MONTHLY WEATHER SUMMARY
By Bill Mork
California Department of Water Resources
June 2004

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The recent trend of wa r mer than normal months in California was interrupted in June 2004 when the mean upper level trough of low pressure near the West Coast  brought an incessant onshore flow of marine air to coastal areas and kept average temperatures near to below normal in much of the State.  Preliminary data show the statewide average temperature in June to be 68.7 degrees, 0.3 degree above normal.  Coolest average temperatures were in the Central Coast with 0.4 degree below normal, the South Coast at 0.3 degree below normal, and the San Joaquin Valley at  near normal levels.  Some cities with significant departures from normal average temperatures in June include Porterville with minus 4.0 degrees, Santa Barbara Airport with minus 2.5 degrees, and San Jose with minus 2.0 degrees.  

Much of the South Coast experienced classic "June Gloom"conditions with night and morning low clouds and only partial afternoon clearing during the month .   Downtown Los Angeles had an average monthly temperature of 69.3 degrees, 1.2 degrees below normal, and had 18 days with below normal temperatures. Areas with average temps about 2 degrees above normal include the Northeast Interior and Sacramento Drainage.  Cities with greatest average temperature departures from normal include plus 3.8 degrees at Burney, plus 3.7 degrees at Idyllwild, plus 3.5 degrees at Lancaster, and plus 3.0 degrees at Redding.  Unusual for June was the absence of 100-degree temperatures at Riverside and San Bernardino and only one day with a high temperature of 100 degrees in Sacramento (June 15).  One of the strongest marine intrusions of the month followed the heat of June 15 with wind gusts to 47 mph reported at Travis AFB near midnight on June 15.

Precipitation in June 2004 was spotty and mostly light.  S tatewide precipitation average was 0.1 inch, about 10 percent of normal.  The only significant precipitation was from scattered showers and thunderstorms associated with upper level low pressure areas on June 8 - 9 and June 28 - 29.  The first upper low brought a few inches of snow to the high Sierra with scattered showers and isolated thunderstorms in the Napa Valley and Sierra.  Some Northern California totals on June 8 - 9 include 0.43 inch at Quincy, 0.37 inch at Mineral, 0.23 inch at Yreka, 0.15 inch at Napa, and 0.08 inch at Redding.  In association with the second upper level low on June 28 , the National Weather service reported severe thunderstorms near Bald Mountain and Red Rock in Mendocino County.  Radar estimates include up to 3 inches of rain and 1.5 - inch diameter hail in that area. The largest remote sensor total was 1.60 inches at Clear Creek, west of Redding, on June 28. Shasta Dam had 0. 60 inch of rain on June 28 .  Most low elevation cities in Central and Southern California had a rainless June. 

In our initial search, the only location in California with above normal precipitation in June was Susanville 2 SW with 0.54 inch, 120 percent of normal. The Northern Sierra 8-Station Precipitation Index in June picked up 0.23 inch, 23 percent of normal. At the end of the month, the Index stood at 46.8 inches, 96 percent of normal to date for the water year ending September 30. This represents 94 percent of the water year normal of 50 inches. Contrast this to Southern California which has seasonal precipitation of only 50 percent of normal. The snowpack had almost completely melted at all snow sensor sites by early June. In many basins, runoff and snowmelt were about one month ahead of average conditions. As of June 30, unimpaired water year runoff ranged from about 90 percent on the North Coast to about 30 percent of average on the South Coast. State reservoir storage peaked in May and by June 30 had dropped to 90 percent of average, about 15 percent less than a year ago.

On June 3, a levee on Upper Jones Tract in the Delta broke, flooding an island. Water shipments to Southern California were temporarily curtailed, in hopes of preventing seawater intrusion toward the State and Federal pumping plants in the Delta. In addition, releases were increased at Shasta and Oroville reservoirs, sending more fresh water to the Delta in order to control salinity. High astronomical tides at the beginning of the month, along with windy conditions in the Delta, contributed to the problem by putting additional pressure on the levees. High astronomical tides were expected to occur at the beginning of July, making it even more urgent that the breach be closed quickly. The breach was closed on June 30.

Thanks to Matt Winston for contributing the last paragraph concerning the levee break.

Page last updated 7/13/04.