DECLARE @t TABLE(L1 INT,L2 CHAR(1), L3 CHAR(1), dt Date, Forecast NUMERIC(10,5))
INSERT INTO @t(L1,L2,L3,dt,Forecast)
VALUES
(1, 'a', 'x', '01-jan-2013', 1.2),
(1, 'a', 'x', '02-jan-2013', 2.0),
(1, 'a', 'x', '03-jan-2013', 3.0),
(1, 'a', 'x', '05-Jan-2013', 5.2);

WITH CTE1 AS (
SELECT L1,L2,L3,dt,Forecast,
       ROW_NUMBER() OVER(ORDER BY dt DESC) AS rn1
FROM @t),
CTE2 AS (
SELECT *,
       ROW_NUMBER() OVER(PARTITION BY DATEADD(Day,rn1,dt) ORDER BY rn1) AS rn2
FROM CTE1)
SELECT L1,L2,L3,dt,Forecast
FROM CTE2
WHERE rn2 = 1
ORDER BY dt;

DECLARE @t TABLE(L1 INT,L2 CHAR(1), L3 CHAR(1), dt Date, Forecast NUMERIC(10,5))
INSERT INTO @t(L1,L2,L3,dt,Forecast)
VALUES
(1, 'a', 'x', '01-dec-2012', 7.2),
(1, 'a', 'x', '01-jan-2013', 1.2),
(1, 'a', 'x', '02-jan-2013', 2.0),
(1, 'a', 'x', '03-jan-2013', 3.0),
(1, 'a', 'x', '05-Jan-2013', 5.2),
(1, 'a', 'x', '06-Jan-2013', 5.2),
(1, 'a', 'x', '06-Jan-2013', 4.2);

WITH CTE1 AS (
SELECT L1,L2,L3,dt,Forecast,
       ROW_NUMBER() OVER(ORDER BY dt DESC) AS rn1
FROM @t)
,CTE2 AS (
SELECT *, ROW_NUMBER() OVER(PARTITION BY DATEADD(Day,rn1,dt) ORDER BY dt, Forecast DESC) AS rn2
FROM CTE1)

select * from CTE2 where rn2 = 1