ORH_wxman Posted February 19, 2012 Share Posted February 19, 2012 I posted this about the NAM in the other banter thread: Its a strange model but can be pretty good at times...but it needs a certain set of variables that aren't always apparent early on...usually I noticed in systems where hydrostatic approximation is not a good idea is where the NAM succeeds since it is not a hydrostatic model...it simulates the actual convection without hydrostatic assumption. It succeeded in beating the Euro in Jan 12 last year because of this...it also won in Dec 5, 2009 but that system it was less obvious. It wasn't as convective as 1/12/11. It tends to do terrible in systems with a lot of moving pieces far from the center of circulation IMHO. I don't have any stats to prove this, but just anecdotel when thinking about storms it has succeeded in versus its larger failures. Link to comment Share on other sites More sharing options...
Absolute Humidity Posted February 19, 2012 Share Posted February 19, 2012 One of the models was completely blowing the 1/26 storm last year up north as it was happening, it may have been the NAM as well. It was the NAM, had a 1.25" blob over DC at 24h and barely anything for NJ NYC. Link to comment Share on other sites More sharing options...
Coach McGuirk Posted February 19, 2012 Share Posted February 19, 2012 NAM looks good for me. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted February 19, 2012 Share Posted February 19, 2012 I understand NWS has budget constraints and limits on what they can do....I have no doubt it is full of talented mets and programmers....Maybe they can improve the model over the next few years...As far as I am concerned, the body of work is quite clear that this is not a model to be paid any credence in the winter....If mets and other forecasters utilize and rely on it for winter storms, it is not the fault of the NWS....it is the fault of the mets/forecasters....If it comes to fruition that this is a whiff up here and a bust in many other places, it isnt the Governments fault, and I hope people who used the NAM as guidance don't play the blame game.... Yeah I agree, nobody should blame a model for their own forecast. The potential for this to occur has been on the table since the inception of this storm when we knew it would be severely positive tilt. Elongated warm fronts and a very moist GOM will wreak havoc on the guidance should MCS's develop...which is currently occuring. Unfortunately it is difficult to use probability snow total maps with the public...but when you have the potential for massive shifts in snow totals where the synoptic development itself is dependent upon convective activity, that is the solid way to go. Link to comment Share on other sites More sharing options...
Ji Posted February 19, 2012 Share Posted February 19, 2012 NAM looks good for me. ya its not going to stick...your in Va beach and the air mass sucks Link to comment Share on other sites More sharing options...
Midlo Snow Maker Posted February 19, 2012 Share Posted February 19, 2012 damn just catching up looks like a huge whiff for dc, man what a south trend, still looks like southside va into ric get the biggest storm of the year Link to comment Share on other sites More sharing options...
baroclinic_instability Posted February 19, 2012 Share Posted February 19, 2012 sure...but I dont sense that the meteorological community at large understands its fortes and biases so to the extent it is put forth as guidance for east coast winter storms....>I think there is a shared responsibility between the forecasting community and the government....Forecasters need to understand the best way to utilize the guidance that is out there and the government has a responsibilty to put out a product that doesn't perform so poorly on the most important aspects....track, QPF, upper level temps, surface temps Trust me I am not defending it at all. Personally I would love to see more "forecasting" these days, but there certainly has been a reliance on models by many forecasters these days. Little effort is put into diagnosing the synoptic/dynamic environment anymore, and too much reliance is put into QPF and the final model output. This is a problem everywhere in forecasting. Link to comment Share on other sites More sharing options...
clskinsfan Posted February 19, 2012 Share Posted February 19, 2012 NAM looks good for me. Yeah. If you like rain. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted February 19, 2012 Share Posted February 19, 2012 I posted this about the NAM in the other banter thread: Its a strange model but can be pretty good at times...but it needs a certain set of variables that aren't always apparent early on...usually I noticed in systems where hydrostatic approximation is not a good idea is where the NAM succeeds since it is not a hydrostatic model...it simulates the actual convection without hydrostatic assumption. It succeeded in beating the Euro in Jan 12 last year because of this...it also won in Dec 5, 2009 but that system it was less obvious. It wasn't as convective as 1/12/11. It tends to do terrible in systems with a lot of moving pieces far from the center of circulation IMHO. I don't have any stats to prove this, but just anecdotel when thinking about storms it has succeeded in versus its larger failures. Full agreement. IMO the NAM is in a "tough" spot since it is non-hydrostatic at 12 km grid. Subgrid scale paramaterizations in a non-hydrostatic model can wreak havoc in certain situations. It is also those traits that make it so useful with deep PV's over moist and intense baroclinic zones. Slow moving single part systems are its forte. Link to comment Share on other sites More sharing options...
