As long as we're talking a week or less, I let the forecast make my decisions. The NWS now accommodates fairly site-specific forecasting, so I get one for the highest elevation area I'm headed for.

Forecast for South Yosemite high country

You can drag the map anywhere you like, click a new area, then zoom in to see whether it's correct for your trip.

The forecast is just a starting point, of course, but excellent for predicting overnight lows and how much foul weather gear you might want.

cheers,