When vines face frost, answer blows in wind

A Walla Walla Valley vineyard warms in the sun, but grape buds could face harm should there be an early-spring return to winter-like weather.

A Walla Walla Valley vineyard warms in the sun, but grape buds could face harm should there be an early-spring return to winter-like weather. Courtesy photo by ESTHER WOFFORD


Recent email brought multiple missives from several regular readers of The Weathervine, many of whom were all too eager to share their own personal top-10 plague lists. A discouraging number of them included an item regarding “wise-acre weathermen who don’t confine their remarks to matters meteorological,” or something very similar.

In view of these comments, this column will henceforth deal solely with the adiabatic lapse rate, occluded fronts, orographic lifting and other such topics that invariably elicit barely stifled yawns and a blank stares among students in his Weather for Viticulturists class.

Last week’s delightfully mild weather saw afternoon temperatures climb into the mid- and upper-60s for a few days and prompted many of our Walla Walla Valley vines to exhibit initial signs of awakening from their long winter slumber. That has given way to something more seasonable following the passage of a sharp cold front on Saturday evening which shaved a good 10 to 15 degrees off those readings on Sunday.

That’s a good thing, because an early bud break in the vineyard is one of the viticulturist’s most enduring seasonal worries as newly broken buds are highly susceptible to damage from frost. The earlier that buds push, the more risk there is to the tender new growth — a risk that will persist until late April in our area.

Our recent mostly rainless trend adds another worrisome component to the frost threat, for rainless skies are often cloudless skies. And it is on clear, calm nights that the threat of frost is at its highest as heat absorbed during the day escapes into the atmosphere unimpeded by a cloud “blanket” that might help trap warmth closer to the ground, where it might moderate an otherwise frosty night.

A severe frost can be absolutely devastating to grapevines whose new green growth can be lost to such a night as water in plants freezes and expands and ruptures cell walls, leaving a wilted, necrotic mess in the light of the following day.

Grape buds contain three distinct growing points, each of which is capable of producing a shoot. Unfortunately, once the primary — and most fruitful — shoot is lost, the secondary shoot, which will likely burst forth once the primary is lost, will provide only a fraction of the fruit primary shoots would have supplied.

If both the primary and secondary are lost, the tertiary will grow, but it will be fruitless and the entire crop will be lost as vines have but one opportunity per year to produce grapes.

This is why your sleep may be interrupted on any given night in late March or April by the unmistakable sound of big engines driving tall vineyard fans whose sole purpose is to stir up the air so that enough of the warmer air aloft is mixed with the colder air near the ground. The action is intended to keep the ambient temperature in the vineyard just above the critical damaging point.

There does appear to be some much-needed rain in our immediate future. March has offered a rather slender 0.21 inches of rain so far in a month that normally sees over 2 inches at the airport.

A warm frontal passage on Tuesday afternoon will kick off the first shot of precipitation followed by more rain and wind as the trailing cold front breezes through the region on Wednesday. Rainfall from these fronts may total a quarter of an inch.

High pressure will build back over southeastern Washington on Thursday and Friday followed by a chance of more rain this coming weekend.

Regrettably, the models are in considerable disagreement over the possibility of rain, with the GFS much more bullish on wet weather than is its European counterpart.

But as far as we know, there is no truth to the rumor making the rounds that North Korean crazy-man Kim Jong Un is making attempts to manipulate the West’s weather in retaliation for sanctions placed on his country for recent multiple missile launches and nuclear weapons tests.

An always reliable source — Dennis Rodman — who a few weeks ago kept company with Kim, has confirmed that no such activity is taking place there.

A lifelong fan of both the weather and the Baltimore Orioles, Jeff Popick is an instructor at the Center for Enology and Viticulture Center at Walla Walla Community College and manages the school’s teaching vineyard. Send your questions and comments to him at jeffrey.popick@wwcc.edu.


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