Well, farmer’s almanac is based on recorded trends. How long it was to record the trends is worth reading more about. But previously recorded weather trends are not without merit in trying to anticipate future trends.
As you probably know there are two Farmer's Almanacs. The Old Farmer's Almanac (since 1792) and the Farmer's Almanac (1818).
They both predict regional weather patterns based on, to one degree or another, sunspot activity, tidal action, planetary position, the Milankovitch cycle and other astronomy cycles, global decadal weather patterns and other factors.
These predictions aren't based on recent observed weather activity but rather on global, lunar and celestial events that reoccur on cycles of varying lengths. When these cycles "line up", so to speak, as is happening now the effects to the earth's climate can be quite severe.
In this case the effect is significant global cooling for a protracted period of time.