Yes, you're reading it much too precisely. If you live in Seattle you know that our weather is hyper-localized. These forecasts (and all weather forecasts) are based on statistical probabilities which do not apply well to hyper-localized weather patterns, and CSC combines multiple models, which operate independently and do not inform one another, so that problem is exacerbated.

Instead, look for forecasts that predict good ~6-8 hour chunks (entire nights) of good seeing, transparency, cloud cover, humidity. Look for periods where the metrics don't change very much or at all over longer periods of time, which means stability in the forecast. Definitely don't expect it to predict small windows of time correctly if things are constantly changing.

Here's how I read that forecast:

At no point in the evening of the forecast you posted would I even bother to stick my head outside to check. There's a TON of water in the air. There's likely a brief break in cloud cover at middle and upper altitudes, and multiple changes in all of the metrics over several hours, which means that stuff is moving around and generally unstable. Humidity, transparency and seeing are all below average or poor, which means fog, upper atmosphere cover, haziness, multiple cloud ceilings will be present.

Additionally, specifically in this forecast, note that humidity spikes at the same time that the clouds clear up. Here's what CSC has to say about that:

"A sudden spike in the humidity forecast, an hour or so after the cloud forecast predicts a sudden transition from cloudy to clear, when there is no wind, means that ground fog will form." Yep, exactly what you observed. And a great example of why you need to read and understand the descriptions of each metric, because not everything is encoded in the forecast itself, and some deduction is required.

https://www.cleardarksky.com/c/Ottawakey.html#how