The subprime market should brace for a significant upturn in delinquencies in the coming months, a new analysis by investment bank Friedman Billings Ramsey suggests. In a report detailing a new statistical model it has developed to gauge subprime performance in markets around the country, FBR said it expects weighted average serious delinquency rates on securitized subprime mortgages to rise to 7.40 percent in April of 2005 – up…