Why is the date of the 2016 Passover a month late when compared to Easter?

The reason for the difference in dates has to do with misunderstanding the solar/lunar calculation of Ex. 12:2.

This month shall be unto you the beginning of months: it shall be the first month of the year to you.

How is that understood? Please note that verse refers to the lunar (months) and solar (year) measurements.

Year in Hebrew is shaneh. It means year as a division of time, of age, a revolution (return) of the sun. It has to first make a complete revolution to accurately mark the beginning of the months.

From Moses to Christ, it was known that the sun first had to have passed the spring equinox and then one looks for the new moon from which to count to the 14th day Passover (or as it too became muddled, the full moon of the 15th).

Here are quotes from Philo of Alexandria, a contemporary of Christ, on how they calculated the month and Passover.

THE THIRD FESTIVAL XXVI. (140) Following the order which we have adopted, we proceed to speak of the third festival, that of the new moon. First of all, because it is the beginning of the month, and the beginning, whether of number or of time, is honourable.

The new moon is the beginning of the month. Next comes Passover on the fourteenth of that month.

THE FOURTH FESTIVAL XXVII. (145) And after the feast of the new moon comes the fourth festival, that of the passover, which the Hebrews call pascha, on which the whole people offer sacrifice, beginning at noonday and continuing till evening.

So, what of the vernal equinox? How does that enter the picture?

I will first jump to Josephus who says this about the year and month calculation of the beginning of the year.

5. In the month of Xanthicus, which is by us called Nisan, and is the beginning of our year, on the fourteenth day of the lunar month, when the sun is in Aries, (for in this month it was that we were delivered from bondage under the Egyptians,) the law ordained that we should every year slay that sacrifice which I before told you we slew when we came out of Egypt, and which was called the Passover; and so we do celebrate this passover in companies, leaving nothing of what we sacrifice till the day following. http://www.ccel.org/ccel/josephus/complete.ii.iv.x.html

And now back to Philo who defines the same mark (vernal equinox) as he describes the Fifth Festival of Unleavened Bread.

This month, being the seventh both in number and order [the original order until changed at Ex. 12:2], according to the revolutions of the sun, is the first in power; (151) on which account it is also called the first in the sacred scriptures [Ex. 12:2]. And the reason, as I imagine, is as follows. The vernal equinox is an imitation and representation of that beginning in accordance with which this world was created. Accordingly, every year, God reminds men of the creation of the world, and with this view puts forward the spring, in which season all plants flourish and bloom; (152) for which reason this is very correctly set down in the law as the first month, since, in a manner, it may be said to be an impression of the first beginning of all, being stamped by it as by an archetypal Seal. ... And this feast [of Unleavened Bread] is begun on the fifteenth day of the month, in the middle of the month, on the day on which the moon is full of light, in consequence of the providence of God taking care that there shall be no darkness on that day.

And see here and here in which the latter states: "But this Aristobulus also adds, that for the feast of the Passover it was necessary not only that the sun should pass the equinoctial segment, but the moon also."

Thus we learn that to properly calculate the first month the sun had to be in Aries, the sun had to pass through the Spring Equinox, and then you look for the new moon. They didn't measure the beginning of the year from only the first full moon after the Spring Equinox. The correct calculation that made sure the sun was in Aries (after the Spring Equinox) necessitates when the intercalary month was added. The sun was in Aries, then they looked for the new moon, and thus the full moon.

As centuries past, the way to count became more muddled. By the time of Constantine (325 CE), the accusation became that the Jews were observing two Passovers in one (solar) year. This happened because they failed to count the solar year properly.

For the OP example shown in 2016, we see this problem in operation. For JW, they only counted the first full moon of 3/23/16 as the day of their memorial. This means the solar/lunar calendar would still be measuring the previous year 2015. In 2015, Passover fell on 4/4/15. For 2015, the sun had passed the Spring Equinox, the first new moon observed, and the full moon was 4/4/15. In 2016, the sun had not passed the Spring Equinox to mark the start of observing the first new moon and thus the full moon. Instead 3/23/16 (and Sunday 3/27/16) was merely the first full moon after the Spring Equinox. In this way, they mistakenly observed two Passovers in one year.

So, that's the reason for the "lag" so called. It's not that Easter was particularly miscalculated in 2016, but rather the JW (and Christian) observance was based on how later Jewish calculations came into play, rather than how Christ would have done it.

PS. To clarify, Easter was observed in 2016 on the first Sunday 3/27 following that first full moon on 3/23.

The Jewish Passover was observed 4/22.

If you love irony sharpening irony, this is a great example. In other words, the answer remains the same, but it's the switch. In Christ's time they observed the Passover on the first full moon after the first new moon after the Spring Equinox. That meant the sun had passed the Spring Equinox (in Josephus' parlance, it was in Aries). That's the correct way to calculate and thus observe the death, burial, resurrection of Christ Jesus.

