Due to the weather, some customers may experience late delivery of The Roanoke Times. We apologize for the delay.
Wednesday, October 16, 2013
This week would be a good time to dig the winter clothes out of the closet and make preparations to protect tender outdoor plants.
A winterlike weather pattern appears poised to bring the season’s first significant cold weather to Southwest Virginia over the next couple of weeks.
A few locations, mostly west of Interstate 77, have had some patchy frost on a few mornings already this fall, but the developing pattern appears likely to paint frost on pumpkins across the whole region by Halloween. Also, don’t be surprised if there is a round or two of mountain snow showers as well.
The pattern developing involves strong high pressure building across the eastern Pacific Ocean and western North America, as far north as Alaska.
This in turn will dislodge cold air near the Arctic Circle, where additional high pressure also will be pushing outward. This cold air will center in eastern Canada, much farther south than what is normal for late October.
Additional high pressure over Greenland may act to further trap the cold air. The strength and location of these high pressure systems will determine the duration and intensity of the autumn cold-air invasion.
Early indications are that we could eventually have some days with lows in the 20s and highs struggling to top 50 by the last week of October, but any forecast model projections this far out are subject to great variation.
Certainly, a period of below-normal temperatures — normals generally run in the 60s for highs and upper 30s to mid-40s for lows in the latter half of October — appears likely.
The cold snap won’t set in quickly. A cold front pushing through our area on Thursday will bring some showers, followed by temperatures near the seasonal norms. A second front over the weekend may bring a bit colder weather by early next week, the leading edge of the projected colder period.
By itself, a push of cold air at the end of October means little for how the subsequent winter will play out.
Each of the past two years had substantial cold shots near the end of October, but turned out quite different — the 2011-12 winter was one of the region’s warmest on record, while the 2012-13 winter started mild and turned cold at the end, lingering into spring.
Many locations west of Roanoke experienced frost into mid-May this past spring, and snow covered our ground as late as April 4. So the time since the last period of cold air is much shorter than we’re usually talking about before the first potential cold snap of fall, with very few truly hot summer days in between.
The coming shot of cold is also a reminder to start taking a look at what the winter ahead might bring. There’ll be more on that — and a chance for you to take your guesses — in the days and weeks ahead.
Weather Journal runs on Wednesdays.
Weather JournalMidday update: More ice likely later