Valentine's day 2012 system

[BrierCreekWx]

That's a great analog for this storm. Usually, surface winds out of the south leading up to precip arrival is a no-go for snow in these parts...but it can happen on rare occasion.

The track of our wave on the modeling has taken a noticeable trend south over the past day (more suppressed). Before, the core of the wave was tracking through Kansas, and now it is tracking through Oklahoma. Also, there is additional vort energy dropping into the backside of the wave, down into TX, so the wave is not weakening as quick as it moves east. The wave is going from slightly positive tilt to slightly negative tilt through the lower MS Valley - and you can see the 700mb RH expand during that time.

Looking at the RH and wet-bulb temps on the GFS forecasted soundings, I estimate 0.26 snow (liquid equiv) at Asheville and 0.09 at Charlotte. There is deep moisture as the precip gets going, with high RH extending up to 350mb.

We'll have to see how this trends in terms of how long the stale, cold air mass can hang around....and how strong and how far south our wave tracks....but I could see this easily trending to a 3-6 inch snow for the mtns.

Here's my thoughts for central NC:

In looking a little more closely at how the partial thicknesses played out in that event: http://www4.ncsu.edu...loop/index.html in comparison to the 12z gfs partial thickness forecast for the event in question: http://raleighwx.ame..._MAGFSLoop.html, raises some concerns.

The 1000-850mb critical snow thickness (around 1300m) was much further south in the 2007 event. In fact, 1000-850mb thicknesses were around 1290-95 at RDU at the onset of precipitation in that event and fell afterwards since there was still some level of dry air (wet-bulb was 27). Looking at this event, dewpoints are forecast to be near 32F at the onset of precip, meaning the wet-bulb is above freezing. The 1000-850mb partial thickness is near 1310 at the onset of precip, meaning that even at the start it's likely to be a rain/snow mix at best for RDU, quickly, VERY quickly, becoming all rain.

Unless this system can somehow speed up significantly, I see this being a few wet flakes mixed in with rain from CLT to RDU east. Even in the INT to GSO zone it looks like a non-event, with maybe a brief period of wet snow that becomes all rain with virtually no accumulation.

How could my forecast ideas be wrong? I feel confident that the high is going to move offshore as modeled, there's nothing to stop that in my opinion. Unless the low tracks further north and faster, which would allow moisture to stream out ahead of it quicker, and also allow for the boundary layer to be as cold as possible, I just don't see how this will trend in our favor. If the low tracks much further south, central NC will be out of the running because by the time precip reaches that area, warm air advection will have warmed the boundary layer too much.

Edit: Just to be clear, when I say "trend in our favor" I am essentially meaning if my above scenario plays out it would be a little more snow before going over to rain. I think that is our best scenario in central NC - snow quickly to rain.

[Cold Rain]

Here's my thoughts for central NC:

In looking a little more closely at how the partial thicknesses played out in that event: http://www4.ncsu.edu...loop/index.html in comparison to the 12z gfs partial thickness forecast for the event in question: http://raleighwx.ame..._MAGFSLoop.html, raises some concerns.

The 1000-850mb critical snow thickness (around 1300m) was much further south in the 2007 event. In fact, 1000-850mb thicknesses were around 1290-95 at RDU at the onset of precipitation in that event and fell afterwards since there was still some level of dry air (wet-bulb was 27). Looking at this event, dewpoints are forecast to be near 32F at the onset of precip, meaning the wet-bulb is above freezing. The 1000-850mb partial thickness is near 1310 at the onset of precip, meaning that even at the start it's likely to be a rain/snow mix at best for RDU, quickly, VERY quickly, becoming all rain.

Unless this system can somehow speed up significantly, I see this being a few wet flakes mixed in with rain from CLT to RDU east. Even in the INT to GSO zone it looks like a non-event, with maybe a brief period of wet snow that becomes all rain with virtually no accumulation.

How could my forecast ideas be wrong? I feel confident that the high is going to move offshore as modeled, there's nothing to stop that in my opinion. Unless the low tracks further north and faster, which would allow moisture to stream out ahead of it quicker, and also allow for the boundary layer to be as cold as possible, I just don't see how this will trend in our favor. If the low tracks much further south, central NC will be out of the running because by the time precip reaches that area, warm air advection will have warmed the boundary layer too much.

