SIGNIFICANT WEATHER (Appendix I)
SIGNIFICANT WEATHER PHENOMENA MATRIX (Appendix J)
ACRONYMS (Appendix K)

APPENDIX I
SIGNIFICANT WEATHER: WMO CODE TABLE 4678

w'w' CODE TABLE 4678 --Significant present and forecast weather

The w'w' groups shall be constructed by considering columns 1 to 5 in the table above in sequence, that is intensity (if appropriate), followed by the descriptor (if appropriate), followed by weather phenomena. For example, heavy rain shower(s) are coded as +SHRA.

- Light 

  Moderate
(no qualifier)
 

+ Heavy 
  or well
  deveoped
  in the case
  of funnel
  clouds) 

VC4 In the
    vicinity 

MI  Shallow 

BC  Patches 

PR  Partial 

DR  Low drifting 

BL  Blowing 

SH  Shower(s) 

TS  Thunderstorm 

FZ  Freezing 

DZ  Drizzle 

RA  Rain 

SN  Snow 

SG  Snow Grains 

IC  Ice Crystals 

PE  Ice Pellets 

GR5 Hail 

GS6 Small Hail
    and/or snow
    pellets 

UP7  Unknown pre-
     cipitation
     in automated
     obs 

BR  Mist 

FG  Fog 

FU  Smoke 

VA  Volcanic
    ash 

DU  Widespread
    dust 

SA  Sand 

HZ  Haze 

PY  Spray 

PO Well-devel-
   oped dust/
   sand whirls 

SQ Squalls 

FC8 Funnel
    clouds(s)
    (tornado or
    waterspout) 

SS Sandstorm 

DS Duststorm 

4  The NWS definition of VC applied to the terminal forecast is: 
   An area encompassed between circles with radii of 5 and 10 statue
   miles, respectively, from the center of the airport's runway
   complex

5  diameter of largest hailstone > 1/4"

6  diameter of hailstones < 1/4"

7  UP shall not be used in NWS-prepared

8  Tornadic activity, including tornadoes, waterspouts, and funnel
   clouds, should no be included in terminal forecasts because the
   probability of occurrence at a specific site is very small.

APPENDIX J
SIGNIFICANT WEATHER PHENOMENA MATRIX FOR
NWS-PREPARED TERMINAL FORECASTS
(footnotes on reverse side)

FOOTNOTES FOR WEATHER PHENOMENA MATRIX FOR NWS-PREPARED TERMINAL FORECASTS

1. - Only one descriptor shall be included for each weather phenomena group, e.g., BCFG.
   
2. - In NWS-prepared terminal forecasts, vicinity is defined as 5SM to 10SM from the center of the runway complex of an airport. In NWS-prepared terminal forecasts, vicinity shall be combined only with fog (VCFG), showers (VCSH), or thunderstorms (VCTS), and only when forecasting prevailing conditions (i.e., initial time period, FM or BECMG groups).
   
3. - Raised by wind to less than 6 feet above the ground.
   
4. - TS may be forecast by itself if no precipitation is associated with the thunderstorm.
   
5. - No intensity is ever given to hail (GR/GS [snow pellets]) or ice crystals (IC).
   
6. - Largest forecast hailstone has a diameter of 1/4 inch or more.
   
7. - Forecast hailstone diameter is less than 1/4 inch.
   
8. - VCTS is a valid combination for all airports for which NWS offices prepare terminal forecasts. [In the METAR code, VCTS shall only be reported by automated stations.]
   
9. - In NWS-prepared terminal forecasts, VCSH shall be used to forecast showers 5-10SM from the airport. [In the METAR code, VCSH shall be used to report any type of precipitation not at point of observation, but > 0 to 10SM.] The type and intensity of showers in the vicinity shall not be specified, i.e., +VCSHRA is not allowed.
   
10. - BR (mist) shall only be used when the visibility is forecast to be at least 5/8SM, but not more than 6SM.
    
11. - For FG (fog) to be forecast with any qualifiers except VC12, MI13, PR14, or BC15, the visibility shall be < 5/8SM.
    
12. - VCFG is used to forecast fog at any visibility between 0 and 6SM in the vicinity (5 - 10SM) of the airport.
    
13. - For MIFG (shallow fog) to be forecast, the visibility at 6 feet above ground level shall be 5/8SM or more and the apparent visibility in the fog layer shall be expected to be less than 5/8SM.
    
