Monday, October 12, 2009

Strong Pacific Storm Eyeing California

UPDATED 7:30 PM PDT, October 12, 2009
By WeatherBug Meteorologist, Andrew Rosenthal

A strong early-season Pacific storm will roar into California later tonight, continuing throughout the day Tuesday into Wednesday, bringing heavy rain, flooding and the threat of mudslides. Rainfall totals, by the time the storm winds down, could be a half-foot or more.

Downpours will arrive early Tuesday morning on the wings of strong autumn storm moving out of the eastern Pacific. Adding even more punch to the storm will be tropical moisture from the remnants of Typhoon Melor. Upon reaching the northern California coast later tonight, heavy rain will be squeezed out like a sponge. Heavy rain will reach the San Francisco Bay Area late tonight and spread along the central coast on Tuesday.

From later tonight through late Wednesday, heavy rain will fall across northern and central California, with rainfall totals of 3 to 6 inches likely along the foothills of the Sierra Nevada and Coast Range. A few areas may even see rainfall reach as high as 8 inches.

The season`s first Pacific storm will also mean heavy snow for portions of the Sierra Nevada. Thanks to the storm`s warm origins, snow levels will climb to near 10,000 feet Tuesday, meaning significant snow will fall above most pass levels, although several inches of snow will still blanket the highest Sierra recreation areas. Below this level, very heavy rain will be squeezed out by the mountains, where some of the highest rainfall amounts will be seen. If you plan to travel up to the mountains, keep an eye on road conditions and be prepared for chain requirements and road closures.

As the storm continues to travel inland, it will bring soggy weather to southern California and the Los Angeles basin. Rainfall totals are likely to be in the 1 to 2 inch range here, bringing a sudden end to the southern California dry season.

This much heavy rain in a short period of time is likely to cause flash flooding, particularly in areas with poor drainage. In addition, significant concerns exist for areas that have recently been burned by forest fires, including those areas around the Angeles National Forest. The heavy rain is likely to cause land- and mudslides as the heavy rain attempts to drain across the burned terrain. A Flood Watch has been issued for the northern Sierra, with a Flash Flood Watch in the southern Sierra. Additional watches are likely this week in southern California.

The storm`s punch will also include strong winds. Winds may gust as high as 60 mph along the coast, and may be higher across the mountains. Already, a High Wind Warning has been issued for the San Francisco Bay Area, and a High Wind Watches along the Central Coast, with Wind Advisories from northern California, including Yosemite National Park, into much of Nevada.

Drivers are urged to use extreme caution on the roads this week, as a summer of dry weather has led to a buildup of oil on roads, making them especially slick. Heavy rain will only exacerbate this problem, so slow down to avoid hydroplaning on the wet roads.