As previously discussed, for IWXXM 2.0 (operational recommended ICAO practice starting in November 2016, software development currently underway) there is an urgent need for new WMO Codes to be publicly available in http://codes.wmo.int. This particular issue relates to two of the three new products in IWXXM: AIRMET, Volcanic Ash Advisory (VAA), and Tropical Cyclone Advisory (TCA).

For each register I've included a suggested location, but it is possible that I've missed an existing BUFR table that has the required information.

AIRMET
http://codes.wmo.int/49-2/AirWxPhenomena - (ICAO Annex 3/ WMO No. 49-2 Appendix 6 Section 2.1):
- Widespread mean surface wind (SFC WIND nn[n]MPS)
- Surface visibility (SFC VIS nnnnM (mm))
- Isolated thunderstorms (ISOL TS)
- Occasional thunderstorms (OCNL TS)
- Isolated thunderstorms with hail (ISOL TSGR)
- Occasional thunderstorms with hail (OCNL TSGR)
- Mountain obscuration (MT OBSC)
- Broken cloud (BKN CLD)
- Overcast cloud (OVC CLD)
- Isolated cumulonimbus cloud (ISOL CB)
- Occasional cumulonimbus cloud (OCNL CB)
- Frequent cumulonimbus cloud (FRQ CB)
- Isolated towering cumulus cloud (ISOL TCU)
- Occasional towering cumulus cloud (OCNL TCU)
- Frequent towering cumulus cloud (FRQ TCU)
- Moderate icing (MOD ICE)
- Moderate turbulence (MOD TURB)
- Moderate mountain wave (MOD MTW)

http://codes.wmo.int/49-2/WeatherCausingVisibilityReduction - 0-20-025 is close but not quite correct - ICAO Annex 3/ WMO No. 49-2 Appendix 6 Section 2.1 under SFC VIS:
- Mist (BR)
- Duststorm (DS)
- Dust (DU)
- Drizzle (DZ)
- Funnel Cloud (FC)
- Fog (FG)
- Smoke (FU)
- Hail (GR)
- Small hail (GS)
- Haze (HZ)
- Ice pellets (PL)
- Dust/stand whirls (PO)
- Rain (RA)
- Sand (SA)
- Snow grams (SG)
- Snow (SN)
- Squall (SQ)
- Sandstorm (SS)
- Volcanic Ash (VA)

VAA
http://codes.wmo.int/49-2/AviationColourCode - ICAO Annex 3/WMO No. 49-2 Appendix 2 Table A2-1:
- RED
- ORANGE
- YELLOW
- GREEN
- UNKNOWN
- NOT GIVEN
- NIL