14. - PRFG (partial fog) indicates that a substantial part of the airport is forecast to be covered by fog (visibility <5/8SM) while the remainder of the airport is expected to be clear of fog.
    
15. - BCFG (patches fog) indicates that patches of fog (visibility <5/8SM) are forecast to randomly cover the airport.
    
16. - FZFG is fog (visibility < 5/8SM) consisting predominately of water droplets at temperatures below 0^oC, whether or not the fog is expected to deposit rime ice.
    
17. - Volcanic Ash (VA) is always included in the forecast when expected. Visibility is not a factor.
    
18. - SN BLSN indicates snow falling from clouds with blowing snow occurring.
    
19. - SQ (squall) is a sudden increase in wind speed of at least 16 knots, the speed rising to 22 knots or more and lasting for at least one minute.
    
20. - Generally, Funnel Clouds should not be forecast in terminal forecasts.
    
21. - Generally, Tornadoes and Waterspouts should not be forecast in terminal forecasts.
    
22. - SS is forecast if visibility is > 5/16SM and < 5/8SM. Forecast +SS if visibility is expected to be < 5/16SM.
    
23. - DS is forecast if visibility is > 5/16SM and < 5/8SM. Forecast +DS if visibility is expected to be < 5/16SM.

In the terminal forecast, no more than 3 significant weather groups shall be used to forecast weather phenomena at or near the airport. If more than one significant weather phenomena is required in the forecast, separate weather groups shall be included. If more than one form of precipitation is forecast, the appropriate contractions shall be combined in a single group with the predominant type of precipitation included first. In such a single precipitation group, the intensity shall refer to the total precipitation and be encoded with one or no indicator as appropriate, e.g., -RASN FG HZ.

APPENDIX K
ACRONYMS

AAWU       Alaska Aviation Weather Unit

AC         Severe weather outlook 

AFOS       An automated system (Automation of Field Operations and Services)
           used by the National Weather Service to standardize and expedite 
           meteorological services 

AGL        Above Ground Level 

ARONET     Alaska Region Operations Network 

ASOS       Automated Surface Observing System 

AWC        Aviation Weather Center 

AWOS       Automated Weather Observing System 

CONUS      Contiguous United States 

CWSU       Center Weather Service Unit 

DRG        Data Review Group 

FA         Area Forecast 

FAA        Federal Aviation Administration 

FMH-1      Federal Meteorological Handbook No. 1, Surface Weather
           Observations & Reports 

ICAO       International Civil Aviation Organization - an organization
           established under the auspices of the United Nations for the 
           promotion and orderly growth of international civil aviation 

IFR        Instrument Flight Rules 

LIFR       Low Instrument Flight Rules 

METAR      Aviation routine weather report. Also refers to the international
           hourly surface observation code format. 

MIC        Meteorologist-in-Charge 

MVFR       Marginal Visual Flight Rules 

NCEP       National Centers for Environmental Prediction 

NEXRAD     NEXt generation weather RADar 

NOAA       National Oceanic and Atmospheric Administration 

NWS        National Weather Service 

NWSFO      NEXRAD Weather Service Forecast Office 

NWSO       NEXRAD Weather Service Office 

NWSTG      National Weather Service Telecommunication Gateway 

OML        Operations Manual Letter 

PIL        Product Inventory List. Communication header used on the NWS'
           AFOS system. 

PIREP      Pilot Report 

PoP        Probability of Precipitation 

RAM        Regional Aviation Meteorologist 

RAN        Regional Air Navigation. An ICAO term used ordinarily as a
           preface to such nouns as "agreement", "meeting(s)", or
           "plans". 

ROML       Regional Operations Manual Letter 

SPC        Storm Prediction Center 

TAF        Aerodrome forecast code format. The international standard for
           the TAF code, FM 51-X Ext. TAF, is included in WMO Manual on 
           Codes, WMO No. 306, Volume I.1, Part A. 

UTC        Coordinated Universal Time 

VAD        Velocity Azimuth Display 

VFR        Visual Flight Rules 

WMO        World Meteorological Organization - an organization established
           under the auspices of the United Nations for the orderly
           advancement of the science and practice of meteorology 

WSEO       Weather Service Evaluation Officer 

WSOM       Weather Service Operations Manual 

WSR-88D    Weather Surveillance Radar - 1988 Doppler 

WW         Local severe storm watch