Hints of fall ahead for people, grapes

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For those of you keeping score, your slightly overconfident meteorologist had a bit of a mixed bag last week in the couple of swings he took on a supposed imminent and rather dramatic change in our hot and dry August weather.

If I may be allowed to indulge in a bit of Bill Clinton-esque word parsing, it was undeniably cooler last Wednesday (high temperature of 90 degrees) than it has been for some time. Although, to be frank, I personally was not inspired by that sort of cool-down to reach for my favorite wool sweater.

In baseball parlance, that was scored as a "scratch" infield hit.

Regarding the wetter part of that same prediction, a bad miss on an 0-2 curveball is the only way to describe the inaccuracy of that misbegotten bit of forecasting.

And so my Florida Keys retirement thing -- something about betting big at the tables if my long-odds forecast last week came to be -- must now be put on hold in favor of a more realistic plan involving working until 85 and retiring to a two-room, cold-water flat in Hoboken, N.J., supported solely by a few monthly dollars from a moribund Social Security fund.

In hopes you do believe that forgiveness is indeed divine, I ask you to permit me to offer a forecast for this coming week.

This one appears to have a much higher probability of success: our beastly hot stretch will come to an end after a round of scattered thundershowers early this week as a cool front sweeps the state from west to east. And by week's end afternoon highs in the low 80s will grace our comely environs with a welcome foretaste of fall in the air.

All this comes to us courtesy of a small southward dip in the jet stream that will allow storms passing to the north to periodically reinforce the cooler westerly flow that will govern our weather. That flow, riding up and over the Cascades, practically ensures a dry regime as air dries out as it descends from higher elevations.

Your weatherperson, for one, will be most grateful for the change -- as will our Walla Walla Valley grapevines. This recent succession of abnormally warm days has created quite a demand for lengthy, deep irrigations to retain a viable canopy of leaves capable of going the distance and remaining functional until the fruit has accumulated sufficient amounts of sugar and flavor to be considered fully ripe and ready for harvest.

In the world of agriculture, grapes have a relatively low water requirement compared to many other crops. In fact, in areas that receive 20 inches or more of rain a year, a mature grapevine can go through an entire growing season without any supplemental water, provided it has a well-developed root system.

Overwatering, however, leads to excessive vegetative growth and green, unpleasant flavors while directing carbohydrates away from the berries where they are most needed. Equally undesirable is underwatering, which results in premature loss of leaves that will make it difficult -- if not impossible -- to properly ripen the bunches that depend on plant nutrition manufactured by those leaves.

It is the vineyard manager's job this time of year to strike that magical balance between the two that allows sustainment of the canopy already in place without adding new leaves and shoot length to the vine. There are several tools that assist in tracking how wet or dry the soil is, from a simple tensiometer (a water-filled tube and gauge inserted in the ground) to a considerably more expensive "pressure bomb." The latter measures a single leaf's water tension through a probe system costing thousands of dollars and relies on the emission of neutrons from a radioactive isotope and the measurement of their speed of passage through the ground.

However, the numbers generated by these tools are virtually meaningless if not supported by one other essential tool in our possession: our eyes. Grapevines are excellent at providing visual clues to their hydration status. It is the coupling of the numbers we read on our machines with these clues that sharpens our ability to supply just the right amount of water at the proper time.

A dash of technology plus a dab of observation is the perfect recipe for a happy vineyard this time of year.

If only weather forecasting could be as reliable.

A lifelong fan of both the weather and the Baltimore Orioles, Jeff Popick is an instructor at the 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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