It’s that time again when the ‘heat high’ becomes the main character of the weather story. Sometimes, the high can be relentless, resulting in endless days of scorching summer heat. But why do we call it a “heat high,” and why do we hear about it so often?
High pressure system characteristics. (Copyright 2026 by KSAT – All rights reserved.)
What is a high pressure system?
A high pressure system can cover Texas or even the entire southwestern United States. Air pressures are highest at the center, and wind flows clockwise around the system. This unique characteristic influences weather patterns significantly.
Within a high pressure area, cloud cover is limited because the air is descending. This downward movement prevents clouds from forming and subsequently hinders rain development. Consequently, high pressure systems are often associated with dry, sunny weather.
Moreover, high pressure systems are known for trapping heat, which can lead to extended periods of above-average temperatures, making summer feel even hotter.
Why is high pressure always around?
High pressure systems are ubiquitous, moving and developing around the globe. During summer, we frequently discuss these systems because our wind patterns tend to weaken, and the jet stream does not consistently push weather systems into Texas or the southern United States. As a result, temperatures rise, pressure builds, and weather conditions remain relatively stable until a low pressure system arrives to disrupt the tranquility.
The longest-lasting high pressure system
In San Antonio, the record for the longest stretch without rain stands at 63 days, occurring in 1993 from June 26 to August 28. A high pressure system dominated the area during this entire period, showcasing the potential for prolonged dry spells associated with these systems.
For those interested in the technical aspects of high pressure system development, understanding the mechanics involves a closer look at atmospheric dynamics.
How does air move?
To comprehend the weather, it’s essential to understand the movements in the atmosphere that impact surface conditions. The troposphere, the layer where all weather occurs, can extend up to 12 miles above the surface at the equator. Within this vast expanse, air constantly circulates as wind.
Air movement is primarily driven by the Sun’s radiation heating the Earth’s surface. Warm air rises, but the Earth’s rotation causes it to shift to the right in the Northern Hemisphere. As it rises, it cools, creating atmospheric circulations known as the Hadley, Ferrel, and Polar cells.
Hadley, Ferrel, and Polar cells are atmospheric circulation patterns. (Copyright 2026 by KSAT – All rights reserved.)
Where does a high pressure system develop?
High pressure systems develop in the troposphere, particularly above 30° latitude, where air from the Hadley and Ferrel cells converges. This accumulation of air leads to increased pressure, which is a common occurrence over southern regions of the United States. Essentially, having a high pressure system over Texas is a natural phenomenon, as air continuously seeks to balance pressure levels.
Conditions under high pressure
As air moves, it carries temperature with it. In the case of a high pressure system, the air is generally warmer due to the absence of cloud cover, which allows for efficient heating. This warmer air creates a feedback loop, further reinforcing the system’s strength as energized air molecules contribute to rising pressure.
Example of high and low pressure set up. (Copyright 2026 by KSAT – All rights reserved.)
When do we get a break?
While we often say a high pressure system is “parked” over
