Kevin Myatt is The Roanoke Times' weather columnist.

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While we were simmering in our hottest day in three years on Monday, something else was cooking in Michigan that would eventually change the meteorological complexion of that day.

Click graphic to enlarge

A cluster of strong thunderstorms erupted. Carried by northwest winds at different layers of the atmosphere circulating around the massive hot high pressure system in the central U.S., the storms began moving to the southeast.

By the time the storms were in Ohio, the storm cluster -- known as a mesoscale convective system, or MCS -- had developed a bow shape on radar. This "bow echo" formation is nearly always the signature of powerful straight-line winds in a thunderstorm complex, as the wind velocity pushes the middle part of the storm lines ahead of the edges. Widespread reports of damage in Ohio confirmed the presence of high winds.

But this rapidly moving complex didn't stop there. It roared through West Virginia, by this time pushing a wall of wind many miles ahead of the actual thunderstorms. This wall of wind, called an outflow boundary or "gust front," kept racing southeast through West Virginia, downing trees and power lines with winds exceeding 60 mph in many places. Even as the thunderstorms themselves began to die, the gust front kept moving southeast.

So by sunset of that hot Monday, the gust front crossed the West Virginia line into Virginia, continuing to knock off tree limbs.

Then, the cool air of the gust front hit the hot, humid air parked over the Shenandoah Valley. The cool air undercut the warm air, lifting it into the sky like a plow blade. Cumulus clouds quickly bubbled toward the stratosphere. A new line of thunderstorms, thin but powerful, quickly formed along the leading edge of the gust front.

In effect, the storm cluster in Michigan and Ohio had replicated itself, on a smaller scale. The bow-echo MCS of hours before had sprung off a "Mini-Me."

This new line of thunderstorms slammed into the Roanoke Valley with high winds and dramatic cloud-to-ground lightning about 8 p.m. on Monday. There was a little rain, too, but it blew through so fast it was hardly noticed. It was the tree-crashing, power line-breaking wind that got everyone's attention, and put thousands in the dark -- and in the stifling heat of houses without air conditioning for the 95-degree day ahead.

So, that was how Monday, July 25, turned into a one-of-a-kind day in Roanoke with a 97-degree high and a 54-mph wind gust. Those were official readings at the Roanoke Regional Airport. The day may have been a little hotter, and the wind a little stronger, at your house.

Monday's storm reports: spc.ncep.noaa.gov/climo/reports/050725_rpts.html

That's hot

Though Roanoke's hottest day was Monday, the short-but-sultry heat wave peaked on a statewide level on Wednesday.

Franklin in southeast Virginia hit 108 officially on Wednesday afternoon. That was only two degrees short of the all-time state record high of 110, set at Balcony Falls in Rockbridge County on July 15, 1954.

Melfa, in the middle of Virginia's Eastern Shore, reported a heat index of 126 on Wednesday. Melfa's high was 104, so presuming the highest heat index occurred at peak heating, that heat index would have required a dew point of between 79 and 80 degrees.

But alas, it's over, at least for now. A strong cold front, unusually strong for this time of year, began slicing into the heat Wednesday evening. Some of you got some more gusty thunderstorms on Wednesday. We'll be getting off and on showers and thunderstorms, along with daytime highs in the 70s and 80s, through the weekend.