Assessing Winter 2015, So Far: Cold and Often (but not Very) Wet

This far, despite several storms that passed near or over us, and despite the historic El Niño conditions that persist in the Pacific Ocean, we haven't gotten much rain yet.  Most of the storms have seemed to peter out just north of us, or pass just to the west, or south.  Yesterday's storm dropped multiple inches of rain in Cambria, Morro Bay, and even San Luis Obispo, while we got just a trace.  I'm not sure I ever remember that happening.  Today, on the solstice, thick clouds sat over the Santa Lucia range to our west, while we spent much of the shortest day of the year in unexpected sun:

And yet, it has felt very much like winter the last month, with no warm stretches, frosts most nights, and several days that have seen at least some measurable precipitation.  So, how do the early days of this winter stack up against recent years?  It's... well... complicated.  Let's see what we can say.

It's been cold.
So, when I say cold, I mean both cold nights and cold daytime highs.  In the last month, we've had 13 nights drop below freezing.  Our average over that period (November 23rd-December 22nd) since 2009 is 8.6 freezing nights.  Last year we didn't have any in that stretch.  As for daytime highs, we've topped 70 only 3 times in the last month, and only barely, while 17 days have failed to make it out of the 50s. That 17 figure is the most going back to when the detailed weather database starts in 2009.

It's rained fairly often, but not much.
Typically, when it's cold here in Paso Robles, it's also clear.  The two other times we've hit double-digits in number of freezing nights in  this period (2011 and 2013) we had just 5 and 2 days with measurable rainfall, respectively.  This year, we've had 10 days recording measurable precipitation, but only accumulated 1.23 inches over the period.  By contrast, the other years we measured double-digit days of precipitation saw much greater rainfall totals.  The number of rainy days and the total precipitation November 23rd-December 22nd for the last 7 years: 

• 2015 (10 days): 1.23 inches
• 2014 (17 days): 7.75 inches
• 2013 (2 days): 0.58 inches
• 2012 (14 days): 6.87 inches
• 2011 (5 days): 0.34 inches
• 2010 (16 days): 9.76 inches
• 2009 (11 days): 5.40 inches

What does this all mean?
I'm not sure it means that much.  Looking at a single month is such a small sample size that it doesn't even correlate significantly with the rest of the winter.  Last winter, and 2012 for that matter, looked like they were setting us up for great rainfall -- and are really indistinguishable in this period from the wet winters of 2009 and 2010 -- only to find the storms take other paths after the new year.  2011 and 2013 saw very dry end-of-years, but we got decent rainfall late in the winter season.  So, while it's tempting to draw larger conclusions, I think it's premature. We're one month into the 5-month stretch -- starting mid-November and ending mid-April -- where there's a good chance of significant rain. We've largely missed out on the first of those 5 months.

So what's the silver lining?
The fact that we've had several nicely distributed days of light rain has meant that the cover crop has gotten a great chance to start growing, and should be in good shape to hold the soil in place when the rains do come.  A photo from this morning shows the vineyard's new soft green coat:

Other silver linings are more big-picture.  The snowpack in the Sierra Nevada is above-average for the first time in years.  The vineyard is conserving the water that it has received; the frosty nights have pushed the vineyard into full dormancy, and the cool, cloudy days have meant that very little moisture is being lost to evaporation.  And most other wine regions in the state have gotten better rainfall than we have, particularly regions to our north:

But the most important silver lining is that El Niño is still on track to produce a very wet next three months.

Anticipating El Niño
This year's El Niño, caused by elevated surface water temperatures in the South Pacific Ocean, is still on track to be one of the strongest ever.  And past El Niños haven't produced much of their effect before Christmas, but have produced Januaries, Februaries, and Marches of roughly double normal rainfall.  It's not a guarantee, but at least the right conditions are in place.  And it does feel different than the past couple of winters, when we went long stretches with clear, warm weather, produced by what meteorologists dubbed the "ridiculously resilient ridge": a persistent high pressure area that deflected the Pacific storm track well to the north of California for months at a time. The more storms that come our way, the better our chances of getting a big one.

And that would be the best possible Christmas present.