 June.
   Section::::Temperature.
  
  Section::::Temperature.:Measuring conditions.
  
  The standard measuring conditions for temperature are in the air, above the ground, and shielded from direct sunlight intensity (hence the term, x degrees "in the shade"). The following lists include all officially confirmed claims measured by those methods.
   Section::::Models.:PMV/PPD method.:Local thermal discomfort.:Draft.
  
  While air movement can be pleasant and provide comfort in some circumstances, it is sometimes unwanted and causes discomfort. This unwanted air movement is called "draft" and is most prevalent when the thermal sensation of the whole body is cool. People are most likely to feel a draft on uncovered body parts such as their head, neck, shoulders, ankles, feet, and legs, but the sensation also depends on the air speed, air temperature, activity, and clothing.
  
  Section::::Models.:PMV/PPD method.:Local thermal discomfort.:Vertical air temperature difference.
   In January, average temperatures range from to . In July, average temperatures range from to . The record high temperature was on June 15, 1961, and the record low temperature was on November 17, 2003. Temperatures reach or higher on an average of 9.9 days. Temperatures drop to or lower on an average of 16.1 days.
   ASHRAE 55-2010 defines SET as "the temperature of an imaginary environment at 50% relative humidity,  average air speed, and mean radiant temperature equal to average air temperature, in which total heat loss from the skin of an imaginary occupant with an activity level of 1.0 met and a clothing level of 0.6 clo is the same as that from a person in the actual environment, with actual clothing and activity level."""
   Hello I Feel the Same is the ninth studio album by American alternative band The Innocence Mission. It was released on October 16, 2015, via Korda Records, a cooperative record label founded by The Ocean Blue, a band with whom the Innocence Mission formed a "long and deep friendship that goes back to some of each band's first shows in Pennsylvania and their major label debut records on Sire and A&M". An edition on translucent green vinyl was released from early January 2016. It is their first studio album since 2010's "My Room in the Trees", making five years the longest gap between studio albums in their career.
   Surface temperature
  
  Surface temperature is the temperature at or near a surface. 
  
  Specifically, it may refer to:
  
  BULLET::::- Surface air temperature, the temperature of the air near the surface of the earth
  
  BULLET::::- Sea surface temperature, the temperature of water close to the ocean's surface
  
  BULLET::::- Surface temperature of a star, often the effective temperature
  
  Section::::See also.
  
  BULLET::::- Instrumental temperature record, the historical record of in situ measurements of surface air and sea temperatures
  
  BULLET::::- Pyrometer, a device that remotely determines the temperature of a surface
  
  BULLET::::- Infrared thermometer, a type of pyrometer
   BULLET::::2. "Feels Like": Gypsy and Servo discuss actual temperature versus the wind chill factor. Servo then begins translating everything Gypsy says into "feels like..." statements, much to her annoyance.
  
  BULLET::::3. "Thanksgiving Clown": Servo dresses up as a clown, thinking it to be a Thanksgiving tradition. Crow consults an old World Book encyclopedia to verify.
   Section::::Alternative approaches.:Original model.
  
  Equivalent temperature was not universally used in North America until the 21st century. Until the 1970s, the coldest parts of Canada reported the original Wind Chill Index, a three or four digit number with units of kilocalories/hour per square metre. Each individual calibrated the scale of numbers personally, through experience. The chart also provided general guidance to comfort and hazard through threshold values of the index, such as 1400, which was the threshold for frostbite.
  
  The original formula for the index was:
  
  where:
  
  BULLET::::- "WCI" = wind chill index, kcal/m/h
  
  BULLET::::- "v" = wind velocity, m/s
   The UHI can be defined as either the air temperature difference (the canopy UHI) or the surface temperature difference (surface UHI) between the urban and the rural area. These two show slightly different diurnal and seasonal variability and have different causes 
  
  Section::::Diurnal behavior.
   The Australian formula includes the important factor of humidity and is somewhat more involved than the simpler North American model. The North American formula was designed to be applied at low temperatures (as low as ) when humidity levels are also low. The hot weather version of the AT (1984) is used by the National Weather Service in the United States. In the United States, this simple version of the AT is known as the heat index.
  
  Section::::External links.
  
  BULLET::::- National Center for Atmospheric Research Table of wind chill temperatures in Celsius and Fahrenheit
  
  BULLET::::- Wind chill calculator
   United States temperature extremes
  
  For the United States, the extremes are in Death Valley, California in 1913 and recorded in Prospect Creek, Alaska in 1971.
  
  The largest recorded temperature change in one place over a 24-hour period occurred on January 15, 1972 in Loma, Montana, when the temperature rose from . 
  
  The most dramatic temperature changes occur in North American climates susceptible to Chinook winds. For example, the largest 2-minute temperature change of occurred in Spearfish, South Dakota, a rise from .
  
  Section::::Lack of extremes.
   During winter months (Dec-Feb), high temperatures can vary between and , while night time temperatures can reach below . In the summer (Jun-Aug), temperatures peak around . The very high summer humidity (average 70%) and low cloud cover can mean that the heat index temperature is or more higher than the air temperature.
  
  BULLET::::- Climatic classification: zone D, 1416 GR/G
  
  BULLET::::- Atmospheric diffusivity: low, Ibimet CNR 2002
  
  Section::::History.
  
  Section::::History.:Ancient and medieval ages.
   In hot areas, some US military installations display a flag to indicate the heat category based on the WBGT. The military publishes guidelines for water intake and physical activity level for acclimated and unacclimated individuals in different uniforms based on the heat category.
  
  Section::::Related temperature comfort measures.
  
  The heat index used by the U.S. National Weather Service and the humidex used by the Meteorological Service of Canada, along with the wind chill used in both countries, are also measures of perceived heat or cold, but they do not account for the effects of radiation.
  