Advanced Meteorology Flashcards

A 'trough of low pressure' on a synoptic chart (weather map) is characterised by:

Answer: A line of closely packed isobars extending from a low centre — often associated with wind shifts, squalls, and deteriorating weather

A trough is an elongated extension of low pressure. Isobars are closely packed and kinked. Troughs are associated with instability, gusty winds, showers, and sharp wind shifts.

The Buys Ballot Law states that in the Northern Hemisphere:

Answer: If you stand with the wind on your back, low pressure is to your left (port)

Buys Ballot's Law: in the Northern Hemisphere, face the wind and low pressure is to your right (actually: stand with wind at your back, low is to your LEFT). Geostrophic wind blows parallel to isobars, anti-clockwise around lows.

A veering wind in the Northern Hemisphere (shifting clockwise, e.g., SW to W to NW) typically indicates:

Answer: A cold front has passed — improving weather behind it

In the Northern Hemisphere, a clockwise (veering) wind shift — especially SW→NW — is the classic post-cold-front signature: pressure rising, temperature falling, visibility improving (though showers may follow).

What is 'radiation fog', and when is it most likely to affect an offshore passage?

Answer: Fog that forms over land overnight as land cools radiatively, and drifts offshore in the morning with the land breeze — most likely in light wind, clear-sky anticyclonic conditions

Radiation fog forms overnight as land surfaces radiate heat. In light anticyclonic conditions, it can drift offshore. Sea fog (advection fog) — a separate type — forms when warm moist air flows over cold water.

For a cross-Channel passage, which Met Office forecast service provides the most detail for skipper-level planning?

Answer: Inshore Waters Forecast combined with the 5-day shipping forecast text and synoptic chart — plus GRIB files for wind modelling

Skilled passage planning uses multiple sources: Inshore Waters Forecast (detailed coastal), Shipping Forecast (overview), synoptic charts, and GRIB numerical model data for wind and wave forecasts.

A 'secondary depression' forming on a cold front can be particularly hazardous because:

Answer: It may intensify rapidly and is often not forecast as accurately as the primary low, causing unexpected severe conditions

Secondary depressions forming on the trailing cold front of a primary low can deepen rapidly (sometimes 'bomb'), bringing unexpected gales. They may not appear on early forecast charts, catching skippers unaware.