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Monday, September 20, 2004

Weather columnist Kevin Myatt: Twisted weather pattern takes a turn

Kevin Myatt is The Roanoke Times' weather columnist.

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For most Southwest Virginians, former Hurricane Ivan ended up as someone else's problem -- unless you were one of those whose property was damaged by tornadoes in Henry or Bedford counties.

But there's no doubting that Ivan was a terrible problem, first and foremost for the Pensacola area of Florida, far more devastated than initial media reports indicated. The damage is comparable to Charley's in some areas.

Ohio, West Virginia and Pennsylvania got the disastrous floods we feared. The moisture of Ivan, defying the typical pattern of the heaviest rains occurring north and east of an inland tropical system's center of circulation, instead formed to the north and west of Ivan, enhanced by a cold front.

We got the opening salvos in a tornado outbreak that would go positively insane over Northern Virginia, with so many twisters up there that National Weather Service teams will need days to document all their paths.

On the east side of Ivan, we were in a zone of intensely humid weather with east and southeast winds at the surface running crossways to those aloft. Some dry air was also sucked into the storm from the southwest, colliding with the moisture. Just enough sunshine to ignite convection (rising warm air and moisture) set the stage for quickly developing rain squalls and thunderstorms that begin to spin with the conflicting winds. Some of these rotating storms spawned extremely localized areas of intense spin that reached ground level as damaging tornadoes.

The tornado warnings came fast and furious for a while, and those who have lived in the Midwest had flashbacks to the tornado outbreaks of their past.

Some in the Roanoke area have suggested that the valley had never, in their memory, been placed under a tornado warning, as eastern Roanoke County, Roanoke city and Salem were for a while early Friday afternoon. Roanoke was hit by a tornado in 1974 and as recently as August 2003 experienced a tornado touchdown in the Hollins area, but neither of those were preceded by National Weather Service warnings. I don't know if this is a question that can be answered definitively, but I'll look into it.

Friday's tornado warning resulted from Doppler radar detection of circulation within a storm a few miles south of Roanoke, moving north. Not all radar-detected circulations result in tornadoes, but all of them have that potential. Warnings were in effect for the counties where tornadoes struck on Friday, as radar picked up on rotation before it reached ground level.

But by Saturday, things felt much different. The winds were gusty, but instead of humid and stormy, a bit chilly and fresh. The air was not stale with haze and moisture, but crystal clear, washed clean. It was like a season had just changed.

Did it? Was Saturday a turning point in our season?

That was the day that former Hurricane Ivan was finally crushed, but not by the north Atlantic high pressure area that we thought might trap it for days and days of downpours. Instead, high pressure from the northwest building behind a cold front simply shoved Ivan aside and out to sea. What was Ivan split into two pieces Saturday, a rather grotesque but long-awaited death for such a famed storm.

It was also the day when Tropical Storm Jeanne, ever so briefly a hurricane (and possibly to become one yet again), got impaled by the mountains of Hispaniola. That was bad news for Haiti, where torrential downpours killed at least 90, but suddenly it was downgraded to a lowly tropical depression. Furthermore, Jeanne is projected to wander listlessly in the open ocean, rather than threaten Florida yet again.

Hurricane Karl is strong but curving north far away from any major land mass, destined to die a slow death over the cold waters of the north Atlantic.

So, suddenly, and thankfully, I can say there's no new tropical system in sight for us. Instead, we can start looking back to the west, where our weather comes from most of the time, to see if we might be heading toward October chill and frost on the pumpkin. In that ongoing war of tundra and tropics, the tundra has finally pushed the tropics aside, at least for a while.

Be thankful. We all need the rest.

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