Year to date

DECLARE @TempData as TABLE
(
Name nvarchar(1111),
MonthName nvarchar(1000), 
CountName int

)

INSERT INTO @TempData
VALUES ('Class 1', 'September 2013', 1),
 ('Class 2', 'October 2013', 4),
('Class 2', 'November 2013', 4),
('Class 3', 'December 2013', 6),
('Class 1', 'January 2014', 2)

SELECT * FROM @TempData

Name    MonthName        CountName
Class 1  September 2013   1
Class 2  October 2013       4
Class 2  November 2013    4
Class 3  December 2013     6
Class 1  January 2014       2

I would like a year to date, so September CountName will remain 1 but OCtober will be Sep + October values ie 4+1 = 6 and so on...

Name    MonthName        CountName
Class 1  September 2013   1
Class 2  October 2013        5
Class 2  November 2013    9
Class 3  December 2013   15
Class 1  January 2014       2