Advisory for quick AM hit of snow/sleet
Summary bold-faced at bottom
Winter 2012-13 is doing it to us again on Tuesday morning. I’ve lost track of how many of these relatively minor, but potentially traffic-troubling, borderline winter-weather situations we’ve had in Southwest Virginia since the first on the day after Christmas. Here’s the setup: A low pressure system is tracking through the Great Lakes, pulling up a swath of Gulf of Mexico moisture northward ahead of a cold front. This is far and away NOT a pattern that produces significant widespread winter weather events in Southwest Virginia. But, because there remains a thick layer of cold, dry Arctic air banked against the Appalachians, as precipitation falls through that air early Tuesday morning (3 a.m. to 9 a.m. is a generally good timeframe to consider for this, right now, from I-77 eastward), evaporational cooling will quickly pull much of the atmosphere below freezing from cloud to ground (or very nearly so) leading to more snow and sleet rather than rain or freezing rain, at least to start. Yes, the temperatures at the surface got into the 50s Monday, but the precipitation is arriving at the coldest part of the 24-hour cycle, surface dew points remain low, and the layers above the surface are still even colder and drier than what we have at ground level. As precipitation falls, the first part of it will evaporate on the way down, and that process removes heat out of the atmosphere, cooling temperatures. With the low so far removed from our region, the flow of moisture is not overwhelming, so we’re talking light amounts, likely no more than a quarter-inch of liquid, and probably closer to a tenth of an inch for most.
Most of this winter’s systems have produced some kind of oddball surprise, sometimes with localized areas getting a lot more precipitation than expected (Floyd County’s power-crippling ice storm on Dec. 26; 3-5 inches of snow in the Roanoke Valley on Feb. 7-8; 4-8 inches around Appomattox this past Saturday) and sometimes with much less occurring (Dec. 29 projected snow largely busting, Bedford County snow hole on Jan. 17). One surprise that is possible Tuesday morning is if the moisture just dries up and very little of anything falls. Another would be if stays just cold enough for snow and the upper-end liquid amounts are realized, there might be more 2-3-inch snow amounts than expected. What I think is most likely is a lot of sleet and some snow gradually giving over to more rain mix for 3-6 hours on Tuesday morning, with widespread 1/2 to 1 inch amounts from the Roanoke Valley and Blue Ridge westward, and locally up to 2 inches. Whatever happens will be over quickly and temperatures will rise well above freezing (40s, some 50s) by Tuesday afternoon.
Regarding the Thursday night-Friday system — well, it looks sort of similar to this with a weakening moisture field advancing eastward with a low far to the northwest and a middling cold air wedge that could lead to some frozen precipitation at the outset.
February 18, 2013 - 6:13 PM
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I don’t have the graphics function down pat on the new format yet, so bear with me. The 2 graphics above are the winter weather advisory area and the NWS snow/sleet accumulation projection map. I figure if I can’t wrap text around them easily I’ll use bigger ones and center them.
Hey Kevin do you think the WWA could extend east any?
I think it’s possible. It’s a very low-end advisory, anyway, mostly being issued because of morning rush hour. Franklin County, where you live, is always the toughest county in these, with about 4 different pieces. The western edge of the county near the Parkway will be more like Floyd county, the nothern part near Boones MIll more like Roanoke County. If the NWS sees good coverage of snow/sleet expanding eastward in the AM, and likely to cause road problems, I would not be surprised to see Bedford and/or Franklin County added.
Not sure if this is where this comment/feedback needs to go –
When I want to go back and read the comments on the previous column – I can’t get to them. Even when I go back to the column and look for them – they are not there. It is like when you do a new column or blog entry all of the comments from the previous one are gone. ????
But on the good side – the font and pictures are “HUGE” – I might not even need my glasses to read it.
I agree that Franklin County is very hard to forecast, since there are several distinct areas totally different from one another. There have been plenty of times I could look north and see Masons Knob engulfed in snow, or look northwest and see Floyd covered. I always wish it makes it here near Rocky Mount, but seldom does.
It’s going to be an interesting forecast for sure, Kevin. 40 minutes ago, the temperature here was 48, with a 21 Dew Point. Now, it’s 44 degrees with a 20 Dew Point. Clear skies here in Pulaski County as far as I can tell…saw some high-level clouds earlier though.
Carol, it appears only the last post is so affected. If you go back 2 or 3 posts, all the comments appear as they should. At least they did for me. Hope it’s just some kind of short-term glitch.
I clicked on the previous thread, both by using my always-used to-work method of clicking on the number of comments at the bottom right of your text, and also by just clicking on the top line. Each time I got just two comments out of the 52 total comments to appear.
