NYStorm Posted January 1, 2012 Share Posted January 1, 2012 What meteorological conditions determine whether an inland runner will spurn a secondary coastal low just off the east cost vs. what meteorological conditions dictate that it remains an inland runner only with no secondary low formation? Thanks! Link to comment Share on other sites More sharing options...
isohume Posted January 1, 2012 Share Posted January 1, 2012 Secondary lows off the coast can easily form due to the natural llvl thermal gradient located there. Anytime you have strong ulvl forcing approaching the area, the chances of secondary cyclogenesis increases due to increasing frontogenesis and deformation when llvl winds respond to the enhanced omega by backing then crossing the thermal gradient creating waa, lift (lower pressure), then a cyclonic flow response. The degree to which models pick this scenario up can vary of course, but generally slower moving open waves (which produce stronger downstream dpva and div) will have a better chance of creating secondary lows. Link to comment Share on other sites More sharing options...
jgf Posted January 4, 2012 Share Posted January 4, 2012 good topic! isohume, this is the meteorology 101 forum..., can you maybe flesh it out a bit? sorry. i've read that GFS tends to over-predict secondary lows - is this true? Link to comment Share on other sites More sharing options...
isohume Posted January 5, 2012 Share Posted January 5, 2012 good topic! isohume, this is the meteorology 101 forum..., can you maybe flesh it out a bit? sorry. i've read that GFS tends to over-predict secondary lows - is this true? I'm not sure what you mean, but I thought I went into too much detail already. Basically what I was saying is the synoptic set up that is more conducive to secondary low formations involve open upper level waves as opposed to closed low situations. Link to comment Share on other sites More sharing options...
LocoAko Posted January 5, 2012 Share Posted January 5, 2012 I'm not sure what you mean, but I thought I went into too much detail already. Basically what I was saying is the synoptic set up that is more conducive to secondary low formations involve open upper level waves as opposed to closed low situations. I think by "flesh it out" he means explain it without frontogenesis and differential positive vorticity advection. (Not sure that is necessarily possible, but yeah). Link to comment Share on other sites More sharing options...
isohume Posted January 5, 2012 Share Posted January 5, 2012 I think by "flesh it out" he means explain it without frontogenesis and differential positive vorticity advection. (Not sure that is necessarily possible, but yeah). Well, I just did then. Can't get much more simplistic than synoptic ulvl heights patterns. Link to comment Share on other sites More sharing options...
jgf Posted January 5, 2012 Share Posted January 5, 2012 ok. what about the GFS question? does GFS tend to over predict formation and severity of secondary lows on the east coast? Link to comment Share on other sites More sharing options...
TalcottWx Posted January 5, 2012 Share Posted January 5, 2012 Well, I just did then. Can't get much more simplistic than synoptic ulvl heights patterns. You are experiencing typhoon tip syndrome. Link to comment Share on other sites More sharing options...
isohume Posted January 5, 2012 Share Posted January 5, 2012 ok. what about the GFS question? does GFS tend to over predict formation and severity of secondary lows on the east coast? That hasn't been my experience, but then again I haven't seen any verification studies on that. I've seen the nam, cmc, ecmwf, etc, all over develop secondary lows at times. You are experiencing typhoon tip syndrome. Uggh, don't want to do that! I'll water it down from now on. I just assume folks know what variables and concepts I'm talking about since I see them used around here so freely. Link to comment Share on other sites More sharing options...
dtk Posted January 5, 2012 Share Posted January 5, 2012 That hasn't been my experience, but then again I haven't seen any verification studies on that. I've seen the nam, cmc, ecmwf, etc, all over develop secondary lows at times. Uggh, don't want to do that! I'll water it down from now on. I just assume folks know what variables and concepts I'm talking about since I see them used around here so freely. I think the first comment is pretty accurate, though I can't exactly reference any detailed, systematic studies or anything. Link to comment Share on other sites More sharing options...
griteater Posted January 5, 2012 Share Posted January 5, 2012 What meteorological conditions determine whether an inland runner will spurn a secondary coastal low just off the east cost vs. what meteorological conditions dictate that it remains an inland runner only with no secondary low formation? Thanks! For me, this is largely based on the type of air mass in place over the northeast and mid-atlantic. If you have a surface low that is tracking into TN/KY, and the air mass over the northeast and mid-atlantic is mild, with no cold air being advected into that region, the surface low is going to continue to track as an inland runner up into the eastern Great Lakes. Under the same scenario, if you have cold air in place over the northeast and mid-atlantic, you are very likely to get a secondary low forming off the VA/NC coast as upper level energy approaches from the west or northwest. Link to comment Share on other sites More sharing options...
Amped Posted January 6, 2012 Share Posted January 6, 2012 Secondary lows is really just a cad signature. There's really just one low AT 700MB. The surface low happens to be split in half by cold air at the surface trapped east of the mountains, hence there's a more dense boundary layer there with higher pressure. The primary over the Ohio Valley (West slopes of the Mountains) is caused by downsloping. It cannot move east unless the mountains move east!!!! When the 500MB low/trough moves east it is forced to abandon the first warm sector over the OV and find a new one. The Gulfstream is usually makes the perfect spot for this since the cold boundary layer if it exists there erodes quickly. Keep in mind surface lows form near the spot with the warmest 850mb temp and the lowest 500mb height combination. Sometimes there are lows in both those places that eventually merge into one big storm. Link to comment Share on other sites More sharing options...
tornadojay Posted January 6, 2012 Share Posted January 6, 2012 At 500 mb, I generally look for the place of maximum divergence as to where surface low would form. A strong, concentrated area of vorticity advecting into base of a trof is helpful in order to drive the divergent height pattern on th lee side of the trof.. that also aids in bringing on the negatively tilted height field, which inherently means greater divergence and a stronger surface low. The baroclinicity along the coast aids in thermal advection as the height fields cross more perpindicularly with isotherms and at greater speeds... that's when you start getting that classic "S" shaped isotherm pattern at 850 mb..... and if you have that kind of strong WAA pattern sitting over you, and you don't see the isotherms budging in any direction over time, you've got some massive forcing going on as the you are warm advecting but the strong dynamic cooling is acting to offset the progress of advecting warmer air into the region... a little something to look for when you're analyzing the models on a big east coast storm Link to comment Share on other sites More sharing options...
nzucker Posted January 7, 2012 Share Posted January 7, 2012 At 500 mb, I generally look for the place of maximum divergence as to where surface low would form. A strong, concentrated area of vorticity advecting into base of a trof is helpful in order to drive the divergent height pattern on th lee side of the trof.. that also aids in bringing on the negatively tilted height field, which inherently means greater divergence and a stronger surface low. The baroclinicity along the coast aids in thermal advection as the height fields cross more perpindicularly with isotherms and at greater speeds... that's when you start getting that classic "S" shaped isotherm pattern at 850 mb..... and if you have that kind of strong WAA pattern sitting over you, and you don't see the isotherms budging in any direction over time, you've got some massive forcing going on as the you are warm advecting but the strong dynamic cooling is acting to offset the progress of advecting warmer air into the region... a little something to look for when you're analyzing the models on a big east coast storm What do you mean by the S-shaped pattern at 850mb? Link to comment Share on other sites More sharing options...
griteater Posted January 10, 2012 Share Posted January 10, 2012 What do you mean by the S-shaped pattern at 850mb? Here's an example... Link to comment Share on other sites More sharing options...
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