The Rare Time When a Rainy Forecast is Unwelcome
April 01, 2015
Overall, we've had a warm spring. In an environment where winter freezes are normal perhaps one third of the nights between December and February, we saw just four below-freezing lows in January and three in February. March saw only one night drop below freezing at our weather station, and that was March 1st. Since March 10th, we've only seen four nights drop into the 30's, none below 38°. The result of all this mild weather has been an early budbreak.
It has been dry, too. Happily, November and December got us off to a good start on our winter rain, but January (0.23 inches total) and March (0.02 inches total) were very dry, and February (3.92 inches) only average. So far for the winter, we've tallied a little over 13 inches of rainfall, which is better than the last few years, but still only about 60% of normal.
So, you'd think that today's forecast, which calls for a series of troughs to dig down south into California and bring likely precipitation next week to our area, would be welcome (image from the US Navy's Fleet Numerical Meteorology and Oceanography Center):
You'd be wrong.
Not all rainfall in April is bad. Last year, we got about an inch and a half of rain right at this time of year for which we were grateful. It came as part of a tropical system that raised humidity levels and dew points, from the south Pacific, not from the Pacific Northwest. Next week's forecast storms are going to be much colder, sliding down from Alaska and bringing with them a much colder air mass aloft. We should be fine while there is cloud cover, but it is in the aftermath of April storm systems like these that we've seen damaging frosts in 2001, 2009 and 2011. Those 2011 storms were so cold that they produced hail and snow at the vineyard during the day:
The cold April nights that followed (both April 8th and April 9th, 2011 got down into the low 20s) cost us, we estimate, something like 40% of our crop from the 2011 vintage. And we had later budbreak that year; Mourvedre and Roussanne were relatively unaffected because they were still mostly dormant. A similar event this year, with even our late-sprouting Mourvedre out around the property, would be devastating.
We're still hopeful that we won't see significant damage this year. The air mass in that 2011 storm was so cold that even at the tops of our hills were several degrees below freezing. That's rare. No one is yet talking about a cataclysm. And there are still several days before these systems arrive, and if this spring has taught us anything, it's to be skeptical of long-term forecasts that predict rain. But we've been lucky the last two years to avoid frost entirely despite our earliest-ever budbreaks. With the increasing agreement about these storms among different weather modeling systems, it seems like we'll face our first real test of the year.
Fingers crossed, please, everyone.