Online forums support civic discourses on local politics, but it is not clear whether they generate decision-relevant outcomes. Using deliberative democracy as a theoretical lens, this paper proposes a coding scheme for understanding the progress of citizens' deliberation through content analysis from a naturally occurring online discussion of a local planning project. By comparing patterns of this online discourse with normative views of deliberative dialogues, we found that important indicators of the deliberative ideal are missing. Our results show that citizens were not able to move towards advanced phases of deliberation as prescribed by deliberative democracy theory; and explain why it failed to develop common ground and joint assessment of alternative courses of action. We further explore possible causes of such patterns and identified a number of barriers that make online discussions less optimal to achieve common ground and collective judgment. Based on such findings, we suggest ways to improve deliberative outcomes by introducing active facilitation and advanced information support.