Embedded Files
The Automated Surface Observing System (ASOS) is one of the major programs of the United States' surface weather observation network. A collaborative effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the Department of Defense (DOD), these automated stations consist of a suite of sensors and instruments that work 24/7 to provide continuous, real-time weather data. Primarily located at airports, ASOS units measure and report critical information such as wind speed and direction, temperature, precipitation type, and visibility, which are essential for safe and efficient aviation, as well as for public weather forecasting and climate research.
Without ASOS observations, flight operations could be delayed, air traffic might be unable to land or take off, and subsequent effects could prevent passengers and cargo from reaching their destinations on schedule, leading to economic repercussions. Surface weather observation is indispensable for day-to-day operations at these locations. By providing critical aviation weather parameters directly at airport runway touchdown zones, ASOS ensures that the information is available where it matters most.
There are around 950 Automated Surface Observing System (ASOS) sites across the United States. Each site is specifically configured to meet the needs of its location, providing crucial, real-time weather information.
What ASOS Reports
Sky condition: cloud height and amount (clear, scattered, broken, overcast) up to 12,000 feet.
Prevailing Visibility and obstructions to vision from zero to 10 miles.
Present weather information: type and intensity for rain, snow, and freezing rain.
Pressure: sea-level pressure, altimeter setting.
Ambient air temperature, dew point temperature.
Wind: direction, speed and character (gusts, squalls).
Precipitation accumulation, both liquid and frozen water equivalent.
Select significant remarks appended to the end of the observation that include variable cloud height, variable visibility, precipitation beginning/ending times, rapid pressure changes, pressure change tendency, wind shift, and peak wind.
Detects significant meteorological changes and issues hourly and special observations whenever weather criteria thresholds are met.
Automatically provides computer-generated voice observations to aircraft in the vicinity via FAA ground-to-air radio frequencies. These messages are also accessible through a telephone dial-in line.
Observes, formats, archives, and transmits observations automatically, issuing special reports when conditions exceed the weather element criteria outlined in FAA JO 7900.5E.
How is Temperature Reported at Airports (like LAX)?
How is Temperature Reported at Airports (like LAX)?
Most airports have a high-quality weather station equipped with multiple weather sensors. This array of sensors is also called Automated Surface Observing System or ASOS. The primary purpose and design for these stations is to serve the airport operations and aviation community. One of the weather sensors in this system measures temperature, which has applications beyond aviation.
An ASOS weather station will take a temperature reading every minute and calculate a running 5-minute average as the current temperature. It will then store the running highest and lowest value for each hour, 6 hours, and calendar day in its internal memory.
While all this is going on internally, the station will also transmit information to the world. Once every hour, the station will send out a complete observation, including the current temperature reported with a precision to the nearest tenth of a degree Celsius. For LAX, this happens every 53 minutes past the hour. Once every 5 minutes, it will also send out a shortened report, which is primarily for the aviation community. While this 5-minute report includes temperature, it only has a precision to the nearest whole degree Celsius and may not match what is being tracked internally.
For those interested in high and low temperatures for a calendar day, the data tracked and stored internally by the station is the most accurate and precise. The station reports the most accurate and precise high and low temperatures for the previous day at around 1am. These are the values used in official climate reports - such as the Daily Climate Report. The daily report also includes the time that the high and low temperatures occurred, which are always in local standard time (which means it is an hour earlier than daylight saving time). This is a standard used across the country for climate reports.
When tracking temperatures on a site like this, it is important to note that the temperatures you see for every 5-minute observation might be a 1 degree or 2 off from what the actual temperature is, and from the temperature being tracked internally for the daily high and low values. This is because the temperature is rounded to the nearest whole degree Celsius before being then converted to degrees Fahrenheit. The high and low temperature could also occur in between the 5-minute observations, which is tracked internally but not reported to the public. Real-time one minute data is not publicly available.
For more information, please visit the official ASOS information page.
Page updated
Google Sites
Report abuse