Below is the NAM model. We call this the 500mb level and it shows us where the "spin" or "vorticity" is in the atmosphere. We typically talk about "Upper-Level Disturbances" based on these maps. The below image is for late Saturday. The bright yellow and oranges indicate an upper-level disturbance moving in behind today's system to our north. This MAY be enough to give us a sprinkle or light shower in SOME parts of Region 8 on Saturday. This is why we have not completely taken out rain chances yet... even though it is only a 20% chance! Click image to enlarge...
Below is the BUFKIT program that lays out certain parameters of the same NAM model and model run. Notice that it DOES show a little sprinkle or shower possible between 5PM-8PM. With that said, it only shows a little over a TRACE of rain. IF this happened, it would hardly be enough to dampen the roads. Click to enlarge and remember that the timestamp goes from right to left.
SOOOOOOO, we are keeping a 20% chance of rain in the forecast for Saturday, BUT the forecast looks completely dry Sun-Thu.