Compressed Weather Report Frames

A compressed weather report frame has a payload of either exactly 28 or 29 bytes.

Callsign	SSID, Path Code & Data Type Code	Compressed Data
4 bytes	1 byte	23 (or 24) bytes
CCCC	D	/XXXXYYYY_csgtrrppPPhbb(S)

where:

• CCCC: 4 bytes for the compressed 6 character Callsign

• D: compresses into 1 byte:

  • the SSID (between SSID 0 [none] and 15; included),

  • the Path Code (between path 0 [none] and 3; included), and

  • the Data Type Code = 0

• /: the Symbol Table Identifier

• XXXX: the Base91 compressed longitude

• YYYY: the Base91 compressed latitude

• _: the weather report Symbol Code

• cs: the compressed wind direction (in degrees) and sustained one-minute wind speed (in knots)

• g: gust (half of peak wind speed in km/h in the last 5 minutes)

• t: temperature (in kelvin above 173.15 K)

• rr: rainfall (in mm) over the past hour

• pp: rainfall (in mm) over the past 24 hours

• PP: rainfall (in mm) since midnight

• h: humidity (in %)

• bb: barometric pressure (in Pa above 50000)

• (S): optionally, snowfall (in cm) over the past 24 hours

Notes:

• All numerical encodings are one or two byte Base256 encodings.

• Here is a fascinating list of weather records.

• The i‑gate adds the Compression Type Byte T right behind cs.

• The parenthesis are not sent; these merely indicate optionality.