andyhb Posted May 12, 2015 Share Posted May 12, 2015 Dedicated thread for this started. 12z GFS appears to be more favorable than other recent runs with an increase in instability along the dryline on Saturday in KS and OK, with a more robust LLJ. A key thing to watch is how dominant the second vort max that rotates around the base of the trough is. This is the one that ends up leading to the Saturday lee cyclogenesis, and associated increase in wind fields. The previous GFS runs appeared to be making the lead vort dominant, which caused the ULL to wrap up significantly and the upper level winds to back. It also encouraged more morning convection over the warm sector. The 12z run appears to follow more in the Euro's thought at making this second vort max stronger/more dominant vs. the lead. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted May 12, 2015 Share Posted May 12, 2015 Forecast soundings/hodgraphs off the 12z NAM for 22/23z for Hebron, NE on Friday Link to comment Share on other sites More sharing options...
Ground Scouring Posted May 12, 2015 Share Posted May 12, 2015 I could be wrong, but is the 12Z ECMWF, while a bit deeper with the trough overall, a bit messier/less consolidated with the secondary vorticity maximum by late Saturday afternoon? Regardless, while the wind fields don't seem to differ much from those in the 00Z run, the arrival of the mid-level jet maximum/trough axis is a bit earlier than in the 00Z run. If I am interpreting the run correctly, that is why afternoon instability by peak heating is notably lower/reduced, apparently due to more convection developing around late morning/midday. Otherwise, the EML does not seem appreciably weaker (or stronger) than in the previous run. I am not placing much stock in one solution (one way or another), but I would like to know if my interpretation is correct. I would add that, overall, the 12Z GFS has shifted more toward the 00Z/12Z ECMWF than the ECMWF has shifted toward the GFS in terms of trough evolution. Link to comment Share on other sites More sharing options...
Quincy Posted May 12, 2015 Share Posted May 12, 2015 The 12z GFS also showed trends of better orienting the upper level trough for Saturday. At least in that respect, certainly trending toward slower and more favorable for severe. Link to comment Share on other sites More sharing options...
andyhb Posted May 12, 2015 Author Share Posted May 12, 2015 I could be wrong, but is the 12Z ECMWF, while a bit deeper with the trough overall, a bit messier/less consolidated with the secondary vorticity maximum by late Saturday afternoon? Regardless, while the wind fields don't seem to differ much from those in the 00Z run, the arrival of the mid-level jet maximum/trough axis is a bit earlier than in the 00Z run. If I am interpreting the run correctly, that is why afternoon instability by peak heating is notably lower/reduced, apparently due to more convection developing around late morning/midday. Otherwise, the EML does not seem appreciably weaker (or stronger) than in the previous run. I am not placing much stock in one solution (one way or another), but I would like to know if my interpretation is correct. I would add that, overall, the 12Z GFS has shifted more toward the 00Z/12Z ECMWF than the ECMWF has shifted toward the GFS in terms of trough evolution. Um, there's not really any appreciable difference in instability between the 00z and 12z Euro runs by 00z 5/17. Link to comment Share on other sites More sharing options...
CoastalWx Posted May 12, 2015 Share Posted May 12, 2015 I could be wrong, but is the 12Z ECMWF, while a bit deeper with the trough overall, a bit messier/less consolidated with the secondary vorticity maximum by late Saturday afternoon? Regardless, while the wind fields don't seem to differ much from those in the 00Z run, the arrival of the mid-level jet maximum/trough axis is a bit earlier than in the 00Z run. If I am interpreting the run correctly, that is why afternoon instability by peak heating is notably lower/reduced, apparently due to more convection developing around late morning/midday. Otherwise, the EML does not seem appreciably weaker (or stronger) than in the previous run. I am not placing much stock in one solution (one way or another), but I would like to know if my interpretation is correct. I would add that, overall, the 12Z GFS has shifted more toward the 00Z/12Z ECMWF than the ECMWF has shifted toward the GFS in terms of trough evolution. I feel like you are being a little too concerned with details tough to nail down this far out. The synoptic setup is pretty good. That's about all you can really say. Good s/w ejecting out into the Plains is usually a recipe for severe. Link to comment Share on other sites More sharing options...
andyhb Posted May 12, 2015 Author Share Posted May 12, 2015 Friday has some pretty solid potential on the dryline/triple point in NE, SD and KS (different areas for different models). Upper winds are a bit weak (to a degree, but they do look reasonable enough), but strong low level wind fields/instability overcame this on Wednesday last week and it looks like they will be in place again. Might be better chances for discrete cells too with the main upper forcing lagging the warm sector a bit. Illustrated by some of the soundings Thundersnow posted above. Link to comment Share on other sites More sharing options...
