In the Forgotten Realms Style Guide (available for download on the DMs Guild), Wizards of the Coast appears to have shifted the months of the year in the Realms's calendar.
Hammer has always been equivalent to January, but now...

According to Brian Cortijo (posting as Garen Thal) on the Candlekeep forums:
Color me unhappy.
This kind of change does zero for me as a DM. It doesn't help me run the game. If anything, it makes things harder.
Hammer has always been equivalent to January, but now...

According to Brian Cortijo (posting as Garen Thal) on the Candlekeep forums:
The Style Guide reflects an in-house decision at WotC to align the winter and summer equinoxes (which are called "Midwinter" and "Midsummer" in our world) with the Midwinter and Midsummer celebrations in-world. I vocally opposed this decision, but refused to make it the hill on which I'd die, which is why the text about the seasons possibly/probably falling back to their previous cycle follows (SCAG, 15).
Basically, the shift of the winter equinox went from Nightal 20 to Hammer 31/Alturiak 0, which is a shift of 40 days. The same for the summer equinox. This would have wrought unholy havoc on crop cycles, and if it becomes a permanent change, will just result in the migration of the annual festivals—which don't care one little bit about the synchronicity of Faerûnian and Earth Midwinter, but absolutely wouldn't keep celebrating a holiday like Greengrass on a date when it's unlikely that there is any actual green grass. (emphasis as the original)
Color me unhappy.
This kind of change does zero for me as a DM. It doesn't help me run the game. If anything, it makes things harder.