MAFOR, an abbreviation of MArine FORecast, is a North American code used in the transmission of marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 weather forecasts to compress a volume of meteorological and marine information into shorter code for convenience during radio broadcasting. The MAFOR forecast usually supplies the period of validity for the forecast, future wind speed and direction, weather, visibility and 'state of sea.'

Format

A MAFOR code begins with a date and time group, followed by the name of the area to which the forecast applies, followed by one or more groups of five figures, which may be followed by another optional group.

Date Group

YYG1G1/ where

• YY is the day of the month in accordance with Coordinated Universal Time
  Coordinated Universal Time
  Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
  
   (UTC)
• G1G1 is the time of the beginning of the valid period of the forecasts in Coordinated Universal Time
  Coordinated Universal Time
  Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
  
   (UTC).
• "/" is the last digit of this group is not used.

Weather Group

1GDFmW1
1: is an identifying number required by international practice. Each code group following the name of the lake will begin with 1.
G: is the code figure for the period of time covered by the forecast given in the group.

Time Period of Forecast Coverage

• 0 - Existing weather conditions at the beginning of the forecast period
• 1 - Forecast valid for 3 hours
• 2 - Forecast valid for 6 hours
• 3 - Forecast valid for 9 hours
• 4 - Forecast valid for 12 hours
• 5 - Forecast valid for 18 hours
• 6 - Forecast valid for 24 hours
• 7 - Forecast valid for 48 hours
• 8 - Forecast valid for 72 hours
• 9 - Occasionally

D: is the code figure for the forecast direction of the wind.

Direction of Wind

• 0 - Calm
• 1 - Northeast
• 2 - East
• 3 - Southeast
• 4 - South
• 5 - Southwest
• 6 - West
• 7 - Northwest
• 8 - North
• 9 - Variable

Fm: is the code figure for the forecast speed of the wind

Speed of Wind

• 0 - Beaufort Number 0-3 (0 - 10 knots)
• 1 - Beaufort Number 4 (11 - 16 knots)
• 2 - Beaufort Number 5 (17 - 21 knots)
• 3 - Beaufort Number 6 (22 - 27 knots)
• 4 - Beaufort Number 7 (28 - 33 knots)
• 5 - Beaufort Number 8 (34 - 40 knots)
• 6 - Beaufort Number 9 (41 - 47 knots)
• 7 - Beaufort Number 10 (48 - 55 knots)
• 8 - Beaufort Number 11 (56 - 63 knots)
• 9 - Beaufort Number 12 (64 - 71 knots)

W1: is the code figure for forecast weather.

Weather

• 0 - Moderate or good visibility (greater than 3 nautical miles)
• 1 - Risk of ice accumulation on superstructure (air temperature between 0°C and -5°C
• 2 - Strong risk of accumulation of ice on superstructure (air temperature below -5°C
• 3 - Mist (visibility 1/2 to 3 nautical miles)
• 4 - Fog (visibility less than 1/2 nautical mile)
• 5 - Drizzle
• 6 - Rain
• 7 - Snow or rain and snow
• 8 - Squally weather with or without showers
• 9 - Thunder storms

2: identifies the group as a supplementary group. The 2 group is valid for the same period as the group that immediately precedes it.
V: is the code figure for the forecast visibility.

Visibility

• 0 - Less than 50 meters
• 1 - 50 - 200 meters
• 2 - 200 - 500 meters
• 3 - 500 meters to 1/2 nautical mile
• 4 - 1/2 to 1 nautical mile
• 5 - 1 to 2 nautical miles
• 6 - 2 to 5 nautical miles
• 7 - 5 to 12 nautical miles

S: is the code figure for the forecast sea state.

State of Sea

Height in Meters

• 0 - Calm (glassy)
• 1 - Calm (rippled) - 0.0 - 0.1
• 2 - Smooth (wavelets) - 0.1 - 0.5
• 3 - Slight - 0.5 - 1.25
• 4 - Moderate - 1.25 - 2.5
• 5 - Rough - 2.5 - 4
• 6 - Very Rough - 4.0 - 6
• 7 - High - 6.0 - 9
• 8 - Very High - 9.0 - 14
• 9 - Phenomenal - over 14

Example of a Marine Forecast=
MAFOR 0403/ - Superior 12646 14755 245H 12720 - Ontario 15820 12804

Referring to the codes above, this may be decoded as follows:
MAFOR 0403/: Marine forecast valid from 03 Coordinated Universal Time of the fourth day of the current month

Lake Superior

Lake Superior

Lake Superior is the largest of the five traditionally-demarcated Great Lakes of North America. It is bounded to the north by the Canadian province of Ontario and the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan. It is the largest freshwater lake in the...

: first 6 hours of the forecast period -wind west at 28 - 33 knots, with rain. Next 12 hours of forecast period - wind northwest 34 - 40 knots, with drizzle. During the same period - visibility 1/2 - 1 nautical mile, with rough seas, wave heights of 2.5 - 4 m. Final 6 hours of the forecast period -wind northwest at 17 - 21 knots, visibility greater than 3 nautical miles

Lake Ontario

Lake Ontario

Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north and southwest by the Canadian province of Ontario, and on the south by the American state of New York. Ontario, Canada's most populous province, was named for the lake. In the Wyandot language, ontarío means...

: First 18 hours of forecast period -wind north 17 - 21 knots, visibility greater than 3 nautical miles, final 6 hours of forecast period - wind north at 10 knots or less, with fog reducing visibility to less than 1/2 nautical mile.

MAFOR Synopsis

Each MAFOR broadcast

Broadcasting

Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...

 is followed by a brief technical synopsis of the current weather map

Weather map

A weather map displays various meteorological features across a particular area at a particular point in time. Such maps have been in use since the mid-19th century and are used for research and weather forecasting purposes. Maps using isotherms show temperature gradients, which can help locate...

 in plain language. The synopsis gives the location of the centers of significant high and low pressure areas, and their forecast motion (direction and speed). Reference is occasionally made to marked wind shift lines, giving the anticipated time at which the wind shift will occur at key points.

The following is an example of the type of synopsis that is issued:
Low Chicago

Chicago

Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...

 moving ENE 35 High New York City

New York City

New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 moving e 15 Wind shift SW to NW Detroit early morning Kingston

Kingston, Ontario

Kingston, Ontario is a Canadian city located in Eastern Ontario where the St. Lawrence River flows out of Lake Ontario. Originally a First Nations settlement called "Katarowki," , growing European exploration in the 17th Century made it an important trading post...

late evening