Celebrating May 15th: the unofficial end to frost season

I've been delaying writing this post so as not to jinx our progress, but I think that we're far enough into May that I can do so safely.  So, here goes.

We seem to have made it through spring without any damage from frost.

This achievement is noteworthy: we only had one other vintage in the previous decade (2005) where we didn't see any frost damage at all. Four vintages saw only minimal frost impact (2003, 2006, 2007, 2010). We incurred light to moderate damage in 2004 and 2008.  And as regular followers of Tablas Creek will know, we have suffered serious damage from frosts in two of the last three years (2009 and 2011).  Frosts are unfortunately a regular hazard in Paso Robles.  The incredible swings in temperature between daytime highs and nighttime lows mean that even days in the low 70's can potentially have frosty nights.  And it's easily capable of being warm and beautiful during February and March, which can trick the vines into sprouting in early April, six full weeks before the May 15th cutoff we consider the unofficial end of frost season.

An ideal winter, for us, would have regular rainstorms from December through March, with the non-rainy periods including nights each week that drop into the mid-20s.  The longer the weather stays frosty, the better, ideally into early April.  Then, it can warm up, with the vines coming out of dormancy in mid- to late-April.  Once that transition happens, it shouldn't freeze again.

Lo and behold, that's what happened (except that the rainstorms were less frequent than we'd have ideally wanted) in 2012.  We'll happily trade a moderate drought year for no frost, particularly after two years of good rainfall have left the soils with healthy amounts of ground water.  Looking back at the climate data, it appears that the crucial difference between this year and last happened in March, when a warm 2011 encouraged early growth, rather than in April, when that growth was subjected to frost.

	Average High	Average Low	# Nights < 35°	# Nights < 32°
March 2011	61.1°	39.1°	6	2 (3/1, 3/18)
March 2012	63.2°	35.8°	13	8 (3/1, 3/3, 3/6-3/8, 3/10, 3/19, 3/23)
April 2011	68.5°	39.0°	7	4 (4/7-4/10)
April 2012	70.0°	42.0°	6	3 (4/6-4/8)

In 2011, there was only one night between March 1st and April 7th where we dropped below freezing, and that night, March 18th, saw our weather station bottom out at 31.8°.  Compare that to 2012, when we saw below-freezing nights regularly through March, including three nights in the twenties.  These freezing temperatures encouraged the vineyard to stay dormant despite the fact that the average daytime highs were actually higher than in 2011.  So, when we saw three genuinely cold nights in early April, almost a year to the day from the devastating frosts of 2011, the vineyard was still dormant.  Then, when it warmed up, it did so conclusively, with only four nights since April 9th dropping down into the 30's and none dropping below 35°.  This 35° threshold is important because our weather station isn't in the coldest part of the property.  If the station's temperature reads 35°, it's below freezing in our coldest hollows.

What will be the impact of this frost-free spring?  Nothing but good.  We're seeing excellent vigor, though perhaps due to the slightly below average rainfall the growth doesn't seem to be excessive.  But every vineyard block, even those in low-lying areas where we're used to seeing weakness due to repeated frost damage, appears to have set a healthy balance of clusters and canopy.  The vines are amazingly regular, and we're able to leave the primary buds and remove any secondary growth in our shoot thinning.  A photo (of a Grenache Blanc block) will give you an idea of how clean everything looks:

After our cool end to winter and our warm beginning to spring, we're more or less on a normal track to flowering, and a couple of weeks ahead of the pace of the past two years.  That's a welcome development; in both 2010 and 2011 we harvested more fruit in November than September.  Now we need to hope for good weather during flowering so that our early assessments of good but not enormous yields turns out to be true, and steady ripening throughout the summer, with a minimum of heat spikes to maintain the vigor of the vines and the balance of the fruit.

But there's time to worry about that later.  As for the end of 2012's frost season, we say hallelujah.