Helm (mountain)

Helm, also known as helms or helm wind, is a local wind that occurs on the western slopes of the Pennine hills in England, specifically in the region of Cross Fell. It is a strong, cold, northeasterly wind that is often accompanied by a stationary cloud formation known as the Helm Bar.

Characteristics:

• Origin: The Helm wind originates as an easterly or northeasterly airflow across the North Sea and the Vale of Eden.
• Formation: As the wind encounters the steep western escarpment of the Pennines, it is forced to rise. This orographic lift causes the air to cool and condense, forming the Helm Bar cloud.
• Helm Bar: The Helm Bar is a distinctive, elongated cloud that sits along the ridge of the Pennines. It is a lenticular or banner cloud, formed by the lifting and cooling of the air.
• Associated Winds: The actual Helm wind is the strong downslope wind that develops on the leeward side (western side) of the ridge, beneath the Helm Bar. It is often gusty and can reach considerable speeds, particularly in valleys that channel the airflow. A less intense, but related, wind known as the "Helm wind of Shunner Fell" can also occur further south.
• Seasonality: The Helm wind is most common during the autumn and winter months when temperature differences between the air mass over the North Sea and the land are greatest.
• Impact: The Helm wind can have a significant impact on local weather conditions, causing sudden temperature drops, strong gusts, and hazardous conditions for outdoor activities. It also affects agricultural practices and can contribute to soil erosion.

Related Phenomena:

• Lee Waves: The formation of the Helm Bar and Helm wind are associated with lee wave activity, where stable air flows over a mountain range, creating a series of oscillating air movements downwind.
• Orographic Lift: The fundamental process behind the Helm wind is orographic lift, where air is forced to rise over a topographic barrier.

Importance:

The Helm wind is a well-known local weather phenomenon and is of interest to meteorologists, hikers, and residents of the area. Understanding its formation and characteristics is crucial for forecasting local weather conditions and mitigating potential hazards.