Ground Scouring Posted May 13, 2015 Share Posted May 13, 2015 There are still some synoptic issues to be worked out for Saturday--and will be until we get within 36-42 hours--such as the evolution of the piece of energy dropping down the west flank of the quasi-Omega (is that a good term?) block over the Yukon. The ECMWF has mostly favored a deeper solution to this piece of vorticity as it comes south off CA Friday/Saturday, and the GFS, while showing a much less conspicuous feature, has gradually trended toward the ECMWF (several runs ago it didn't even show it at all). If this feature deepens/consolidates, it could deflect the main trough over the Rockies even farther north as it ejects on Saturday. That would mean an even stronger EML, which could hurt the prospects for severe activity farther south (i.e., in OK), but would favor targets farther N toward NE/Dakotas. It could also impinge on the ejecting trough by forcing some height rises on its SW flank, narrowing wavelengths somewhat, but I doubt that this will affect the overall evolution of the trough itself (my interpretation could be wrong; if so, please explain why). What does strike me on the 18Z GFS is its reflection of a steady trend toward a more dominant EML overnight Friday/Saturday, based on the wind vectors. Given overall trends, I daresay that if early convection becomes a problem Saturday, it may be more due to bad timing of the lead impulse than due to a poor/non-existent EML. The 700-mb RH on the GFS shows late-morning convection over TX/OK, but it clearly seems more like forcing-related feedback given the decent quality of the EML shown. The 18Z GFS continues to show a more noticeable shift toward the ECMWF in terms of a more consolidated secondary vorticity maximum rotating around the base of the trough, which also looks more akin to the ECMWF in terms of breadth/wavelength and tilt. A few more days and better sampling of the Pacific are needed, but so far I am becoming a bit less worried/cautiously optimistic (pending more data) about the EML, which seems likely to be a more active participant on Saturday than it has recently--and look how recent events still ended up with significant tornadoes. I will also add that the GFS shows even more outstanding shear parameters on its latest run; if adjusted to account for convective feedback bias (meaning more instability), then the environment depicted would be more than sufficient for a major outbreak even with some back-veer-back present, which is not a given. Still, all this is preliminary, but the trends still look potentially ominous for a large part of the Plains. Check out the 18Z GFS soundings. Link to comment Share on other sites More sharing options...
MidwestChaser Posted May 13, 2015 Share Posted May 13, 2015 http://www.twisterdata.com/index.php?sounding.x=468&sounding.y=330&prog=forecast&model=NAM&grid=221&model_yyyy=2015&model_mm=05&model_dd=12&model_init_hh=18&fhour=78¶meter=THTE&level=2&unit=M_ABOVE_GROUND&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false&sounding=y&sndclick=y Yummy Link to comment Share on other sites More sharing options...
forkyfork Posted May 13, 2015 Share Posted May 13, 2015 I feel like you are being a little too concerned with details tough to nail down this far out. The synoptic setup is pretty good. That's about all you can really say. Good s/w ejecting out into the Plains is usually a recipe for severe.this is a nice look Link to comment Share on other sites More sharing options...
BuffaloWeather Posted May 13, 2015 Share Posted May 13, 2015 Would you guys say this outbreak coming up is more favorable for Tor. than Saturday? Link to comment Share on other sites More sharing options...
jojo762 Posted May 13, 2015 Share Posted May 13, 2015 Would you guys say this outbreak coming up is more favorable for Tor. than Saturday? has similar dynamics... And is seemingly a carbon copy from last week... Really the only thing that would lead it to being better than last Saturday is having a legit EML in place to curb morning convection from ruining everything. Which the models are showing generally..EDIT: Also, as has been mentioned, the GFS (which had been leaning toward having morning convection) has started to fold to the ECMWF of showing less of a thermodynamic impact from morning storms (if any actually develop) Link to comment Share on other sites More sharing options...
