Marine Weather Interpretation Flashcards
6 cards from real SVOP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Marine Weather Interpretation flashcards as text
How does fog form over coastal waters and what are the two most common types encountered by mariners?
Answer: Advection fog (warm moist air moves over cold water) and radiation fog (land cools overnight causing moisture to condense) — both cause near-zero visibility
Advection fog is the most common marine fog: warm moist air moves over cold water (e.g., Gulf Stream/Labrador Current interface), cools to dew point, and fog forms. Radiation fog forms over adjacent land overnight and can drift over coastal waters in the morning.
What is 'freezing spray' and why is it particularly dangerous for small commercial vessels?
Answer: Spray that freezes on contact with the vessel's superstructure, rapidly adding ice weight, raising the centre of gravity, and potentially capsizing the vessel
Freezing spray occurs when air temperatures are well below 0°C and sea spray freezes immediately on contact with the vessel. Ice accumulates on decks, superstructure, and rigging — sometimes at rates of several centimetres per hour — rapidly adding topside weight and reducing stability.
What is a waterspout and how should a vessel respond when one is sighted?
Answer: A rotating column of air and water connecting a cloud to the sea surface — vessels should alter course immediately to avoid it and report to MCTS
A waterspout is a rotating column of moist air — essentially a weak tornado over water — that can cause severe, localised wind shifts, waves, and damage. Vessels should alter course significantly to avoid them, reduce speed, and report the sighting to MCTS on Ch 16.
What is 'significant wave height' as used in marine weather forecasts?
Answer: The average height of the highest one-third of all waves in a sea state — representing what a mariner would visually observe as the 'average' wave height
Significant wave height (Hs or SWH) is defined as the mean height of the highest one-third of waves. It closely matches what an experienced observer would call the 'average' wave height, since humans naturally notice the larger waves more.
What is the significance of wind shadow and acceleration zones around headlands and islands?
Answer: Headlands block wind on the leeward side (wind shadow) but can accelerate and funnel wind around their tips, creating localised strong gusts exceeding the general forecast
As wind flows around headlands and islands, it is compressed and accelerated at the tips and in gaps, sometimes 20–50% stronger than the forecast wind speed. Leeward areas are calmer but wind shadows have abrupt edges where conditions change rapidly.
What is an upper-level trough and how does it affect marine weather?
Answer: An elongated area of low pressure in the upper atmosphere that can trigger rapid surface weather deterioration, squalls, and thunderstorms even when the surface forecast is benign
An upper-level trough is an area of low pressure in the upper atmosphere (500–300 hPa level) that can cause rapid development of surface lows, severe squalls, and unstable conditions even when surface charts appear quiet. Monitoring upper-level charts is part of professional weather assessment.