Kevin Myatt is The Roanoke Times' weather columnist.

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Follow the bouncing ball of heat.

Much of last week, the central United States experienced the core of the heat. Temperatures soared above 100 from the Rio Grande to the Canadian border, and beyond.

But things have shifted this week, and the cauldron of intense heat has moved to the western U.S., where locations all the way to the very coast of the usually cool, damp Pacific Northwest are experiencing roasting temperatures above 100 not often seen.

If it seems to you that it's the same heat wave as last week that merely changed addresses, you're largely correct.

Following the weather pattern in July and August is usually as simple as following the big ridge of high pressure and its lethargic movements over the U.S.

In summer, the main jet stream, which divides cool polar air from warmer subtropical air, retreats to the U.S.-Canada border area, sometimes well north into Canada. Without this 100-mph-plus river of air to steer things around, vigorous storm systems to stir the air are few and far between.

This often allows one particular area to heat day after day, frequently over an area of dry soil, like the Great Plains have been for several months. This mass of hot air, rising many miles in the atmosphere, usually becomes the key player in the U.S. weather pattern through midsummer.

Late last week, the "heat dome," as this mass of hot air with a high-pressure ridge is often called, shifted westward. A high-pressure system rotates clockwise in our hemisphere, so as it shifted westward, the clockwise flow around it began to pull cooler air down from Canada into the eastern U.S. and eventually even into the parched and baked central U.S.

As a general rule, if one side of the U.S. is unseasonably hot, the other side of the nation is unseasonably cool. This has to do with the rises and dips in the jet stream. If the jet stream is rising up over a ridge of high pressure in the west, it's probably dipping southward in the east.

The jet stream dipped all the way into the Ohio Valley over the weekend. This propelled a rather strong cold front well to the south, pushing away the heat, but also triggering mighty thunderstorms.

We've had some rather cool mornings after this turn of events, with lows in the mid-50s to near 60.

Slowly, this week, the high-pressure ridge that has been bringing excessive heat to the far west will shrink and also begin to build back toward the middle of the country.

One thing we have not seen this summer is the core of the hot air dome set up shop in the eastern U.S. Even when we started getting hot last week, we were on the eastern fringe of the high-pressure ridge, and it didn't take much to erode it as our mini-heat wave broke at midweek.

I would not be surprised to see the heat ridge build strong again over the central U.S. in the next couple of weeks. The ground and vegetation are extremely dry in much of that region, so turning it into an oven won't take long.

And once it does that, the potential is there for it to expand east again.

I think our chances are 50-50 that we'll have one day in August that becomes Roanoke's first 100-degree day in seven years.

See the latest tidbits on weather, locally and nationally, on Kevin Myatt's Weather Journal blog at blogs.roanoke.com/weatherjournal/