I am going to apply to UC this fall but with a 2.8 GPA, would my fall grades this year make an impact? I was planning on transferring to UCR or UCD but I am not sure.
Your Fall 2020 grades will be considered since you provide them to the UCs in January on the TAU (transfer academic update).
You can use this website to get a feel for the average GPAs that are accepted for specific UC campuses and majors: https://www.universityofcalifornia.edu/infocenter/transfers-major
For 2019, the 25th to 75th percentile GPA of students admitted to Psychology at UCR was 2.95-3.57 and 3.46 - 3.86 at UC Davis. This puts you below the 25th percentile for both schools.
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Psych is surprisingly competitive at a lot of schools. Even at Merced, the 25th percentile GPA for admitted psych transfers is 2.83. Interestingly, the 25th percentile for the Cognitive Science at Merced is lower than for psych - 2.72 - so that might be an alternate major to consider. https://catalog.ucmerced.edu/preview_program.php?catoid=11&poid=1258
Are you applying to CSU schools also? Are you getting a Psych AA-T?
Got into Berkeley with a 3.37 anything is possible. The average for my major at Berkeley was 3.6-3.9 last year.