Even a light windbreaker tied around your waist can be a big help when temperatures drop. Consider the duration of your planned activity , and the time it might take to return to your car. Then, go over your equipment checklist to ensure that you are well outfitted. Constantly evaluate your activity. A chance of rain shouldn't be much of a detriment if you are sport climbing at Smith Rock, but could prove to be life-threatening if you are attempting the Diamond on Colorado's Longs Peak.
Timing is everything with forecasting .
Don't let your goals cloud your thinking, or change your forecast. If there is uncertainty in the forecast, then there should be uncertainty in your plans. Forecasting is an ongoing process. Constantly re-evaluate whether or not you should proceed. Imagine the worst weather scenario for the day.