Are rain pants necessary?

2.75 oz significant?..lol. Oh yeah, this is lightweight backpacking. Well, I have gotten cold legs before in Colorado but it was morning temps in the 30's and I was walking through overgrown and very wet vegetation that drenched my pants within a minute of hiking through it. It did make an impact on me so I always take pants. If the forecast is dry or no thunderstorms and you are hiking with others, you will live ; ). If no rain pants taken, I would take something dry to change into in camp.

"Saving 2.75 oz for me would be significant."

Do you have full use of your legs?

I guess the real question is are you OK with your butt/crotch being wet/cold or will this just not happen this time of year (i.e. no downpours and 70F+ weather).

I find that if my upper legs get wet, the wetness gets sucked into my shorts/boxers and even synthetic ones are not awesome when wet for hours.

Yes, you should take the rain skirt. If you have to ask either you are either banking on it not raining at all, or you never tried it like that in extended rain. First of all, your legs get wet WITH a rain skirt. Unless you have an anorak or a poncho its not your legs, but the entire lower half of you body that is the issue. Your rain jacket will make this even worse since all the run off is going to run down into your..ahem.. crotchal area. While this might be refreshing for 30 minute during a 90 degree day, much less so for hours on end, and potentially very bad if it is windy and in the 50s. You can get hypothermia quite easily spending extended time in the low 50's, especially if you don't have enough rain protection to keep your core temperature up. At the very least have an alternate plan if it get chilly enough – some dry underwear in your pack will cover the entirely wet crotch issue, but then again they weigh just as much.

BTW, the stupid light extreme aside, the reason so many people like rain skirts is that they are more comfortable to hike in because of the ventilation – the lighter weight was originally an extraneous bonus feature, but it seems like a lot of people on here now think the whole point is to save weight.

A cut up garbage bag & duct tape will work just as well, and maybe you can get it down to 1.5 oz. Otherwise the modded driducks are a great, nearly disposable alternative to stupid light.

You should take a look at the zpacks poncho groundsheet (if you are going to the extreme of considering cuben) instead – replaces rain jacket and pants, groundsheet, and pack cover, and has better ventilation than any rain suit – ideal for the kinds of mild condition you are referring to. Also at the very least ifit is your groundsheet you will always get to use it every day :-)

3 days gives you a pretty good forecast
Its unlikely that you would have any extended precipitation that wasnt forecast, you could always wait out scattered showers.

But prudence, is just to bring them, things dont dry quick in the humid SE compared to CO or CA, NM, etc. Its almost like…they dont dry at all.

While I'm a bit blown away by the statement that 2.75oz would represent a significant weight savings…I generally don't use rain pants when I hike in the rain. I live in Alaska, so my guess is that our rain is similar to Colorado- cold. I wear quick dry nylon pants so they dry quickly once I'm out of the rain, and provided I keep my core warm and dry I've never felt at risk of hypothermia. However, if I knew I was going to be in extended rainy conditions, I probably would bring rain pants. And if I didn't have dry sleep clothes to change into- and with the OP being obsessed over 2.75oz I do have to wonder what other items may be missing from his pack- then I would most definitely ensure that my pants stayed dry and clean.

I love my zpacks rain kilt. I have only used it once in rain, but use it every night as a ground cloth for my gear when I am sleeping, or to sit on when the ground is wet, it is very much a multi use piece of gear.

If the weight was important, I wouldn't hesitate to drop the kilt in summer. I take a light rain kilt typically in summer but it's not that essential

Depends entirely on temperature (and how warm you hike). I wouldn't say rain pants are necessary unless it's less than 40-45 degrees. Basically shoulder season weather in the mountains.
In an emergency you can wear your long underwear under your pants and even when soaking wet they will keep you tolerable (especially if they are wool). I've worn my fleece lined tights in rain/sleet/snow weather and my legs were ok when wet.

No. Pants will suffice for the legs. For the torso, an umbrella and windshirt are nice while hiking and an emergency poncho in camp. According to me!

Three years ago I would have said no. I always thought that even if it was raining, if my top was warm and dry I would be OK and I could keep my self warm enough by moving.

Then two springs ago, I was doing a long day hike with a chance of thundershowers so I tossed in my rain shell. The showers materialized along with wind. I was perfectly fine while going up hill and got to the top of the high point. But on the way down, I started to get hypothermic. I had to run back to the car to stay warm enough.

Now if there is a chance of rain and wind, I bring the rain pants. if it is summer and warm, I might bring the kilt.

Since the OP does not say whether rain is in the forecast, I think the question is not answerable.

If rain is forecast, and the temps will reach 50 degrees, 2.75 oz seem a small price for a large margin of safety.

I am with Pete. I don't pack them unless I KNOW I am getting soaked. Ii wear nylon pants and bring base laers. Never been terribly uncomfortable.

I always have my MLD chaps. Take up no room and little weight. They are great for going through morning wet plants more than anything.

In the Pacific NW, the shoulder seasons and winter can bring long bouts of cold rain, so wearing rain pants as your primary bottom shell can be practical.

For warmer weather with a poncho I'm covered to the knees, so I can leave the rain pants. With a poncho and tall gaiters, you only have about 3" of leg exposed.

Getting my lower legs wet isn't bad, but a wet butt/crotch is cold and chafing and wet thighs restrict movement, so I would take pants with a jacket. The rain funnels off a jacket, giving your legs a double dose so to speak.

If you do the light shorts and wind pants combo, many athletic style wind pants are very water repellent, but not as breathable and have unsealed seams. I've found unlined Nike/Rebok/New Balance type pants in the 6oz range.

I wonder if a rain kilt could be designed to supplement a the weather end of a tarp?

As you can probably tell from the responses to your query, whether you decide to use rain pants or not depends upon where you travel, when you'll be out on the trails, how you respond to wet conditions, how much you're obsessing about saving ounces, etc. You need to check into the conditions into which you'll be placing yourself, and them decide whether or not you really need the pants.

Just FYI: when I get out in near my home (in north-central Colorado) in the summer, I don't take rain pants, because even if I get caught in a downpour, it generally doesn't last long. Plus, my hiking shorts are moisture-wicking material, so they dry out within an hour after being soaked. And I'm relatively cold-tolerant so being a little damp isn't much of a concern. But I've kept rain pants in my closet for the times I know I'll be out in steady, cold, rainy conditions.

Whenever I have worn them I've been very glad to have them. I don't seem to overheat in waterproof trousers, but this is probably because I only put them on in wet AND cold conditions.

I am still experimenting in this area and sometimes carry both a rain skirt and waterproof trousers (weight weenies feel free to shudder now). I prefer to use a rain skirt jacket, rain skirt poncho or poncho only combo below the bush line and in warmer rain and have found these to work well. My next experiment will be with a jacket, MLD long eVent gaiters, shorts and a rain skirt. The MLD event gaiters are so light they will spend most of the time in my pack. A long jacket plus gaiters and shorts has historically been the favoured clothing set up of the NZ tramper. I suspect this will work well for me in anything but really cold wind driven rain. In these conditions I have found WB trousers and a jacket the most effective way to remain warm.

I have tried my Montbell wind pants in wet conditions, combined with shorts and a rain skirt. I found that the Montbell pants quickly became saturated below the knee and clung to my skin and seemed to sap heat away from me.