Weather descriptions have recently referred to a “ridge of High Pressure”. What is the “ridge”? According to the Glossary of Meteorology a ridge is an elongated area of relatively high atmospheric pressure. This almost always associated with the maximum area of anticyclonic wind flow. If the ridge is particularly strong, storms systems move along the edge of the ridge, and are deflected from the normal storm patterns. Areas under the ridge miss out on the rains, while those along the edges can see repeated storm systems. This can lead to very dramatic rainfall differences within short distances.
Mary Knapp, Weather Data Library