Wow this trip planner is awesome!! If you are planning a trip or even some kind of outdoor event, this is such a useful tool. It analyzes the history of the weather of a given date and tells you what the chances of it being cold/hot/rainy/cloudy on that particular day(s). I checked my tentative wedding date April 18th (2009!) and I got this:

Historical Summary for April 17 – April 19

Temperature:
The Average High Temperature is 69 F with a historical range of 63 F to 80 F
The Average Low Temperature is 53 F with a historical range of 49 F to 56 F
There is a 0% chance of a Hot Day (temperature over 90°F / 32°C).
(0 days out of 21 in historical record)
Most consecutive days found in historic record: 0
There is a 0% chance of a Freezing Day (temperature below 32°F / 0°C).
(0 days out of 21 in historical record)
Most consecutive days found in historic record: 0

Warm
Daily Precipitation:
The Average Daily Precipitation is 0.00 with a historical range of 0.00 to 0.01
There is a 5% chance of a Precipitation Day.
(1 day out of 21 in historical record)
Most consecutive days found in historic record: 0

Dry
Cloud Cover:
Average Cloud Cover is mostly sunny
There is a 10% chance of a Cloudy Day.
(2 days out of 21 in historical record)
Most consecutive days found in historic record: 2

Clear
Wind:
The Average Wind is 2 mph with a historical range of 0 mph to 6 mph
There is a 0% chance of a Windy Day (average wind over 10 mph / 15km/h).
(0 days out of 21 in historical record)
Most consecutive days found in historic record: 0

Humidity:
The Average High Dew Point is 51 F with a historical range of 44 F to 58 F
The Average Low Dew Point is 39 F with a historical range of 13 F to 53 F
There is a 0% chance of a Humid Day (dew point over 65°F / 18°C).
(0 days out of 21 in historical record)
Most consecutive days found in historic record: 0

Looks like the perfect day for a wedding!! :)