On the map (below) the toggles for wind contours, heights and barb show what is typically displayed on the 300 mb chart. At this altitude, the direction of the wind almost always blows parallel to the contours. Therefore, contours of equal wind speed (isotachs drawn at 20 kt intervals) are common on this chart. The jet stream is identified where the wind speed is 70 kt (81 mph / 130 km/h) or greater (colored shading). Like the 200 mb chart this chart is primarily used to locate the jet stream. For example, a height value of "912" means the actual height is 9,120 meters (29,921 feet). By adding a zero to the end of the four digit height value reveals the actual height in meters. But the height ranges from near 27,000 to 32,000 feet (8,200 to 9,600 meters).įor the heights of each 300 mb contour the last digit, 0 (zero), is omitted from the chart. The lines represent the height, in meters, of the altitude where the air pressure is 300 mb.Īn air pressure of 300 millibars is said to occur near 30,000 feet (9,100 meters) in elevation. The air pressure everywhere on this map is 300 millibars.
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