Additive data groups (see Table 24-6) are only reported at designated stations and are primarily used by the NWS for climatological purposes. Most have no direct impact on the aviation community but a few are discussed below.

At designated stations, the hourly temperature and dewpoint group are further coded to the tenth of a degree Celsius. For example, a recorded temperature of +2.6°C and dewpoint of -1.5°C would be coded T00261015.

The format for the coding is as follows:

T Group indicator.

0 Indicates the following number is positive; a 1 would be used if the temperature was reported as negative at the time of observation.

026 Temperature disseminated to the nearest tenth and read as 02.6.

1 Indicates the following number is negative; a 0 would be used if the number was reported as positive at the time of observation.

015 Dewpoint disseminated to the nearest tenth and read as 01.5.

No spaces are between the entries. For example, a temperature of 2.6°C and dewpoint of -1.5°C is reported in the body of the report as 03/M01 and the hourly temperature and dewpoint group as T00261015. If the dewpoint is missing, only the temperature is reported; if the temperature is missing, the hourly temperature and dewpoint group are not reported.

The following maintenance data groups, sensor status indicators and the maintenance indicator, are only reported from automated stations.

Sensor status indicators are reported as indicated below:

A maintenance indicator ($) is coded when an automated system detects that maintenance is needed on the system.

There are three kinds of aircraft observations: Pilot Weather Reports (PIREP), Aircraft Reports (AIREP), and Volcanic Activity Reports (VAR). Both PIREPs and AIREPS have two types: