(i reckon i’ll be postin’ questions right up till the very last minute, which is april 15th)…i was wonderin’ if some of you pct ‘vets’ out there could help us decide the best places to carry a little extra ‘winter protection’ (e.g. insulated jackets, etc)…we’ve of course heard of the famous ‘chilly’ nights in the desert and the frozen shoes/boots in the sierra…who’d like to help us out with some advice?..merci beaucoup!
maw-ee
One of the coldest sections is indeed SoCal. The desert gets really chilly at night and I had a bunch of unpleasant nights in my 40 degree bag, even wearing clothes. Maybe 1/3rd of the nights were bitterly cold, and I started almost a month after you are planning to. The Sierra was cold at night, and in fact Cali was in general until I got past South Lake Tahoe. I finished at Manning on August 21, so WA was very pleasant, with only a few cold nights at the very end.
Personally, I’d carry insulation the entire way. Carry a warm hat the entire way. Carry gloves the entire way. I’d take my 20 degree bag from the border to SLT or so, then switch to the 40 degree one for the border run.
Suge
On my PCT hikes, I rarely ever felt really cold except in late September/early October in WA which had consistent cold rain. Cold & wet is never a fun combo!
As for the SoCal desert, it sometimes got below freezing, but it was a pleasant low humidity cold.
At high elevation in the Sierra you may run into some chilly, sub freezing nights as well, but then again unless its windy, its normally a ‘dry’ pleasant cold.
I no longer swap gear out on my hikes - it saves getting ‘burned’ by a freezing night when you least expect it! 
Happy Trails!
freebird
There are 2 places it’s doubtful you’ll need a warm jacket, long johns, or a wool hat. One is from about Sonora Pass in the northern sierra north to Ashland, OR. By then you’re in the middle of summer, and never sleeping over 8000’. The other smaller place you could do without is from Agua Dulce to Kennedy Meadows.
But i do agree that in Sections A-D of SoCal the nights are colder than most people expect.
markv
Agree with Freebird about Washington state. Cold and wet is never fun. Heavier gloves and a good hat. A sleeping bag liner and extra clothing too. Regardless, travel light, freeze at night (ha). Enjoy… WB
Wilderness Bob