Altimeter full real.

[bravoalpha]

If the weather goes dynamic you can still use the "basic tools" for bombing: a map, and the stopwatch. From your direction and the IAS, and from your path you can calculate the wind, the GS, and correct your path.
Height is not so easy to figure out if the pressure is changing, but ground objects, roads or areas has a length and with on the map and in the sight. The scale of them gives the AGL.
Of course there could be different wind layers with wind effect on the falling bombs so nothing could guarantee the perfect hit!