When the temperature is not available, this group is not encoded. When the dew point is
not available, the temperature is encoded as "02/."
The altimeter setting is a measurement of the atmospheric pressure in inches of
mercury reported to the nearest hundredth of an inch. This altimeter setting is what the
pilot sets into the aircraft altimeter. When properly set, the altimeter will indicate the
altitude above mean sea level (MSL) of the aircraft at the location for which the value
was determined. An altimeter value of 29.99 is encoded as "A2999."
Remarks and Additive Data
In addition to the regularly reported data, a METAR or SPECI contains a remarks
section at the end of the sequence. The three categories of the entries in the remarks
section that you need to be aware of are as follows:
Remarks about surface-based obscuring phenomena that identify the type of
phenomena obscuring the sky and the amount of the sky covered
Remarks made to elaborate on any of the coded data in the observation report.
Generally, these remarks are made to amplify significant weather in the
Runway surface condition (RSC) and average runway condition readings (RCR) codes
are included in the remarks section whenever conditions on the runway produce less
than the normal braking conditions for landing aircraft. Different codes may be
combined, and each condition should be followed by a decelerometer value. A
decelerometer is a device use to determine braking action. Table 1-19 describes how
RCRs relate to braking action and landing roll.
Equivalent Braking Action
Percent Increase in Landing
02 to 05
100 or more
06 to 12
99 to 46
13 to 18
45 to 16
19 to 25
15 to 0
Table 1-19 -- Description of how RCR, relate to braking action and landing roll
Table 1-20 lists RSC codes used to describe runway conditions and their meanings.