Global Forecast System

1. Atmosphere

https://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

Air pressure above sea level is calculated as

\[p\,\text{(hPa)} = P_0 - \left(P_0 \cdot 2.26 \! \times \! 10^{-5} \cdot h\right)^{5.26}\]
engtoolbox pressure v elevation
Figure 1. Pressure vs. Elevation
Height (ft) Height (m) Pressure (psia) Pressure (hPa) Air density (kg/m3)

0

0

14.696

1013.3

1.225

10,000

3,048

10.108

697.0

0.905

20,000

6,096

6.759

466.0

0.653

30,000

9,144

4.373

301.0

0.459

40,000

12,192

2.730

188.0

0.303

50,000

15,240

1.692

117.0

0.188

60,000

18,288

1.049

72.3

0.116

70,000

21,336

0.651

44.9

0.072

80,000

24,384

0.406

28.0

0.044

90,000

27,432

0.255

17.6

0.027

100,000

30,480

0.162

11.2

0.017

110,000

33,528

0.100

6.92

0.011

2. Forecasts

Global Forecast System | NOAA | National Centers for Environmental Information

Upper-level wind forecast

https://mag.ncep.noaa.gov/model-guidance-model-area.php

Select GFS then CONUS. Look at the Upper Air section.

The first number is the pressure level in millibars / hectopascals, and wnd_ht means: wind + geopotential height at that pressure surface.

These are constant-pressure surfaces, not fixed geometric altitudes above the ground!

mesonet wind barbs
Figure 2. Wind barbs from Mesonet.org

Wind is shown with wind barbs.

Height is shown as contours of geopotential height in decameters (110 → 11.0 km).

[ [ Draw a side view of the pressure contour. ] ]

Think of these as “winds at pressure layers” rather than “winds at exact altitudes.” A high-altitude balloon rising through the troposphere would roughly pass through:

925 → 850 → 700 → 500 → 300 → 250 → 200 hPa

3. Flight simulator