MANDATORY PRESSURE LEVELS

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Level Remarks Temp.
Range
Critical Thickness For Snow
Standard Height
Above Sea level
1000 mb
0 meters
0 feet
925 mb
750 to 800 meters
2460 to 2624 ft
850 mb
Besides the surface, 850mb is used to calculate temperature advection.  Also used in weather forecasting to determine high temperature on sunny, warm days and also used to determine maximum wind gust on sunny, well-mixed days.
0 to + 40 in summer

-40 to +20 in winter

1000 to 850 = 1300 meters

850 to 700 = 1540 meters

1500 meters
4921 ft
700 mb
The "free atmosphere" begins here.  This pressure level skims the tops of the Rockies, so, for practical purposes, there is little ground about this level.  The last mandatory level in the lower troposphere
-15 to +15 in summer

-40 to +5 in winter

1000 to 700 = 2840 meters
3000 meters
9842 ft
500 mb
This pressure marks the approximate level where half the weight of the local air column is below and half the weight is above.  Thus, 500mb is considered to represent the middle troposphere
-25 to 0 in summer

-45 to -10 in winter

1000 to 500 meters = 5400 meters
5500 meters
18044 ft
400 mb
The approximate level where winds steer well-developed hurricanes.  The first mandatory level in the upper troposphere
7000 meters
22965 ft
300 mb
The pressure level near the cruising altitude of most commercial aircraft.  The approximate pressure at the summit of Mount Everest.
-55 to -35
(marginal seasonal changes)
9000 meters
29527 ft
250 mb
The typical pressure level of the jet stream over the middle latitudes.
10500 meters
34448 ft
200 mb
The typical pressure level of the tropopause over the middle latitudes.
-60 to -45
(marginal seasonal changes)
12000 meters
39370 ft
150 mb
13500 meters
44291 ft