California: Multi-inch rains denting drought

It never rains in California, but girl, don't they warn ya

It pours, man, it pours -- Albert Hammond

The skies finally opened up over California this week.

The deepest drought in modern history is not over yet. But if this week's rain restored hope to drought stricken California, the forecast may have them dancing in the streets of San Francisco.

Parts of the Bay Area have already soaked up more rain this week than in the past year.

As expected the streets of San Francisco have gone from drought to flood in about 48 hours.

The delivery system for the abundant and welcome rainfall? A tropical moisture plume getting sucked into California by a potent upper level low pressure system off the coast. Watch as the swirling low taps into a deep tropical moisture plume.

Here's more from the University of Wisconsin's Cooperative Institute for Meteorological Satellite Studies blog.

As of 25 November 2014, much of the state of California was experiencing extreme to exceptional drought conditions.  However, the development of a large occluded mid-latitude cyclone over the far eastern Pacific Ocean during the 01 December – 02 December time period began to draw high values (up to 60 mm or 2.4 inches, darker red color enhancement) of total precipitable water (TPW) northward from the Inter-Tropical Convergence Zone (ITCZ), as seen on AWIPS images of the MIMIC TPW product.

An animation of hourly MIMIC TPW images from 30 November – 02 December  showed the northward surge of moisture toward the California coast, and also hinted at a complex inner structure associated with the occluded low.

This week's rainfall appears to be just the first in a series of storms that may dent the drought in parts of California. As much as a foot of rain is needed to erase drought conditions, but areas around San Francisco may get half of that total with the combined totals from this week's rains and forecast rainfall in the next 16 days.

Here's the latest rainfall output for San Francisco from the National Oceanic and Atmospheric Administration's Global Forecast System, which cranks out an eye opening 5.01 inches in the next 16 days.

Mark Twain is often credited with saying... "It takes a flood to end a drought." Northern California may be on the verge of manifesting that reality in the next few weeks.