26 Feb 2014

Welcome rain expected for drought-hit California

Californians are breathing a sigh of relief, as much needed rain is expected to fall across the drought-hit state at the end of the week.

California is currently in the midst of a severe drought. In January, State Governor, Jerry Brown, declared a drought emergency across the state, following its driest year on record.

In 2013, California had just 32.8 per cent of the rainfall that it would normally expect to see, leaving fresh water reservoirs with a fraction of their normal reserves.

drought_california_g_wpSuch a dry year left the state prone to wildfires, triggered by high temperatures and lightning strikes. The flames were then fanned by the dry, gusty Santa Ana winds that the state is renowned for.

According to US drought monitor, 68.3 per cent of California was in extreme drought as of 18 February, with 14.6 per cent in exceptional drought.

us_drought_NOAA_wpWhy has it been so dry?

California relies on rain and mountain snow moving in off the Pacific Ocean, driven by the jet stream – the fast-moving ribbon of air five miles up in the sky that forms and steers areas of low pressure.

However, during the last year – especially during autumn and early winter – the jet stream has been persistently stuck much further north than usual, resulting in a blocking area of high pressure forming over the state.

This has kept the weather largely dry, as the usual train of low pressure systems travelled further northwards into western Canada, taking the rain and snow there.

How much rain is expected?

With the jet stream switching back to a more typical position, it will allow a feed of moisture from the Pacific Ocean.

This will spawn areas of low pressure which will move across south western states of the US, including California, from Thursday onwards.

The latest information suggests that much of California will have one to three inches of rainfall during the next week. Mountainous areas will receive as much as five to six inches, which will fall as snow over the highest elevations.

us_7daysrain_NOAA_wpWhilst the rain will be welcome, given the fact that the state is gripped by drought, so much rain falling on dry ground quickly may cause some flash flooding problems.

I’ll be keeping an eye on how much the forthcoming rain erodes the drought and posting updates on Twitter – @liamdutton

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