burgertime Posted February 9, 2011 Share Posted February 9, 2011 Well we are going to have good mid and upper level forcing over our area thanks to a pretty potent jet streak according to the RUC. This is not something that is forecast to occur... its happening right now. Thats why you are seeing the finger of higher precipitation streaming northward into Tennessee and Kentucky... this feature is providing the forcing to allow the band to setup despite the lack of a strong 850mb or 700mb low. This jetstreak is forecast to move to the NE at a rather rapid pace, so we should continue to see the precipitation expand as it moves westward, not fall apart like the NAM is suggesting. The RUC has a much better handle on whats going on in my opinion and even it might be underdone. I think this is why the NWS in Greenville has been pretty bullish on accumulating snowfall... since it looks like the upper features are in place. My opinion is that if we already have precipitation upstream, and our system will be moving into an area of increased upper level divergence, thats not going to weaken the precipitation all that much, and the surface low should actually intensify. I'm pretty sure the storm New Year's day had the same type of setup. Every model painted practically nothing here then when it arrived we had a good .5 of rain. Not saying that will happen but IIRC the rain was taking the same path and we were supposed to loose everything on the transport to the low. In that storm it didn't happen. I would love to see some maps though leading up to it as the thread I was looking through had no maps just everyone in WNC basically saying nothing was going to happen. Need to look through the late Dec. thread I guess. Link to comment Share on other sites More sharing options...
strongwxnc Posted February 9, 2011 Share Posted February 9, 2011 OBS thread folks!! Link to comment Share on other sites More sharing options...
CaryWx Posted February 9, 2011 Share Posted February 9, 2011 That's bold Phil. You're a genious if you've got that pegged correctly. I'm rootin' for ya. Link to comment Share on other sites More sharing options...
FoothillsNC Posted February 9, 2011 Share Posted February 9, 2011 My opinion is that if we already have precipitation upstream, and our system will be moving into an area of increased upper level divergence, thats not going to weaken the precipitation all that much, and the surface low should actually intensify. that entrance region of the jet is one thing I was thinking about a couple days ago when I saw the models shifting the precip south, and figured there is always a chance here of actual enhancement to the precip, the RUC is shwoing that now, but I still don't know if its right. I'd rather wait a few more hours to bite into it. Living here I can see absolutely anything happening from enhancement to actual pure decay of the moisture field, and this is harder than usual to predict so its probably safest to go a low end event, which is what most are doing. One area I do trust a lot more with the RUC is just to our south, outside the effects of the mtn. chain, around BHM ATL to CAE where there will def. be good moisture for quite a few hours. Link to comment Share on other sites More sharing options...
burgertime Posted February 9, 2011 Share Posted February 9, 2011 I'm pretty sure the storm New Year's day had the same type of setup. Every model painted practically nothing here then when it arrived we had a good .5 of rain. Not saying that will happen but IIRC the rain was taking the same path and we were supposed to loose everything on the transport to the low. In that storm it didn't happen. I would love to see some maps though leading up to it as the thread I was looking through had no maps just everyone in WNC basically saying nothing was going to happen. Need to look through the late Dec. thread I guess. Actually looking in the Dec. thread the GFS three days out had the lee side in .5 while everyone else was pretty much in 1 to 2 inches...it was also a straight gulf low storm so never mind. Link to comment Share on other sites More sharing options...
beanskip Posted February 9, 2011 Author Share Posted February 9, 2011 Not sure how lee troughs set up and work, but I was noticing the 700 RH field on the 19z RUC. Check out this series of maps and the RH that seems to take up residence in the lee of the Apps in N.C. 14 hours 15 hours 16 hours 17 hours 18 hours Nice catch or Ha-RUC-cinnations? Link to comment Share on other sites More sharing options...
burgertime Posted February 9, 2011 Share Posted February 9, 2011 Not sure how lee troughs set up and work, but I was noticing the 700 RH field on the 19z RUC. Check out this series of maps and the RH that seems to take up residence in the lee of the Apps in N.C. 14 hours 15 hours 16 hours 17 hours 18 hours Nice catch or Ha-RUC-cinnations? http://www.theweatherprediction.com/habyhints/129/ Link to comment Share on other sites More sharing options...
DAWGNKITTEN Posted February 9, 2011 Share Posted February 9, 2011 that entrance region of the jet is one thing I was thinking about a couple days ago when I saw the models shifting the precip south, and figured there is always a chance here of actual enhancement to the precip, the RUC is shwoing that now, but I still don't know if its right. I'd rather wait a few more hours to bite into it. Living here I can see absolutely anything happening from enhancement to actual pure decay of the moisture field, and this is harder than usual to predict so its probably safest to go a low end event, which is what most are doing. One area I do trust a lot more with the RUC is just to our south, outside the effects of the mtn. chain, around BHM ATL to CAE where there will def. be good moisture for quite a few hours. I don't understand what you and Phil are exactly talking about..."entrance region"....could you explain it in layman's terms, what that means for AL, GA, NC, SC? Link to comment Share on other sites More sharing options...
phil882 Posted February 9, 2011 Share Posted February 9, 2011 Another thing I'd also like to add is that the 15z SREF guidance might be having problems with moisture transport, as they are predicting some heavy precipitation amounts over the Gulf Coast, which is likely limiting moisture transport further north due to convection. I simply don't see any major convection going on in the Gulf of Mexico currently. Link to comment Share on other sites More sharing options...
burgertime Posted February 9, 2011 Share Posted February 9, 2011 I don't understand what you and Phil are exactly talking about..."entrance region"....could you explain it in layman's terms, what that means for AL, GA, NC, SC? If I understand it correctly, basically the jet forces the upper levels through that point, this causes more moisture to go towards that area....I think anyways. Link to comment Share on other sites More sharing options...
snowforme Posted February 9, 2011 Share Posted February 9, 2011 http://www.theweathe.../habyhints/129/ I was looking for an explanation of that as well, seeing as though it appears Wake County is smack dab in the middle of it. Thanks for posting! I just love being in the middle of the big white dot! Link to comment Share on other sites More sharing options...
FoothillsNC Posted February 9, 2011 Share Posted February 9, 2011 Not sure how lee troughs set up and work, but I was noticing the 700 RH field on the 19z RUC. Check out this series of maps and the RH that seems to take up residence in the lee of the Apps in N.C. 14 hours 15 hours 16 hours 17 hours 18 hours Nice catch or Ha-RUC-cinnations? good eyes Skip. I was just looking at surface obs and there is indeed a lee trough right now, ahead of the cold front in Tenn. There is actually excellent low level convergence seen on the wind fields right now and lines up perfectly with the expanding precip shield in Alabama and Tenn, so this is a potential fly in the ointment for us. In a good way. I think we'll need to pay very close attention to the radar and RUC trends now Link to comment Share on other sites More sharing options...
DAWGNKITTEN Posted February 9, 2011 Share Posted February 9, 2011 If I understand it correctly, basically the jet forces the upper levels through that point, this causes more moisture to go towards that area....I think anyways. Thanks Burger...appreciate it!!! Link to comment Share on other sites More sharing options...
phil882 Posted February 9, 2011 Share Posted February 9, 2011 I don't understand what you and Phil are exactly talking about..."entrance region"....could you explain it in layman's terms, what that means for AL, GA, NC, SC? The entrance region of a jet streak (just a fancy term for an area of much higher wind speed in the upper atmosphere) is an area where there is very strong divergence going on. Divergence is just the spreading out of air parcels over a location. Once you get to the top of the atmosphere, if you have wind that is forcing some air to go in one direction, while some air is going in the opposite direction, you are left with a void right where the air use to be since its not being replaced by the air to the left or to the right. Thus, in order to replace the air, you have to force the air below to rise. Rising motion helps produce clouds and precipitation, so divergence aloft is typically a very beneficial thing if you wan additional clouds and precipitation. Link to comment Share on other sites More sharing options...
beanskip Posted February 9, 2011 Author Share Posted February 9, 2011 good eyes Skip. Makes my day! (And it needed some help!) Link to comment Share on other sites More sharing options...
