Change is in the air: Brief cold, then much warmer
Saturday’s 80-degree weather in Roanoke is giving way to a short snap of colder weather that could even produce a few snow showers in the highest elevations on Tuesday night and early Wednesday. But after a couple of chilly mornings in the 30s to low 40s, very warm weather is likely for the weekend as upper-level high pressure builds just west of our region. That dome of high pressure will bring June-like temperatures, with highs possibly reaching the mid 80s by the weekend. This appears to be the start of a weather pattern change that will switch us from a mostly cool, moist pattern to a very warm pattern that will, at first, be drier as well. The Climate Prediction Center is suggesting the likelihood of warmer than normal weather in the Appalachians/Mid-Atlantic/Southeast/Tennessee Valley region for the next two weeks. In time, some rainy systems may start eroding the high pressure dome. But for the next several days, after this brief shot of fairly cold weather, expect toasty warmth and drier weather.
April 20, 2009 - 9:58 PM
RSS feed 
The warmer and drier weather will be welcome. The rain has been nice, but it’s dampened my outdoor work on finishing some landscaping projects I started. Maybe now I’ll get a chance to finish them and get some weed n feed put down to cut back on my dandelion forest of a yard!
Hey Kev,
Is there a possiblity of frost or freeze warning going out for tonight or Wedsnesday for Christiansburg?
Hey Kevin, what is the best Web site to see the most up-to-date moving radar images of weather in our area?
For example, if I am thinking about taking a walk but it looks like it’s clouding up on the horizon, can I go to a site and see if there’s a storm heading my way and how much time I might have?
Sorry to get back so late. I’ve been on the road all day (returning from parents’ house in Arkansas).
As for radar: I like the National Weather Service best
http://www.erh.noaa.gov/rnk/
For national/regional radar … which you can click for local views …
http://radar.weather.gov/Conus/
As for frost/freeze … looks like it hovers a little above freezing right now, even in NRV … could be on the borderline of a frost advisory, but that would depend on whether the weather service considers the NRV to be in its growing season yet or not.
Great links to the NWS radar Kevin. I use those all the time at home and work, they are the ones I like best. I found that many of the others show a lot of false echoes and virga, while the NWS is usually pretty well spot on. As for frost, we put out frost cloth last night to protect flowers, but it didn’t get quite cold enough. Clouds hung on and the winds were steady. Now it looks like a band of light showers is about to roll through, I suspect some higher elevations might see a few flakes from it.
So much for just higher elevations. It’s snowing down at the floor of the NRV from Fairlawn to Christiansburg, according to my wife. She said it was snowing all during her drive on 114. Temps in the mid 40′s, but depoints in the lower 30′s. After the relatively nice weekend and the forecast for this upcoming weekend, this is certainly a mild system shocker.
Light to moderate snow flurries here in Floyd for past hour.
Was rather surprised to see it.
Other John: From Roanoke’s perspective, NRV is the “higher elevations” … but in this case it does seem the snow dipped a little lower than expected.
I was thinking the peaks would get it, but we just had a heavy squall go through that briefly whitened the mulch beds at the office, with temps still in the mid 40′s. Only in April.
You’re very near the upper limit of temperature when snow can make it to the surface … I think I’ve read that is 47 degrees … requires very cold, dry air aloft to right above the surface.
That would hold with what I saw in the weather modeling then. It had kept showing a very cold pool aloft, with the 540 line dropping through our area today. Looks like that’s happened.
Here’s a very technical (lots of complex math!) explanation of snow with above-freezing surface temperatures … this comes to the conclusion that snow can reach the surface under prime conditions at 46 degrees:
http://www.sciencebits.com/SnowAboveFreezing
Sleet, being a denser form of ice, can reach the surface at even higher temperatures, into the 50s on rare occasions. And of course hail is so heavy it plunks down with temperatures in the 70s and 80s.
These flurries are going to seem funny if we crank out a 90 or two this weekend … not out of the question at all.
Indeed Kevin. Still, the first week of March goes down as one of the more extreme flips I’ve experienced, going from a half foot of snow and about 10 degrees on Tuesday to the low 80′s and no snow by Saturday. The largest one-day flip I lived through happened in Virginia Beach. We had a very warm winter day in the mid-70′s, sunny, with a good breeze. Next morning it was in the mid 20′s with 3 inches of snow. We’ve had several days similar to that up here, but that one still sticks out in my mind since it was at the beach.
We have a photo of snow — today! — on Bent Mountain. It’s here on our Southwest Roanoke County community news site:
http://blogs.roanoke.com/rtblogs/swoco/2009/04/22/7079/
Here are a couple of snow photos from George Ewen in Craig County. Not the grainy nature to some of the snow on the hood of his truck — that indicates some partial melting on the way down, not unusual in situations when the temperature is above-freezing at the surface. Those would be “snow grains” … but snow, nonetheless.
http://blogs.roanoke.com/rtblogs/weatherjournal/files/2009/04/snow2.jpg
http://blogs.roanoke.com/rtblogs/weatherjournal/files/2009/04/snow3.jpg