October 19, 2012 - Look for the first significant rainfall throughout the region since late April. It has been mostly dry for about six months, It is time to get winter-ready throughout Northern California.
The first month of autumn has been quite mild this year with most of the days over the last month seeing daytime highs above season normals.
If forecast models are correct, this mild weather pattern is about to see a significant change thanks to a cold low pressure system expected to drop out of the Gulf of Alaska.
A slight drop in daytime temperatures today will be followed by more cooling going into the weekend. As the main low pressure system becomes established off the coast on Sunday.
Cloudiness and cooler air will bring daytime highs down to several degrees below normal.
A frontal band associated with this low pressure system is currently forecast to swing through Northern California Sunday night into Monday. This frontal passage is expected to bring precipitation to most of Northern California.
Weather model projections range the amount of rainfall Monday into Tuesday between about a quarter and a half an inch in the Central Valley. This rainfall will translate into snowfall over the mountains.
Snow levels with this cold system will be fairly low for this time of year ranging from about 5000 feet over Shasta County to around 6000 feet over the Northern Sierra Nevada. This puts snowfall down to the major Trans-Sierra passes where a few to several inches of snow will be possible.
This amount of snow could easily produce travel difficulties especially this early in the season when drivers could be caught off guard.
There is still some uncertainty in the exact timing of this system but all current indications point towards next week starting out much wetter and cooler than the previous month.
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