Kevin Myatt is The Roanoke Times' weather columnist.

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Used by permission of Mike Hollingshead

E-mails have been circling the planet with a series of attached images, including the one displayed with this column, claiming the photos are from Hurricane Katrina in Mississippi. Perhaps you have received one of these.

I have received an e-mail twice in the last few days, each time with the same photos and words claiming they are from Mississippi. I also received the same photos via e-mail in May, long before Katrina, in a forwarded e-mail claiming the photographs were from storms near Perth, Australia.

These photos are real storm photos, excellent ones at that, but they're not from Mississippi or Australia. These photos are the work of storm chaser Mike Hollingshead of Blair, Neb., and they depict supercell thunderstorms he has photographed in Iowa and Nebraska. Without his permission, the images are being e-mailed with false claims of what they depict, and those e-mails then get forwarded endlessly.

Check out his Web site at extremeinstability.com.

DRY AIR MAKES TEMPERATURES SPREAD OUT

A summer of muggy nights in Southwest Virginia has given way to a September of warm days and cool nights.

The average low temperature for the August just past was the warmest on record in Roanoke, and the second warmest on record in Blacksburg.

This followed a July that also had the warmest average low on record in Roanoke, and tied for the warmest on record in Blacksburg.

Tropical air that flooded the area in early July hung on with few breaks until the end of August, holding the temperatures up on one muggy summer night after another. Average daytime highs were nothing special through this period.

The average low temperature in August at Roanoke Regional Airport of 68.7 degrees beat out the previous highest average August low of 68.06 in 1995. Record-keeping at the airport began in August 1948.

Blacksburg's average low temperature for August, 63.5, was a little cooler than the average August low of 63.65 way back in 1955, a little less than three years after official readings began there.

Summer, as recognized by meteorologists, ends on Aug. 31, and meteorological autumn begins Sept. 1. That's mostly a designation made out of calendar convenience, but this year, that switch of "seasons" heralded a clear shift in our day-to-day weather, as much drier air moved in behind the passage of Hurricane Katrina's remant circulation.

The most telling difference in September and the summer can be found in the wider gap between daily high and low temperatures.

In Roanoke, the difference between the high and low averaged 17.8 degrees in August, only 16.5 degrees in July and 18.5 degrees in June. But in the first 13 days of September, the difference between high and low averaged 26.2 degrees. Tuesday had a temperature spread of 35 degrees, from a low of 53 to a high of 88.

Blacksburg's numbers are similar. After averaging a 19.2-degree temperature spread in August, 18.5 degrees in July and 21.9 degrees in June, the daily spread balooned to 29.5 degrees in the first 13 days of September. Blacksburg had a temperature spread of 40 degrees on Tuesday, from 46 in the morning to 86 in the afternoon.

Drier air, with less of the insulating quality of water vapor, heats and cools faster than humid air. In summer's tropical humidity, there was less difference in temperatures from day to night; in the drier air we've had most of September, the gaps are wider.

However, on Wednesday, we were reminded again what a little tropical moisture can do to overnight lows, even with nights getting longer. With some new tropical moisture spun westward from Hurricane Ophelia, Roanoke's low of 70 and Blacksburg's low of 64 each tied records for the warmest low recorded on Sept. 14.