Each winter, we wait to hear the words "the storm door is open". What this means is that the jet stream, which brings weather systems across the pacific toward North America, has dropped far enough south that the moisture it contains streams over California instead of over the Pacific Northwest. If we're really lucky, we start hearing terms like "Pineapple Express", which means that the more southerly flow of the jet stream has drawn a plume of tropical moisture up from the warm waters around Hawaii, supercharging the air currents as they pass over the California coast.
If you take a look at the most recent water vapor map from NOAA (or, even better, view the animations on the always fascinating NOAA Web site), you'll see that the storm door is open, and the Pineapple Express is barreling into California as we speak:
The rainfall we're expecting just over the next two days should have a measurable impact on our annual totals and on our local drought. Also from the National Weather Service (in this case, their Twitter feed), the 48-hour rainfall predictions:
It's encouraging that this rain is going to stretch across all of California, unlike a couple of recent storms that have mostly hit in the north.
And, even better, this is just one of a series of storms that are lined up across the Pacific, which the southerly jet stream is poised to aim at us in sequence. After this storm (3-4 inches predicted) we're forecast for another inch or two on Monday, another decent storm Wednesday, and a third next weekend. If all goes as planned, we'll have accumulated somewhere around 15 inches of rain by the end of the month, which would give us a huge head-start toward the wet winter we've all been hoping for.
Last winter, which was one of the driest on record in California, saw an exceptionally resilient ridge of high pressure over the south Pacific. This ridge diverted the jet stream and all its associated moisture further north, soaking the Pacific Northwest and leaving California in its shadow. It wasn't until March that this broke down, at which point there just wasn't enough time for the state to make up the rainfall deficit. We feel fortunate that we did get seven inches of late-season rain; it made the difference between the 2014 vintage being very dry and it being potentially catastrophic. But that doesn't make us any less happy to hear about this particular open storm door. Bring it on.
Meanwhile, if you're interested in keeping up with what's going on here, I highly recommend you follow John Lindsey, the meteorologist for our local utility PG&E. His Twitter feed is my go-to source for local forecasts, maps and updates.