Patrol Weather Question of the day.

What is a Rex Block?

The Rex Block is a blocking pattern that in relation to the United States occurs most often in early fall and spring and most often occurs along the West Coast. A Rex Block has two adjacent highs and lows. The most impressive Rex Blocks will have a strong low pressure next to a strong high pressure. The high pressure will be located in a generally north direction from the low pressure. The low associated with the Rex Block is not completely cut-off from the upper level flow, but does have little east-west movement. Strong ridging north of the low causes the airflow to move from high latitudes to low latitudes with little comparable west-east movement of the air. The airflow pattern follows a backward "S" trajectory.  Air flows into the West Coast of Canada then flows south into the Pacific off the Mexican West Coast. The Rex Block is a stuborn pattern because of its North South orientation. Once the flow leaves the Rex Block, it can finally make some significant progress to the east.