Anyway, I hardly ever disagree with you, Kevin, but I think that for elevations below 1500′ here in the Roanoke valley, the most we will see is a bit of sleet before 8:30 AM, and that will melt when it hits the roads. And I don’t think the precip will start in ROA city until 6:30.
3 a.m. is not meant as an “it will start at this time” parameter — 3 a.m. to 9 a.m. is meant as the general bounds for when frozen precipitation is most likely to occur in the entire area east of I-77, not just Roanoke. Starting at 5 or 6:30 a.m. is well within those bounds.
What you say is certainly possible, Doug, but the counter argument would be that the Roanoke Valley will have even deeper cold, dry air aloft for more evaporational cooling to occur. And sticking on roads may not mean ice so much as slush — if it’s sleet, that could actually be worse than if it is snow.
“7″ and “13″ are disagreeing with you. But you might end up right. By a bit of sleet I was also talking tiny sleet pellets, not the big sleet pellets that can quickly turn a road mushy.
Just clicked on Channel 7′s web site and it’s almost verbatim what I have. Coating to 1 inch of snow/sleet for Roanoke/Blacksburg/Floyd/Lexington to Fincastle.
http://www.wdbj7.com/news/wdbj7-weather-forecast-discussion,0,2780518.story
The real disagreeing body out there is HPC — ZERO PERCENT chance of 1 inch for Roanoke and New River valley, small percentages I-77 corridor and WVa border area.
http://www.hpc.ncep.noaa.gov/pwpf_24hr/prb_24hsnow_ge01_2013021900f024.gif
Being a borderline situation, it is definitely within the realm of possibility it could go to more rain/sleet mix early. Would not be a shock.
I should point out that what I have above is pretty much right in line with NWS-Blacksburg. I’m not going out on a limb here.
It’s now a half-hour since my last update, and the air temp is down to 38 and still falling here. Starting to see a downward tick in the barometer as well. But, the Dew Point is edging upward a bit, now up to 23 degrees.
Channel 13 on the other hand, as Doug mentions, is going for a less aggressive winter weather forecast than other outlets, with no significant accumulation expected.
http://www.wset.com/weather
They may be right. We’ll see. I’m expecting sleety slush, at least Roanoke and west.
While we’re at it, we’ll throw Channel 10′s forecast in the mix. More in line with NWS-Blacksburg, Channel 7, and what I have above.
http://www.wsls.com/weather
Channel 7 changed its tune since 5:20 definitely, and possibly from 6:20. I will know when I check radar early A.M. whether the timing I mentioned will be correct.
It would not break my heart at all if this turns into a bunch of above-freezing rain/sleet mix. I’m tired of these nuisance winter weather events, I have somewhere to be fairly early tomorrow, and it would help protect my snow meter for 1 week if we could stay under an inch.
Also, I do think it will probably be closer to 6 a.m. when it starts in Roanoke … but I’ve seen too many of these rush in 2-3 hours faster this season, so a little cushion doesn’t hurt. And also, it will start in New River Valley sooner, and especially out toward Wytheville and west.
Whats the late week snow potential looking like?
Weak, I would say, Kevin from Turkeycock.
Agree fully about NRV and points west. And I should have taken into consideration the fact that you went 4 snowflakes rather than 6 this week. If this itsy system nails both of the snow meter cities with 1 inch or more of snow, you ought to wave the white flag and ditch the snow meter idea, because somebody or something is out to get you. :>) :>) :>) :>) I must admit that this season it has been MUCH MORE difficult than I ever imagined. And all of it after January 1, I believe.
To tweak Turkeycock Kevin’s question……….What’s the late week cold air wedge potentail looking like? Do you think it will hold at all?
I had to travel to Wytheville this afternoon and got stuck behind a “pre-storm treatment” truck. Didn’t realize how badly the brine smelled. I do appreciate them being out there and treating the roads though. Also they had the electronic signs up saying the area was under a winter weather advisory.
Any realistic chance this could be a pure snow chance for Roanoke Valley? I think it could happen with the proper convergence. I usually compile my forecast data from the basement and this is what I am ciphering.
Already 35F with 47% humidity. Haven’t I heard on here about we don’t get much when storm systems come from the west towards the east and we all know about those mountains and what they do to those approaching systems. Plus the air is dry and it will take awhile till anything is able to reach the ground. Guess we will just need to wait and see what it is like in the morning.
We’ve got a bit of a southerly wind at the moment…I can smell the foundry from the front porch. Temps have accordingly jumped up to 41, while the dew point is also up, now at 26. Skies are still clear though…it will be an interesting race to see if we can touch the freezing mark with precipitation falling, or not.
