A weather fax shows a complex synoptic chart for the NE Atlantic with a deep LOW at 960 hPa centred on 55°N 30°W, an OCCLUDED FRONT extending SE, and a HIGH at 1030 hPa over the Azores. You are at 48°N 20°W planning a route to the Azores. What does this chart tell you?

A. Chart analysis: (1) Deep LOW at 960 hPa — severe storm. Isobars will be very closely packed around this centre indicating high gradient winds (potentially storm force 10-11 near the centre); (2) Occluded front: the warm and cold fronts have merged — the system is mature and the warm sector has been lifted off the surface. The occlusion brings cloud, precipitation, and moderate winds along its line but the associated squalls are less violent than a cold front; (3) HIGH 1030 hPa over Azores — the Azores High is a semi-permanent anticyclone; a 1030 hPa High in this position suggests settled conditions over the Azores but a significant pressure gradient between the Low (960 hPa) and High (1030 hPa) = 70 hPa difference over ~1500nm = a strong gradient and likely gale conditions in the transition zone between them; (4) Your position at 48°N 20°W is between the Low and High — check the isobar spacing to estimate the wind speed at your position. A route to the Azores (heading SSW) would take you toward the High and likely improving conditions.

B. An occluded front means the weather has finished — behind an occlusion the weather always clears. The route to the Azores through the occlusion is safe.

C. A 960 hPa Low is a standard Atlantic depression. Winds will be force 6-7 near the centre — not severe weather requiring route adjustment.

D. The Azores High at 1030 hPa blocks all Atlantic depressions from reaching Portugal and the Azores. Your route to the Azores is guaranteed to be in calm conditions regardless of the Low.

A. Buys Ballot's Law (Northern Hemisphere): stand with your back to the wind — the centre of lowest pressure (the depression) lies approximately 90° to 120° to your LEFT (and slightly forward). Wind from SW, standing with back to SW means facing NE — the depression centre lies to the NW or NNW of your position. Backing wind (SW to S) means the depression is approaching from the west or northwest — you are in the WARM SECTOR of an approaching depression (between the warm front and cold front). Expected sequence: (1) Barometer continues to fall; (2) Wind continues to back and freshen; (3) Warm front will pass with steady rain; (4) Wind veers to W-NW as cold front arrives; (5) Violent squalls, heavy rain, and rapid pressure rise as the cold front passes; (6) Barometer rises rapidly; (7) Wind veers to NW-N; clearing showers with good visibility.

B. Stand facing the wind — the depression lies 90° to your right. Wind from the SW means the depression is to the NW. Veering wind means the depression is passing to the south.

C. Buys Ballot's Law only applies in the Southern Hemisphere. In the Northern Hemisphere, the depression lies to the right of the wind direction.

D. A falling barometer at 2 hPa/hour indicates a stationary anticyclone nearby. The backing wind confirms high pressure to the east.

A. ADVECTION FOG — the dominant fog type on the Grand Banks. Mechanism: warm, moist air from the Gulf Stream (sea surface temperature 15-20°C) flows northward and encounters the cold Labrador Current (SST 2-8°C). The warm air is cooled below its dew point by contact with the cold sea surface, causing condensation — fog forms. Characteristics: persists regardless of time of day (unlike radiation fog which disperses with daytime heating); very dense, may last days; geographically fixed to the temperature boundary zone. Other fog types: Radiation Fog — over land, forms on calm clear nights as the land surface cools; disperses with morning sun; does not persist at sea. Sea Smoke (Arctic Sea Smoke) — cold dry air over relatively warm water; water vapour condenses immediately above the surface into low wisps — opposite mechanism to advection fog. Avoidance: route planning to avoid the Grand Banks fog zone (approximately 43°-47°N, 45°-55°W) in spring/summer; alternative routes further north or south.

B. Radiation fog forms on the Grand Banks because the sun cannot penetrate the ocean and heats the sea surface at night. This is the most common fog type at sea.

C. Grand Banks fog is frontal fog forming ahead of Atlantic depressions. It is associated with the warm front and disperses when the front passes.

D. Steam fog forms when the cold Labrador Current water evaporates into the warm overlying air. This is only 1-2 metres deep and does not significantly affect navigation.