Cold Canadian air visits Valley, decides to stick around for a while

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Winter arrived early this year for the Walla Walla Valley as a strong Canadian cold front brought a frigid air mass to the Lower 48, plunging our local temperatures to some 10 to 15 degrees below normal for the date.

For the last several days, highs have been confined to the mid- and upper 30s, with lows in the teens to low 20s — except in some of our colder locations to the west of town, where single-digit readings were recorded on several nights.

These temperatures, while uncomfortably chilly for most, pose no threat to the Valley’s grapevines, which have slipped into their dormancy by this time of year. In fact, the unusually cold weather will promote their increasing tolerance to even colder weather that might occur over the next two months or so, by encouraging them to go into an even deeper dormancy than they currently enjoy.

Most of our local grape varieties are fairly tolerant of temperatures down to zero or a few degrees below. There are a few notable exceptions, like merlot, which does not care for that sort of weather at all. If the 16-day Global Forecast System outlook issued yesterday is accurate (and we have already seen how debatable that may be), our local merlot vines and others may get a real test in about 10 to 12 days or so — but we are getting a bit ahead of ourselves here.

A large dome of high pressure has put a cap over the Walla Walla Valley in the form of an inversion, whereby cold air is trapped at the surface with warmer air aloft, contrary to the normal state of the atmosphere. Thus, higher elevations have actually enjoyed warmer afternoon temperatures over the last several days than those of us on the Valley floor. This inversion does not allow for the normal mixing of the atmosphere through the usual convective processes, which helps explain why the air has become increasingly polluted with particulate emissions since last week and visibilities have dropped. This situation will not improve until the air that is trapped near the ground gets mixed out by some incoming system that will stir up the atmosphere, and thus eliminate the inversion. It appears as if this might happen by Wednesday or Thursday, when a fairly weak impulse might provide just enough wind to restore the atmosphere to its normal state.

The influx of cold air was responsible for a variety of nasty weather nationwide as it teamed up with a broad swath of Pacific moisture to bring copious rains to Southern California, Arizona and New Mexico, while dumping a mix of snow, sleet and freezing rain over the higher elevations of those states as it moved out of the southern Rockies into the southern Plains. It might even play havoc with preholiday traffic as it makes its way through the Gulf Coast states and swings up to the Northeast, where inland regions might get a taste of some icy weather just before Thanksgiving Day.

Locally, there will be no such issues to mar the holiday, which due to its rare coincidence with Hanukkah has this year taken on the name “Thanksgivikkuh.” Because of the idiosyncrasies of the Jewish calendar, which is based on lunar cycles, it is most unlikely that such a coincidence will occur again, barring any future revisions in that calendar. Therefore, your ever-expanding forecaster will forego the mashed potatoes this year in favor of a heaping platter of potato latkes — which is not a bad trade at all.

Fair weather on Thursday, with slightly warming temperatures into the mid-40s, will allow for a reasonably comfortable after-meal walk to help burn off some of those calories. Rain does not return to our forecast until perhaps late Saturday or Sunday. The aforementioned bone-chilling cold does not show up in the 16-day forecast until the following weekend (with lows down to minus 8!), but the unreliability of this model, especially as it gets out to the end of its forecast period, is a well-known fact.

Happy Thanksgiving to all!

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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