Edit: Just to be clear, when I say "trend in our favor" I am essentially meaning if my above scenario plays out it would be a little more snow before going over to rain. I think that is our best scenario in central NC - snow quickly to rain.

I agree 100%. I haven't looked at the partials quite frankly because the H5 setup is so bad for this area....so it's not even worth it for me. Maaaaybe we'll get lucky and see a couple of token flakes, like you said, but the bottom line is, the cold air is stale and retreating, and the warm advection is incoming handsomely. There's no strong, cold high to the north and nothing to lock it in even if it was there. I don't see any way this can trend better either. But as bad as this winter has been, I can understand why people want to talk about it, I guess.

[BrierCreekWx]

I agree 100%. I haven't looked at the partials quite frankly because the H5 setup is so bad for this area....so it's not even worth it for me. Maaaaybe we'll get lucky and see a couple of token flakes, like you said, but the bottom line is, the cold air is stale and retreating, and the warm advection is incoming handsomely. There's no strong, cold high to the north and nothing to lock it in even if it was there. I don't see any way this can trend better either. But as bad as this winter has been, I can understand why people want to talk about it, I guess.

I can understand that, and I feel the same way. At this point, I'm pulling for just a couple flakes. Given the right timing, such as in 2007, central NC can see some accumulation before the changeover in this type of event. In this instance though, it just looks like the period of return flow is too long before the moisture moves in. That will be the thing to watch in the models (the timing of the arrival of moisture), if it can speed up significantly we might have a shot at seeing a little more. I honestly don't think the track of the low matters, because central NC is going to changeover to rain, and fast, no matter what track it takes. Bottom line is that I think we maximize our amount of snow with a low track that brings moisture to us as quickly as possible.

[tazaroo]

I don't know why you guys think it can't even trend in our favor. Of course the models could be wrong either for the better or worse. They almost always are at least off some at anything past 48 hours.

Its just a waiting game now.

[WilkesboroDude]

NWS Blacksburg

Evaporative cooling may keep snow in longer across the mountains and north of Highway

460. Warm nose edges into southwest and Southside Virginia in the

afternoon to convert them over to rain. With this new

development...kept probability of precipitation at a chance but did lower afternoon highs

into the 40s...previously had 50s. Convection associated with the

surface low should keep snowfall amounts low and under 3

inches...maybe lower. A lot can change between now and then. Lets

get some continuity before raiding the grocery stores of bread and

milk.

[BrierCreekWx]

I don't know why you guys think it can't even trend in our favor. Of course the models could be wrong either for the better or worse. They almost always are at least off some at anything past 48 hours.

Its just a waiting game now.

Sure, anything can happen. But looking at the large scale atmospheric pattern, there is nothing to stop the parent high from sliding offshore. If and when that happens, any chances of a significant all-snow event are essentially done. After that, it's really just about how the timing of the moisture will impact residual cold air in place. If it comes in before the return flow from the Atlantic has significantly modified the air in place, a pretty nice insitu cold air damming episode can develop, but that's really the only option you have left on the table once that high is offshore. In this case, the timing is off by a good 6-12 hours for a really nice insitu cad event to develop in my view. Since all the models are in fairly good agreement, it's doubtful they will all increase the timing significantly faster, but again, anything can happen and like I said earlier the timing of the moisture arrival is the key thing to watch for this setup.

[FoothillsNC]

Here's my thoughts for central NC:

In looking a little more closely at how the partial thicknesses played out in that event: http://www4.ncsu.edu...loop/index.html in comparison to the 12z gfs partial thickness forecast for the event in question: http://raleighwx.ame..._MAGFSLoop.html, raises some concerns.

The 1000-850mb critical snow thickness (around 1300m) was much further south in the 2007 event. In fact, 1000-850mb thicknesses were around 1290-95 at RDU at the onset of precipitation in that event and fell afterwards since there was still some level of dry air (wet-bulb was 27). Looking at this event, dewpoints are forecast to be near 32F at the onset of precip, meaning the wet-bulb is above freezing. The 1000-850mb partial thickness is near 1310 at the onset of precip, meaning that even at the start it's likely to be a rain/snow mix at best for RDU, quickly, VERY quickly, becoming all rain.

