| Air Mass | Satellite photos | Sea - air temperature difference (F°) |
| very unstable | cloud sheets | >+8° |
| unstable | cell clusters | +4° to +8° |
| average | stratus | 0 to +4° |
| stable | surface obscured | -4° to 0 |
| very stable | low fog or stratus | <-4° |
The estimator determines surface winds from a balance between pressure gradients, Coriolis forces and frictional drag on the surface—a factor that depends on the stability of the air. If you have reason to believe the air mass is more or less stable than average you can specify it with this option. Generally air within a High or within the warm sector of a frontal wave is stable, which would lead to less wind speed for the same gradient.
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