2009.02.26
UPDATED 4:30 PM: Let's go there ... a weekend snow threat
UPDATE, 4:30 PM: There are theories by the dozens bouncing around about this weekend's winter storm threat. But the Hydrometeorological Prediction Center is, at least for now, a believer in our snow drought coming to a screeching halt late Saturday into Sunday. The HPC, in its latest forecast update, has all of Southwest Virginia not only in a slight to moderate risk of 4-plus inches, but even a slight risk of 8-plus inches with a narrow swath of moderate risk. HPC has updated its maps but not yet updated its discussion. I will be interested to see their reasoning for this forecast. (The discussion is briefly noted in a comment below.) END UPDATE
It looks like the batters are coming to the plate for the bottom of the ninth inning of our winter without a significant winter storm. A complicated storm system is taking shape for Saturday and Sunday that will first likely send Gulf of Mexico moisture northward as light rain but gradually change to sleet and snow as colder air moves in from the north. The Hydrometeorological Prediction Center is swinging for the fence right now, with moderate to high risks of 4-plus inches of snow for everyone from Blacksburg and Roanoke northwestward and slight risks even into the Piedmont region. These risk areas have a tendency to shift 3 days out, so take it with some skepticism (OK, a lot of skepticism in this winter).
My early take on it is that I think there's a good chance we will see sleet and snow plummeting from the sky over much of the area by Saturday evening, but I'm not sure of whether it will be heavy enough and long enough in duration to accumulate too much from Roanoke south and east. The idea that previous days' warm temperatures can entirely prevent snow accumulation is somewhat overrated (it was 76 the day before the 6-to-10 inch snow on March 30, 2003, and had been above normal for most of the month), but it does usually take a heavy fall of wet snow to build a slush layer underneath to allow widespread snow accumulation, beyond grass and trees, following mild days. Today and Friday will be quite mild, as highs around 60 are possible.
These few days of cold coming up appear to be a blip in the overall trend toward milder weather that will likely resume by the middle of next week. So indeed, this may be the last chance to keep Roanoke out of the record books for least snowy winter on record.
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Beyond the initial overrunning moisture that may change to sleet and snow ... there is also the question of what happens with the strong upper-level low behind this moisture surge, where it closes off and helps trigger a surface low sometime Sunday that could move up the coast ... it is a very, very complicated storm system, by far the most interesting storm system that has affected our region this entire winter season, whatever it ends up doing in regard to precipitation ... rain is almost certain, at least some sleet and snow are likely, but I have still have a lot of doubt about whether the accumulating stuff will work into Roanoke Valley ... and I would still be doubtful even without the skepticism of a nearly snowless winter locally.
That said, I would be remiss if I didn't say that the pieces of a major eastern US winter storm are on the board, with the potential (emphasis, potential) for several inches of snow EVEN in our region ... the question is whether those pieces come together this particular time, and exactly how they come together to determine who gets the biggest dump.
Comment by kevinmyatt — February 26, 2009 @ 10:35 am
I am worried that we may get dry slotted. Can't wait to see how the afternoon model runs turn out. This is a complex system, and depending on where the pieces of energy end up pulling apart, how far they drift, intrusion of cold air, etc. - we could get thumped or bumped.
Comment by Julie — February 26, 2009 @ 10:47 am
It's my fault. We are going camping this weekend.
Comment by Henry — February 26, 2009 @ 12:56 pm
Thanks for the heads up, Kev.
I'll tune back in later tomorrow.
Comment by Brandon R. — February 26, 2009 @ 12:58 pm
I bet it will snow, because the weather is so beautiful today I have decided to take down all of my snowmen in the house, stuffed and otherwise! And my wreath on the door that said "Let it snow", to which I took a permanent marker and added the word PLEASE! I also have two statues of kids throwing snowballs in the front garden area. I am also putting them away. I hate to be so pessimistic, but I have waited so long fo snow, I just have to accept it and move on with my life! Maybe next year!!
Comment by Wanda — February 26, 2009 @ 1:24 pm
One thing I noticed with the models that seems a tad weird, it shows the approximate rain/snow line staying west of the mountains in our area through almost the entire storm, before moving east. The weird part is that it shows the cold air going south west of the mountains into Alabama and Georgia and then moving north east of the mountains. Very weird, I wonder if there was a glitch, because I don't recall seeing temperatures do anything quite like that. As for the rain/snow question, I'll go with Doug's IWBIWISI approach.
Comment by Other John — February 26, 2009 @ 2:36 pm
I will believe the snow only when I see it snowing.
In the meantime, I have been reading the posting for awhile and I have question about where everyone is getting the information on the weather models.
Comment by Jason — February 26, 2009 @ 2:46 pm
There is a very real chance that this could be a BIG snow for Georgia, South Carolina, parts of NC and not so much here, with the upper low digging farther south ... that would be a bitter pill to swallow for a lot of frustarted snow fans in this area. But there is still a lot of time for adjustments and even wholesale changes. We're still 48-plus hours out from the snow part of this system.
I'm one of the IWBIWISI people too. Some winters, it seems like every system finds a way to snow a little ... not many lately, but 2003 was something like that. Others, like this one, it seems like it always finds a way not to.
Looks like good rain for a lot of people Friday and Saturday, whatever happens with the snow.
Comment by kevinmyatt — February 26, 2009 @ 3:43 pm
I don't think I'll care either way so long as we get in on the moisture flow. Everything I've seen modelwise shows a pretty healthy slug going through, and hopefully we'll get a good dose of it.
