2009.01.26
Light snow possible this morning, but is Tuesday's ice threat waning?
Don't be surprised to see a few snowflakes drifting down this morning from the New River and Roanoke valleys northward ... I saw a few when my dog insisted on a 6 a.m. walk. A weak disturbance is squeezing out some light snow as it zips through the region this morning. The radar echoes will probably be a little overblown (more is falling than actually reaching the ground) but a dusting to locally up to an inch is not impossible this morning, especially in mountain areas west of Roanoke. This round of snowflakes should be over by noon.
The bigger issue, of course, is the Tuesday situation that still has a winter storm watch flying for Blacksburg, Roanoke and points northward (plus Franklin and Floyd counties to the south). Forecast models are continuing to trend a little warmer as overrunning precipitation is swept northward by a fairly weak low pressure system early Tuesday. If that trend proves to be real, rather than a figment of silicon imagination in a computer, then the likely result would be less snow and sleet and more rain or freezing rain on Tuesday. Seeing as almost everyone doesn't like ice, a narrow escape from the ice storm is a growing possibility for many areas (probably not the usual cold spots that get ice in borderline situations) if the warm trends continue. But there is considerable doubt about it, as models often overestimate surface temperature in a cold air damming situation, though this one is definitely not a strong setup. And how much evaporational and/or dynamic cooling will there be with the onset of precipitation into what at first will be cold, dry air? The Hydrometeorological Prediction Center continues to show a slight risk of signfiicant (.25-inch) ice for most of Southwest Virginia, with a moderate risk north of Roanoke and Blacksburg. So let's keep the vigilance for Tuesday morning, but be aware that it might end up being mainly a cold rain for many.
The newest wrinkle is the possibility of some snow on the backside of the storm by Wednesday as cold air moves in behind the departing low. The Hydrometeorological Prediction Center's snowfall forecast map for Day 3 (Wednesday morning to Thursday morning) reflects that possibility, with a slight risk of 4-plus inches extending to just east of Roanoke and a moderate to high risk in the more mountainous areas to the west and southwest. Some of this is upslope-enhanced, but there may be enough moisture behind the storm with a new push of cold air for snowfall in some parts of the area come Wednesday. Beyond the regular upslope stuff, the National Weather Service in Blacksburg isn't really biting on this yet, and I would say I'm skeptical, seeing as we don't get many significant snowfalls out of rain-changing-to-snow situations. But it's definitely something to stick in the back of our minds as we keep our focus on the Tuesday ice potential.
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Kevin,
I understand little about the forcasting of weather. However, you do a good job of putting it in laymans terms. I will continue to pray for snow, as that is how we pay the bills in the winter. Thanks and keep up the good work.
Tracy Bryant
Comment by Tracy Bryant — January 26, 2009 @ 8:19 am
We had a dusting of the hominy snow this morning at our house. It was mostly confined to gable lines on houses and collected by windshield wipers on cars. There was a little more in Montgomery County near Belview since cars and rooftops were white, but that was about it.
Comment by Other John — January 26, 2009 @ 8:20 am
Is it just me, or is that red, a 70% threat of 4" + snow for Galax, Wythville, Blacksburg, etc? And I don't see this on the models anywhere?
Comment by Zach — January 26, 2009 @ 10:25 am
The 70 percent I'm seeing is a little west and southwest of those locations ... more like Tazewell ... but yes, it is a 70 percent chance says HPC, and a 40 percent shot a little further east closer to Wytheville and Blacksburg (and maybe you) ... I will try to figure out where this is being derived.
Comment by kevinmyatt — January 26, 2009 @ 11:05 am
What has really damped down the winter storm risk for our region with this system is that it appears a little bit stronger low pressure system will develop. Earlier, it basically looked like a thick slug of moisture overrunning cold air at the surface. Now, the low develops to our west and moves northwest of us, and though it's not especially strong, becomes an agent in pulling warmer air northward. So instead of a total "overrunning" event we almost have a quasi-Appalachian runner type low, and unless the cold air damming is really strong, which it isn't, we don't get much wintry weather out of those.
Comment by kevinmyatt — January 26, 2009 @ 11:23 am
So, probably another miss for our region again,huh?
Comment by Angela — January 26, 2009 @ 12:13 pm
Kevin, are you surprised that we are still going into a Winter Storm Watch tonight? If it's basically going to be rain - why haven't they cancelled the watch yet?
Comment by Bradley — January 26, 2009 @ 1:08 pm
Depends on how you define miss. There will almost certainly be some winter precipitation almost everywhere from the New River and Roanoke valleys northward. A 4-inch plus snow is unlikely. A 1-inch snow/sleet accumulation is probably about a 50/50 chance for the valleys, more to the north, less to the south. Some ice/sleet, almost everyone except the lower areas near the NC border will probably see some of that. Significant ice storm, defined as at least .25 inch of ice, that's the hardest to determine right now, but odds are less than they appeared a day ago that a wide area will get that, based on forecast models.
But weather doesn't happen in computers, it happens in the atmosphere.
We are struggling to achieve forecasted highs in the 40s today, so unless the sun comes out to pump us out, we may start out colder going into the evening. The most critical factor, in my opinion, will be how much precipitation arrives early in the event.
BTW ... before someone asks ... sleet officially counts as snowfall by weather service standards, but glaze ice doesn't ... so if sleet or a snow/sleet combination totals 1 inch at WDBJ (Channel 7) in this event, the first part of the snowfall contest is fulfilled ... there aren't many who have picked dates in late January or early February for the first 1-inch snowfall.
