Central Illinois Posted December 22, 2015 Share Posted December 22, 2015 4k NAM has a pretty intense squall line from Chicago down to central Arkansas at 15z. It moves about 250 miles or so northeast in six hours and is over central Indiana and western Lower Michigan at 21z. 4k NAM fires up discrete supercells to the southwest of this across western Tennessee and northern Mississippi. Am wondering if the supercell threat has shifted east a bit into Indiana and Ohio for wed evening. Will we see supercells behind this squall line in Illinois? Sent from my XT1563 No kidding that Squall Line looks very intense...WRF-ARW and WRF-NMM both say yes Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 22, 2015 Share Posted December 22, 2015 Some bust potential on the long range RAP down south... but I don't think it has as much skill as HRRR... especially this far out. Just something to keep an eye on. Link to comment Share on other sites More sharing options...
PGM Posted December 22, 2015 Share Posted December 22, 2015 No kidding that Squall Line looks very intense...WRF-ARW and WRF-NMM both say yes Yeah, it looks very intense. I am just wondering how it will influence things (for better or worse...) regarding later in the day... Link to comment Share on other sites More sharing options...
Quincy Posted December 22, 2015 Share Posted December 22, 2015 I haven't taken a detailed stance on this yet, but I can see huge signals (particularly shear) in favor, while some limiting factors could mess things up. The NAM is already lit up by mid-morning across Arkansas and I could see that initial quasi-squall line in Illinois being junky, but not without damaging wind and brief tornado potential. It's into Indiana where I am not sold yet, but it's hard to ignore the crazy shear the NAM is pumping out up there (80-90 knots). Link to comment Share on other sites More sharing options...
cyclone77 Posted December 22, 2015 Share Posted December 22, 2015 DVN mentions the possibility of a few tors in their southeast CWA tomorrow, but I'd argue there's a shot of some tor activity closer to the QC if some of the latest models are to be believed. Initiation takes off over extreme eastern IA on some of the high-res models. Definitely not the big potential as areas further to the east and south, but this is definitely something worth watching. Aaaannnd I'll be stuck at work as usual lol. Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 Wright-weather.com did a write-up on this event. It's quite rare they do this. But every time I've read the blog and it includes me, the severe threat busts for me. This was true for 6/12/13, 11/17/13, and I don't recall of any more recent events I've been included in. It's a curse, of sorts. http://blog.wright-weather.com/?p=1068 Parameters favorable for widespread severe storms from the Gulf Coast northward into the Mississippi and Ohio Valleys. The Ohio and Tennessee Valleys are at the highest risk for widespread damaging winds. Supercells, with a few violent tornadoes are quite likely as well. Here is a breakdown of the likelihood of severe weather in a given area, starting Wednesday morning continuing through Thursday Morning. Link to comment Share on other sites More sharing options...
andyhb Posted December 23, 2015 Share Posted December 23, 2015 Some bust potential on the long range RAP down south... but I don't think it has as much skill as HRRR... especially this far out. Just something to keep an eye on. That's when the event is projected to start. Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 That's when the event is projected to start. Oops. I thought it was supposed to start later than that. I've seen so many model projections, I dunno why it never clicked in my head that the event starts earlier. Link to comment Share on other sites More sharing options...
Stebo Posted December 23, 2015 Share Posted December 23, 2015 Just to give you an idea of the strength of moisture advection, Memphis was 48/44 at 14z 8 hours ago, now they are 61/60. There are several places across MS/AL with dew points already in the mid and upper 60s. I wasn't expecting this type of moisture advection into Western TN until closer to midnight, so it is very surprising to see it ahead of schedule. Link to comment Share on other sites More sharing options...
Chicago Storm Posted December 23, 2015 Share Posted December 23, 2015 Just to give you an idea of the strength of moisture advection, Memphis was 48/44 at 14z 8 hours ago, now they are 61/60. There are several places across MS/AL with dew points already in the mid and upper 60s. I wasn't expecting this type of moisture advection into Western TN until closer to midnight, so it is very surprising to see it ahead of schedule. I wouldn't say it's ahead of schedule. For example... The 0z NAM from last night had 60F DP's running from SE. Arkansas, up towards Memphis, then into far N. Tennessee. 0z OBS are pretty much on track with that. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2015 Share Posted December 23, 2015 Terre Haute at 3z Thursday off the 18z NAM. CAPE in excess of 1000 J/kg. 500 mb winds of 100 kts. Pretty nasty. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2015 Share Posted December 23, 2015 weenie long range backup RUC Link to comment Share on other sites More sharing options...
Superstorm93 Posted December 23, 2015 Share Posted December 23, 2015 Obs are pretty good-looking already. Moisture creeping north Link to comment Share on other sites More sharing options...