usedtobe Posted February 19, 2012 Share Posted February 19, 2012 I think there are times when you can use the nam so I'm not as negative as some. When all the models have a similar surface and qpf it will have the better temp field on average as it is better with damming events. It also sometimes does a better job with the mesoscale banding and CSI when the system is well behaved.. No model is good with lots of moving parts and the nam is then is usually worse than the GFS and Euro. Link to comment Share on other sites More sharing options...
Coach McGuirk Posted February 19, 2012 Share Posted February 19, 2012 ya its not going to stick...your in Va beach and the air mass sucks I don't live in Virginia Beach. Link to comment Share on other sites More sharing options...
clskinsfan Posted February 19, 2012 Share Posted February 19, 2012 I don't live in Virginia Beach. Yeah. You live in Yorktown and have the same boundary temp issues on the NAM. Link to comment Share on other sites More sharing options...
ORH_wxman Posted February 19, 2012 Share Posted February 19, 2012 Now that we are done bashing the NAM it may be too far south.....doesn't matter much for me but for the places still in the game for good snow, I'd use the GFS tonight as my primary forecasting tool and hope the Euro generally agrees with it...still high bust potential but that is going to be the best forecast.....using those 2 models the best one knows how....The NAM has to be disregarded on this one.... I would agree its probably too far south...for the same reasons I spoke of above. Its non-hydrostatic so it can have a lot of problems when there is a lot of convection far from the center and then convection near the center too at the same time...it will have trouble resolving the larger scale synoptic lift I think...but it obviously could be onto something since its always the first model out with the new 00z data. But I usually just hold it off to the side if it shows a different solution on a new raob primary run and wait for the others to chime in. This was never an obvious system until later in the game where the NAM would be poor...early on it looked a bit more tighter wrapped and it kept trending more strung out with its dynamics and convection, so I think that is where the NAM got in trouble really bad. For those who aren't familiar, "hydrostatic" means an assumed balance in the atmosphere between the pressure gradient and gravity, but when steep convection is evident then this balance can be out of whack a bit...but overall its a good assumption and that is what most global models use...but models like the NAM and most (if not all?) SREFS are non-hydrostatic and actually will go into hydrostatic imbalance if the convection simulates it on their model (which does happen in real life for brief times)....but it can often cause problems in modeling if the convection is off a bit...esp synoptically when the convection is far off from the center. I'm no expert on this, but this is what I have read in the past and seen it play out in actual systems as mentioned above. I could be in slight error in my explanation but I think I managed to cover the basics of it. Anyone who knows more can correct me. Link to comment Share on other sites More sharing options...
Coach McGuirk Posted February 19, 2012 Share Posted February 19, 2012 Yeah. You live in Yorktown and have the same boundary temp issues on the NAM. Yeah, If you've seen my posts I've expressed the boundary layer problems for the Hampton Roads. Link to comment Share on other sites More sharing options...
clskinsfan Posted February 19, 2012 Share Posted February 19, 2012 NWS is starting to cancel some WWA's for the northern counties. Link to comment Share on other sites More sharing options...
mitchnick Posted February 19, 2012 Share Posted February 19, 2012 RGEM is further south too EZF on north, fuggetaboutit, and probably a bit south of that (per RGEM) Link to comment Share on other sites More sharing options...
Midlo Snow Maker Posted February 19, 2012 Share Posted February 19, 2012 Yeah, If you've seen my posts I've expressed the boundary layer problems for the Hampton Roads. atleast you get some QPF and have a chance i guess better than others Link to comment Share on other sites More sharing options...
