A World of Weather, Edition 3: Chapter 5 Introduction

CHAPTER 5

PRESSURE AND WIND PATTERNS ALOFT The low- and high-pressure systems that you routinely see on television weather maps are not just surface features. Indeed, most of these L's and H's represent only the lobby in a skyscraper of lows and highs that top out in a penthouse "L" or "H" in the upper troposphere. High-rise lows and highs are not vertically plumb, however; they typically "lean" with height like the famous tower in Pisa, Italy.

Before we can discuss in detail the vertical structure of lows and highs (and its implication for the weather), we need to get an idea of how upper-level lows and highs are constructed. To this end, a meteorologist (a.k.a. "atmospheric architect") looks at floor plans of lows and highs at various altitudes. Some of the more revealing layouts, often referred to as constant pressure maps, are rather simple to read. Like the blueprints of a cozy rustic house with sunken living rooms and inviting lofts, they show elevations of sunken valleys of cold air and lofty mounds of warm air.