Autumn is Here.
UPDATE (Nov 3): Well, autumn arrived in terms of the temperature, but the rain last night turned out to be kindof a dud. Most places picked up between 0.05" and 0.20" (in the foothills), but most of the basin just saw light rain. However, overnight the temperatures plummeted, and we are now waking up to a very cool morning with lows in the high-40s to low-50s! Brrrrrrr (in a good way).
A bit of energy rotating around behind yesterday's storm will keep today cloudy and cool. There will be a slight chance of showers and possibly a mountain thunderstorm this afternoon before everything winds down for a *very cold* night tonight. Even downtown LA will probably dip below 50 tonight.
ORIGINAL POST (Nov 2): October 2015 was the warmest October on record for Downtown Los Angeles. +7 degrees Fahrenheit above normal. It was so hot. If you include September, the 61 days between September 1 and October 31 averaged 6.5 degrees Fahrenheit above normal! That is, to be quite frank, just extraordinary. Below is an image I made showing the departure from "normal" of each day's average temperature. Only 4 days were below-normal.
But, have no fear: autumn is here!
A strong frontal system is currently working its way down from the Bay Area. The front received a big injection of upper-level energy this morning, which amplified it significantly. You can see it in the satellite image showing dense, cold cloud tops:
The front is a pretty routine "rainy season" frontal system. Currently soaking the Central Coast (Monterey has picked up over an inch of rain) and dumping MUCH-NEEDED snow in the Sierra Nevada, this storm is all-around good news for the drought parched state. Unfortunately, by the time it gets to LA it will have petered out substantially. Right now I'm expecting around 1/4" of rain falling in the Los Angeles area beginning around 5 or 6pm and continuing until around 2am (timing is not exact). Here's a simulation of what the radar might look like around 7pm:
The rain will spread from northwest to southeast, meaning Ventura County/Simi Valley should see rain beginning slightly early, and OC and points eastward seeing rain beginning probably after 9pm.
The other story is the temperature!
This storm is dragging down a cold pool of North Pacific air, which is slowly shoving the hot, dry air mass from the weekend to the East. The translation is that temperatures will have a very hard time getting out of the low 70s today and will FINALLY drop into the 50s tonight! (For the first time since June)
The rest of the week looks clear, but cooler, as this fall air mass promises to stick around for a while :)