500 Millibar Constant Pressure Map
250 Millibar Constant Pressure Map
300 Millibar Constant Pressure Map
Interpreting the Upper Wind Charts
500 Millibar Constant Pressure Map
The 500 millibar constant pressure chart ranges in elevation from 16,000 feet (4,980 meters) to nearly 20,000 feet (6,000 meters) and is considered the "middle" of the atmosphere.
250 Millibar Constant Pressure Map
This chart (as well as the 300 mb chart) is primarily used to locate the jet stream. The jet stream is identified by where the wind speed is 70 kt (81 mph / 130 km/h) or greater (blue shading). Therefore, contours of equal wind speed (isotachs, drawn at 20 kt intervals) are common on this chart. At this altitude, the direction of the wind almost always flows parallel to the contours.
300 Millibar Constant Pressure Map
An air pressure of 300 millibars is said to occur near 30,000 feet (9,100 meters) in elevation, but the height ranges from near 27,000 to 32,000 feet. This chart is primarily used to locate the jet stream. The jet stream is identified by where the wind speed is 70 kt (81 mph / 130 km/h) or greater (blue shading). Therefore, contours of equal wind speed (isotachs drawn at 20 kt intervals) are common on this chart. At this altitude, the direction of the wind almost always blows parallel to the contours.
The black lines represent isoheights, or geopotential contours. Because the actual height of the 300 millibar surface is heavily influenced by the density of the column of air below, this gives us a rough temperature map of where the atmosphere, in general, is quite cold (low heights) and quite warm (high heights). Not surprisingly, we see a vast area of low height in the polar regions.
Lines packed close together indicate a strong height (or pressure) differential, implying a strong pressure gradient. This means strong winds. And it's here that we find the jet stream. The jet stream is indicated by colored shading, with green indicating winds of 100 knots, yellow of 120 knots, red for 140 knots, and white for 160 knots.
Wind Speed Indicators
Wind speeds on weather maps are in knots (kt); one knot equals 1.15 mph and 1.85 km/h. Each long barb represents 10 kt and short barbs represent 5 kt. A pennant is used to represent 50 kt. Total the barbs and pennants to determine the wind speed at that location. The longest line (shaft) points in the direction FROM which that wind is blowing.
Examples:
500 Millibar Constant Pressure Map
The 500 millibar constant pressure chart ranges in elevation from 16,000 feet (4,980 meters) to nearly 20,000 feet (6,000 meters) and is considered the "middle" of the atmosphere.
250 Millibar Constant Pressure Map
This chart (as well as the 300 mb chart) is primarily used to locate the jet stream. The jet stream is identified by where the wind speed is 70 kt (81 mph / 130 km/h) or greater (blue shading). Therefore, contours of equal wind speed (isotachs, drawn at 20 kt intervals) are common on this chart. At this altitude, the direction of the wind almost always flows parallel to the contours.
300 Millibar Constant Pressure Map
An air pressure of 300 millibars is said to occur near 30,000 feet (9,100 meters) in elevation, but the height ranges from near 27,000 to 32,000 feet. This chart is primarily used to locate the jet stream. The jet stream is identified by where the wind speed is 70 kt (81 mph / 130 km/h) or greater (blue shading). Therefore, contours of equal wind speed (isotachs drawn at 20 kt intervals) are common on this chart. At this altitude, the direction of the wind almost always blows parallel to the contours.
The black lines represent isoheights, or geopotential contours. Because the actual height of the 300 millibar surface is heavily influenced by the density of the column of air below, this gives us a rough temperature map of where the atmosphere, in general, is quite cold (low heights) and quite warm (high heights). Not surprisingly, we see a vast area of low height in the polar regions.
Lines packed close together indicate a strong height (or pressure) differential, implying a strong pressure gradient. This means strong winds. And it's here that we find the jet stream. The jet stream is indicated by colored shading, with green indicating winds of 100 knots, yellow of 120 knots, red for 140 knots, and white for 160 knots.
Wind Speed Indicators
Wind speeds on weather maps are in knots (kt); one knot equals 1.15 mph and 1.85 km/h. Each long barb represents 10 kt and short barbs represent 5 kt. A pennant is used to represent 50 kt. Total the barbs and pennants to determine the wind speed at that location. The longest line (shaft) points in the direction FROM which that wind is blowing.
Examples: