KYLE GREEN The Roanoke Times

A man surveys the damage done by trees downed in the 2700 block of Jefferson Street in Southwest Roanoke after a tornado moved through Tuesday night.

Kevin Myatt is The Roanoke Times' weather columnist.

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Is it possible that Roanoke will follow up its first confirmed tornado in 34 years with its earliest 100-degree day in 77 years?

Yes, it is possible. It's even more likely that some daily record high temperatures dating to the Great Depression or even to World War I will fall during the next week.

A major, potentially historic, early June heat wave is headed for much of the East, including Southwest Virginia.

A high pressure system -- a huge mass of stagnant, hot air -- is building in from the south, and it will park for the next several days.

The hot weather is following a warm front that moved northward through the region on Tuesday.

That warm front probably played some role in Tuesday's tornado, providing a focusing mechanism for different air masses to clash over the region, enhancing severe thunderstorm development. By pushing well north of the area, it also kept severe weather away from us on Wednesday.

Wednesday's high vaulted to 92, the first 90-degree day of 2008. Thursday followed with a high of 93, after a morning low of 75, by the far the warmest for any June 5 on record.

Highs in the mid- and upper 90s are expected in Roanoke most days through at least Wednesday. That would put us close to record highs on any of those days, all of which date to between 1914 and 1939. Blacksburg's record highs in the upper 80s and low 90s for those dates are also likely to be challenged.

If we get that close, a high of 100 can't be ruled out in Roanoke.

Roanoke's earliest 100-degree temperature was on June 3, 1936, so that record is safe.

But, since Roanoke's official weather record-keeping began in 1912, there are no other dates on which 100-degree highs have been recorded between June 4 and June 19. The second earliest 100-degree high temperature was on June 20, 1931.

So a heat wave of this caliber may not be entirely unprecedented, but it is certainly extraordinary. You have to go back to 1999 just to even find a few days in the mid-90s this early in June.

Humidity levels will vary, but could be high enough on some days for heat index values in the danger range of 105 degrees or higher.

So much heat and humidity means that there will be lots of fuel to fire thunderstorms. But the warm air aloft will likely block most of the updrafts needed to create such storms.

The mountain ridges west of Roanoke will have the best chance of seeing a stray thunderstorm develop during the heat wave. The storms will be isolated, but could be intense over small areas for a few minutes, providing a quick blast of heavy rain and gusty winds.

For the most part, though, this is going to be an extremely hot and dry period that will exacerbate our long-term drought, and could make outdoor activities dangerous.

There is no clear sign when the hot weather will break.

Heat waves and drought often become a vicious cycle. Heat dries the surface out, and a dry surface intensifies heat by withering heat-absorbing plants and radiating collected heat in the dry ground. The less heat that's used up in evaporating ground moisture, the more that's available to heat the ground and air.

Plus, with the jet stream retreating northward this time of year, large domes of hot high pressure are hard to dislodge.

The dog days of summer are a couple of months early.

Last word on the tornado

Looking at weather balloon data from Blacksburg early Tuesday evening is quite revealing as to how a supercell thunderstorm and a tornado occurred over Roanoke.

On our annual Plains storm chase, a key factor we look at is helicity, which is the ability of the air to move upward in a spiral. A helicity reading of 250 meters squared per seconds squared is considered to be indicative of a significant tornado threat.

The helicity over Southwest Virginia on Tuesday about 7 p.m. registered a startlingly high 712.

Winds were out of the south-southwest at the surface, out of the southwest up a little higher, then out of the west at the next layer, and finally out of the northwest at the highest level. This is known as a "veering profile," in which wind direction changes slightly with height. It is very conducive for the development of rotating thunderstorms and tornadoes.

Tuesday's atmosphere was not very unstable, which means there wasn't a steep temperature difference between a warm lower layer and cooler upper layers.

The wind dynamics compensated for the limited instability.

If it had been more unstable, we could easily be cleaning up from some roof-removing EF-2 tornadoes instead of the tree-toppling EF-0 twister that happened.