‘Tempest’ brought winds, cooler temps, but relatively little rain

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Your tanned, rested and ready weatherperson is recently returned from a rejuvenating week seaside in Ocean Park, where he did some serious work on his avoirdupois with a steady diet of clam chowder and fried oysters. While he was stuffing his face, the weather world went on without him: One of the strongest thunderstorms in recent memory ripped through Walla Walla last Thursday evening, doing some real damage around town and scaring the living daylights out of just about everyone here.

A deep area of low pressure that had been circulating just off the coast for some time pumped large amounts of moisture into the state from the south. This, when combined with some robust daytime heating and the extra energy supplied by a 90-knot jet stream overhead, resulted in the formation of a line of severe storms that originated south of Pendleton and rambled north at nearly 45 miles per hour.

Its arrival here in Walla Walla was announced by the appearance to the southwest of a menacing gray-and-black wall cloud, which looked like it contained all the demons of the underworld swarming inside its malevolent core. A pelting wind-driven rain descended upon the city and the gusty outflow from the cold downdrafts in the thunderhead slashed across town. The winds brought down all manner of branches, limbs and entire trees, from College Place to the airport, as they blasted their way to the northeast, leaving a couple thousand households and businesses without power due to downed electrical lines.

The rain was of relatively brief duration and amounted to generally less than two-tenths of an inch in most locations, but the wind was epic. At the airport, a gust to 61 miles per hour was recorded just before a power failure there took the instrumentation offline. Throughout the city, a jumble of overturned garbage cans, lawn furniture and pieces of shrubs and trees littering streets and yards bore silent testimony to the ferocity of the storm. Some customers were without power until Friday as crews scrambled to fix damaged lines.

In the wake of the tempest, much-cooler air dropped Friday’s high by about 15 degrees into the low 70s for an early taste of fall, as the culpable low center continued to swirl into northeast Washington and northwesterly winds on its back side transported a drier and more stable flow into our region.

The deleterious effects of the violent weather on our local grapes appear to have been minimal. The key to the light damage was the modest amount of rainfall, which failed to thoroughly wet the ripening clusters and give fungal infections like Botrytis cinerea (bunch rot) a chance to get established, and the lack of hail, which could have easily torn open the delicate berries and exposed them to a host of further injuries from insects, birds and a range of molds and rots.

In other parts of the state, the rainfall was anything but inconsequential. In a few orographically (mountain) enhanced locations, copious amounts of rain fell, closing several major roads due to mud- and debris-slides. One such incident led to an aborted visit by your forecaster and his traveling companions to North Cascades National Park (see ubne.ws/1ewlGuK), where State Route 20 was closed indefinitely for the second time in the last four weeks as mud and rocks inundated the roadway in numerous locations. A few spots in the southern Cascades recorded rains of biblical proportions — over 6 inches in a couple of places — a real tribute to the low pressure system that contained precipitable water in the amount of two to three standard deviations above the norm for this time of year.

Our current week’s weather will be much more benign. With strong high pressure now in charge, subsiding air will warm afternoon temperatures back into the 90-degree range by midweek. These temps will continue to hover under sunny skies until late in the weekend, when a weak Pacific low approaches the region with somewhat cooler air and just a slight chance of a shower or two by Monday.

In the longer term, look for more significant cooling around Sept. 18, while the smart-money folks (those who correctly predicted WSU’s stunning upset of USC this past Saturday and a 49ers victory versus the overrated Seahawks this coming Sunday evening) are going all in on a major change to fall on Sept. 23/24, with rain and much cooler weather on tap that week.

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