In the Rabbinic Jewish calendar a synodic lunar month consists of 29 days, 12 hours, and 793 divisions. There are 1080 divisions in an hour. (Louis A Resnikoff, "Jewish Calendar Calculations", Scripta Mathematica 9,191-195(1943). This is the value from Ptolemy's Almagest and is equal to 29.530594 days. Two-hundred thirty-five synodic lunar months make up 19 solar years in the Rabbinic calendar. (Resnikoff). That means that 19 solar years consists of 6939.689622 days. Divided by 19, this gives an implied solar year of 365.2468 days. This is slightly longer than the mean time between two Spring equinoxes, which is currently 365.242374 days. (Wikipedia). So there is a slight solar drift in the Rabbinic calendar. The present-day Rabbinic calendar was developed in the period A.D. 700-950, though a late Jewish tradition gives a date in the 4th century. (Sacha Stern, Calendar and Community Oxford University Press, 2001.) Over the intervening centuries this solar error has accumulated to where, as davidlol wrote in his answer, the earliest that the Feast of Unleavened Bread can now fall in the Gregorian calendar is March 26th. The result is that, at the present day, the Feast of Unleavened Bread and Easter are in different lunar months in 3 years out of every 19. These are the 3rd, 11th, and 14th years of the Western Easter cycle, which correspond respectively to the 19th, 8th, and 11th years of the Jewish cycle. The year 2016 was the 3rd year of the Western Christian cycle and the 19th year of the Jewish cycle.

A "rectified" Jewish calendar has been proposed which would eliminate the slow solar drift in the Rabbinic calendar. It would include an occasional intercalation cycle of 11 years among the cycles of 19 years.

Why are the dates for Passover and Easter almost a month apart this year? (2016)

It is because at times the Jewish lunar calendar has an extra month added to it, thus this discrepancy occurs at times.

The Jehovah's Witnesses time their Memorial as being based on the current apparent movements of the actual physical moon and sun, as observable from Jerusalem.

The Jewish lunar calendar has more fluctuations involved in its’ computations.

Here's Why Passover Is So Late This Year

Passover begins this Friday, later than usual and almost a month after the Christian celebration of Easter, which fell on March 27 this year.

The Jewish holiday falls on the same day in the Jewish calendar every year, but because that calendar is based on the lunar cycle, the celebration of Passover varies according to the Gregorian calendar.

In order to keep the Hebrew year aligned with the seasons of the solar calendar, the Jewish calendar regularly includes leap years that add an extra month—and 2016 is one of them. Leap years occur seven times in a 19-year cycle, and this year pushed Passover into late April.

The Jewish Passover does not always occur on the first full moon on or after the Spring Equinox!

First, some background information:

Our current 19-year intercalary cycle was instituted by Hillel II in the fourth century CE. The calendar is a lunisolar calendar which typically has 12 months. A normal year is 354 days, which is approximately 11.25 days shorter than the solar calendar. To correct for this, the Hebrew calendar has a leap year every 2 or 3 years for a total of 7 times every 19 years. In those leap years, instead of a single day (which we add to our solar calendar), an entire month is added.

Now your question:

According to Wikipedia, at the time when the calendar started, the earliest Passover (corresponding to the 16th year of the 19-year cycle) fell on the vernal equinox and Passover always fell on the first full moon following the equinox.

Over the centuries, there has been a very slight seasonal drift in the calendar (the average year is just over 6.5 minutes longer than the Gregorian calendar). As a result, the calendar has shifted about 7 and a half days later relative to the equinox. But since the months themselves cannot be shifted by a full week (since the new month is tied to the new moon) the result is that in certain leap-years, the leap-month which is supposed to correct for the drift is inserted a year earlier than it should have been to actually match the equinox. This currently happens in the 8th, 11th, and 19th years of the 19-year cycle. Basically, in those years, there has been one more leap year than there actually "should have been" between the fourth century and today.

As you mentioned, this year Passover is not on the first full moon following the vernal equinox. That is because, this year is the 19th year of the current 19-year cycle, which is one of the years where the leap-month is added "prematurely". At this point, there is not much concern about Passover occasionally falling out on the second full moon after the equinox. There is no requirement in the Torah that it fall on the first full moon. There is, however, a requirement that Passover must fall in the Spring (it is called the Spring Festival). If the current calendar were to be followed indefinitely, Passover would eventually fall in the summer due to continued seasonal drift. This would be problematic, but it is not of immediate concern because it would take millenia for this to happen. The hope is that the messiah will come well before then and re-introduce the court-based institution of the months and leap years.

Some bonus information:

You may have noticed that I mentioned that our current calendar was instituted in the fourth century. Of course, the time period that Christians are interested in occurred before this time. Prior to the establishment of the fixed (calculated) calendar, the leap years were determined by the courts. The main factors that the courts took into account was the relationship between Passover and the equinox. They needed to make sure that Passover always fell after the vernal equinox. In addition, however, they could consider other factors that affected the ability of the people living throughout Israel to properly observe the Pesach festival. If the winter rains had destroyed the roads and bridges (which would prevent people from far away from making the festival pilgrimage) or they had destroyed the ovens for roasting the paschal sacrifice, the courts could institute a leap year in order to allow an extra month for the roads and ovens to be fixed before the festival (see Rambam - Mishneh Torah, Kiddush HaChodesh, Chapter 4, Halakha 5).

In a year which was declared a leap-year for one of those reasons, it is entirely likely that such an additional month would push Passover to the second full moon following the equinox. So even before the set calendar and seasonal drift, it was possible for Passover to fall out not on the first full moon. I am not aware of how often this happened (if it ever actually happened at all), but it is most likely (in my opinion) that Passover did occur in the first full moon following the equinox (as it does in most years now and probably in almost all years back then) in the year Christians believe Jesus was killed . - Does Passover occur on the first full moon after the equinox?

The Christian method for calculating Easter is not the same as the Jewish for calculating Passover. This was settled in the fourth century in Council of Nicea. Christians use the Sunday after the first full moon after the spring equinox as the date for Easter. While the Jewish tradition maintains the lunar calender. A complete explanation is given in the Wilton Bulletin.