I found this explanation from the local CBS station to be helpful. Explains why some websites are predicting one thing while the others another. Probably basing them off of different models.
So will this year be another year for the weather record books?
It is possible.
Very warm air will be flowing into New England this weekend, temperatures will top 70 by Sunday.
A cold front will be the key to this forecast.
The big question is when will it pass through.
The best bet right now would be late on Monday, meaning the heat would peak on Marathon Day, perhaps topping 80 degrees, challenging the record for the date of 84 degrees set back in 2003.
Not the forecast that runners were hoping for.
However if that cold front speeds up a bit, and some models are hinting at this, much more seasonal air would flow in from the northwest and temperatures would be in the 50s and 60s, much more tolerable.
There are, of course, several days to go and we will be tracking the evolution and progression of the cold front which will either be the runners best friend or a record breaking worst enemy!
http://boston.cbslocal.com/2012/04/10/boston-marathon-weather-forecast-update-80-degrees-possible/