MAFOR marine forecast 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 1 Group 2 Group 3 Group 4 Group 5
YYG1G1 0AAAam 1GDFmWm (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 AAAa , it shall be inserted at the place of this group.
Group 2
am Code Portion of the Maritime Area
0 Whole of the area AAA
1 Northeast quadrant of the area AAA
2 Eastern half of the area AAA
3 Southeast quadrant of the area
4 Southern half of the area AAA
5 Southwest quadrant of the area AAA
6 Western half of the area AAA
7 Northwest quadrant of the area AAA
8 Northern half of the area AAA
9 Rest 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
0 Beginning of period 0 Calm 0 0 - 10 0 Visibility greater than 3 nm
1 Valid for 3 hrs 1 Northeast 1 11 - 16 1 Risk of accumulation of ice on superstructures
2 Valid for 6 hrs 2 East 2 17 - 21 2 Strong risk of accumulation of ice on superstructure
3 Valid for 9 hrs 3 Southeast 3 22 - 27 3 Visibility ≥ 1 nm and ≤ 3 nm
4 Valid for 12 hrs 4 South 4 28 - 33 4 Visibility < 1 nm, including fog
5 Valid for 18 hrs 5 Southwest 5 34 - 40 5 Drizzle
6 Valid for 24 hrs 6 West 6 41 - 47 6 Rain
7 Valid for 48 hrs 7 Northwest 7 48 - 55 7 Snow, or rain and snow
8 Valid for 72 hrs 8 North 8 56 - 63 8 Squally weather with or without showers
9 Occasionally 9 Variable 9 64 + 9 Thunderstorms

Group 4

2VSTxTn M
  • V: Visibility
  • S: State of the sea
  • Tx: Maximum air temperature
  • Tn: Minimum air temperature
Group 4
V
Code
Visibility S
Code
State of the Sea
Descriptive
Height
(meter)
Tx,Tn
Code
Temperature
(degrees Celsius)
0 Less than 50m 0 Calm 0 0 Less than -10
1 50 - 200m 1 Calm 0 - 0.1 1 -10 to -5
2 200 - 500m 2 Smooth 0.1 - 0.5 2 -5 to -1
3 500 - 1000m 3 Slight 0.5 - 1.25 3 About 0
4 1 - 2km 4 Moderate 1.25 - 2.5 4 1 to 5
5 2 - 4km 5 Rough 2.5 - 4.5 5 5 to 10
6 4 - 10km 6 Very rough 4 - 6 6 10 to 20
7 10 - 20km 7 High 6 - 9 7 20 to 30
8 20 - 50km 8 Very high 9 - 14 8 Greater than 30
9 50km + 9 Phenomenal > 14 9 Not 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 moving Pw
Code
Period of waves
In seconds
0 Calm 0 10
1 Northeast 1 11
2 East 2 12
3 Southeast 3 13
4 South 4 14 or more
5 Southwest 5 5 or less
6 West 6 6
7 Northwest 7 7
8 North 8 8
9 Variable 9 9
    / 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.

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