Garmin GXM 40 - Manual (Page 21)

GXM 40 Owner’s Manual 
XM WX Weather Features
Surface Pressure
This feature displays pressure isobars and pressure centers. The isobars connect points of equal pressure. Pressure readings
can help determine weather and wind conditions in an area. High-pressure areas generally are associated with fair weather.
Low-pressure areas generally are associated with clouds and the chance of precipitation. Isobars that are packed closely
together show a strong pressure gradient. Strong pressure gradients are associated with areas of stronger winds. Pressure
units can be displayed in millibars (mbar), inches of mercury (inHg), and hectopascals (hPa).
Strong Pressure Gradient Pressure Isobars Strong Pressure Gradient Pressure Isobars