Unless this system can somehow speed up significantly, I see this being a few wet flakes mixed in with rain from CLT to RDU east. Even in the INT to GSO zone it looks like a non-event, with maybe a brief period of wet snow that becomes all rain with virtually no accumulation.

How could my forecast ideas be wrong? I feel confident that the high is going to move offshore as modeled, there's nothing to stop that in my opinion. Unless the low tracks further north and faster, which would allow moisture to stream out ahead of it quicker, and also allow for the boundary layer to be as cold as possible, I just don't see how this will trend in our favor. If the low tracks much further south, central NC will be out of the running because by the time precip reaches that area, warm air advection will have warmed the boundary layer too much.

Edit: Just to be clear, when I say "trend in our favor" I am essentially meaning if my above scenario plays out it would be a little more snow before going over to rain. I think that is our best scenario in central NC - snow quickly to rain.

I agree with you on the surface winds, and thats the number one problem going on right now with the surface high progged to go offshore. But that just might be a little bit erroneous on the models as there's stilla good bit of confluence in the northeast at the time before precip begins, and a lot of times the models fail to put a high there, and also one develops in central Va or northern NC during a weak in-situ CAD event. I've seen several do that and sometimes the models still miss a meso high right up until the event begins. There's a lot of details that will be ironed out over the weekend, and a lot actually depends on the currently developing system that bombs out eastern Maine. We definitely need the timing and location of the southern system to not be delayed at all, there's a few ways this can shake out, either good or bad. Also the GFS has dewpoints to start well into the lower 20's with surface temps near freezing, so evap. cooling can help the first few hours of the event, but any strong sw winds at the surface will hinder areas esp. east of the mountains. Right now the models are both honing in on the western Carolinas and Georgia to keep a cool layer from the mtns and just next to the mountains as in-situ cad holds on, probably for the whole event, but it still might not be enough to keep as snow (but I do think it starts as snow from just north of Atlanta up interstate 85 to RDU and points west. Looks like Tennessee is mostly snow as they utilize all the precip as snow from warm advection before any strong sw or se winds occur for that area. Its an usual setup overall, and I don't like south winds usually for snow events in lower elevations...I recall one two years ago that managed to rain around here at -4 at 850. A lot of different things can happen locally though and each situation is slighly different. For the mountains , so long as the low doesn't pull north this could be a good event....just depends on how much moisture there is, and if any dryslotting occurs quickly, as some areas in NC are prone to. Also a thing to watch is how quickly moisture blossoms eastward before winds turn southerly....could be a couple quick inches anywhere that has snow to start, but as you stated many would go over to rain.

[IWC]

Robert, Glad to see you here posting thanks! I keep up with your site too.

[CAD_Wedge_NC]

I can understand that, and I feel the same way. At this point, I'm pulling for just a couple flakes. Given the right timing, such as in 2007, central NC can see some accumulation before the changeover in this type of event. In this instance though, it just looks like the period of return flow is too long before the moisture moves in. That will be the thing to watch in the models (the timing of the arrival of moisture), if it can speed up significantly we might have a shot at seeing a little more. I honestly don't think the track of the low matters, because central NC is going to changeover to rain, and fast, no matter what track it takes. Bottom line is that I think we maximize our amount of snow with a low track that brings moisture to us as quickly as possible.

Haven't looked at any locations to my east, but for MBY (elevation 1100 ft) according to the 18z GFS MeteoStar, the bulk of the precip is over before 850's get higher than 0c.... taken literally, 0.33 falls @ 850's <0c and another .08 falls @ 850's >0c. Surface temps are 33 degrees at the onset and rise during the event to 35 degrees at the very end. Dewpoints start at 32 and rise to 35. That would imply a couple of inches of snow followed by some drizzle at the end. Not sure if I buy that yet. Ground temps would certainly be supportive of some accumulation after the upper teens to around 20 for forecasted lows in the days prior. Now, if this thing trends a little quicker, we might have a nice storm to track. It sure has some possibilities. It will be interesting to see what tonight's runs have in store.