Thundersnow12 Posted May 13, 2015 Share Posted May 13, 2015 The 0z NAM is pretty scary for Nebraska on Friday. Then has a 120kt upper leve jet max rounding the base of the trough by 12z Saturday crossing into NM. Link to comment Share on other sites More sharing options...
andyhb Posted May 13, 2015 Author Share Posted May 13, 2015 The 0z NAM is pretty scary for Nebraska on Friday. Then has a 120kt upper leve jet max rounding the base of the trough by 12z Saturday crossing into NM. You're not kidding, extreme low level shear with strong low level backing over much of the central/eastern portions of the state by 00z. 21z in N KS is also explosive looking. Storms may be a bit HP given high PWATs and the venting aloft isn't incredibly strong, but any storm that maintains more classic characteristics for any length of time in that environment could do some serious things. Of course, all caveats with using the longer range NAM apply, also. Link to comment Share on other sites More sharing options...
jshetley Posted May 13, 2015 Share Posted May 13, 2015 I'm starting to think this may turn out a lot like 1993 from Texas to the upper midwest as far as the long term pattern goes. Link to comment Share on other sites More sharing options...
andyhb Posted May 13, 2015 Author Share Posted May 13, 2015 Friday looking bigger in NE on the 12z GFS now. Link to comment Share on other sites More sharing options...
ZackH Posted May 13, 2015 Share Posted May 13, 2015 I'm finding it hard to criticize much for Friday as far as a chaseable setup at this point.. Some early convection could be a concern, but right now the models don't think it will be an issue. For Saturday, I don't like the nearly meridional flow... direction shear is becoming less than ideal, and then there's the whole widespread convection in the morning and pretty much all day. Will already be out so will probably at least chase somewhere, but I'm not too excited about a large tornado threat at this point. That could change fairly quickly, though. Link to comment Share on other sites More sharing options...
Quincy Posted May 13, 2015 Share Posted May 13, 2015 Friday certainly looks like the better chase day. Nebraska an obvious target, but that could extend into parts of South Dakota depending on warm front movement. The dryline will likely be a player southward into Kansas too. Saturday tends to look like a mesoscale mess, similar to last Saturday. Will probably have several smaller targets with less confidence, especially if there are one or more ongoing MCSs in the morning. Link to comment Share on other sites More sharing options...
Ground Scouring Posted May 13, 2015 Share Posted May 13, 2015 I'm finding it hard to criticize much for Friday as far as a chaseable setup at this point.. Some early convection could be a concern, but right now the models don't think it will be an issue. For Saturday, I don't like the nearly meridional flow... direction shear is becoming less than ideal, and then there's the whole widespread convection in the morning and pretty much all day. Will already be out so will probably at least chase somewhere, but I'm not too excited about a large tornado threat at this point. That could change fairly quickly, though. 1) Can you show me the less-than-ideal directional shear/meridional flow? 2) Can anyone show me the STJ that would cause less of an EML (or the factor resulting in widespread early convection)? I don't see it, and the ECMWF shows considerable destabilization on Saturday. Link to comment Share on other sites More sharing options...
ZackH Posted May 13, 2015 Share Posted May 13, 2015 1) Can you show me the less-than-ideal directional shear/meridional flow? 2) Can anyone show me the STJ that would cause less of an EML (or the factor resulting in widespread early convection)? I don't see it, and the ECMWF shows considerable destabilization on Saturday. Well meridional means south to north... pretty much all of the models show a more south to north flow orientation rather than a SW to NE orientation... because of this, you have quite a bit of unidirectional flow above 850mb... can make things messy with splitting storms running into each other. And that's not even taking into account VBV issues. The GFS has been hinting at an EML developing, but in the wrong place. I am not discounting a widespread severe event with some tornadoes, but at this juncture I do not see anything screaming outbreak of strong tornadoes. Again... could easily change in one model run, though. Earlier you asked about the STJ... around this time of year, you'd expect it around 250mb... polar jet is probably around 300. Link to comment Share on other sites More sharing options...
WishingForWarmWeather Posted May 13, 2015 Share Posted May 13, 2015 Can someone explain like I'm 5, what veer-back-veer means? I've tried to understand on my own, but, it's not working. Link to comment Share on other sites More sharing options...
