While we have been having a relatively warm winter in the United States, it cannot compare to what winter is like in Israel. It is the rainy season there, the time of year that Israel greens up, with cooler temperatures and rain (which feels like a miracle every time I experience it) in between
"Tu" (the Hebrew abbreviation of 15th) in the month of Shvat was set (Hillel's opinion generally overrules Shammai's) as the beginning of the tithable year for tree fruit: Calculating the tithe on fruit starts again for fruit that sets after that date.
In a few weeks we will be celebrating Tu BiSh’vat. There are numerous approaches you could take in planning your celebration.