Kevin Myatt is The Roanoke Times' weather columnist.

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If you thought the days were unusually cool in September, you were right.

In fact, in Roanoke and Blacksburg, they've never been known to be cooler.

Roanoke's average high temperature for the month of September was 74.2 degrees, setting a record for the coolest average high temperature for the month of September. Official weather records for Roanoke Regional Airport date to August 1948.

Blacksburg's average high temperature of 70.6 degrees was also the coolest average high temperature for September on record there dating to 1953.

It was more than 8 degrees cooler than the average high for September 2005 in Roanoke, and more than 9 degrees cooler in Blacksburg. The average high for the September just completed was 4.6 degrees cooler than normal in Roanoke, and 4.7 degrees cooler than normal in Blacksburg. Statistical norms are figured as the averages for the years 1971 through 2000.

The overall September mean temperatures of 65.1 degrees in Roanoke and 60.9 degrees in Blacksburg, averaging highs and lows together, are not shabby either. Roanoke's mean was tied for the fifth coolest September on record, and the coolest September experienced since 1984. It was tied for the sixth coolest in Blacksburg, and the coolest September there since 1988.

Many nights in September were cool, but nothing radical. The average low of 56.1 degrees in Roanoke was only a half-degree below average, while the average low of 51.3 in Blacksburg was actually six-tenths of a degree above average.

So, why was September so cool, especially in the day?

There were no hurricanes hitting the coasts and coming inland toward us to bring in steamy air from the tropics. There were no stagnant high pressure areas to stall leftover, stale summer heat over us. There were cold fronts moving through in regular procession, bringing pieces of Canada's cold into our region repeatedly.

The biggest single factor was the activity and location of the jet stream. This time of year, it's usually starting to pick up a little vigor as it hangs out mostly near the U.S.-Canadian border, with a few ripples in it starting to bring some cool air south. In 2006, it has been going full blast and diving far south of the border in deep troughs.

Another result of the jet stream's energy and southern dips has been severe weather, like Thursday's hailstorms.

The contrast between this September and last is stark.

In September 2005, Roanoke's high temperature topped 80 on 23 days, including two over 90. In September 2006, the high topped 80 on only seven days and never reached 90 -- in fact, it never got above 84.

In September 2005, Roanoke's high temperature was in the 70s on six days and in the 60s only once, the last day of the month. In September 2006, the high was in the 70s on 14 days and in the 60s on nine days, including the first day of the month.

So, in a year in which the first seven months were the hottest January-August period on record in the continental United States, it is refreshing to see that cool weather records still can occur.

But as I cautioned in my Sept. 23 column about weather and climate, don't try to take our cool September as anything larger than the result of weather patterns over a few weeks. Its significance in the larger issues of world climate is miniscule.

Still, it will be interesting to see if this cool September is the harbinger of more cool times to come as we move through fall toward winter. October isn't beginning that way, as temperatures are likely to be far above normal today.

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