Donegal Airport EIDL: crosswind, gust, and low-level shear

Donegal Airport (EIDL), also known as Carrickfinn, is situated on the north-west coast of County Donegal, adjacent to the Atlantic Ocean. This location exposes the airport to prevailing westerly and south-westerly winds, which can present significant operational considerations for aircraft. The terrain surrounding the airport is relatively low-lying but the proximity to the open ocean means there is minimal friction to reduce wind speeds over the approach paths.

The primary runway at EIDL is designated 10/28, meaning its magnetic headings are approximately 100° and 280°. This orientation is a critical factor in determining the crosswind component for various wind directions. Understanding the wind's direction and speed relative to this runway alignment is essential for pilots and ground operations. The Wind Agent provides the Shear Glass, which can be configured to show wind at multiple heights, assisting with awareness of low-level conditions during approach and departure.

The crosswind component is the portion of the wind blowing perpendicular to the runway, which can significantly affect aircraft handling during take-off and landing. For runway 10/28 at Donegal Airport, winds from the south-west through to the north-west will typically generate a crosswind component. The maximum demonstrated crosswind component for an aircraft is commonly cited in its flight manual and is a critical operational limit.

For a wind direction (FROM) of 220° (SW) and a speed of 20 knots, the crosswind component for runway 28 (heading 280°) is calculated as approximately 19 knots. For runway 10 (heading 100°), the same wind would result in a headwind of approximately 7 knots and a crosswind of 19 knots. Conversely, a wind from 040° (NE) at 20 knots would be a crosswind of approximately 19 knots for runway 28 and a headwind of 7 knots for runway 10.

The Wind Agent's crosswind metric can be configured for specific runway headings, allowing pilots to monitor the forecast crosswind component directly against their aircraft's limits. The exceedance fan can then illustrate the probability of exceeding these limits.

Gusts are sudden, brief increases in wind speed. At Donegal Airport, gusts are a frequent concern, particularly with strong westerly and south-westerly flows from the Atlantic. The gust factor, which is the ratio of gust speed to mean wind speed, can be higher in unstable atmospheric conditions or when wind interacts with local topography, even if subtle.

For aviation, gusts can lead to rapid changes in indicated airspeed, requiring prompt control inputs. During landing, a gust can increase lift or cause a sudden sink, while during take-off, it can affect acceleration and climb performance. The reported gust speed in a METAR is the maximum observed wind speed within the last 10 minutes.

Commonly cited operational limits for gusts vary by aircraft type and operator. For example, some general aviation aircraft might have a maximum demonstrated crosswind gust limit of 20 knots. The Wind Agent's Shear Glass displays both mean wind speed and gust speed at 10 metres, allowing for a clear comparison against these limits.

Low-level wind shear is a significant change in wind speed and/or direction over a short distance, typically within the first few hundred metres above the ground. It can occur due to various meteorological phenomena, including frontal passages, sea breezes, or terrain effects. At Donegal Airport, the coastal location can contribute to shear, especially when there are temperature differences between the land and sea, or during frontal systems.

Wind shear can be particularly hazardous during take-off and landing. A sudden decrease in headwind can lead to a loss of airspeed and lift, while an increase can lead to an unexpected climb. Pilots are trained to recognise and manage wind shear, but accurate forecasting and real-time observation are crucial.

The Wind Agent's Shear Glass provides modelled wind speeds at 10, 80, 120, and 180 metres above ground level, allowing for an assessment of wind shear potential. A significant difference in speed or direction between these heights indicates the presence of shear. The Agreement Spine can also highlight model disagreement on shear, indicating higher uncertainty.

Access to current and short-term forecast wind conditions is paramount for aviation safety and planning. The Wind Agent provides a detailed meteogram for Donegal Airport, showing forecast wind speed, gust, and direction for the coming days. This includes data from multiple forecast models, allowing for an assessment of forecast confidence.

METAR (Meteorological Aerodrome Report) observations from EIDL provide measured wind data, including mean wind speed, direction, and any reported gusts. These observations are critical for validating forecasts and understanding current conditions at the airport.

Pilots commonly use this information to make go/no-go decisions, select appropriate runways, and anticipate potential challenges during flight phases. The Agreement Spine feature within The Wind Agent allows for a quick visual comparison of different model outputs against observations, highlighting areas of consensus or divergence.

The climatology of Donegal Airport is dominated by its Atlantic exposure. The wind rose for this location typically shows a strong prevalence of winds from the westerly and south-westerly sectors, particularly during the autumn and winter months. These are often associated with the passage of deep Atlantic depressions. Spring and summer tend to see lighter winds on average, though strong winds can occur in any season.

Understanding the seasonal patterns of wind speed and direction helps in long-term planning and provides context for daily forecasts. For example, knowing that south-westerly winds are statistically more frequent in winter can inform expectations for crosswind conditions during that period.

The climate band chart illustrates the typical range of wind speeds for each month of the year, based on reanalysis data. This allows users to determine whether a particular forecast is within the normal range for the season or represents an unusually strong or weak wind event.