Thursday, May 14, 2015

Parts of Drought-Stricken California May Quadruple Their Average May Rain In Two Days (FORECAST)

Jon Erdman
Published: May 14,2015





 
After a winter and early spring yielding record low Sierra snowpack compounding a crippling multi-year drought, parts of California will now see a strangely out-of-season soaking through Friday.
Satellite image and jet stream midday Thursday along the West Coast. Teal-shaded streamlines depict the strongest jet-stream level winds, illustrating the sharp southward plunge of the jet stream off the West Coast.

Rain/Snow Forecast



















You can thank the jet stream for that.
For much of this past winter and early spring, the polar jet stream had taken a large northward migration into Canada, keeping Pacific storms away from the West Coast.
Instead, for the next few days, the jet is taking a sharp southward plunge over the eastern Pacific Ocean, steering vigorous upper-level disturbances into Southern California.
The upshot of this is showers and even some thunderstorms with hail, are possible in parts of particularly Southern California through late Friday.
(INTERACTIVE: West Coast Radar Loop)
Some rainfall totals in Southern California may exceed an inch, especially in locations where thunderstorms persist. Beware of the potential for debris flows and slides near recent wildfire burn areas.
Snow will also blanket the Sierra Nevada as well as the San Gabriel Mountains of Southern California. Accumulations should remain less than a foot in these areas, generally above 6000 feet.
(INTERACTIVE: NWS Winter Alerts)
While this precipitation may be considered "manna from heaven" in this sun-worshipping state, it is only a tiny drop in a massive bucket that is this multi-year drought.
Let's stick to the positive news, here. How unusual is this May rain?

How Rare is a May California Soaking?

January-April was the third driest such period on record in California, exceeded only by 2013 -- the state's record driest year -- and 1977.
Average rainfall in downtown Los Angeles in the wettest and driest six-month periods.
California drought monitor analysis from May 12, 2015. The darkest brown shading corresponds to the area of most exceptional drought.
(NOAA/USDA/NDMC)
From May through October, only 9 percent of the year's average rain fell in Los Angeles.
In May, that monthly average was a mere 0.26 inches of rain as the dry season started to set in.
You can understand state water managers completely throwing in the towel for the 2014-2015 water year by now.
However, L.A. may pick up four times their average May rainfall in just one or two days through late Friday.
In fact, L.A. has only recorded 13 Mays since 1878 with at least an inch of rain, for an average return interval of once every 10-11 years. This last occurred in 2003.
In San Diego, this would be even more unusual.
Only once since 1930 has this city synonymous with picture-perfect weather seen a one-inch rainfall in May -- May 8, 1977 -- when 1.49 inches was measured at Lindbergh Field.
Sierra snow isn't all that typical in May, either.
Tahoe City, California, only averages 2.3 inches of May snow. By this time of year, spring snowmelt of the heavy Sierra snowpack is well underway, replenishing the state's reservoirs, a prime source of drinking water.
Senior weather.com meteorologist Nick Wiltgen noted the winter storm warning issued for the Sierra was the latest-in-season such warning by the National Weather Service in Sacramento since 2011.
To reiterate, this welcome May event is a tiny drop of drought relief.
(MORE: Strong El Nino Ahead?)
While often overstated and oversimplified to imply relief is certain, the developing El Nino may offer hope the Pacific storm track may not be blocked from California as often next fall and winter, when the real wet season returns to a thirsty state.

MORE: California's Multi-Year Drought

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