8.3.5.2 Manual input remarks. Manual input remarks are prefaced with the phrase “OBSERVER WEATHER.” As a general rule the manual remarks are limited to:
a) Type and intensity of precipitation.
b) Thunderstorms, intensity (if applicable), and direction.
c) Obstructions to vision when the visibility is less than 7 miles.
EXAMPLE.
“Remarks...density altitude, two thousand five hun-dred...visibility variable between one and two...wind direction variable between two four zero and three one zero...observed weather...thunderstorm moderate rain showers and mist...thunderstorm overhead.”
8.3.5.3 If an automated parameter is “missing” and no manual input for that parameter is available, the parameter is announced as “MISSING.” For example, a report with the dew point “missing,” and no manual input available, would be announced as follows:
EXAMPLE.
“Ceiling one thousand overcast, visibility three, precipita-tion, temperature three zero, dew point missing, wind calm, altimeter three zero zero one.”
8.3.5.4 “REMARKS” are announced in the follow-ing order of priority:
a) Automated “REMARKS”:
1) Variable visibility.
2) Density altitude.
b) Manual Input “REMARKS.” As a general rule, the remarks are announced in the same order as the parameters appear in the basic text of the observation.
EXAMPLE.
“Remarks, density altitude, two thousand five hundred, visibility variable between one and two, wind direction variable between two four zero and three one zero, observer ceiling estimated two thousand broken, observer temperature two, dew point minus five.”
8.4 Automated Surface Observing System (ASOS)/Automated Weather Sensor System (AWSS)
8.4.1 The ASOS/AWSS is the primary surface weather observing system of the U.S. The program to install and operate these systems throughout the U.S. is a joint effort of the NWS, the FAA and the Department of Defense. AWSS is a follow.on program that provides identical data as ASOS. ASOS/AWSS is designed to support aviation operations and weather forecast activities. The ASOS/AWSS will provide continuous minute-by-minute observations and perform the basic observing functions necessary to generate an aviation routine weather report (METAR) and other aviation weather information. The information may be transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID. ASOS/AWSS transmis-sions on a discrete VHF radio frequency are engineered to be receivable to a maximum of 25 NM from the ASOS/AWSS site and a maximum altitude of 10,000 feet AGL. At many locations, ASOS/ AWSS signals may be received on the surface of the airport, but local conditions may limit the maximum reception distance and/or altitude. While the automated system and the human may differ in their methods of data collection and interpretation, both produce an observation quite similar in form and content. For the “objective” elements such as pressure, ambient temperature, dew point tempera-ture, wind, and precipitation accumulation, both the automated system and the observer use a fixed location and time-averaging technique. The quantitative differences between the observer and the automated observation of these elements are negligible. For the “subjective” elements, however, observers use a fixed time, spatial averaging technique to describe the visual elements (sky condition, visibility and present weather), while the automated systems use a fixed location, time averaging technique. Although this is a fundament-al change, the manual and automated techniques yield remarkably similar results within the limits of their respective capabilities. (See FIG GEN 3.5.26 and FIG GEN 3.5.27, Key to Decode an ASOS/ AWSS (METAR) Observation.
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