The bet's on rain by mid-October

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In the blink of a dust-filled eye, a full chill that broke records on several consecutive nights last week chased out what was left of summer in the Walla Walla Valley.

Though your forecaster knows only too well he is only as good as his last correct prediction, he was obliged (only somewhat grudgingly) to accept the plethora of plaudits that came his way for his uncannily accurate prognostication.

But in the spirit of full disclosure, he must admit the Nostradamus-like qualities frequently ascribed to his predictive abilities have on occasion not expressed themselves quite as correctly as they did in last week’s forecast.

To be sure, there are more than a few (former) friends and acquaintances who still persist in harboring some silly grudge against him for having touted so heavily a can’t-miss investment of their hard-earned life savings with a fellow named Madoff a few years back. Still others are only too quick to remind him of the election-eve call he made back in ’88 for a Dukakis landslide — though the candidate admitted the risibly clownish photo of him perched in a tank turret sporting a gunner’s helmet did him no favors with the electorate.

Nor did last week’s predicted outbreak of cold Canadian air bode well for our local grape growers. Under conditions that maximize radiational cooling — clear skies, light winds and low relative humidity — temperatures plummeted rapidly after sunset to record low levels at many locations in the Walla Walla appellation. The chilling provided both a serious headache and an excellent object lesson for growers and vineyard managers as to the potential hazards of practicing their craft on the often unforgiving hard edge of southeastern Washington viticulture.

As usual, it was almost always a question of elevation.

Cold air, being denser and heavier than warmer air, tends to flow like water from high spots to low. Those who had vineyards with some elevation and a slope that allows for cold air drainage into surrounding lowlands emerged relatively unscathed as minimum temperatures in most of those locations remained at or just above critical levels.

Those who were on the receiving end of that drainage, however, bore a serious burden as readings dropped into the low- and mid-20s on a few of those icy nights. Fruit froze and leaves crisped, putting an abrupt end to what had been a gloriously benign season up until then and forcing growers to scramble to salvage what they could from damaged plants.

Sunday morning’s temperatures were perfectly illustrative of this elevation-related phenomenon. At 5 a.m. the thermometer at an automated weather station just south of Touchet (elevation 518 feet) hovered at a frosty 25 degrees while a scant five miles or so away over the state line in Oregon at Butler Grade (elevation 1,789) the reading of 44 seemed positively toasty by comparison.

One need not venture to Touchet to observe such an occurrence. Right here in town, the difference between the temperature at the Walla Walla Regional Airport (elevation 1,204) and College Place (elevation 791) is frequently on the order of 8 to 10 degrees on clear, calm nights — particularly during the spring and fall.

But back to prognostications. Our below normal temperatures should modify slightly this week, though minimum readings will remain on the chilly side as high pressure continues to be the major player over the Pacific Northwest.

This persistent high is responsible for the increasingly distressing lack of rainfall in the state over the past two months. Several locations in southeastern Washington have recorded zero percent of their normal precipitation for August and September — including Dayton, the Whitman Mission and Walla Walla’s officially recorded .01 inch of wetness, which hardly qualifies as a drought-buster.

Though our grape growers would dearly love to make it through the current month with little or no rainfall — your forecaster included — others are beginning to despair of the extreme dryness. Fortunately for the latter, the medium-range models are hinting at a possible breakthrough of a moister westerly flow off the Pacific at the end of the week or over the coming weekend.

However, as usual, the two models used for such purposes are squabbling like ill-paired college roommates. The Global Forecast System is the faster and more robust, with the putative system while the European Centre for Medium-Range Weather Forecasts model the slower and weaker.

Let’s go with the ECMWF on this one and call for some increasing clouds late Friday into Saturday with a miniscule chance of rain. The week of Oct. 15 now looks like a much better bet for something more substantial.

Nostradamus says.

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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