Amped Posted February 19, 2012 Share Posted February 19, 2012 I would agree its probably too far south...for the same reasons I spoke of above. Its non-hydrostatic so it can have a lot of problems when there is a lot of convection far from the center and then convection near the center too at the same time...it will have trouble resolving the larger scale synoptic lift I think...but it obviously could be onto something since its always the first model out with the new 00z data. But I usually just hold it off to the side if it shows a different solution on a new raob primary run and wait for the others to chime in. This was never an obvious system until later in the game where the NAM would be poor...early on it looked a bit more tighter wrapped and it kept trending more strung out with its dynamics and convection, so I think that is where the NAM got in trouble really bad. For those who aren't familiar, "hydrostatic" means an assumed balance in the atmosphere between the pressure gradient and gravity, but when steep convection is evident then this balance can be out of whack a bit...but overall its a good assumption and that is what most global models use...but models like the NAM and most (if not all?) SREFS are non-hydrostatic and actually will go into hydrostatic imbalance if the convection simulates it on their model (which does happen in real life for brief times)....but it can often cause problems in modeling if the convection is off a bit...esp synoptically when the convection is far off from the center. I'm no expert on this, but this is what I have read in the past and seen it play out in actual systems as mentioned above. I could be in slight error in my explanation but I think I managed to cover the basics of it. Anyone who knows more can correct me. Certainly a lot of convection far from the center. The Srefs and ETA all come way south also. Thanks for the insight. Amazing how this winter is finding ways to suck that are too complex for most of us to understand. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted February 19, 2012 Share Posted February 19, 2012 I would agree its probably too far south...for the same reasons I spoke of above. Its non-hydrostatic so it can have a lot of problems when there is a lot of convection far from the center and then convection near the center too at the same time...it will have trouble resolving the larger scale synoptic lift I think...but it obviously could be onto something since its always the first model out with the new 00z data. But I usually just hold it off to the side if it shows a different solution on a new raob primary run and wait for the others to chime in. This was never an obvious system until later in the game where the NAM would be poor...early on it looked a bit more tighter wrapped and it kept trending more strung out with its dynamics and convection, so I think that is where the NAM got in trouble really bad. For those who aren't familiar, "hydrostatic" means an assumed balance in the atmosphere between the pressure gradient and gravity, but when steep convection is evident then this balance can be out of whack a bit...but overall its a good assumption and that is what most global models use...but models like the NAM and most (if not all?) SREFS are non-hydrostatic and actually will go into hydrostatic imbalance if the convection simulates it on their model (which does happen in real life for brief times)....but it can often cause problems in modeling if the convection is off a bit...esp synoptically when the convection is far off from the center. I'm no expert on this, but this is what I have read in the past and seen it play out in actual systems as mentioned above. I could be in slight error in my explanation but I think I managed to cover the basics of it. Anyone who knows more can correct me. If it is too far S it may not be by much. One certainty we know now is convection is well displaced from the main parent cyclone. The frontal zone is grossly elongated with a secondary diabatic low over Florida. Advective processes across the warm sector are being severely inhibited by this, and shortwave ridge building/amplification are weak. The upper shortwave is of much lower amplitude as a result and will thus have a much faster phase speed aloft meaning the defo band will have less time to materialize before the fast upper low begins forcing the development of the secondary coastal. That defo band will not have much time here to dump heavy precip. Link to comment Share on other sites More sharing options...
Clinch Leatherwood Posted February 19, 2012 Share Posted February 19, 2012 Full agreement. IMO the NAM is in a "tough" spot since it is non-hydrostatic at 12 km grid. Subgrid scale paramaterizations in a non-hydrostatic model can wreak havoc in certain situations. It is also those traits that make it so useful with deep PV's over moist and intense baroclinic zones. Slow moving single part systems are its forte. But would that have been negatively impacting it's 12-18h 500mb forecasts for the last 3-4 days? I realize it may come into play now with the QPF and enventual evolution of the system but it seems to have had great difficulty in getting close to pinpointing the position and speed of embeded s/ws even over the continental US. Link to comment Share on other sites More sharing options...
Coach McGuirk Posted February 19, 2012 Share Posted February 19, 2012 atleast you get some QPF and have a chance i guess better than others What are you talking about? You're supposed to get at least 4 inches of snow. Link to comment Share on other sites More sharing options...
