Looking at the forecast in the link I provided before, here is my rainy days forecast.
http://forecast.weather.gov/MapClic...051696777&site=riw&unit=0&lg=en&FcstType=text
With it being Spring break and this storm happening over a weekend it could be good and bad.
Friday for better or worse the Friday forecast went from rain likely to unlikely as the storm isn't coming until night. With luck it will be raining by 5pm, is may sound funny, but what this means is locals won't show up to make a very busy Friday night.
Saturday is looking to be the lowest wait time day of Spring Break. If it's raining in the morning few are going to show up making for a slow day. With this high likelyhood of rain it's possible F! won't run as rain can cancel that night show.
Sunday could be bad, if it's sunny in the morning it could get very crowded if rain kept the crowds out the day before. If it's rainy probably small crowds as some will be ending their trip and already missed a day will go anyway, but some will stay in if they are locals or on a longertrip.
Monday could be bad with a small chance of rain or very busy if it's the first reasonable day.
Tuesday should be back to the normal crowds if Monday has light on and off showers and people went back to the park. If not the mostly sunny forecast will bring in tons of crows stuck inside the last few days.
Rain can cancel the parades. It's not in the forecast but wind often comes with rain and may cancel the fireworks.
Attractions that close during rain are in this list.
Disneyland Park
Alice in Wonderland
Dumbo the Flying Elephant
Pirate's Lair on Tom Sawyer Island
The Mad Tea Party
Gadget's Go Coaster
Disney California Adventure
Redwood Creek Challenge Trail