jojo762 Posted May 13, 2015 Share Posted May 13, 2015 1) Can you show me the less-than-ideal directional shear/meridional flow? 2) Can anyone show me the STJ that would cause less of an EML (or the factor resulting in widespread early convection)? I don't see it, and the ECMWF shows considerable destabilization on Saturday. I'm seeing more of a problem with either VBV or BVB than meridional flow according to the 00Z EURO... 12Z GFS did show a largely unidirectional wind profile at about 700mb and up... But low level turning/low level hodographs were still pretty impressive. Basing off of current guidance we will probably see a big severe weather day, but the best tornado threat will likely be relegated to mainly SC KS/Central OK.. And even then the tornado threat may ultimately not even be that high. I see a ENH or MDT risk for large hail/dmg winds, and maybe a 10% hatched area for tornadoes somewhere maybe at best. Basing off of the problems with VBV or BVB and thermodynamic issues due to morning cold pools (probably SBCAPE of 1000-2500J/KG at best.) Of course all that could change though... The 12Z GFS/NAM were both in good agreement about the effects of morning convection on instability too.. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted May 13, 2015 Share Posted May 13, 2015 Forecast sounding off the 12z NAM for 1z Friday evening for Ord, NE after convection fires. See possible hazard type.. Link to comment Share on other sites More sharing options...
JoMo Posted May 13, 2015 Share Posted May 13, 2015 Can someone explain like I'm 5, what veer-back-veer means? I've tried to understand on my own, but, it's not working. Try the VBV section here: http://www.ustornadoes.com/2015/03/30/how-to-forecast-tornadoes-looking-for-what-could-go-wrong/ Link to comment Share on other sites More sharing options...
jameswx Posted May 13, 2015 Share Posted May 13, 2015 I'm seeing more of a problem with either VBV or BVB than meridional flow according to the 00Z EURO... 12Z GFS did show a largely unidirectional wind profile at about 700mb and up... But low level turning/low level hodographs were still pretty impressive. Basing off of current guidance we will probably see a big severe weather day, but the best tornado threat will likely be relegated to mainly SC KS/Central OK.. And even then the tornado threat may ultimately not even be that high. I see a ENH or MDT risk for large hail/dmg winds, and maybe a 10% hatched area for tornadoes somewhere maybe at best. Basing off of the problems with VBV or BVB and thermodynamic issues due to morning cold pools (probably SBCAPE of 1000-2500J/KG at best.) Of course all that could change though... The 12Z GFS/NAM were both in good agreement about the effects of morning convection on instability too.. Yeah, as it stands with the model runs right now it certainly looks like there is still a legit tornado threat with the forecasted lower level winds. However, it looks to me like there will be a lot of cells crashing into each other and creating a QLCS mess. Not good from a chasers standpoint. Hopefully the veer-back problem works itself out. SC OK/N TX doesn't look nearly as bad for VBV per the NAM as it does further north. Link to comment Share on other sites More sharing options...
ZackH Posted May 13, 2015 Share Posted May 13, 2015 Yes I would like to point out that I am speaking specifically from a chasing point of view and not an overall threat. The lower levels are plenty supportive of tornadoes... But when you have that unidirectional profile over 850/700 you will have splitting cells running into each other creating a mess everytime. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
jojo762 Posted May 13, 2015 Share Posted May 13, 2015 Yes I would like to point out that I am speaking specifically from a chasing point of view and not an overall threat. The lower levels are plenty supportive of tornadoes... But when you have that unidirectional profile over 850/700 you will have splitting cells running into each other creating a mess everytime. Sent from my iPhone so.. There is still a good chance we get a few discrete/semi-discrete right splits that produce tornadoes or? Link to comment Share on other sites More sharing options...
Misstertwister Posted May 13, 2015 Share Posted May 13, 2015 Is it just me or does the cap look pretty stout from OUN Friday. 12.2 on the sounding my buddy texted me. I know Saturday looks to be a bigger day in OK somewhere thiugh Link to comment Share on other sites More sharing options...
andyhb Posted May 13, 2015 Author Share Posted May 13, 2015 Is it just me or does the cap look pretty stout from OUN Friday. 12.2 on the sounding my buddy texted me. I know Saturday looks to be a bigger day in OK somewhere thiugh Assuming that is just using the traditional way of measuring a cap, that is quite a weak cap actually. You usually don't start talking about strong caps until you start getting up near 100 J/kg. NE on Friday continues to look potent across basically all guidance. Low level shear is plenty for tornadoes already by 18z if the NAM is on the right track. Link to comment Share on other sites More sharing options...
jojo762 Posted May 13, 2015 Share Posted May 13, 2015 Assuming that is just using the traditional way of measuring a cap, that is quite a weak cap actually. You usually don't start talking about strong caps until you start getting up near 100 J/kg. both the 12Z GFS/NAM show a pretty negligible cap across Oklahoma at 7pm on Friday... But neither show any convective development across the area either.. Link to comment Share on other sites More sharing options...
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