Kevin Myatt is The Roanoke Times' weather columnist.

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An ice storm warning was in effect Saturday evening. But was it really an ice storm?

It depended on where you were.

Certainly, enough places in the counties along and west of the Blue Ridge had at least a quarter-inch of ice collect on tree limbs and exposed objects to justify such a warning.

But for the second time in 2007, the most populous area under that ice storm warning, the Roanoke Valley, largely escaped ice by a single degree of temperature.

Some of the higher-elevation areas in the valley had some ice coating the trees overnight Saturday, and there was some spotty ice on metal objects along the fringe of the valley's populated area. But, like in the much more severe Feb. 13-14 ice storm, it was almost exclusively a cold rain for most of the valley floor.

A reader on my Weather Journal blog posted the following: "For Roanoke City, this is just another overhyped rain event. This big bowl seldom gets any of the predicted action."

I asked Phil Hysell, the meteorologist who coordinates warnings from the National Weather Service in Blacksburg, why an ice storm warning could not have been posted for Roanoke County -- which includes most of the Roanoke metro area's higher elevation areas -- while leaving Roanoke city and Salem out.

After all, this is not uncommon at all for severe thunderstorm warnings, which can even be issued for a portion of a locality, such as "eastern Roanoke County."

It comes down to the type of computer software used to issue warnings, Hysell told me by e-mail. Watches and warnings covering periods of many hours or days are issued on the basis of county codes. So when Roanoke County is included in winter storm watches or warnings, the cities of Roanoke and Salem that it surrounds are automatically included.

Severe thunderstorm and tornado warnings lasting several minutes to an hour are issued on a much smaller scale, and weather service offices around the country have been working for years to narrow those down even further to name specific communities rather than entire counties.

Hysell advised going beyond just the geographic description of a winter weather advisory.

"This is why it's important to read the entire text of the warning, and not just focus on the county it covers," he wrote. "During this past ice storm, the initial ice storm warning on Friday afternoon, over 24 hours before the event began for Roanoke County, [stated] 'One quarter to one half inch of ice is expected ... with the most ice along the higher elevations of these counties.' "

I also asked Hysell why the warning couldn't specify a certain elevation. I remember this being done for a heavy snow warning back in March 2001 that was issued for Roanoke County above 2,000 feet. That storm behaved just as forecast, with Bent Mountain and Poor Mountain getting 4 to 8 inches of wet snow while most of the Roanoke Valley only got a little snow and sleet mixed with rain.

"Issuing elevation-based ice storm warnings is something our office is exploring, but the nature of how freezing rain develops makes it much more difficult to predict than snow," Hysell said.

It would take me longer than I have space left in this column to explain why that is the case, but I agree with Hysell.

A man in my church who lives part of the way up a steep ridge in southern Roanoke County said that the trees in his back yard were coated with ice Sunday morning while the trees in his front yard, a little lower in elevation, were merely wet. With snowfall, you would rarely see that kind of extreme gradient, but rather a gradual progression over several hundred feet.

I know the Roanoke Valley has had some bad ice storms in its history, but from my experience here over the past eight years, it seems that it takes a special set of circumstances for a bad ice storm to develop.

The urban heat-island effect may be partly to blame, as warmth builds in the concrete, asphalt and other building materials in an urban area on sunny days, storing heat that is released later. Also, elevation itself plays a role when cold air moves in at a slightly higher level and then fails to fully sink to the valley floor without slightly warming.

If we're on the razor's edge, as we were this weekend, it seems the Roanoke Valley floor usually escapes with minimal ice or no ice at all. If the cold is overwhelming and we're several degrees below freezing, it seems so often that the precipitation turns to bouncy sleet rather than tree-breaking ice.

But keep in mind that both this weekend and Feb. 13-14 were just one-degree escapes for much of the Roanoke Valley. Sooner or later in one of these close-call ice storms, it will be a couple of degrees colder, and the ice storm warning will prove true all the way down to the Roanoke River.