Mamore Gap, Co. Donegal: upland wind and wind chill

Mamore Gap is a mountain pass traversing the Urris Hills on the Inishowen Peninsula, Co. Donegal. It connects the coastal road from Buncrana to Clonmany with the interior of the peninsula. The pass itself reaches an elevation of approximately 240 metres above sea level, making it significantly more exposed to wind than the surrounding lowlands and coastal areas.

The topography of the pass, with steep ascents and descents and surrounding higher ground, channels and accelerates airflow, particularly from westerly and south-westerly directions. This funneling effect, combined with the general increase in wind speed with altitude, means that wind conditions at Mamore Gap are often considerably more severe than those reported for nearby valley or coastal stations.

For walkers, cyclists, and other upland users, this exposure translates into a greater risk of being buffeted by gusts and experiencing a more pronounced wind chill, even on days when the general forecast for the region appears moderate. The Wind Agent's Shear Glass allows for height-adjusted wind speeds to be assessed at the typical height of a person in the pass.

Wind speeds at Mamore Gap are subject to significant variation due to its exposed mountain environment. Unlike open, flat terrain where wind profiles are more predictable, the complex topography of the Urris Hills can induce localised acceleration and turbulence.

Commonly cited characteristics for upland wind include:

• Higher Mean Speeds: Wind speeds typically increase with altitude. At 240 metres, the mean wind speed can be 20-40% higher than at a 10-metre reference height in an open, flat area, depending on atmospheric stability.
• Elevated Gust Factors: The gust factor (ratio of gust speed to mean wind speed) can be higher in turbulent mountain environments. While a gust factor of 1.3 is commonly cited for open terrain, values of 1.5 or greater are not uncommon in complex terrain, particularly in the lee of ridges.
• Sudden Gusts: Airflow over ridges and through gaps can create sudden, powerful gusts that can destabilise a person, even when the average wind speed appears manageable. These gusts are often difficult for mesoscale models to resolve precisely.

The Wind Agent's exceedance fan provides the probability of wind speeds exceeding a user-defined limit at a specific height, which is particularly relevant for assessing risk in such exposed locations.

Wind chill is a measure of how cold it feels to a human body due to the combined effect of air temperature and wind speed. As wind speed increases, heat is removed from exposed skin more rapidly, making the perceived temperature significantly lower than the actual air temperature. This effect is particularly pronounced in exposed upland areas like Mamore Gap.

The commonly cited formula for wind chill temperature (WCT) is based on the work of the Joint Action Group for Weather Information in North America (JAG/TI), and is expressed in degrees Celsius as:

WCT = 13.12 + 0.6215 * T - 11.37 * V^0.16 + 0.3965 * T * V^0.16

Where T is the air temperature in °C and V is the wind speed in km/h at 10 metres. For example, an air temperature of 5 °C with a 30 km/h wind results in a wind chill of approximately 0 °C. If the wind speed increases to 60 km/h, the wind chill drops to approximately -4 °C.

In Mamore Gap, where wind speeds can be consistently high, the wind chill factor can quickly lead to hypothermia if appropriate clothing is not worn. The Wind Agent provides a delta-T chart to show the difference between air temperature and wind chill, highlighting periods of increased risk.

The complex terrain around Mamore Gap can generate significant turbulence, particularly when wind flows over ridges and down into valleys. This phenomenon is known as lee-side turbulence or rotor effects.

When wind encounters a mountain or ridge, it is forced upwards and over. On the downwind (lee) side, the air can become highly disturbed, forming eddies and rotors. These areas can experience sudden changes in wind direction and speed, with strong downdrafts and updrafts. For walkers, this can mean being unexpectedly buffeted or even knocked off balance. For drone operators, such conditions can be hazardous.

The prevailing westerly and south-westerly winds in Ireland mean that the eastern slopes and areas immediately to the east of Mamore Gap are often in the lee. Conversely, easterly winds would create similar effects on the western side of the pass. Understanding the wind direction relative to the topography is crucial for anticipating these turbulent zones.

Mountain rescue organisations commonly advise that conditions in the lee can be more hazardous than on the exposed windward side due to the unpredictable nature of the airflow.

The current and forecast wind conditions for Mamore Gap are presented in the meteogram. This chart provides a detailed hourly breakdown of wind speed, gust speed, and direction, adjusted for the specific elevation of the pass. It allows users to track the progression of wind conditions over the coming days, identifying periods of high wind or significant gusts.

Key elements to observe on the meteogram for upland planning include:

• Gust Speed: Pay close attention to the forecast gust speed, as these are the short, sharp increases in wind that can pose the greatest challenge for stability and safety.
• Wind Direction: Note any significant shifts in wind direction, as these can alter exposure to terrain features and potentially move you into or out of lee-side turbulence.
• Agreement Spine: The Agreement Spine indicates the level of consensus among different forecast models. A narrow spine suggests higher confidence in the forecast, while a broad spine indicates greater uncertainty, which is common in complex terrain.

Always cross-reference the forecast with current observations from nearby stations, such as Malin Head, to gauge the accuracy of the model for the specific conditions.

The wind climatology of Mamore Gap, like much of the west coast of Ireland, is dominated by westerly and south-westerly airflows. These directions are associated with the passage of Atlantic depressions, which are most frequent and intense during the autumn and winter months.

• Autumn and Winter (October - March): This period typically brings the strongest winds, highest gust speeds, and lowest temperatures. The combination of high wind and low temperature significantly increases the wind chill factor, making conditions particularly challenging for upland activities.
• Spring (April - May): Often sees a transition, with a mix of strong winds and more settled periods. As the jet stream begins to shift northwards, there can be more easterly components, though these are less frequent.
• Summer (June - September): Generally the calmest period, with lighter winds and higher temperatures. However, even in summer, frontal systems can bring periods of strong wind, and the exposure of Mamore Gap means that wind speeds will still be elevated compared to sea level.

The wind rose chart illustrates the historical distribution of wind directions and speeds for this location, providing context for the prevailing conditions throughout the year.