Cheeznado Posted February 9, 2011 Share Posted February 9, 2011 HRRR trending nicely.... Link to comment Share on other sites More sharing options...
burgertime Posted February 9, 2011 Share Posted February 9, 2011 The entrance region of a jet streak (just a fancy term for an area of much higher wind speed in the upper atmosphere) is an area where there is very strong divergence going on. Divergence is just the spreading out of air parcels over a location. Once you get to the top of the atmosphere, if you have wind that is forcing some air to go in one direction, while some air is going in the opposite direction, you are left with a void right where the air use to be since its not being replaced by the air to the left or to the right. Thus, in order to replace the air, you have to force the air below to rise. Rising motion helps produce clouds and precipitation, so divergence aloft is typically a very beneficial thing if you wan additional clouds and precipitation. lol guess I was totally wrong in my explanation. So glad to have all the great mets here and you have been on top of this Phil. If we get a nice surprise kudos to you for sure! Link to comment Share on other sites More sharing options...
VeronicaCorningstone Posted February 9, 2011 Share Posted February 9, 2011 The entrance region of a jet streak (just a fancy term for an area of much higher wind speed in the upper atmosphere) is an area where there is very strong divergence going on. Divergence is just the spreading out of air parcels over a location. Once you get to the top of the atmosphere, if you have wind that is forcing some air to go in one direction, while some air is going in the opposite direction, you are left with a void right where the air use to be since its not being replaced by the air to the left or to the right. Thus, in order to replace the air, you have to force the air below to rise. Rising motion helps produce clouds and precipitation, so divergence aloft is typically a very beneficial thing if you wan additional clouds and precipitation. Phil, you have a wonderful way of explaining things - I could picture what you were explaining as I read it. Thank you for your insight on this forum. Looking forward to seeing you get that red tag in May. Link to comment Share on other sites More sharing options...
WXinCanton Posted February 9, 2011 Share Posted February 9, 2011 The entrance region of a jet streak (just a fancy term for an area of much higher wind speed in the upper atmosphere) is an area where there is very strong divergence going on. Divergence is just the spreading out of air parcels over a location. Once you get to the top of the atmosphere, if you have wind that is forcing some air to go in one direction, while some air is going in the opposite direction, you are left with a void right where the air use to be since its not being replaced by the air to the left or to the right. Thus, in order to replace the air, you have to force the air below to rise. Rising motion helps produce clouds and precipitation, so divergence aloft is typically a very beneficial thing if you wan additional clouds and precipitation. awesome stuff as usual Phil! You going to put up a call map? Link to comment Share on other sites More sharing options...
EmersonGA Posted February 9, 2011 Share Posted February 9, 2011 Question is, is it right? It sure looks good on it's simulated radar. I sure hope it's right. Those 30 dz returns are getting close to MBY. Link to comment Share on other sites More sharing options...
DAWGNKITTEN Posted February 9, 2011 Share Posted February 9, 2011 The entrance region of a jet streak (just a fancy term for an area of much higher wind speed in the upper atmosphere) is an area where there is very strong divergence going on. Divergence is just the spreading out of air parcels over a location. Once you get to the top of the atmosphere, if you have wind that is forcing some air to go in one direction, while some air is going in the opposite direction, you are left with a void right where the air use to be since its not being replaced by the air to the left or to the right. Thus, in order to replace the air, you have to force the air below to rise. Rising motion helps produce clouds and precipitation, so divergence aloft is typically a very beneficial thing if you wan additional clouds and precipitation. Thank you very much....appreciate the time you took to explain it. Link to comment Share on other sites More sharing options...
Rankin5150 Posted February 9, 2011 Share Posted February 9, 2011 Looks like there is great lift taking place on the radar. The trend to a more dynamic setup continues... http://www.intellicast.com/National/Radar/Current.aspx?animate=true Link to comment Share on other sites More sharing options...
beanskip Posted February 9, 2011 Author Share Posted February 9, 2011 Also a similar signature at 18 hours on the 18z NAM. http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/18/images/nam_700_018l.gif good eyes Skip. I was just looking at surface obs and there is indeed a lee trough right now, ahead of the cold front in Tenn. There is actually excellent low level convergence seen on the wind fields right now and lines up perfectly with the expanding precip shield in Alabama and Tenn, so this is a potential fly in the ointment for us. In a good way. I think we'll need to pay very close attention to the radar and RUC trends now Link to comment Share on other sites More sharing options...
