I haven't messed around finding B.C.s from velocity myself, but here are some general thoughts
You need to know if your atmo pressure from NOAA is corrected or not.
The NOAA data for my local airport (KEAT, ~1280' ASL) is available as both corrected (29.90" Hg this morning), or raw ('station') pressure (28.58" Hg). The NOAA data for Raton (6350' ASL), as an example, is only available as corrected pressure (30.13" Hg). The actual uncorrected pressure at the range there (6600' ASL) is more like 23.7" Hg, which is a huge difference.
If you can get the raw uncorrected station pressure, then you need to uncheck the box 'Corrected pressure' in JBM and Exbal. Otherwise it takes that pressure and *then* corrects it for the altitude.
If all you can get is the corrected pressure, and the altitude, then enter them and make sure the box for 'Corrected pressure' *is* checked. It may not be quite as precise as having your own Kestrel
or similar weather meter
on site to take actual raw pressures, but it will likely be close.