This year (2011) the dating of Pentecost is interesting.
In AD 33 the Lord's ascension was Saturday 13th June, and Pentecost was Monday 22nd June. ('The Restored Vision' gives these and many other dates). As the Gregorian calendar is 2 days out of step with the Julian calendar the modern anniversaries are the 11th June and the 20th June.
The Exodus was Friday 12th May, 1639 BC, the 15th day of the 1st month. So the 1st day of the 1st month was the 28th April. The beginning the of first month can be no later than this, and up to about 30 days earlier. (There could be up to one day of variation depending one the exact timing of the new moon at the beginning of the luni-solar cycle). This year there was a new moon on Sunday, 3rd April, and this must have been the new moon corresponding to the 1st day of the first month. The 15th day of the first month must therefore have been Sunday 17th April. The divine Sabbath is Friday (see 'The Restored Vision' page xxi). So 'the morrow of the Sabbath' must therefore have been Saturday 23rd April, and Pentecost in the luni-solar calendar is therefore Saturday 11th June.
So this year we have an unusual alignment of the calendars: The days of the week match the corresponding days in AD 33, and the solar date of the ascension falls on the same day as the luni-solar Pentecost. Myself I think the Lord will come on the solar anniversary of His ascension. However there are many who think He will come on Pentecost. This year there is a rare opportunity for both views to be correct. However I believe the proper order is that the Lord descends and raises the 'dead in Christ' on the anniversary of His ascension, then on the anniversary of Pentecost we who are still alive are transformed and we are all caught up to a meeting in the air .
This year the anniversary of the ascension will be 9 years and 9 months after 9/11/2001, and of Pentecost will be 9 years, 9 months, and 9 days after 9/11. I think almost everyone knows that 9/11 was a wake up call, and there are ample references concerning the biblical uses of the numbers 9, 99, and 999.
Reference: 'The Restored Vision', A. E. Ware.