NEGa Posted February 9, 2011 Share Posted February 9, 2011 the way I look at this, even though all models have gotten wetter, as many suspected they would esp. in Ala, GA and the eastern Carolinas, the basic same premise holds in the lee areas and the central Piedmont region of NC and northwest SC area because of a bad transfer of energy that is forecast to happen. Our only hope here for any significant, or even just .10" of precip in that big hole is for the precip to be strong and with good forcing coming out of GA, and to be honest, thats asking a lot in any year with a marginal situation, and in this particular special setup, its even going to be harder to overcome all the negative factors. The writing on the wall, all ensembles and individual members, operations show this same general gap, some have a little precip and others have a brief window of snow, but usually this doesn't give much surprises here. Unlike times when we're watching an overrunning event, where moisture can drift a little more north and west than initially shown, this one looks like much less of a chance of that happening. However, its not totally out of the question, I just wouldn't bank on anything more than 1" in that general area, and some areas may get only 5 minutes of flakes. it is certainly hard to ignore that most guidance is very light with qpf for eastern ga and the carolinas. this is a situation where 50 miles can make a huge difference west to east. if it can hold together just a little longer into ga, then e ga and the upstate may see some snow. if it weakens 50 miles to the west, most of us in n c ga to the east (except far east) carolinas will be screwed. its pathetic when we are hoping and gasping for a simple .10-.15" of qpf lol Link to comment Share on other sites More sharing options...
Rankin5150 Posted February 9, 2011 Share Posted February 9, 2011 Does anyone know what the current pressure is for the low in the gulf? TIA! Link to comment Share on other sites More sharing options...
Lookout Posted February 9, 2011 Share Posted February 9, 2011 good eyes Skip. I was just looking at surface obs and there is indeed a lee trough right now, ahead of the cold front in Tenn. There is actually excellent low level convergence seen on the wind fields right now and lines up perfectly with the expanding precip shield in Alabama and Tenn, so this is a potential fly in the ointment for us. In a good way. I think we'll need to pay very close attention to the radar and RUC trends now There is already a very thick mid level cloud deck with hints of some low level cloudiness. Indeed radar is already picking up virga out of these clouds. Link to comment Share on other sites More sharing options...
audioguy3107 Posted February 9, 2011 Share Posted February 9, 2011 Looks like there is great lift taking place on the radar. The trend to a more dynamic setup continues... http://www.intellicast.com/National/Radar/Current.aspx?animate=true Be wary of that intellicast radar.......tends to look alot better than ground truth. Link to comment Share on other sites More sharing options...
DAWGNKITTEN Posted February 9, 2011 Share Posted February 9, 2011 Does anyone know what the current pressure is for the low in the gulf? TIA! If I'm not mistaken it's 1014, but could be reading it wrong... Link to comment Share on other sites More sharing options...
phil882 Posted February 9, 2011 Share Posted February 9, 2011 awesome stuff as usual Phil! You going to put up a call map? Working on that right now... don't have much time for a discussion though, as I have a lot of work to do in my classes tonight. I'm hoping for a snow day Link to comment Share on other sites More sharing options...
NEGa Posted February 9, 2011 Share Posted February 9, 2011 I'd be a bit surprised if your area didn't get something, which I have been thinking most of the way. Still don't think an inch is not out of the question because the column is so cold ratios should be high so you won't actually need much liquid. Ruc is still awful on surface temps/dewpoints. This morning it was showing dewpoints around 32 or 33 by now, and of course dewpoints remain in the upper teens/near 20. It continues to be about 10 degrees higher on dewpoints vs the nam/gfs and off around 15 degrees vs reality. I wonder though if this is part of the reason for it's impressive precip? i hadnt paid much attention to the dewpoint imby until my ob a few minutes ago (its 19, way lower than i had anticipated). with evap cooling we should lose some qpf but should get to freezing at least (upper 30s now) ruc is messing with my mind - i havent paid as much attention to its temps as i have its qpf. its done ok moisture wise (which is why i am still secretly optimistic for an inch) Link to comment Share on other sites More sharing options...
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