A shelf cloud marks the leading edge of a band of storms at Fincastle on Monday, Sept. 21. Streaky storms dumped locally heavy rain, while missing others, typical of much of the mid to late summer into early fall in western Virginia. Courtesy of Daniel Argabright.
A shelf cloud marks the leading edge of a band of storms at Fincastle on Monday, Sept. 21. Streaky storms dumped locally heavy rain, while missing others, typical of much of the mid to late summer into early fall in western Virginia. Courtesy of Daniel Argabright.

So quickly, cool-season catchwords like cold-air damming, overrunning moisture and even a nor’easter are part of our regional weather scene that hadn’t previously been willing to let summer go.

A week ago, it looked like this would be another unseasonably warm week with only spotty storms for Cardinal News’ Southwest and Southside Virginia coverage area. But some hints of a coastal low and push of cooler air from eastern Canada down the east side of the Appalachians began coalescing into more consistent signals, and ultimately model forecast consensus that we are seeing come to fruition in the atmospheric reality around us for a few days.

In the long range, we haven’t turned the corner into full-fledged fall yet, with the overall atmospheric pattern still likely to tilt a little warm in weeks ahead, Also, there is as yet no indication of frequently recurring general rainfall. Even this one, with some potential to be that, has turned out underwhelming for some locations while others have gotten a nice and still much-needed soaking.

Hold on to thoughts of cooler weather being here to stay -- odds tilt to warmer than normal temperatures over most of the U.S., most strongly in the East, as September flips to October. Courtesy Climate Prediction Center, NOAA.
Hold on to thoughts of cooler weather being here to stay — odds tilt to warmer than normal temperatures over most of the U.S., most strongly in the East, as September flips to October. Courtesy Climate Prediction Center, NOAA.

But for now, a few days of genuine autumn weather have broken out, with damp coolness on this Wednesday and a nice weekend of 40s and 50s lows and 60s and 70s highs ahead.

You may have had to root through your closet to find a jacket for the first time in three or four months.

All of this is the result of the combined flow of an offshore “nor’easter” low and high pressure oozing cooler air down the east side of the Appalachians from the northeast.

A nor’easter is called a nor’easter because its counterclockwise circulation and track along or parallel to the East Coast circulates northeast winds along the coast and points inland. That northeast fetch is typically a chilly one, moist closer to the low, but pulling down cool, dry air farther away from the low center as the wind flow turns more northwest.

Dark clouds mark the arrival of wetter weather early Tuesday, Sept. 22, at Baywood in Grayson County. Courtesy of Patrick Butler.
Dark clouds mark the arrival of wetter weather early Tuesday, Sept. 22, at Baywood in Grayson County. Courtesy of Patrick Butler.

This one is going to meander a bit off the Mid-Atlantic and New England coast. It may end up placed in the just the spot for a windy, rainy day in Boston on Saturday when Virginia Tech plays Boston College — while Blacksburg has a picture-perfect dry early fall day, each resulting at least in part from the nor’easter.

High pressure in southeast Canada is acting in tandem with the low, pressing a cool wedge of air along and east of the mountains, a process we often call “cold-air damming.”

This isn’t as hard set a cold-air damming pattern as we can see in the winter with high pressure built all the way across southern Canada and the northern tier of the U.S., but it has been enough to bring a chilly, damp Wednesday, the kind of day stuck in the 50s and lower 60s we haven’t seen since May.

The blue colors shows 50s and 60s temperatures expected for Wednesday, and also clearly mark how a cold-air damming wedge oozes down the east side of the Appalachians with warmer temperatures surrounding it on three sides. Courtesy of National Weather Service.
The blue colors shows 50s and 60s temperatures expected for Wednesday, and also clearly mark how a cold-air damming wedge oozes down the east side of the Appalachians with warmer temperatures surrounding it on three sides. Courtesy of National Weather Service.

We have also had moisture lifted up and over the cooler dome of air trapped against the mountains for intermittent periods of light rain and drizzle.

Some locations that got the heavier rain in streaky storms Sunday through Tuesday may get 2 to 4 inches total out of this week’s rain, but the rain has proven a little too patchy and light to really count as the widespread, soaking general rain we’re still in need of with the drought.

Getting those kinds of rains once or twice a week most of the next six months or so could entirely alleviate the drought by spring and restore most of the missing water in reservoirs and the underground water table. That is especially true once the canopy of tree leaves becomes a carpet instead, allowing more runoff as less is absorbed by plant roots and the leafy umbrella.

Mammatus clouds bubble downward on the backside of a line of thunderstorms Monday over southwest Roanoke County. Photo by Erica Myatt.
Mammatus clouds bubble downward on the backside of a line of thunderstorms Monday over southwest Roanoke County. Photo by Erica Myatt.

El Niño, the irregularly recurring warming of equatorial Pacific sea surface temperatures currently pumping toward record levels, often creates the sort of juiced subtropical branch of the jet stream that steers repeated wet storms across the southern U.S. But there can sometimes be too much of a good thing, with repeated heavier storm systems leading to flooding.

(And for now, we won’t discuss whether or not these wet storms will run into cold air for wintry wonder once the season gets colder.)

So at this stage, if you’re rooting for autumn temperatures to take hold, you can take this as a positive sign that we’re deep enough into the southward-shifting jet stream flow of fall that a cooler few days can develop fairly quickly even when it has been warm and sticky.

And if you’re wanting the rain to ease the long-term drought, this coastal low setup is at least vaguely familiar of something we often seen during an El Niño cool season, and may be at least suggestive of its growing influence.

Cooler weather is inevitable, and wetter weather is likely in weeks and months ahead.

Journalist Kevin Myatt has been writing about weather for 20 years. His weekly column, appearing on Wednesdays, is sponsored by Oakey’s, a family-run, locally-owned funeral home with locations throughout the Roanoke Valley.  

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Kevin Myatt has written about Southwest and Southside Virginia weather for the past two decades, previously...