[BrierCreekWx]

I agree with you on the surface winds, and thats the number one problem going on right now with the surface high progged to go offshore. But that just might be a little bit erroneous on the models as there's stilla good bit of confluence in the northeast at the time before precip begins, and a lot of times the models fail to put a high there, and also one develops in central Va or northern NC during a weak in-situ CAD event. I've seen several do that and sometimes the models still miss a meso high right up until the event begins. There's a lot of details that will be ironed out over the weekend, and a lot actually depends on the currently developing system that bombs out eastern Maine. We definitely need the timing and location of the southern system to not be delayed at all, there's a few ways this can shake out, either good or bad. Also the GFS has dewpoints to start well into the lower 20's with surface temps near freezing, so evap. cooling can help the first few hours of the event, but any strong sw winds at the surface will hinder areas esp. east of the mountains. Right now the models are both honing in on the western Carolinas and Georgia to keep a cool layer from the mtns and just next to the mountains as in-situ cad holds on, probably for the whole event, but it still might not be enough to keep as snow (but I do think it starts as snow from just north of Atlanta up interstate 85 to RDU and points west. Looks like Tennessee is mostly snow as they utilize all the precip as snow from warm advection before any strong sw or se winds occur for that area. Its an usual setup overall, and I don't like south winds usually for snow events in lower elevations...I recall one two years ago that managed to rain around here at -4 at 850. A lot of different things can happen locally though and each situation is slighly different. For the mountains , so long as the low doesn't pull north this could be a good event....just depends on how much moisture there is, and if any dryslotting occurs quickly, as some areas in NC are prone to. Also a thing to watch is how quickly moisture blossoms eastward before winds turn southerly....could be a couple quick inches anywhere that has snow to start, but as you stated many would go over to rain.

The only thing I don't really agree with you on is that precipitation isn't really beginning at 114 hours. If you look at the sounding, it isn't saturated below about 700mb at that time. By the time precipitation starts to reach the ground, it's a good bit warmer. We can certainly agree to disagree, but I don't think this has potential to be much of anything from CLT to RDU, and definitely not all snow to start. But hey, I hope you're right and I'm wrong because I am as big of a winter weather as anyone here!

[NCStateMMY]

The only thing I don't really agree with you on is that precipitation isn't really beginning at 114 hours. If you look at the sounding, it isn't saturated below about 700mb at that time. By the time precipitation starts to reach the ground, it's a good bit warmer. We can certainly agree to disagree, but I don't think this has potential to be much of anything from CLT to RDU, and definitely not all snow to start. But hey, I hope you're right and I'm wrong because I am as big of a winter weather as anyone here!

The key is from 700 to the surface. It is quiet dry below there. Look at the wet bulb (blue line). Evaporative cooling will very likely occur as the column saturates if the rates are high enough. That will certainly put the temperature below freezing.

[BrierCreekWx]

The key is from 700 to the surface. It is quiet dry below there. Look at the wet bulb (blue line). Evaporative cooling will very likely occur as the column saturates if the rates are high enough. That will certainly put the temperature below freezing.

That's a pretty confident statement, (or correction?!). Did you look at the soundings beyond that time? Warm air advection quickly raises the entire layer temperature above freezing because the high is offshore and the winds through the entire column are out of the south and southwest.

[WilkesboroDude]

IMO, this first system this weekend is laying out the ground work for the system next week. We most certainly need a few arctic nights to cool our ground temps esp. east of the mountains. The teens in the forecast for the mountains this weekend could be too warm with a fresh snow pack.

Really hope the system speeds up some.

[HKY_WX]

gfs/euro look interesting for next week in parts of NC. time to start paying attention to that one.

[burgertime]

If the DGEX shows little snow for us during a potential threat, does that mean we will get a blizzard?

[packbacker]

gfs/euro look interesting for next week in parts of NC. time to start paying attention to that one.

You talking about the day 8-9 time period?

[jburns]

Yeah it just looks like another example of precip chasing cold. Also for those of you hoping for a quicker onset of precip to make the difference, don't. Even if it does speed up it will push the cold out earlier as well. Outside of the mountains and maybe a bit of slop in the foothills we are spectators for this event.

[HKY_WX]

You talking about the day 8-9 time period?

nevermind i'm weary been a long day. the tuesday system and flipping back i noticed that's what we're talking about.i thought some were referencing the flurry/frontal system tom'.

[WilkesboroDude]

Yeah it just looks like another example of precip chasing cold. Also for those of you hoping for a quicker onset of precip to make the difference, don't. Even if it does speed up it will push the cold out earlier as well. Outside of the mountains and maybe a bit of slop in the foothills we are spectators for this event.

