Kevin Myatt is The Roanoke Times' weather columnist.

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A funny thing happened on the way to a midsummer heat wave: A touch of autumn broke out.

Historically, this past weekend, July 20-23, is the warmest of the year. Roanoke's normal high for those dates is a few decimals above 87 degrees, the normal low around 66. Blacksburg's normal high is 83, its normal low 60.

Instead, Roanoke's highs were close to 80, and its lows in the upper 50s to near 60. Blacksburg got no higher than the upper 70s, with lows in the lower 50s. Blacksburg tied a record low Monday at 50 degrees, equaling the record set July 23 five years ago. Roanoke was 3 degrees off a record low Sunday morning, when the low was 58. Some more outlying areas saw lows in the 40s.

And then came Tuesday, when clouds and rain kept temperatures below 70 most of the day.

Summer has definitely been short-circuited for a few days. And a heat wave that was expected to envelop the northern United States and eventually spread through much of the East may be fizzling as well.

First, a strong cold front for this time of year was pushed southeastward through the area late last week. Cool, dry air from Canada moved in behind this front. That had been expected for several days beforehand. It appeared as if this cool air could last only a few days before typical heat and humidity once again took over, possibly leading toward a significant heat wave by next week.

But then, an upper-level low -- a counterclockwise swirl of cold air several thousand feet up in the atmosphere -- got stuck spinning over our heads.

That was not entirely expected. Some computer forecast models began catching on to the possibility a couple of days before it happened, but it wasn't a slam-dunk that it would occur.

This upper-level low has become a "cutoff low," which means that it has become separated from the jet stream, the main channel of winds high in the atmosphere that steers storm systems.

The jet stream dipped southward to bring us cooler air over the weekend, but then pulled quickly back over Canada, where it's supposed to be this time of year. Before it did, enough strong winds moved south through the jet stream to break loose a swirl of cold air over us. With the jet stream back in Canada, the upper-level low has nothing to really push it anywhere, so it's just been spinning in place.

It has kept unseasonably cool air in place at the surface. In the past couple of days, it also has allowed for the development of showers and thunderstorms as very modest warming helps bubble gradually increasing humidity into unusually cold air aloft.

Now, this upper-level low is doing something really weird: It's drifting west, toward the Ohio Valley, opposite the typical flow of the weather pattern.

This rogue weather feature will have some effects not foreseen just a few days ago.

For one, with it continuing to spin as it moves to our west, it will start sweeping southwest winds into our area. That will bring Gulf of Mexico moisture, so our chances of rain, looking dismal a few days ago, are quite good many days this week. That could help us some with our long-term dryness, though it probably will not be a remedy for a long-term issue.

Secondly, the upper-level low is acting as a roadblock to keep a hot dome of high pressure from spreading eastward as had been expected. Through at least the first half of next week, extreme heat will have trouble advancing any farther east than the Dakotas.

Eventually, the upper-level low will slowly spin itself out. Gradually, by early next week, we'll get back to more typical summer weather with temperatures in the mid-80s to low 90s, lows in the 60s to low 70s and daily doses of scattered showers and thunderstorms as humidity keeps building. But the intense heat, with highs challenging 100, will be stymied.

Whether it's a heat wave denied or merely delayed, we'll have to wait and see.