Weather - realistically, how far can you look ahead in the week(s) for accuracy?

This board appears to have a few weather gurus that post quality information during storms.

For a generic question, how far can one look ahead in the coming days and/or weeks for an accurate report?

For example, looking at tomorrow's weather, it calls for partly cloud with a high of 80 and low 63. That, I assume, is probably 95%+ accurate.

Tuesday calls for thunderstorms with 70% precipitation and a high of 78 and low of 63. That's a little ways out, and the showers could potentially scatter. I assume that is 65% accurate.

Looking at December 21, the weather calls for 40% chance of precipitation, with a high of 60 and low 0f 46. I assume that's probably 15% accurate.

So, how far can one realistically look ahead for a "reasonable prediction", and by reasonable, I mean hot, cold, snow, heavy rain, severe winds, etc. 4-5 days?