RYA Yachtmaster Advanced Meteorology 2 — Questions and Answers
Question 1: The gradient wind speed can be estimated from isobar spacing on a synoptic chart. What does very closely spaced isobars indicate?
- Strong winds — tightly packed isobars indicate a steep pressure gradient and high wind speeds (Correct answer)
- Light winds — closely spaced isobars mean stable air
- Fog — closely spaced isobars indicate humidity
- Rain — closely packed isobars are found only in frontal rain bands
Correct answer: Strong winds — tightly packed isobars indicate a steep pressure gradient and high wind speeds
Pressure gradient = rate of pressure change with distance. Closely packed isobars = steep gradient = strong gradient wind. Widely spaced isobars = light winds. This is the fundamental relationship between isobar spacing and wind.
Question 2: What is the 'sea breeze' and how does it affect a coastal passage plan?
- A daytime onshore breeze caused by differential heating of land and sea — land heats faster, air rises, drawing in cooler sea air (Correct answer)
- A breeze created by the tidal stream
- An offshore wind that blows only at night
- A wind caused by frontal passage
Correct answer: A daytime onshore breeze caused by differential heating of land and sea — land heats faster, air rises, drawing in cooler sea air
Sea breezes develop on sunny days along coastlines — warm air rising over land draws in cooler air from the sea. They typically start mid-morning, strengthen to 10–15 knots by afternoon, then die off at sunset. Planning around them improves upwind sailing.
Question 3: Which weather situation is most associated with dense sea fog in the English Channel?
- Warm, moist southerly air flow over the cold Channel water in spring and early summer (advection fog) (Correct answer)
- Winter anticyclones
- Cold northerly airstream
- Thunderstorms
Correct answer: Warm, moist southerly air flow over the cold Channel water in spring and early summer (advection fog)
Advection fog forms when warm, moist air (from the SW) advects (flows) over the relatively cold Channel sea surface. Spring and early summer, when sea surface temperatures lag behind air temperatures, is the most fog-prone season.
Question 4: A sky with 'mackerel' cloud patterns (altocumulus in rippled patches) indicates:
- Instability at medium level — possible deterioration, showers, or thunderstorms in the next 12–36 hours (Correct answer)
- Very stable air and good weather for several days
- Ground frost forming overnight
- A cold front has already passed
Correct answer: Instability at medium level — possible deterioration, showers, or thunderstorms in the next 12–36 hours
Altocumulus (mackerel sky) indicates humidity and instability at altitude. The sailor's saying 'mackerel sky, rain is nigh' reflects the fact that this cloud type often precedes unstable, deteriorating weather.
Question 5: In the BBC Shipping Forecast, the term 'cyclonic' for wind direction means:
- Wind directions around the area will be variable and confused due to a nearby low-pressure system or trough (Correct answer)
- Winds are uniformly south-westerly
- Gale force winds throughout
- The forecast area is free of wind
Correct answer: Wind directions around the area will be variable and confused due to a nearby low-pressure system or trough
'Cyclonic' in the Shipping Forecast means wind directions will vary around the compass in an unpredictable pattern due to a complex low or trough passing through the area. Skippers should expect rapidly changing conditions.
Question 6: How does a 'warm sector' between a warm front and cold front typically present to a vessel in the English Channel?
- Steady southerly or south-westerly winds, mild temperatures, reduced visibility, drizzle or low cloud — often uncomfortable but predictable (Correct answer)
- Clear skies and strong north-westerly winds
- Fog banks and flat calms only
- Gale-force winds and heavy rain throughout
Correct answer: Steady southerly or south-westerly winds, mild temperatures, reduced visibility, drizzle or low cloud — often uncomfortable but predictable
The warm sector typically brings steady SW winds, mild damp air, low cloud, and drizzle — grey and unpleasant but manageable. The approaching cold front behind it may bring the more violent weather.
RYA Yachtmaster Advanced Meteorology 2
The gradient wind speed can be estimated from isobar spacing on a synoptic chart.
What does very closely spaced isobars indicate?