The advantage of YesterdaysWeather for estimation is its simplicity while providing a reasonable level of accuracy.  However, it does not make sense to ignore the impact of known future events on future velocity.  For instance, scheduled vacations, new staff, etc.

'''Therefore'''

Just use YesterdaysWeather as a starting point.  Factor in known future events into estimations for expected velocity.  Be conservative on any adjustments and learn from experience.  It is important that this is a discussion with the involved parties and not just a mechanical adjustment.