Friday, September 25, 2009
Weather columnist Kevin Myatt: As a sticky September winds down, autumn moves in
Kevin Myatt is The Roanoke Times' weather columnist.
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When you feel your foot go to sleep, it's time to move around to get the blood flowing.
That's what this weather pattern is getting ready to do. The circulation has been cut off, so it needs to start moving to get the air flowing again.
We've been in a really stagnant weather pattern for a couple of weeks.
Most of that time, there has been some kind of low pressure system spinning off to our west or southwest. It hasn't been close enough to give us a lot of rain, as appeared likely about a week ago, but it has been just close enough to spin in moisture for many humid, at times dreary, days.
Georgia and some neighboring states experienced a different result from the stalled weather pattern earlier this week. Bands of torrential rain continuously moved over some of the same places this week, resulting in massive and deadly flooding.
A stagnant weather pattern like this isn't uncommon in September, but it's usually a result of July and August weather hanging around an extra month.
This summer, however, featured an unusually fast-flowing weather pattern with an atypically south-diving jet stream that kept systems moving along and often brought some cooler air into our region. So this persistent sticky stuff seems a bit out of place after the mild summer of 2009.
A series of events across the Northern Hemisphere will allow the jet stream to dip farther south and trigger a progression of cold fronts that will bring weather at least resembling autumn to our region by next week.
Thursday was likely the last sultry summerlike day for a while.
Temperatures will cool about 10 degrees today as a cold front sags in from the north.
The mercury may not get out of the 60s on Saturday as a stronger cold front pushes some rain our way. Once that front is by us, the pretty weather sets in. Expect several days next week with sunny skies, highs in the 60s and 70s, and lows in the 40s and 50s.
In the bigger picture, the developing pattern change may indeed signal the start of our inevitable march into autumnlike weather.
As the sun angle lessens and the days get shorter, the mean jet stream position drops southward. The jet stream, generally speaking, marks the dividing line between warm, sticky subtropical air and cool, dry polar air. That's a big part of why much of the nation's unsettled weather is focused along the jet stream.
So step by step, we begin moving toward winter.
There are already a few trees here and there changing color, but the large-scale foliage change may get going in earnest, starting at the highest elevations and working downward, if we can manage a few chilly mornings next week.
And mountain snow showers are probably only a few weeks away.
That should get the blood flowing for many of you.
