Dense fog, low visibility, fog advisories, and low-cloud events worldwide
This fog monitor tracks active fog and low-visibility events worldwide, identifying regions where visibility is reduced below safe thresholds for ground, air, and marine traffic. Users searching for fog near me, dense fog advisory, or visibility map can see active fog conditions and dissipation forecasts.
Radiation fog forms on clear calm nights when ground cooling chills the overlying air to its dew point — common in valleys and after rainfall. Advection fog develops when warm moist air flows over a cooler surface, producing the persistent fog over the Grand Banks where warm Gulf Stream air meets cold Labrador Current waters. Upslope fog forms as moist air is lifted up rising terrain. Steam fog appears when cold air moves over warmer water, lifting visible water vapor.
Visibility above 10 km is considered unrestricted. Mist reduces visibility between 1 and 10 km. Fog by international definition reduces visibility below 1 km. Dense fog drops visibility under 400 metres, and zero-visibility conditions can occur in extreme cases with visibility below 50 metres. Aviation visibility minima for instrument approaches typically require 800 metres or more, while CAT III autoland systems permit landings below 100 metres.
Fog is a leading cause of multi-vehicle pile-ups on highways, and reduced visibility produces a disproportionate share of crashes per kilometre driven. Aviation suffers extensive delays and cancellations during fog events at major hubs. Maritime shipping uses radar and AIS to navigate fog, but small craft and ferries can face hazardous conditions when visibility drops below 1 km in busy waterways.
Fog is notoriously difficult to forecast precisely because it depends on small changes in temperature, dewpoint, and wind. Forecast models indicate when conditions favor fog, but exact timing and density vary block by block. Persistent valley fog and marine layer fog show more predictable patterns and are part of regional climatology in places like California's Central Valley and the Po Valley.
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