It's important to check the forecast before you start a trip to Lake Mead.  Believe me, if the conditions are bad it is well worth rescheduling for another weekend.  In fact, it's a good idea to plan with 2 adjacent weekends for each lake trip, the 2nd weekend is a backup plan if bad weather is forecasted on the 1st weekend.   Below is the historical data on the average high and low temperatures to expect.

Spring/Summer

Fall/Winter