Quincy Posted December 23, 2015 Share Posted December 23, 2015 However, notice that the HRRR is much more modest with terms of instability with northward extent, in comparison to the NAM, at least through 12z. If you loop these graphics, you will notice that a chunk of instability does surge north-into the Middle Mississippi Valley overnight, but perhaps the morning instability push is stunted a bit due to some sort of mesoscale boundary, draped from Arkansas to central Mississippi. Correction that the previous graphic was comparing HRRR SBCAPE to NAM MUCAPE. Still, the NAM is more robust with northward extent with respect to surface-based instability. Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 The main difference between the models appears to be a cap. Here's the sounding for north-central Mississippi on 2 models, for the same time, at the same location HRRR: http://i.imgur.com/IPLYvkO.png NAM: http://i.imgur.com/IPLYvkO.png West KY... HRRR: http://i.imgur.com/BJUqHCe.png NAM: http://i.imgur.com/jupLKUo.png S IL.... HRRR: http://i.imgur.com/ShkBKVO.png NAM: http://i.imgur.com/kwDzWCX.png The lapse rates otherwise seem similar. In fact, the mid-level lapse rates are steeper on HRRR. It's just the cap that's holding the instability down. Link to comment Share on other sites More sharing options...
Chicago Storm Posted December 23, 2015 Share Posted December 23, 2015 It's just the cap that's holding the instability down. What? Link to comment Share on other sites More sharing options...
HillsdaleMIWeather Posted December 23, 2015 Author Share Posted December 23, 2015 At this point it appears the NAM is verifying pretty well. Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 What? I'm saying the temp profiles are similar other than that inversion, which HRRR is slightly more aggressive with. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2015 Share Posted December 23, 2015 I'm saying the temp profiles are similar other than that inversion, which HRRR is slightly more aggressive with. There is a few degrees difference with sfc temps/dews though...it's similar but a few degrees can be significant. NAM also looks a bit cooler around 600 mb which would affect CAPE values. Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 There is a few degrees difference with sfc temps/dews though...it's similar but a few degrees can be significant. I suppose so. But who knows how HRRR responds during the day... maybe it'll make up for the difference via heating/greater moisture advection Anyway... 00z 12km NAM comes in with even uglier STP values down south. But the STP values up here are slightly lower at 00z Link to comment Share on other sites More sharing options...
MattPetrulli Posted December 23, 2015 Share Posted December 23, 2015 00z NAM is probably the most aggressive yet. Biggest change from 18z NAM is the strength of the LLJ in MS at 18z. 18z NAM had a 60-70 Knot LLJ in MS at 18z. It's now a 70-80 knot LLJ in this latest run 18Z NAM: http://pasteboard.co/eJ1lSUj.png 00Z NAM: http://pasteboard.co/eJ36H5y.png Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 00z NAM is probably the most aggressive yet. Biggest change from 18z NAM is the strength of the LLJ in MS at 18z. 18z NAM had a 60-70 Knot LLJ in MS at 18z. It's now a 70-80 knot LLJ in this latest run 18Z NAM: http://pasteboard.co/eJ1lSUj.png 00Z NAM: http://pasteboard.co/eJ36H5y.png Yeah I take that back about the STP values up north. STP values are greater and more widespread through Indiana at 03z. Link to comment Share on other sites More sharing options...
Hoosier Posted December 23, 2015 Share Posted December 23, 2015 Sim reflectivity has a broken line of cells near the IL/IN border at 3z before crossing into Indiana. Link to comment Share on other sites More sharing options...
HillsdaleMIWeather Posted December 23, 2015 Author Share Posted December 23, 2015 Yeah I take that back about the STP values up north. STP values are greater and more widespread through Indiana at 03z. Yeah, starting to look more serious across Central Indiana/Southern Ohio, also increased in South MI. Link to comment Share on other sites More sharing options...
ClicheVortex2014 Posted December 23, 2015 Share Posted December 23, 2015 Oh, man... 4km NAM Brutal to the south though Link to comment Share on other sites More sharing options...
Chicago Storm Posted December 23, 2015 Share Posted December 23, 2015 Sim reflectivity has a broken line of cells near the IL/IN border at 3z before crossing into Indiana. Link to comment Share on other sites More sharing options...
Quincy Posted December 23, 2015 Share Posted December 23, 2015 The 4km NAM is less unstable across the Ozarks/Middle Mississippi Valley/Tennessee Valley compared to 18z. At least through 10hr. Looks like morning contamination brings the NAM closer to the latest HRRR runs, which are more realistic. Link to comment Share on other sites More sharing options...
Stebo Posted December 23, 2015 Share Posted December 23, 2015 4km NAM blows up a squall line out of the prefrontal trough which blocks all the moisture north, NAM12 disagrees with that though. Link to comment Share on other sites More sharing options...
Chicago Storm Posted December 23, 2015 Share Posted December 23, 2015 The 4km NAM actually has the main event being early day convection (Round 1), which forms into a line as it pushes east. This leaves behind an OFB, which hinders moisture recovery and instability across IL/IN for later development. Link to comment Share on other sites More sharing options...
Stebo Posted December 23, 2015 Share Posted December 23, 2015 The 4km NAM actually has the main event being early day convection (Round 1), which forms into a line as it pushes east. This leaves behind an OFB, which hinders moisture recovery and instability across IL/IN for later development. It is the most aggressive with the strength of morning convection across AR that moves northeast. Link to comment Share on other sites More sharing options...
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