The Quirky Update is easy to get, assuming that you already know the rules to follow.

Here's an example with your sample data.

DECLARE @Value float=0,

@id int

UPDATE t SET

@Value = MaxRollingValue = CASE WHEN Value > @Value THEN Value ELSE @Value END,

@id = RID

FROM #dat t WITH( TABLOCKX)

OPTION( MAXDOP 1)