If you want to know what the weather will be like on your upcomming trip check out:
http://www.wunderground.com/tripplanner/index.asp
"The Trip Planner helps you plan for your upcoming trip or event. Simply choose the start date and end date of your event or trip. The Trip Planner will search our historical database for the weather conditions during those dates in past years. The results will help you decide how hot, cold, wet, or windy it will be!
Weather statistics based on searched dates from 1975 to present. Probabilities (chance of) statistics indicate the chance of an event or condition per day (ie. a 30 percent chance of a cloudy day indicates that each day has a 30 percent chance of being cloudy)."
Example, I searched Jan. 7-14 and here is some of the info I got.
Temperature
Average High Temperature is 72 F
historical range 50 F to 84 F
Average Low Temperature is 49 F
historical range 21 F to 70 F
There is a 0% chance of a Hot Day (temperature over 90°F) (0 days out of 192 in historical record).
Most consecutive days found in historic record: 0
There is a 92% chance of a Warm Day (temperature over 60°F) (176 days out of 192 in historical record).
Most consecutive days found in historic record: 8
There is a 6% chance of a Freezing Day (temperature below 32°F) (12 days out of 192 in historical record).
Most consecutive days found in historic record: 3
Daily Precipitation
Average Daily Precipitation is 0.09
historical range 0.00 to 3.02
There is a 21% chance of a Precipitation Day (40 days out of 192 in historical record).
Most consecutive days found in historic record: 4
Cloud Cover
Average Cloud Cover is mostly sunny
There is a 8% chance of a Cloudy Day (3 days out of 40 in historical record).
Most consecutive days found in historic record: 1
Wind
Average Wind is 6 mph
historical range 0 mph to 14 mph
There is a 12% chance of a Windy Day (average wind over 10 mph) (5 days out of 40 in historical record).
Most consecutive days found in historic record: 1
Humidity
Average High Dew Point is 51 F
historical range 30 F to 66 F
Average Low Dew Point is 41 F
historical range 21 F to 64 F
There is a 30% chance of a Humid Day (dew point over 65°F) (12 days out of 40 in historical record).
Most consecutive days found in historic record: 8