This is what I have. They have it until 10am. I live pretty close to there, and the blue is coming through pretty nicely
This is the forecast for Chino Hills:
Scattered light showers will continue through 10 AM over and west of the mountains. Additional rainfall totals will generally be less than a tenth of an inch. There will also be patchy dense fog with visibility less than one quarter mile at times.
Today
High: 72
Partly cloudy. Scattered showers in the morning. Patchy fog in the morning. Highs 67 to 72. Light winds. Chance of measurable precipitation 40 percent.
Tonight
Low: 52
Partly cloudy. Lows 49 to 55. Light winds.
I don't think the grass will be muddy. The grass there is pretty dense, and on a slight incline, so I think any rain would run down into the pond rather than sit and soak. Also, in this area, it did not rain very hard. We only got a light sprinkle for a few hours in the night.
There are also covered patio areas, though they may be reserved. If not, we could certainly move under one. But I don't think its going to be bad.
I plan to still go.