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Dry December: Rain lags

Rainfall 4% of normal; Sierra snowpack at 40%

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Dry December: Rain lags

Walkers along the Stanialus River at it passes by Caswell State Park south of Manteca.

Bulletin file photo/


POSTED December 27, 2017 12:10 a.m.

The weather outside isn’t frightful.
And that could be a problem if it continues.
A ridge of high pressure in the Pacific Northwest is keeping December unusually dry in California prompting water managers to take notice.
While no one is ready to warn about a possible drought year, the numbers do point to a dry trend.
For the Central Sierra that covers the Stanislaus River watershed that Manteca, Ripon, and Lathrop rely on as well as the drainage basin for the Tuolumne and Merced rivers December rainfall is 4 percent of normal and the snowpack is at 40 percent of average for this time of year.
  “It points to how we always have to be mindful of how we use water,” noted South San Joaquin Irrigation District General Manager Peter Rietkerk.
The dry weather and above average temperatures has triggered some farmers to inquiry about the possibility of an early winter irrigation run if conditions persist. Rietkerk said staff is currently exploring options in the event the need arises.
The Accuweather forecast for Manteca doesn’t call for a possibility of rain until Jan. 8 and then it may be only a drizzle. After that a little rain is predicted for Jan. 17 before the first solid rain of 2018 is expected to hit on Jan. 21.
The high pressure ridge in the Pacific Northwest is being blamed for dry instead of wet conditions in Southern California that has extended the fire season leading to the largest fire ever in recorded state history. The conditions could persist until early spring.
That wasn’t predicted by the 30 plus weather models that try and predict precipitation patterns on the West Coast.
“Surface water is also important to those that rely on wells (such as the cities of Ripon and Stockton plus Manteca and Lathrop that have a hybrid surface/well water system) as it recharges the ground water,” Rietkerk noted.
Despite the warm and dry December, the Stanislaus River flows are above normal for this time of year.
The United States Geological Society reported flows on Monday at Ripon were at 693 cubic feet per second or roughly the volume of water represented by 693 basketballs passing a given point in a second. The median flow for this time of year is 372 cubic feet per second. The historic low flow was during the 1978 drought when it was a 32 cubic feet per second on Dec. 26. The historic high is 11,900 cubic feet per second in 1965.
Releases from New Melones Reservoir are going strong because it is at 1,993,063 acre feet of water or 83 percent of its 2.4 million acre foot capacity. That is 145 percent of average for Dec. 26 for the second highest water in storage in terms of percentage of average among the state’s eight largest reservoirs. Only McClure Lake on the Merced River at 664,902 acre feet or 147 percent of average is higher. Throughout the drought, New Melones had the lowest water of all major reservoirs.
The Bureau of Reclamation needs to get the level at New Melones below 1.97 million acre feet for flood control operations.
“The reason why flows are so high right now is there is still a sizeable runoff from last year’s snowpack (on the Stanislaus watershed),” noted Rietkerk.
Don Pedro Reservoir on the Tuolumne River — a concern of rural South Manteca residents — is at 123 percent of average or 1.3 million acre feet of its 2.03 million acre-foot capacity. It is at 81 percent of capacity.
Flows at Vernalis where the Stanislaus River joins the San Joaquin River were at 1,650 cubic feet per second on Monday, below the median for the date of 2,200 cubic feet per second. The historic high for Vernalis was in 1956 at 39,500 cubic feet per second while the low was in the drought year of 1978 at 587 cubic feet per second.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com

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