Campbell Scientific PWS100 Present Weather Sensor - Manual (Page 107)

Appendix A. PWS100 Output Codes
The codes that are used in the PWS100 are taken from WMO Manual on Codes
1995 edition, Suppl. No. 5 (VIII.2005), Rec. 5 (CBS-XIII). Table A-1 shows
the weather types available as output from the PWS100. Codes in italics are not
implemented. Codes in bold are extensions of the WMO 4680 table to allow
single Metar code output for different output combinations.
The table contains new intensity limits for mixed events which are explained
subsequent to Table A-1 and shown in Tables A-3 to A-8.
WMO codes 20 to 25 are used to report precipitation, fog or thunderstorms
observed during the preceding hour but not at the time of observation (the time
of observation in the case of the automated PWS100 is the latest set message
period and so could be 1 minute, 1 hour or any user defined interval, the
preceding hour being the hour before this period. Hence if 1 hour message
intervals are set the preceding hour is from 2 hours ago to 1 hour ago. If 1
minute message intervals are set then the preceding hour is from 1 hour 1
minute ago to 1 minute ago. All other codes are for precipitation, fog or
thunderstorms observed during the latest observation period.
NWS codes shown are used with an intensity indicator ‘+’ for heavy, ‘-’ for
light and no indicator for moderate. For example ‘R+’ means heavy rain and
‘S’ means moderate snow.
WMO METAR codes (Code Table 4678) include a code for the weather at or
near the station of significance to the aeronautical operations. The PWS100
being a sample based instrument cannot detect precipitation not at the site and
so such codes cannot be given by the instrument. Some other codes such as
those for dust devils and volcanic ash are not covered by the PWS100 METAR
output. The METAR codes shown are used with an intensity indicator ‘+’ for
heavy, ‘-’ for light and no indicator for moderate. For example ‘+RA’ means
heavy rain and ‘RASN’ means moderate mixed rain and snow. Where there
are mixed events, the order of the codes output indicates the prevalence of the
components (most prevalent is listed first). When no precipitation is detected,
NSW is output for the METAR code.
The table below indicates some of the more common METAR codes the sensor
can output, however in accordance with the standards, the sensor will output
codes with up to three different precipitation types in one message if those
types are detected and are above the mixed event thresholds (see Section
7.4.5).
TABLE A-1. PWS100 output codes.
Weather Type WMO 4680
Code
METAR
4678 Code
NWS
Single
Code
NWS
Multiple
Code
Intensity
Limits
mmh
-1
Particle Size (mm)
or Range (km)
Limit
No significant weather
observed 00 NP C C 0 -
A-1