Comment by kevinmyatt — January 26, 2009 @ 1:12 pm
Brandon, the NWS has been burned too many times by a 34-degree rain turning into a 32-degree ice storm that knocks out power ... the margin is razor thin for the first half of the event, especially with the known geographical quirks in our area that often defy the models (not to mention a cold ground from weeks of below-normal temperatures) ... they're acting out of caution keeping the watch, because it would be clumsy to drop the watch, then have to issue a warning later if something changed slightly ... a watch is not a warning, and it's often that a watch will lead to advisories rather than a warning ... I expect that we'll be under a winter weather advisory later while places I-64 and north get placed under a warning
Comment by kevinmyatt — January 26, 2009 @ 1:18 pm
Can I pick my snow date now! The odds will be in my favor!
Comment by Ralph — January 26, 2009 @ 1:53 pm
If I wanted rain in January, I would have stayed in SC.
Comment by Snowless in Roanoke — January 26, 2009 @ 2:51 pm
There's almost always rain in January here ... if you consider that our average January snowfall of about 6 inches is only 0.6 inch of rain, but we average 2.3 inches of rain for the month, even in a "normal" January snow makes up only a little more than a quarter of our January precipitation ... so if you don't want rain in January, you might need to go farther north ...
Sorry, Ralph, the contest is closed ... in
1972-731975-76 (CORRECTED) Roanoke's first 1-inch snow od the season didn't happen until March 12, a whopping 2 inches ... If we get to Feb. 20 and still haven't had our first 1-inch snowfall in the 'Noke, I'd give us an odds-on chance of beating that year for snow futility ... I think there are some very warm days ahead in early February, so getting an inch of sloppy snow before the changeover might be our last chance for a whileComment by kevinmyatt — January 26, 2009 @ 3:17 pm
Okay,Kevin, thank you for your reply. I've noticed that Accuweather and Weather.com have us for some freezing rain or just plain rain..with maybe a little snow while NOAA still has us under and Winter Storm Watch. I'm hoping the cold air stays in place (more so than expected) and that the moisture moves in quickly.
Comment by Angela — January 26, 2009 @ 3:18 pm
Sorry, Kev. I didn't mean no rain at all but at least some snow.. which, besides a few light flurries this morning, we haven't had in Roanoke
Comment by Snowless in Roanoke — January 26, 2009 @ 3:21 pm
Here we go again... This is just getting silly. At least I'll see snow in Snowshoe in a few weeks.
Comment by P. Kelley — January 26, 2009 @ 3:30 pm
I will be posting an update a little later, but it looks like the NWS is doing what I mentioned earlier: A winter storm warning for the counties north of Roanoke/Blacksburg (including Botetourt) and a winter weather advisory for most of the rest of the Roanoke and New River valleys.
Comment by kevinmyatt — January 26, 2009 @ 3:35 pm
They're now calling for just a cold rain near my house, with maybe a slight chance of some mixing toward morning, but little else. The HPC has also removed most of the ice & snow odds for the region, with some scant 10% odds for ice tonight and tomorrow for only some of the region, with no real chance of a 4+ inch snow in the area either, except a 10% chance in the highlands tomorrow. Looks like we might miss out on yet another winter storm, although with the odds having leaned toward an ice event, I'll take the rain again. After such a promising start, this winter has been downright disappointing.
Comment by Other John — January 26, 2009 @ 4:01 pm
The HPC odds are only for .25-inch or more of ice ... so the advisory level stuff would not be covered by it ... and it only takes .01 inch of ice on a roadway to make it treacherous ... I'm not disputing that a major winter storm may be averted, I just don't want folks getting cocky on the roadways that there will be no ice anywhere
Comment by kevinmyatt — January 26, 2009 @ 4:07 pm
Thanks for mentioning that Kevin...I listed the 4" amount for the snow but forgot to mention the 1/4" of ice that the HPC threshhold is about. I found it interesting in looking at the NWS site though. They call for less than 1/10" of ice and less than 1/2" of snow...mostly rain, for me. However, their graphical forecast seems to show much higher snow & ice amounts, which completely cotnradict their written forecasts. Any ideas as to why that might be? Obviously this storm is all over the place with uncertainties...but it's odd to see variances within the NWS.
Comment by Other John — January 26, 2009 @ 4:27 pm
I think some of the forecasts are mainly generated off models while others have human forecaster input ... I would have to check with the NWS folks to clarify that ... I'll ask them on a slower day.
Comment by kevinmyatt — January 26, 2009 @ 4:49 pm
Thanks. It makes it confusing to figure out what'll be happening, especially in a borderline system like this one...so any explanation as to why it happens and which forecast should be considered "more accurate" would help.
Comment by Other John — January 26, 2009 @ 5:03 pm
Notice on this map where the rain, ice and snow areas intersect and it gives a good idea why our forecast is so muddled
http://www.hpc.ncep.noaa.gov/noaa/noaa.gif
I'll be away for a bit but keep commenting if you like ... I'll get them up later
Comment by kevinmyatt — January 26, 2009 @ 6:33 pm
What a map...it looks a lot like some of the precip. maps I remember from growing up in Hampton Roads. We always had to deal with the rain/snow line for winter storms there, and the slightest track deviation would mean the difference between a cold, hard, driving rain and a full-blown blizzard. More often than not in Virginia Beach, we were on the rain side. But man, when we got on the snow side, those were the biggest snowstorms I've experienced that I remember. I haven't experienced anything close to that in this area, which is sad since it's supposed to snow more in the mountains than at the beach!
Comment by Other John — January 26, 2009 @ 9:49 pm