Well, they say cut-off lows are the forecaster's nightmare, and it's easy to see why, as last night's forecast of occasional showers turned instead into a gutter-busting sustained heavy downpour. Rainfall totals and forecasts have jumped overnight. They're now calling for 2-3 inches of coastal-area rain and 4-6 inches of foothill-area rain today before the big storm hits.
The tragic part of the forecast calls for the cutoff low to delay the arrival of the main storm, allowing it to pick up subtropical moisture (the dreaded pineapple express). This will push the rainfall totals up even higher, but it will also push up the snow level, from a current 5000' to 8000' or higher, destroying all that precious white stuff that's been laid down at the lower elevations. That won't impact the higher backcountry elevations, but it will nuke most of the local ski areas' snowpacks.
If you can get there, Mt. Baldy Ski Area looks like the way to go today (though expect delays/a late start as they work to dig themselves out).
SoCal Rains; Mountain Snows
The Well-Cooked Andy
A Very Cool August
Wahoo Gullies Are Burnt