What constitutes a “cold front” is a lot different in July than it would be in January, but one that slipped in the “backdoor” from the north has brought on some short-fused, relative relief from heat, humidity and flooding downpours.
For a couple of days, we have had highs in the 70s and 80s across Southwest and Southside Virginia, rather than the mid 80s to lower 90s, occasionally a little higher here and there, that have been common for about two weeks.
It is also less humid. The dew point — a much more stable measure of atmospheric moisture than relative humidity — has dropped from the low to mid 70s common during our recent sticky-stormy stretch back into the 60s. That’s still not exactly prime comfort, but by comparison, it is a breath of fresh air.
Temperatures will be a little hotter on Thursday and then Friday and Saturday will see some mid to upper 90s east of the Blue Ridge and into the Roanoke Valley, with mid 80s to lower 90s over most of the rest of our region. We’ll get back to why that is happening below.
Also mostly gone for now are the daily cauliflower towers of cumulus clouds, the rumbles and flashes, and the spotty downpours that have brought flash flooding to some locations while being much tamer for many others. 
Highly variable rainfall
We’ve followed the flash flood in and near Dante — pronounced “daint” — in Southwest Virginia in Cardinal News with a couple of recent articles (click here and here). Illustrating how localized the downpours have been, one reader noted that his family’s farm just one valley away from Dante had not received enough rain to significantly raise the creek level.
Similarly, Galax, an independent city along the border between Carroll and Grayson counties, has measured over 11 inches of rain 22 days deep into July, with over 7 inches falling in a four-day period last week. Rainfall topped 2 inches on two of those four days in Galax, including Saturday when there was some serious flooding in the area. But drive 45 minutes up Interstate 77 to Wytheville, and there has been only a little more than 2 1/2 inches total for the entire first three weeks of July, with no days having had more than eight-tenths of an inch.
While the moisture has been especially thick and the daytime heating sufficient to initiate the process of lifting it aloft into thunderstorms, the focusing mechanisms for storms have been a bit diffuse, based on subtle upper-level atmospheric disturbances, poorly defined fronts, outflow from storms that have already collapsed, and terrain features. So the heavy rain has not been widespread in nature, but focused in narrow bands with slow-moving thunderstorms, difficult to predict on a day-to-day basis.
The moisture and afternoon storms will start to rebuild over the weekend into next week. There may be a little more focus to their development at times, which we’ll get to below. 
Reshuffling weather pattern
It’s called a “backdoor” cold front because it swings in from the north, out of New England, rather than the more typical cold fronts that slide east or southeast from the Great Lakes and Ohio Valley across the Appalachians.
But while the front itself has brought a couple days’ relief from sticky dew points topping 70 and many highs topping 90, its occurrence also gives us a clue about a retooling of the weather pattern that may portend some of the summer’s hottest temperatures in the next couple of weeks.
The front was pushed southward by the clockwise flow around high pressure over the central U.S., an intensifying “heat dome” that looks to become a dominant feature of the weather pattern east of the Rockies for the remainder of July into early August.
Previously, high pressure situated over the Atlantic, called the “Bermuda high” for pretty obvious reasons based on its location, has been a key feature in our weather, as its clockwise flow pulled in a plume of extremely thick atmospheric moisture from as far away as the Caribbean over much of the eastern two-thirds of the nation.
This feature won’t entirely be going away, and may help renew the flow of moisture into the region by the weekend into next week. 
With more influence coming from the heat dome high to the west in days ahead, we will see periodic surges of heat expanding from it, a bit hotter in air temperature than what we’ve had with the sticky-stormy pattern.
Many of our hottest periods historically have spread over us from the northwest, not the south or southwest that would seem more logical. It’s often the case that extreme heat in Chicago is more a forerunner of similar heat happening here than would be similar temperatures in Atlanta, Nashville or Dallas.
But we may also see a few more fronts get circulated near or through area from the northwest or north, and perhaps, a better chance of organized storm clusters diving in from the Ohio Valley.
This may make some people nervous who are still shaken by June 29, 2012, but it’s important to remember that not every squall line moving in from the northwest in summer is a derecho, and even if one does meet the elusive definition of a derecho, it won’t necessarily be like THAT derecho was.
The best hope for those who are not fond of heat and high humidity is that some of these fronts can bring another brief break from the heat wave down the road. But there may be some sticky days pushing toward 100 and some big rumbly storms to go through to get to those breaks, if they occur at all.
We have a lot of summer left, with all of its flash and sizzle. 
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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. Sign up for his weekly newsletter:
