The phrase "a developing pattern" is correct and usable in written English.
It can be used to describe a trend or sequence that is in the process of evolving or becoming more defined over time.
Example: "Researchers observed a developing pattern in the data that suggested a correlation between the variables."
Alternatives: "an emerging trend" or "a growing pattern".
"We think there is a developing pattern with Senator Obama where he is willing to reverse core positions, like on Iraq, and which show he is not a change agent but just a typical politician," said Brian Rogers, a spokesman for Mr. McCain.
Among them are Cardinal Bernard F. Law, who resigned his post as archbishop of Boston as a result of the scandal; Cardinal Edward M. Egan of New York for failing in his former post as bishop of Bridgeport, Conn., to remove a priest with a developing pattern of accusations; and Cardinal Roger M. Mahony of Los Angeles for resisting grand jury subpoenas that sought church files on accused priests.
Positive health claims make it too easy to slide into, and be blind, to a developing pattern of alcohol abuse, she says.
"The incredibly inappropriate comments from Senator McConnell's team mark a developing pattern and demonstrate just how out of touch McConnell is with the women of Kentucky.
Women were more likely to experience a developing pattern than men, independent of baseline distress.
Within the various cultures the art of representing things by painted images has rarely shown a continuously developing pattern toward greater realism.
In the present paper we apply a recently developed pattern recognition algorithm SPs to the problem of automated detection of artificial disturbances in one-second magnetic observatory data.
The commitment to covering the residents' basic needs is a strongly developed pattern.
The SP500 is developing a pattern called an ascending triangle, which has similar implications as pennant patterns.
Developing a pattern language is a non-trivial problem.
