MAFOR Decode Table

Environment Canada issues MARine FORecast (MAFOR) coded forecasts as part of their marine weather products for the Great Lakes and the St.Lawrence and Saguenay Rivers.

Sample MAFOR string
Group 1Group 2Group 3Group 4Group 5
YYG1G10AAAam1GDFmWm(2VSTxTn)1(3DkPwHwHw)1

Group 1

YYG1G1/

  • YY: Day of the month
  • G1G1 : Time of commencement of forecast (UTC). Midnight is encoded as 00.

Group 2

0AAAam
The maritime area to which the whole forecast or set of forecasts refers. If the geographical name for the forecast region is used instead of the indicator AAAam, it shall be inserted at the place of this group.
Group 2
am CodePortion of the Maritime Area
0Whole of the area AAA
1Northeast quadrant of the area AAA
2Eastern half of the area AAA
3Southeast quadrant of the area
4Southern half of the area AAA
5Southwest quadrant of the area AAA
6Western half of the area AAA
7Northwest quadrant of the area AAA
8Northern half of the area AAA
9Rest of the area AAA

Group 3

1GDFmWm
  • G: Forecast period
  • D: Direction from which the wind is blowing
  • Fm: Wind speed
  • Wm: Forecast weather
Group 3
G
Code
Forecast  Period
Descriptive
D
Code
Wind
Direction
Fm
Code
Wind
Knots
Wm
Code
Forecast Weather
0Beginning of period0Calm00 - 100Moderate to good visibility (greater than 5 km)
1Valid for 3 hrs1Northeast111 - 161Risk of accumulation of ice on superstructures
2Valid for 6 hrs2East217 - 212Strong risk of accumulation of ice on superstructure
3Valid for 9 hrs3Southeast322 - 273Mist (visibility 1 – 5 km)
4Valid for 12 hrs4South428 - 334Fog (visibility > 1 km)
5Valid for 18 hrs5Southwest534 - 405Drizzle
6Valid for 24 hrs6West641 - 476Rain
7Valid for 48 hrs7Northwest748 - 557Snow, or rain and snow
8Valid for 72 hrs8North856 - 638Squally weather with or without showers
9Occasionally9Variable964 +9Thunderstorms

Group 4

2VSTxTnM
  • V: Visibility
  • S: State of the sea
  • Tx: Maximum air temperature
  • Tn: Minimum air temperature
Group 4
V
Code
VisibilityS
Code
State of the Sea
Descriptive
Height
(meter)
Tx,Tn
Code
Temperature
(degrees Celsius)
0Less than 50m0Calm00Less than -10
150 – 200m1Calm0 – 0.11-10 to -5
2200 – 500m2Smooth0.1 – 0.52-5 to -1
3500 – 1000m3Slight0.5 – 1.253About 0
41 – 2km4Moderate1.25 – 2.541 to 5
52 – 4km5Rough2.5 – 4.555 to 10
64 – 10km6Very rough4 – 6610 to 20
710 – 20km7High6 – 9720 to 30
820 – 50km8Very high9 – 148Greater than 30
950km +9Phenomenal< 149Not forecast

Group 5

3DkPwHwHw
  • Dk:  Direction from which swell is moving
  • Pw:  Period of waves
  • HwHw :  Height of forecast waves, in units of 0.5 metres
Group 5
Dk
Code
Direction from which the swell is movingPw
Code
Period of waves
In seconds
0Calm010
1Northeast111
2East212
3Southeast313
4South414 or more
5Southwest55 or less
6West66
7Northwest77
8North88
9Variable99
  /Calm or not determined

Note 1: MAFOR groups 4 and 5 are not included in the Canadian MAFOR bulletins issued by the Meteorological Service of Canada and are being provided for reference purposes only. This is consistent with the World Meteorological Organization's coding regulations for the MAFOR bulletins.