Guide to marine weather forecasts: chapter 8

Major Weather Elements Included in the Marine Forecasts

Wind Element

Wind

Included in the forecast for Day 1 and 2?  Yes.
Included in the forecast for Day 3, 4, and 5? Yes.

Days 1 and 2

Wind is a compulsory element in all regular marine forecasts; in the context of the marine forecast, wind is defined as the prevailing or mean wind speed and direction expected at 10 meters above sea level.

The term gusts may be used when the mean wind speed is observed or expected to increase by 10 knots or more for short durations, on the order of seconds. Example: Wind south 25 knots with gusts to 35 along the coast.

Days 3, 4 and 5

Wind is the only element included in the extended marine forecast. Extended marine forecasts will have less detail than the regular marine forecast, with a maximum of three significant changes in wind stated for Day 3, and a maximum of two significant changes stated for Days 4 and 5.

A significant change in observed or forecast winds for Days 1 to 5 is defined with reference to the following criteria:

• Change in wind speed of at least 10 knots;
• Change in wind direction of more than 45 degrees when at least one of the compared wind speeds is greater than 10 knots. Note that for marine forecasts issued for Ontario Region, the criterion is a change of 45 degrees or more.
• Change in the wind warning category. A change from 15 to 20 knots will be considered a significant change when the strong wind warning program is in effect. Note that for marine forecasts issued for Ontario Region, the criterion is a change from 10 to 15 knots, and applies year round.

Weather Conditions, Precipitation and Visibility Element

Weather conditions and precipitation, visibility

Included in the forecast for Day 1 and 2?  Yes.
Included in the forecast for Day 3, 4, and 5?  No.

Days 1 and 2

Weather conditions and precipitation are elements that are included in the regular marine forecast. If these elements are expected to reduce visibility to 1 nautical mile or less, this will be stated. Precipitation amounts are never stated.

Freezing Spray Element

Freezing spray

Included in the forecast for Day 1 and 2?  Yes.
Included in the forecast for Day 3, 4, and 5?  No.

Days 1 and 2

Freezing spray refers to ice build-up on marine infrastructure such as vessel hulls, decks, guy wires, etc that may affect vessel stability or deck operations. The impact of icing due to freezing spray is also dependent on individual vessel characteristics and operating conditions.

A freezing spray warning is issued when ice accretion resulting from freezing spray is expected to reach moderate criteria, defined as ice accretion rates of between 0.7 and 2 centimetres per hour (cm/h); or severe criteria, defined as ice accretion rates exceeding 2 cm/h.

A significant change in freezing spray is defined as the onset or cessation of freezing spray conditions, or when freezing spray intensity changes from moderate to severe, or vice versa.

Air Temperature Element

Air temperature

Included in the forecast for Day 1 and 2? Yes^{Footnote 1} .
Included in the forecast for Day 3, 4, and 5? No.

Days 1 and 2

Air temperature is expressed in degrees Celsius and it must be mentioned if it is expected to be zero or below zero °C. The temperature is not mentioned if it is expected to remain above the freezing point.

A change in air temperature is considered significant when temperature falls below the freezing point or when there is a change of 5 degrees or more. (Note: A significant change in temperature does not necessitate an update of the regular forecast).

* Note that marine forecasts issued for Ontario Region do not include air temperature.