CONGREGATION
AHAVAS
SHOLOM
First the short answer (details are discussed in the links below):
(This discussion applies outside Israel. In Israel is different)
We start saying tal umatar, in the evening, 60 days after Tekufa Tishrei. Tekufa Tishrei at one time corresponded to the autumnal equinox. But becuase the calculation of the tekufa was based on a solar calendar year of 365.25 days, and we now know the solar calendar year to be closer to 365.2425 days, the tekufa has drifted about 13 days. In the 22nd century, because February 2100 will not be a leap year, the schedule will drift another day and tal umatar will begin on December 5, 6 or 7.
Ordinarily, we would start saying tal umatar in the evening on December 4. But during a year that precedes a civil leap year we start saying it on December 5. In 2003, we did not start tal umatar until Dec 6 because it was a year before a civil leap year and Dec 5 was a Friday. This situation occurs only once in 28 years.
For a more detailed explanation, you may wish to look at the following:
Sephardic Institute (requires Adobe Acrobat)
