Monitoring the arrival of spring migratory birds using the 1000-500mb thickness chart

Part I How the Thickness chart is used

• The 1000-500mb Thickness chart is useful for tracking air mass advection. (movement of air masses into a given area)
• The lines on the chart are called contours.
• The contours represent how tall a volume of atmosphere is and height is a function of temperature. Tall volume=warm air. Short volume=colder air.
• 1000mb (364ft ; 111meters) to 500mb (18,289 ft; 5576 meters)
• These contours can be used to estimate the temperature profile based on how tall a given volume of atmosphere happens to be; for example:
• 5100 (meters thick) represents the boundary of an arctic air mass
• 5400 (meters thick) represents the boundary of a freezing air mass. The 5400 contour is useful when predicting frost and freeze events during the growing season, and is used as a rough estimate of a rain/snow line when forecasting mixed precipitation events.   (give or take 60-100meters)
• 5700(meters thick) represents the boundary of a tropical air mass.