Crowds can be very heavy the first few to several days, e.g., Jan 1 is Tuesday next year and many schools will be off that entire week as part of winter break, meaning Jan 1 through 4 or 5 will likely have huge crowds. Thereafter, they are generally very manageable and tame although Martin Luther King day and weekend produce some heavier crowds. Weather is unpredictable. I have been in Jan when it was mid 70s to low 80s and sunny everyday, with mid 50s to low 60s at night for a week. I have also been when the high hardly broke 50 for 5 days in a row, the low was in the low 40s and even down into the 30s and it rained some everyday. Pools are a possbility in the former weather but not in the latter. I have also been when the weather is between those two extremes but you get one or two extreme days (e.g., mid-60s most of the week, high 40s to low 50s at night, and then one day where the high was 48 and the low was 39)