Executive Update
Hydrologic Conditions in California
10/31/2007




Northern Sierra Precipitation Accumulation (1) 

Rainfall & Snow Water Content (in inches) 
 
   

Water Year Amount to Date (since Oct. 1,2007): 
3.60        
Average to Date: 
2.90        
Percent of Average to Date: 
124 %   
Average for the Water Year (Oct. 1 through Sep. 30) 
50.00        
Percent of Average for the Water Year(Oct. 1 through Sep. 30) 
7 %   


 (1)  
Northern Sierra (Sacramento, Feather, Yuba, and American River Basins)
 


Snowpack Water Content

Region
 
Water Content
 (in inches) 
%
Avg to Date 
%
April 1 Avg (2)

Northern Sierra 
---                    
--- (3)                    
---                    
Central Sierra 
---                    
--- (3)                    
---                    
Southern Sierra 
---                    
--- (3)                    
---                    
Statewide 
---                    
--- (3)                    
---                    


 (2)  
April 1 is the date of normal maximum accumulation for the season.
 (3)  

'Percent Average to Date' is not calculated this early in the WY when the historical average is small.
 


Forecast of Regional Water Supply Indices (5) 

Index 
Unimpaired Runoff 
 (in 1000 AF) 
Year Type

8 River Index for September
343.2       
n/a  
Sacramento Valley Water Year Type Index (40-30-30)    @ 50%
6,200       
Dry
Sacramento Valley Water Year Type Index (40-30-30)    @ 90%
6,000       
Dry
San Joaquin Valley Water Year Type Index (60-20-20)   @ 50%
2,000       
Critical
San Joaquin Valley Water Year Type Index (60-20-20)   @ 75%
1,900       
Critical



 (4) 
For more information see Sacramento & San Joaquin Valley Water Year Type Index forecast:  Latest |  Previous 
     (issued monthly from December 1 through May 1)   
 


Key Reservoir Storage As of 10/30/2007 midnight 

Reservoir 
River 
Storage 
 (in 1000 AF) 
Avg Storage
 (in 1000 AF)
% 
 Average
Capacity 
 (in 1000 AF) 
% 
 Capacity
Flood Control (6) 
Encroachment 
 (in 1000 AF) 

Trinity Lake 
Trinity 
1,429   
1,615  
 
88   
2,448   
58   
---        
Shasta Lake 
Sacramento 
1,801   
2,756  
 
65   
4,552   
40   
-2,111        
Lake Oroville 
Feather 
1,455   
2,166  
 
67   
3,538   
41   
-1,708        
New Bullards Bar Res 
Yuba 
587   
534  
 
110   
966   
61   
-213        
Folsom Lake 
American 
285   
498  
 
57   
977   
29   
-447        
New Melones Res 
Stanislaus 
1,427   
1,303  
 
110   
2,420   
59   
-553        
Don Pedro Res 
Tuolumne 
1,240   
1,298  
 
96   
2,030   
61   
-450        
Lake McClure 
Merced 
303   
449  
 
67   
1,025   
30   
-377        
Millerton Lake 
San Joaquin 
172   
189  
 
91   
520   
33   
-264        
Pine Flat Res 
Kings 
190   
349  
 
54   
1,000   
19   
-684        
Isabella 
Kern 
109   
159  
 
68   
568   
19   
-65        
San Luis Res 
(Offstream) 
808   
1,101  
 
73   
2,039   
40   
---        



 (5)  

Temporary encroachment into seasonally reserved flood storage space; requirements can vary considerably on a daily basis 
due to numerous variables: rainfall amounts, anticipated snowmelt, time of year, soil moisture, etc.
 
 


Selected Cities Precipitation Accumulation As of 10/30/2007 

   
Jul 1 to Date 
 2007 - 2007 
 (in inches) 
% 
 Avg 
Jul 1 to Date 
 2006 - 2006 
 (in inches) 
% 
Avg 
% Avg 
 Jul 1 to Jun 30 
 2007 - 2008 

Eureka  
6.55                
181        
0.71                
20        
17                    
Redding  
4.28                
152        
0.26                
9        
12                    
Sacramento  
1.12                
85        
0.16                
12        
6                    
San Francisco  
2.13                
166        
0.33                
26        
11                    
Fresno  
0.24                
27        
0.08                
9        
2                    
Bakersfield  
0.41                
79        
0.29                
56        
6                    
Los Angeles  
1.47                
181        
0.34                
42        
9                    
San Diego  
0.42                
57        
0.81                
109        
3                    


 

Comments
At the end of Water Year 2007 (October 1, 2006 through September 30, 2007) California statewide hydrologic conditions were as follows:  precipitation, 65% of average to date; runoff, 50% of average to date; and reservoir storage, 80% of average for the date.  

A series of troughs during October, the first month of Water Year 2008, kept temperatures throughout the State generally below normal, despite a period of strong, warm Santa Ana Winds in Southern California.   Precipitation during October was generally above normal in Northern California, with most rainfall falling in a two-day period from October 18-19.  This storm brought heavy rains over far Northwestern California and the first monitor stage of the new water year at Dr. Fine Bridge on the Smith River.  

In general, seasonal precipitation during Water Year 2007 was significantly below average, especially in Southern California, where record dryness occurred at some locations.  On September 30, the Northern Sierra 8-Station Index had a seasonal total of 37.3", which is about 75% of the average for an entire Water Year (50.0").  During Water Year 2007, the Northern Sierra 8-Station Index had the sixth driest January and March on record.  In contrast, the other large precipitation months of December and February were above normal at 101% and 170% of average, respectively.  The Water Year 2007 October through September seasonal total of 37.3" is the 24th driest year out of 88 years of record.  In both Northern and Southern California, this year's severe fire season began early because of the dryness.

The latest National Weather Service Climate Prediction left (CPC) 90-Day long-range seasonal weather outlook (for November through January), issued October 18, suggests above average precipitation for Northern California (including most of the Pacific Northwest) and below average for Southern California.  The central part of the State is expected to have average rainfall.  Temperatures are expected to be above average for much of southeastern California and near average for the rest of the State.  The latest CPC long-range weather outlook for November, issued October 31, suggests above average temperatures for all of California.  Below average precipitation is expected for all California.  Both the one- and three-month forecasts suggest that precipitation will be below average for the American Southwest.  

The pattern of this year's long-range forecasts are influenced by the continuing development of weak to moderate La Nina conditions (cooler than average sea-surface temperatures) across the tropical Pacific.  Current conditions suggest that La Nina conditions may continue to strengthen into early next year and then fade during the latter part of winter.  La Nina events influence the position and strength of the jet stream over the Pacific Ocean, which in turn affects the winter precipitation and temperature patterns across the United States and other locations in the world.  La Nina conditions can favor a wetter than average Pacific Northwest and a drier than average American Southwest.  California sits in the transition zone with the northern mountains of the State potentially wetter than average, and the Central Valley and Southern California potentially drier than average.  In addition, during La Nina years, weather in Northern California can be highly variable, with both wet and dry scenarios possible.  Southern California has a more consistent tendency toward dryness.

Updates to the Executive Summary will generally be issued weekly through the wet months of winter and spring.  Beginning about June 1, this product is updated monthly through the dry season during the summer and fall.  The next update of this product will be issued about Tuesday, December 4, 2007, unless there are significant hydrologic changes.