Heavy Rains Make Modest Dent in California Drought

A very moist “Pineapple Express” atmospheric river of moisture from the Hawaiian Islands is bringing much-needed rains to nearly all of California today. As of 7 am PST Thursday, Downtown Los Angeles had received 0.97" of rain since midnight. The last calendar day when Los Angeles received more than 1" of rainfall was over two years ago--Oct. 5, 2011, when 1.15” fell. Substantial rains also fell in Central California, and heavy rains triggered a rock slide that shut down Highway 1 in Big Sur Wednesday night.


Figure 1. Total precipitable water (TPW) for Thursday, February 27, 2014. TPW is how much rain (in inches) would fall at a given location if one condensed out all of the water vapor in a column above the location into rain. For reference, 1 inch = 25.4 mm. A narrow “Atmospheric River” of moisture is seen extending from the subtropics near Hawaii into Southern California. A larger pulse of moisture is curled up a few hundred miles offshore, and will arrive on Friday. Image credit: University of Wisconsin SSEC.


Figure 2. Rains that fell over California on February 8 - 9 raised water levels on the critical Central California reservoir Folsom Lake by twelve feet in one day, and boosted water levels above the record low levels set during 1977. Rainfall in the Folsom Lake drainage basin on February 26 - 27 has been about 0.5 - 1.5", which will raise the lake level even more. Image credit: California Department of Water Resources.

An even wetter storm coming Friday and Saturday to California
A second, stronger storm system will hit California on Friday and Saturday, generating 1 - 3" rainfall
totals for most coast and valley locations in Southern California, with 3 - 6" in the foothills and coastal mountain slopes. The powerful storm will be capable of spawning severe thunderstorms with wind gusts in excess of 58 mph, and a few waterspouts and weak tornadoes. The NWS office in Los Angeles is warning that Friday and Saturday's storm has the potential to bring rainfall rates of up to 1 - 2" per hour in the foothills and coastal mountain slopes, which will be capable of causing debris flows in areas recently burned by fires. About a foot of snow will likely fall from 6000 feet to 7000 feet, and 1 - 3' of snow is likely above 7000 feet. In the Sierras of Central California, 1 - 2' of snow is expected.

This storm, which has been named "Titan", will move eastwards over the weekend,and an Arctic front will combine with moisture associated with Titan to produce near-blizzard conditions across the northern Rockies Friday into Friday night. As it moves through the Central Plains, the storm will strengthen and begin to pull Gulf moisture northward into the cold air, triggering moderate to heavy snows across portions of Kansas, Nebraska and Missouri Saturday night into Sunday. The snow will spread across Illinois, Kentucky, Indiana, Ohio, West Virginia, and portions of the Mid-Atlantic and Northeast U.S. on Monday, and along the southern side of the snow band, a significant ice storm is likely. The ice storm will affect Oklahoma through Southern Missouri, northern Arkansas and northern Kentucky Saturday night and Sunday, and by Sunday night, parts of the Mid-Atlantic across Virginia and Maryland may also see significant icing. Small changes in the track of the storm will move the areas of freezing rain tens of miles north or south of the current forecast, so stay tuned to the latest forecasts.


Figure 3. The February 25, 2014 U.S. Drought Monitor showed 95% of California in drought, with 26% of the state in the highest level of drought, "Exceptional." Image credit: U.S. Drought Monitor.

Drought situation in California still extreme despite today's rains
While this week's rains and snows in California are a welcome respite, they will put only a modest dent in what is one of the worst droughts in California history. Today's U.S. Drought Monitor showed that the portion of the state in "Exceptional Drought"--the worst category of drought--was 26%, nearly double the previous week's value. This year is the first year since the Drought Monitor product began in 2000 that portions of California have been in "Exceptional Drought". California's area experiencing the two highest categories of drought, extreme to exceptional, increased to 74% this week, and only 5% of the state was not in drought (the Mojave Desert region of Southeast California, where almost no agriculture happens anyway, since it is desert.) To break the drought, much of the state needs more than 12" of precipitation.

Wunderground's weather historian Christopher C. Burt discusses how this week's storm will affect California rainfall totals in his latest post.


Video 1. The new ‪Radius ‬hyper-local weather information app‪, powered by Weather Underground‬

Wunderground Releases New Hyper-Local Weather Information App
Weather Underground released today a new app for iPhone and iPod touch called Radius™. Using Radius™, users can set a designated radius from a desired location to receive free push notifications of NWS severe alerts, lightning, and precipitation heading into that area. Our new predictive radar tool can then be used to determine precisely when to take cover.

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Jeff Masters