2009.08.21
Severe threat today depends on sunshine, placement of front
Southwest Virginia is straddling the southern edge of a large slight risk zone for severe weather stretching all the way to New England, according to the Storm Prediction Center. A rather strong cold front will push into extremely humid tropical air mass that has produced daily (but streaky) "monsoonish" type rains in our area. The questions for our immediate area upon which our risk of severe weather hinges are (1) how much sun will break through morning clouds and fog to create instability? and (2) how far east will the front be when maximum instability occurs? The more sun, the warmer it will be, and therefore the more unstable it will be and the greater the potential will be for severe thunderstorms, with damaging winds as the primary threat. But if the front pushes a little farther east than expected, the main focus for severe weather will shift east with it into central and eastern Virginia. The greatest threat for widespread and violent severe weather will be farther north, from northern Virginia to New York, where shearing winds will be greater and more likely to produce storm rotation.
In any event, at least another showery day with locally heavy rainfall is likely again today. Saturday, too, could be a little showery, as the front may be unable to push all the way off the coast as Hurricane Bill well off shore resists it. But then, from Sunday into the middle of next week, the cool, dry pattern I write about in today's Weather Journal column sets in. The overall pattern will last much longer than that, but there may be a hot day or two late next week before a reinforcing cold front arrives.
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The word "rotating" and areas like Northern VA and New York do not go together especially considering the tornadoes in Toronto yesterday.
Did you see the video of that, Kevin?
Comment by Brandon R — August 21, 2009 @ 10:28 am
Haven't seen it, Brandon. Do you have a link? Looked but didn't find anything fresh. Did find a news story about somebody killed by a tornado in southern Ontario.
Torandoes in the Northeast U.S. and southeast Canada in mid to late summer are not really as rare as some might think.
Comment by Kevin Myatt — August 21, 2009 @ 10:50 am
Here are a few of the videos:
http://www.youtube.com/watch?v=FuMsSs2vSHo&feature=player_embedded
http://www.youtube.com/watch?v=TTxTWc0ShAg&feature=player_embedded
http://www.youtube.com/watch?v=bLHDE9dNM2c&feature=player_embedded
Comment by Brandon R — August 21, 2009 @ 11:09 am
Impressive videos. A few sporadic tornadoes are not unusual, but this level of tornado activity is not common in that region.
Comment by Kevin Myatt — August 21, 2009 @ 11:20 am
There is one more video that I could not find. It's the one I originally saw on CNN.
It was in a very heavily populated area and you can see the Tornado (easily an EF-2) ripping off roofs and sending cars flying through the air. If I find it, I'll post it.
Comment by Brandon R — August 21, 2009 @ 11:22 am
We had a fair amount of sun earlier this morning but now I see very thick clouds and only a few pockets of blue sky scattered about. I've been fairly surprised that we haven't had more rain despite the soupy atmosphere, but everything has been very streaky. We've recorded just barley a half inch of rain this week.
Comment by Other John — August 21, 2009 @ 11:56 am
Looks like at least where I'm at now, the sun burned through the clouds because we've got a lot of blue sky, sun, and temps warming substantially now. It was somewhat mild when I left for lunch, but was quite warm when I returned.
Comment by Other John — August 21, 2009 @ 1:34 pm
Severe thunderstorm watch has gone up in the Piedmont, generally Charlottesville to Lynchburg to Danville and eastward.
http://www.spc.noaa.gov/products/watch/ww0728.html
Comment by Kevin Myatt — August 21, 2009 @ 1:37 pm
Despite how soupy it is with the dew points in the low 70's and a fair amount of sun this afternoon, Radar is not lighting up near here at all. Some storms popping north and a few south, but it looks like the bulk of the energy is well north of the state pushing through New England and the upper Mid Atlantic. Even with the front approaching, we've got less rain here than in past days.
Comment by Other John — August 21, 2009 @ 4:15 pm
There may be some mid-level dry air working in. There is one fairly potent storm approaching Lexington as I write this, but definitely not the monsoon weather of recent days.
Comment by Kevin Myatt — August 21, 2009 @ 4:33 pm
That's what I figured, a semi-return to the dry-slotting of the past winter and spring. But, given how much rain we've had, this isn't such a bad thing this time around.
Comment by Other John — August 21, 2009 @ 4:45 pm
The old mailman here. My early warning device just went off, even though there is nothing at all close to us on Nexrad radar. The early warning device is my dog, Blondie. He is quivering. He only does that under two circumstances: someone is setting off firecrackers; OR, we will be hit (or have a near miss) with a t-storm within 20 or 30 minutes. And I do not hear any firecrackers ......
Comment by Doug Griggs — August 21, 2009 @ 5:06 pm
But could he be reacting to a storm in another direction, like toward Lexington? Whenever there's thunder within about 50 milesin any direction, my dog gets in the tub.
Comment by Kevin Myatt — August 21, 2009 @ 5:23 pm
I'm starting to feel a change in wind direction. It has been a long time since the wind blew through my northwest facing window.
Comment by Nate — August 21, 2009 @ 6:32 pm
Perhaps you are right, Kevin, about my dog. Definitely a false alarm as far as us getting a tstorm. However, our satellite feed was cut off briefly right after that for a couple of minutes, even though there was no rain and no thunder audible to us humans. He is resting peacefully now. But he is still no WeatherDog, who was our other dog, Cindy, who lived in the late 80s and throughout the 90s. She was unbelievable.
Comment by Doug Griggs — August 21, 2009 @ 8:36 pm
There are a few isolated storms popping this evening along what may be the frontal boundary. One is southwest of Roanoke headed northeast. Don't know if it will hold together, but I wouldn't rule out a rumble and a brief downpour in some areas just yet.
Comment by Kevin Myatt — August 21, 2009 @ 10:20 pm
Heavy rain in south Roanoke County now, and a narrow line of storms moving northeast along the Blue Ridge. A flash flood warning is in effect for Roanoke/Roanoke County/Salem, as well as parts of Floyd and Montgomery counties. It's actually very reminiscent of the training scenario that caused localized flooding in the Roanoke Valley back on July 22-23 ... right down to the part of me dashing home from work through heavy rain.
http://blogs.roanoke.com/rtblogs/weatherjournal/2009/07/23/watching-for-a-new-round-of-storms-today/
Comment by Kevin Myatt — August 22, 2009 @ 12:05 am
Looks like these storms are blowing through faster with not quite as torrential downpours as those on July 22-23. But I do see some amounts over 1 inch in the southern and eastern parts of the Roanoke Valley ... much like that previous event.
http://www.afws.net/data/va/Roanoke.HTM
Comment by Kevin Myatt — August 22, 2009 @ 12:56 am
Storm knocked out power in my apartment building. Believe it was due to lightning hitting something. Power is back on but the phones are still down. It was nasty for a bit here.
Some roads in southeast Roanoke are closed because of flooding.
Comment by Brandon R — August 22, 2009 @ 1:08 am