Comment by Other John — February 26, 2009 @ 3:55 pm
I've updated with links to the latest HPC maps, which are very bullish for snow in our region.
The one thing that I am bit skeptical of is how far south the models are wanting to dig the upper-level low ... there doesn't seem to be any strong blocking in the Atlantic that would force such a southerly dip ... I think it will ease northward in some future model runs, but whether it gets all the way up to us, well, I don't know ...
Comment by kevinmyatt — February 26, 2009 @ 4:35 pm
Jason/all, Penn State University posts many of the models on their meteorology school's website (they call it the wall map). I use these most of the time, but you can also see a lot of great info/interpretation/discussion on the Eastern US Weather Forum: http://www.easternuswx.com/bb/index.php?act=SF&s=&f=15 . If the link doesn't come thru, just Google it. I have learned an incredible amount from this forum. You will have to join to be able to see a lot of the model grabs that get posted, but it's free. And I'll warn you, it's addicting!
Comment by Julie — February 26, 2009 @ 5:06 pm
Here is HPC's reasoning for the very snowy forecast maps, boiled down after a long explanation:
"WE OPTED TO DRAW A BROAD SLIGHT RISK STARTING
IN THE TN VALLEY AND EXTENDING IT INTO THE MID ATLANTIC REGION.
THIS WAS DONE NOT BECAUSE WE ARE CONFIDENT THAT THERE WILL BE
HEAVY SNOW AND/OR FREEZING PRECIPITATION OVER SUCH A LARGE REGION.
RATHER IT IS A REFLECTION THAT THERE IS STILL QUITE A RANGE OF
POSSIBILITIES IN BOTH PCPN AMOUNTS/COVERAGE AND LOCATION OF THE
PCPN AS SHOWN BY THE VARIOUS MODELS AND BY A FAVORABLE SYNOPTIC
PATTERN WITH A COLD HIGH TO THE NORTH AND A CLOSED LOW TO THE
SOUTH."
In other words ... they're making an educated guess of a wide area in which significant snow is possible ...
Complete discussion is linked here:
http://www.hpc.ncep.noaa.gov/discussions/qpfhsd.html
Comment by kevinmyatt — February 26, 2009 @ 6:00 pm
It looks like this could be very borderline- again.
Comment by Brandon R. — February 26, 2009 @ 10:34 pm
For another point-of-view, I just looked up TWC's Weekly Planner. They show rain on Saturday, a pale green for Sunday (snow changing to rain?), and snow showers for Monday. We will be dry for Tuesday according to the Weekly Planner, but the eastern half of Virginia will still be getting snow showers. Sounds like this system has real potential. That is 4 straight days (Friday - Monday) of good possibility of precip. YAY. Boy, do we need it. Now watch ... the entire 4-day total precip for RRA will be something relatively meagre like 1.25 inches. Hey, Kevin, still another month with precip on the 27th and 28th!!
Comment by Doug Griggs — February 26, 2009 @ 11:08 pm
Kevin, I'm confused
Is the potential storm that is going to bring us snow the first wave, the overrunnig event? Or is it the upper level low that follows behind? Or is is a merge of the two that no models are picking up on. I'm very confused as to why the HPC has us in a mod - to likely chance of 4" + of snow. Every single major model has the Upper Level low diving WAAAY south of us. ANd too warm with the overrunning even? Am I misssing something?
Comment by Zach — February 26, 2009 @ 11:14 pm
The North American Model tonight spreads a swath of snow across the area with the coastal low late Sunday into early Monday. The Global Forecast System, though, keeps the low way south, so inland Georgia is getting drilled (maybe even snow for Savannah and Jacksonville!). I might be out to lunch, but I'm not buying the extreme south solution on this. It may miss us, probably at least a 50-50 chance it will, but I'm thinking more like the eastern Carolinas if that happens.
In both of these models, the storm's northward trek is agonizingly slow. If they're anywhere close to right, this could be a very long-duration event for someone.
The models seem to be speeding the cold up a hair on Saturday night, though the precipitation then is pretty light.
I'm intrigued by this storm just on a meteorological standpoint. It could be a rare event, whatever happens. I'm not ruling it out being a unique event for our corner of the world.
Comment by kevinmyatt — February 26, 2009 @ 11:14 pm
Wow. WDBJ 7 website shows only mostly cloudy forecast for both Sunday and Monday!! High/Low forecasted to be 38/32 for Sunday and 38/25 for Monday!! Sombody is going to be very right for Sunday and Monday, and somebody else is going to be very wrong. I am not predicting which is which. OK, Kevin and the gang, what say you folks? Sounds like Kevin is with the wunderground/generally precip forecasts, not Channel 7.
Comment by Doug Griggs — February 26, 2009 @ 11:18 pm
Zach: Your "confused" analysis is about as good as anyone else's right now! HPC seems to be betting that the models are digging too far south with the upper low ... and tonight's NAM is lending some support to that. The overrunning event gets cold only at the very end, so it appears to me that they're aiming toward the upper low firing up a coastal.
Doug: 1.25 inches is almost exactly what HPC is showing for total 3-day precip in our area ... I will be posting that a little later.
Comment by kevinmyatt — February 26, 2009 @ 11:21 pm
Doug: If the storm does dig WAY far south and slides east of us out to sea, the WDBJ forecast will be right on the money. And that's well within the envelope of possibilities.
By Saturday morning I might take a stab at what will happen with some degree of "certainty." (Very relative term where weather is concerned). Right now all I'm content to say is there is serious potential, and I do think we'll be wet the next 2 days before the wintry issues develop.
Comment by kevinmyatt — February 26, 2009 @ 11:25 pm