Not Quite a ‘Miracle March’ for California

Not Quite a ‘Miracle March’ for California

Following an abnormally dry February, a pair of ‘atmospheric river’ events brought copious rain and snowfall to central and northern California between March 4-14. This resulted in reservoirs in northern California reaching or exceeding 100% normal capacity for the first time in years. Snow depths in the mountains also met or exceeded normal values for March. However, as the water year and the El Nino wind down, the overall season is ending up as just an average one, not the hoped for ‘much above’ average that was expected given the powerful El Nino that was present. Here are the details for the end of March.



The latest drought monitor report for California (made on March 29th) shows some improvement in drought conditions across the state, especially in the northern and coastal central regions. Below is the same map as it looked exactly a year ago on March 31, 2015:



Precipitation

The heavy precipitation that affected the northern two-thirds of the state from March 4th to 14th brought seasonal averages up to around normal for the central part of the state and a bit above normal in the northern locations. The mountain areas fared especially well as the 19.01” of rain and melted snow that accumulated in Blue Canyon (central Sierra) attests. Below are the seasonal (July 1, 2015 to date) precipitation totals for select sites as they stood on February 29th and how they now stand today (March 31st).





Seasonal precipitation for select sites (arranged geographically from north to south) at the end of February (top table) compared to where they now stand at the end of March (bottom table). Improvement was seen statewide aside from Southern California where the situation deteriorated.

During the past month the northern-track bias for Pacific storms continued to focus on the Pacific Northwest, as it has all season. Seattle has seen 43.33” of precipitation since their water year began last October 1st, some 156% of normal. The anomaly is much the same for Portland, Oregon as well. The storm track drifted far enough south in March to affect central California but not far enough to help the southern portion of the state. Los Angeles has only seen 6.59” of rainfall since October 1st versus a normal of 13.38” for the period (so only 49% of average).

Although April can sometimes bring heavy rain and snow to the state (see this blog I posted last April on the subject) the water season is, for the most part, over and the snowpack in the mountains will now begin its big melt. Unfortunately, it is now obvious that this winter’s powerful El Nino has come up short for California so far as precipitation is concerned. Most climatologists were confident that we would see a repeat of the 1982-1983 and 1997-1998 events that brought much above normal precipitation to the entire state. The silver lining is that the far northern region where the state’s most important reservoirs are located, did see above average precipitation and are in relatively good shape (capacity-wise) at this time.

Reservoirs

As mentioned above, northern California has enjoyed an abnormally wet winter and the state’s two largest reservoirs, Lake Shasta and Lake Oroville, are, for the first time in almost four years, at or above their historical levels for March 31st.





March saw heavy precipitation in northern California increasing Lake Shasta’s capacity from 83% on March 1st to 109% on March 31st. Likewise, Lake Oroville went from 75% to 113%. Folsom Lake was forced to release water during the month due to over capacity (a controversial move). Above are maps of reservoir capacities as of the end of February (top map) compared to the end of March (bottom map). Maps provided by the California Department of Water Resources.

Snow Pack

Heavy snowfall blanketed the central and northern Sierra during March. Sugar Bowl Ski Resort (near Lake Tahoe) reported an astonishing 125” of snowfall between March 5-14 at the 8,300-foot level on their slopes. However, despite the big snows, the snowpack and its water content remains below average as of the end of March at 87% of normal.



Snow pack water equivalent as of March 31st shows a range from 97% of normal for the date in the northern Sierra to just 72% of normal in the southern Sierra. Map provided by the California Department of Water Resources.

Although this is a bit discouraging it is a huge improvement over where we stood last year at this time when the statewide average water content of the snowpack was a miserly 5%.



California snowpack water content by region this season (thick blue line) compared to last season (thin blue line—the lowest on record) and during the big El Nino season of 1982-1983 (the highest on record). The pale blue shaded area is the average. Graphs provided by the California Department of Water Resources.

Summary

As the water season draws to a close the bottom line is that it was not a remarkable one if not at least adequate. State officials plan to be more generous with their water allocations this year for agricultural concerns but it is likely that drought emergency conservation efforts will continue unabated for the foreseeable future. Of course, in the long term, the situation is still as grave as ever with ground aquifers almost depleted. A single ‘normal’ rainy season is not going to mitigate this issue.

Christopher C. Burt
Weather Historian