National radar looking impressive right now. Will gulf moisture feed into the southern end of it and continue to re-energize the “tail”?
I’m expecting a few of those fast falling wet flakes around 7 a.m. and then maybe a bit of sleet and transitioning to rain all before 9 a.m. here in Franklin County. After that, some light rain and drizzle with the sun peeking through just after lunch and the highs jumping to near 50 around 2 p.m. with the wind kicking up in the afternoon from the southwest. I don’t see anything slick coming south of the Parkway though (trying to jinx myself).
Looking back into the archives, it does appear that most threads are resetting after 50 comments are made, so we can only view the few most recent ones. Hope this will be fixed, as I quite often like to peek back and read through some of the posts. Otherwise, really liking the new design.
UGH….I really don’t care for this new layout! I’m having a hard time navigating everything right now.
I have reported the disappearing comments issue to the proper technical personnel for them to look into and hopefully correct.
I think an all-snow event will be possible if the moisture moves through fairly quickly. Warming aloft is inevitable tomorrow, but if the precipitation moves through before that can happen, it could be all-snow, or very nearly so (maybe some sleet or rain to start, and at the end.
Even if that were to happen, I think we would talking 1-2 inches, maybe locally 3, not much more.
Late week, there will be a wedge. Question isn’t so much whether it holds — it will be scraped out — but how strong it is and how much moisture gets into it before it erodes.
A forecaster in Pittsburgh expresses his frustration and conflict on this one:
THIS IS NOT A FORECAST THIS METEOROLOGIST WOULD LIKE TO DO AGAIN. MODEL SOLUTIONS FLY DIRECTLY IN THE FACE OF FORECASTER INTUITION…HOWEVER THE SOLUTIONS ARE BOTH CONSISTENT ON A MODEL- TO-MODEL AND RUN-TO-RUN BASIS. THIS MAKES THROWING THEM OUT A PERILOUS ENDEAVOR …BY NO MEANS IS THIS A CONFIDENT FORECAST
I like the new foremat on my I-phone in particular, it’s easier to read. Now if I can figuire the rest the darn thing out I might even get a radar image or two.
In Buchanan, we are at 43 with a dew point of 21. I have TWC, Yahoo and Weatherbug all on iphone. Each one shows a different temp and dew point. Who do you think is most accurate and is there a better app for phones? Of course, I frequently check this blog.
I will generally defer to others on apps and website accuracy on temperatures, though I would probably go with Weatherbug likely having a working weather station in Buchanan.
Dont have a clue what it s gonna do but just checkin to see if my post works. Gonna keep my kids out of school tomorrow I think, no matter which.
The 6pm news out of Bristol talked about the models showing a better chance of frozen precip even as far west as northern Lee and Scott Counties in all of Wise and Russell Counties. If that is the case, our end of Washington Co will be in the wintry weather. No WWA out this way but temps are down to 38 with a fairly stiff breeze. Morning will tell the story.
Spring…oh Spring… please hurry up and get here….
Radar is looking pretty impressive what do you think Kevin? And how much do you think Vinton will get out of all this
kevin, Your Roanoke forecast high on Friday is 7 degrees warmer than Wytheville. A little cold air damming?
Down to 27 in Blacksburg at 10:25pm and still dropping. If it does snow it will be very powdery……..never thought that was a possibility just 24 hours ago.
Well, I’m near Lexington, and the temp on my Davis is holding relatively steady at 27 with clear skies. Kids are already banking on school being delayed or cancelled in the morning.
How much accumulation of sleet/snow will come to salem
Rick: If you’re talking about the temperatures below the blog nameplate, those come from the National Weather Service (there is a small tagline there that says that). So they’re not my temperatures. I can’t take credit or blame. But yes there is a bit of a wedge that will erode SW to NE.
Blacksburg Mike: Temperatures are going to be warming aloft from advection once the atmosphere reaches its maximum amount of cooling from evaporation (and, so far, some radiational cooling). Snow consistency is more determined by temperatures at cloud level. Would suspect we start out sort of powdery and then see wetter, clumpier snow as the morning progresses — again, as you say, IF it is snow, and it doesn’t warm aloft too fast.
Andrew: Salem is in the 1/2 to 1 inch zone described in the boldfaced line above.
Gonna get off the blog now in anticipation of being up early, not just for this weather situation, but some other things.
This is a borderline situation with mixed data tonight. There’s not much that would really shock me with this aside from widespread really heavy amounts (4+ snow, 0.25-inch ice accretion). Use caution driving in the morning. It may be slick somewhere you go even if it isn’t at your house.