Los Altos Weather – Hot and Dry September

September is always beautiful in northern California — warm and dry. But this September was our the warmest month in the past three years, hotter than even our summer months. Coupled with little rain, the hot weather extends the stress on our plants during our drought.

The average monthly high temperature in my home town of Los Altos, California, was 82º in September, hotter than even our summer months for the past  3 years and 2º warmer than any other month.

September hottest month in past 3 years
September hottest month in past 3 years

In September we got almost no rain, .01″, compared to the average of .15″.

Almost no rain in September
Almost no rain in September

This combination of hot temperatures and little rain continues the water stress on our plants during our 4-year-old drought.

Drought continues

The Drought Monitor shows that drought continues for much of the American West. The brown shows exceptional drought, and the red shows extreme drought. What’s worst is that the exceptional drought includes the Sierra Nevada mountains, the source of water for most of California.

Drought continues in the West
Exceptional drought covers source of California’s water

The weather outlook for October, a dry month for California, is for the drought to “persist/intensify”.

Drought to continue in October
Drought to continue in October

Beyond October, the outlook for rain looks much better. The high-pressure ridge that has been pushing storms away from California has dissipated after four years.

The US National Weather Service is forecasting above-normal rainfall for most of California during November-February. This would certainly help, but the forecast rain won’t make up for the past 4 years.

Above-normal rain forecast for California this winter
Above-normal rain forecast for California this winter

Our local groundwater doing well

The groundwater in our Santa Clara Valley is improving this year, thanks to water conservation by our suburban water users. Since May, groundwater pumping is well below the 5-year average. Due to the drought, manage recharge of the aquifer is below the 5-year average.

Groundwater pumping below 5-year average due to conservation
Groundwater pumping below 5-year average due to conservation

The groundwater level in our valley is going up, as shown above for a Santa Clara Plain well. The groundwater has been steadily rising all year, even through the summer. The rising groundwater level indicates that the recharge exceeds the groundwater pumping this year. Note that in every other year since 2003, the groundwater level fell or stayed constant during our dry summer.

This calendar year we pumped about 30,000 AF more groundwater than we replace through managed recharge.

Pumped nearly 30,000 AF more than managed recharge
Pumped nearly 30,000 AF more than managed recharge

The other factor affecting groundwater is natural recharge, where water seeps into the aquifer through the water cycle (rainfall and runoff). Evidently the natural recharge this year exceeds 30,000 AF. Our town has only received 4.27″ of rain this calendar year, far below the normal of 10.59″.

Snowpack

Another source of water, California’s mountain snowpack and glaciers remain in bad shape. Yosemite’s largest glacier is disappearing. The Lyell Glacier “has lost about 90 percent of its volume and 80 percent of its surface area from 1883 to 2015” and “could melt and disappear in as soon as five years”.

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Published by

charley280

I enjoy travel, art, food, photography, nature, California native plants, history, and yoga. I am a retired software engineer. The gravatar is a Nuttall's woodpecker that visited our backyard.

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