My experience living in Dallas, Texas, which has some 1500 miles of accurate weather data as systems come across the north american continent from west to east.... usually the 10 day weather forecast was accurate to within 4 hours. This is really helpful for planning sailing trips, etc. Usually three days out the weather prediction is accurate to within 30 minutes.
As for the California SF Bay area, weather prediction is mostly useless, day to day weather prediction is wildly inaccurate. I think just on Friday there was a prediction that we were going to have a bunch of fog through Tuesday, and it was clear the next day. Wild storms will be predicted, and then never appear, and other times weather that was going to hit Oregon smashes in to the bay for three days. Many times we've gone out sailing expecting calm forecasted weather (Mother's Day 2016) and got 25mph winds and other times we went out expecting forecasted 15mph winds and it was closer to 6-8mph.
My guess is that the lack of HD weather radar in the pacific and the complex topology of the coastal areas and the bay, and also the chaotic interaction between ocean and inland weather systems make for a much more challenging forecasting system than doing forecasting of the plains states. The unique geography of the golden gate being a venturi tube between the low pressure 55F/13C pacific ocean marine layer and the high pressure 95F/35c central valley some forty miles inland creates what the local slang describes as "the wind machine".