I will take my slop!

[jburns]

I will take my slop!

lol Enjoy......maybe.

[FoothillsNC]

Robert, Glad to see you here posting thanks! I keep up with your site too.

thanks but it has been a long process. Almost done (I think) but as Steve can attest to, its been a challenge to get it up and running.

The only thing I don't really agree with you on is that precipitation isn't really beginning at 114 hours. If you look at the sounding, it isn't saturated below about 700mb at that time. By the time precipitation starts to reach the ground, it's a good bit warmer. We can certainly agree to disagree, but I don't think this has potential to be much of anything from CLT to RDU, and definitely not all snow to start. But hey, I hope you're right and I'm wrong because I am as big of a winter weather as anyone here!

I wouldn't use soundings just yet, but rely on synoptics the most, then soundings later. I certainly wouldn't rule out anything just yet though. If the models are right on the RH field and the 5H, then the surface high will probably (partially) re-locate inland in Virginia....be looking for that on future runs. That would help areas esp. from CLT westward on maintaining a ne or east wind at the surface.

[HKY_WX]

I like the odds for a weak-moderate event on Tuesday for a few reasons. One is the overal setup favors it with the cutoff low developing north of Maine and the ridging to the northeast near Greenland. This will force the system in the Missouri Valley to dig as opposed to shear out or streak north into the Ohio Valley and prevent this from trending too far north.

This weekend's frontal system will set this up by laying down the boundary far south into the Deep south. Dewpoints on the gfs sounds for HKY Monday afternoon are in the single digits. This will really promote wetbulbs being very low in much of the state.

I could see this as a situation where it starts as snow and slowly changes to sleet and then zr/rain depending on location. Best areas are definitely Mountains/foothills and I40 N areas in NC.

[valkhorn]

That's a narrow band of moderate snow from Chattanooga eastward. Knoxville looks like it's on the 3" line or thereabouts. This is a much narrower and heavier band than 12Z had.

18Z GFS:

[burgertime]

Comparing the 00z NAM @84 and the 18z GFS @90...the NAM is colder and has what loos like more moisture out in TX. Also energy in the west was stronger at 500mb.

[Chattownsnow]

in reference to burgertime...

00Z NAM at hr84

18Z GFS at hr87

It seems the NAM does run colder and wetter compaired to the GFS, especially in its longer range depictions (60hr-84hr) from what I have noticed with many oncoming events.

[tarheelwx]

00z NAM @81 hrs is wetter and faster than 18z @ 84 hrs. However, hp is a bit weaker and I'd say it isn't quite as cold.

TW

[griteater]

This storm reminds me of the February 1, 2007 event. It was a front end thump imby with out any sort of high pressure locking in cold air. Wetbulbing and residual cold air was enough to drop 2.75 inches at my house from that storm before it switched over to rain.

Another similar event occurred the very next year, Jan 17, 2008. It also had a very marginal temp setup. Charlotte reported surface winds out of the south for several hours leading up to precip start and during the first few hours of precip, before weak damming kicked in....snow for the first 4 hours, then freezing rain, then rain.

Here's the snowfall map....which, I think is a decent match for next Tues based on current modeling.

[LithiaWx]

Let's compare apples to apples guys..I don't really advocate getting this picky but here we are.

[toxictwister00]

Another similar event occurred the very next year, Jan 17, 2008. It also had a very marginal temp setup. Charlotte reported surface winds out of the south for several hours leading up to precip start and during the first few hours of precip, before weak damming kicked in....snow for the first 4 hours, then freezing rain, then rain.

Here's the snowfall map....which, I think is a decent match for next Tues based on current modeling.

I thought about this date pertaining to this storm also. We only picked up about a half an inch imby before the snow transitioned to sleet/freezing rain then to rain.

[burgertime]

00z NAM @81 hrs is wetter and faster than 18z @ 84 hrs. However, hp is a bit weaker and I'd say it isn't quite as cold.

TW

You should be comparing 18z @84 with 00z@78 or 18z @75 with 00z@81...in which case the 00z is colder with 850 temps if you look at the eastern section of Florida correction got mixed up 18z was slightly colder...probably splitting hairs with that though.