ORH_wxman Posted February 19, 2012 Share Posted February 19, 2012 If it is too far S it may not be by much. One certainty we know now is convection is well displaced from the main parent cyclone. The frontal zone is grossly elongated with a secondary diabatic low over Florida. Advective processes across the warm sector are being severely inhibited by this, and shortwave ridge building/amplification are weak. The upper shortwave is of much lower amplitude as a result and will thus have a much faster phase speed aloft meaning the defo band will have less time to materialize before the fast upper low begins forcing the development of the secondary coastal. That defo band will not have much time here to dump heavy precip. Yeah you make a good point...a lot of people say "convective feedback" when a model strings out a low and act likes it wrong...often it is, but it actually does happen and your description is exactly how it happens...it totally shuts down the warm conveyor belt on the front side of the low at times or in the mean really slows it down...so it can be very real which I know Scott (coastalwx) and I often tell people in the NE subforum who are quick to look at convective feedback. Usually when the GFS does it its wrong because its horrible at convection and even if there is convective feedback the GFS usually places it wrong, but when the Euro is doing it, I listen and its been doing it a lot on its runs. Close in, the NAM can finally become useful at it too..its usually cruddy at the far off convection more than 36 hours out, but it can start pinning down MCSs and such within 36 hours which make it better off. But again, I usually still go with the Euro in complex system...when they are tightly wrapped and lots of convection all near the center, I like the NAM...ala Jan 12 last year. Link to comment Share on other sites More sharing options...
Amped Posted February 19, 2012 Share Posted February 19, 2012 Rgem is in. Looks like we are finally starting to see a consensus. Link to comment Share on other sites More sharing options...
Logan11 Posted February 19, 2012 Share Posted February 19, 2012 Still looks like it has at least .6" in RIC. RGEM is further south too EZF on north, fuggetaboutit, and probably a bit south of that (per RGEM) Link to comment Share on other sites More sharing options...
MidlothianWX Posted February 19, 2012 Share Posted February 19, 2012 RGEM is further south too EZF on north, fuggetaboutit, and probably a bit south of that (per RGEM) Rgem is in. Looks like we are finally starting to see a consensus. The RGEM may be a nudge south overall with the precip but it is much better than the NAM...the heavier banding still roles through Central VA and areas up to CHO and down toward LYH do well. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted February 19, 2012 Share Posted February 19, 2012 Yeah you make a good point...a lot of people say "convective feedback" when a model strings out a low and act likes it wrong...often it is, but it actually does happen and your description is exactly how it happens...it totally shuts down the warm conveyor belt on the front side of the low at times or in the mean really slows it down...so it can be very real which I know Scott (coastalwx) and I often tell people in the NE subforum who are quick to look at convective feedback. Usually when the GFS does it its wrong because its horrible at convection and even if there is convective feedback the GFS usually places it wrong, but when the Euro is doing it, I listen and its been doing it a lot on its runs. Close in, the NAM can finally become useful at it too..its usually cruddy at the far off convection more than 36 hours out, but it can start pinning down MCSs and such within 36 hours which make it better off. But again, I usually still go with the Euro in complex system...when they are tightly wrapped and lots of convection all near the center, I like the NAM...ala Jan 12 last year. Completely agree, "convective feedback" is a totally misused and misunderstood term since convection often time plays a massive role in systems of large magnitude. While positive tilt waves can pan out nicely under certain circumstances, this is exactly why I hate positive tilt configs since convection will under nearly all circumstances result in negative synoptic feedback. Negative tilt systems see the opposite effect as DMC can feed through the WCB forcing massive pressure falls and rapid intensification. I will take negative tilt anyday even if it means messing with extreme warm advection killing snow totals and massive dryslots. As for coastalwx, he mentioned to me he is highly interested in latent processes and DMC with synoptic cyclones. I may have to contact him for something I am writing regarding a storm out here. Link to comment Share on other sites More sharing options...
usedtobe Posted February 19, 2012 Share Posted February 19, 2012 The GFS looks to be really sheared so it too will keep dc pretty dry. Time for bed. Link to comment Share on other sites More sharing options...
Ian Posted February 19, 2012 Share Posted February 19, 2012 The GFS looks to be really sheared so it too will keep dc pretty dry. Time for bed. i dunno i think we get some sprinkles Link to comment Share on other sites More sharing options...
dtk Posted February 19, 2012 Share Posted February 19, 2012 This model sucks. This is probably a fluke run too. Even dtk can't defend this model please don't speak for me, thanks. Link to comment Share on other sites More sharing options...
stormtracker Posted February 19, 2012 Author Share Posted February 19, 2012 Total and complete debacle. We won't see one flake tomorrow. Remember that dream run of the NAM last week? Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.