Lab 12: Mid-lat Cyclones & Upper-Level Chart Analysis

Purpose: This lab will prepare you in analyzing weather features on a map including identifying air masses, weather fronts, areas of upper-level divergence and convergence, areas of circulation, and temperature trends, then comparing to a surface chart to assess the vertical structure of a mid-latitude cyclone. This will build upon concepts learned (i.e., fronts, contouring, etc.) and further build your confidence in identifying these features.

Learning Objectives: The purpose of this lab is to learn how to contour isobars, identify air masses, and locate weather fronts on a surface weather map. 

Mid-latitude Cyclones Overview

Mid-latitude cyclones are low pressure systems in the middle latitudes of Earth. They have counterclockwise winds around them and fronts attached. 

Upper-level Chart Analysis

Mid-latitude cyclones are formed from upper air divergence. This upper air divergence is caused by trough and ridging patterns. Troughs indicate colder temperatures while ridging indicates warmer temperatures. 

Vertical Structure

In order for a mid-latitude cyclone to form / stay mature, upper-level divergence needs to be present to constantly move air out of the column. This needs to happen as air is converging at the surface (low-pressure). Once there is no longer upper-level divergence above the mid-latitude cyclone, it occludes, with the cold fronts cutting underneath the warm front and the low-pressure system weakening. 

Next Page: Mid-Latitude Cyclone Overview