This Wednesday, August 3rd, the Twin Tiers may face a type of blocking pattern called a “blocking high.” A blocking high occurs when a center of high pressure sets up in a way that prevents other weather systems from moving through. These other systems are forced to go around the blocking pattern.

Imagine a strong center of high pressure forming over a region. This is represented as a big blue “H” on a weather map. The persistent weather systems associated with this blocking high are major heat waves, and precipitation is typically blocked from moving through the pattern.

High pressure is associated with sinking air, and the downward motion compresses and warms the air while trapping heat rising from the earth’s surface at the same time. This is what leads to temperatures much greater than average within the blocking pattern, as well as heat waves if the pattern lasts for three days with temperatures greater than 90 degrees. Blocking highs typically last for a few days. Eventually, these patterns will weaken when a short wave moves over the top of the high causing it to decrease with an end to the heat wave.

Why it matters:

Looking for blocking highs matters for all weather forecasters because it helps them determine if there are going to be long periods of extreme heat. It also helps them to know if areas outside the blocking high might get affected by different types of extreme weather.