Annual Weather Summary: November 2017 to October 2018 Winter will be colder than normal, especially in the south, with the coldest periods from late November into early December and in late December, mid-January, and early February.
It is an adjective that serves to modify nouns. Nouns modified by every are singular and must be written in such a manner. For example: Every <person> involved in the crash died. The reason for this singularity is because the word every literally means each, and refers to a single entity. Moreover, another reason for this is every is derived from the terms everything and everyone.. Notice here that obviously thing and one are singular objects.
The collective noun number, when preceded by a, is treated as a plural: A number of solutions were suggested. When preceded by the, it is treated as a singular: The number of solutions offered was astounding. Other common collective nouns are class, crowd, flock, panel, committee, group, audience, staff, and family.