Advanced Meteorology Flashcards

The gradient wind speed can be estimated from isobar spacing on a synoptic chart. What does very closely spaced isobars indicate?

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.

What is the 'sea breeze' and how does it affect a coastal passage plan?

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.

Which weather situation is most associated with dense sea fog in the English Channel?

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.

A sky with 'mackerel' cloud patterns (altocumulus in rippled patches) indicates:

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.

In the BBC Shipping Forecast, the term 'cyclonic' for wind direction means:

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.

How does a 'warm sector' between a warm front and cold front typically present to a vessel in the English Channel?

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.