Thanks to a recent string of storms that drenched the region during the month of January, the Tuolumne River Watershed received more than 20 inches of precipitation — an amount that Turlock Irrigation District utility analyst Jason Carkeet regarded as record breaking.
“Total watershed precipitation for January has been 20.07 inches. That is a new record maximum for January,” said Carkeet. “Our record goes back to 1931, and the wettest January prior to this one was in 1969 with 19.76 inches. January 1997 had 17.39 inches.”
The rainfall amount in January more than doubles the monthly historical average of 6.35 inches for the month. This total is also more than last January’s rainfall total of 9.40 inches and a drastic improvement from January 2015, which only saw 0.09 of an inch of precipitation for the entire month.
Looking at the 2017 precipitation year, which began in September, January marks the third month so far that has surpassed its historical average. In October, the Tuolumne River Watershed received 5.96 inches of precipitation, which was 4 inches more than the historical average. December surpassed its historical average of 5.94 inches as well with 7.62 inches.
With January at a close, the Tuolumne River Watershed has now received 36.65 inches of precipitation, which is 194.8 percent of the region’s historical average of 19.02 inches for the period between September and January. Carkeet said that although there are seven more months in the precipitation year, the region has “about an average year’s precipitation already in the bag.”
“Since the beginning of the precipitation year on September 1st, we have already had 36.65 inches of precipitation in the watershed, which is just over the average annual total of 36.07 inches for an entire year,” said Carkeet. “The average total precipitation for the September-through-January period is roughly 19 inches.”
Carkeet said that despite the fact that the 2017 precipitation year — especially January — has gotten off to a wet start, that does not indicate what the rest of the year will look like.
“In 1997 for example, the September-through-January total for precipitation was 44.55 inches. Nonetheless, the total precipitation for the remainder of the year was only 3.33 inches — nearly 14 inches less than the period mean of 17.05 inches,” said Carkeet.
While the most recent issue of the United States Drought Monitor summary map shows some areas in the northern part of California are no longer classified as being in a drought, and that the National Drought Mitigation Center, which produces the summary map, may at some point classify conditions in the area as no longer in a drought, Carkeet said that the issue is more complicated than that. He said that because the summary map is a complex product based on several indices, models and various metrics, the NDMC does not recommend using the U.S. Drought Monitor to infer specific details about local conditions.
“The year for our basin has been very wet so far, and Don Pedro will be full come summer time,” said Carkeet. “However, this year may be followed by several more dry years, and that would put us back in the condition we were over the past few years.”
To kick off the month of February, there is a 30 percent chance of rain after 4 p.m. Wednesday with new precipitation amounts of less than a tenth of an inch possible, according to the National Weather Service. The rainy forecast will continue into Wednesday night with an 80 percent chance of rain mainly after 10 p.m. with new rainfall totals between a quarter and a half an inch possible. There will be a 90 percent chance of precipitation Thursday, mainly before 10 a.m. and rain is likely to continue with a 60 percent chance Thursday night.