2015-11-11 EVENT: KS, NE, MO, IL, IA, AR, TN, KY, TX, OK, LA

[Andy Berrington]

Holy MAULs, Batman! The NAM is really gunning on steep lapse rates despite saturated layers. That's an artifact of the convective parameterization scheme, and I'm not sure how legitimate those lapse rates are. Guess we'll see.

I don't think the lapse rates are unrealistically steep given how cold the 500 mb temps will be close to the low (it's outputting ~7 C/km more or less), although with saturated layers that would be null and void.

 

[Ben Holcomb]

MOD NOTE: Merged the Target Area event thread and introductory chasing thread to keep discussion in one place. Some great posts in the introductory forum, wanted them to be grouped with this thread in the future.

 

[Ben Holcomb]

I've finally had a chance to peruse the 12Z and now the 18Z NAM as well as look at some observations and here's what I've noticed:

• The trough is extremely powerful looking on water vapor. Take a gander over at COD or your favorite satellite source for the south pacific hemispherical product in a long loop.
  
• 925 RH shows what could be icky clouds all morning over much of the 'target area'
• The 700mb dry punch is pretty astounding into the sfc low
• Speaking of the SFC low, its stacked very close to the 500mb low. Cold core play possible?
• Lots of low tops on whatever may form.
  
• Storms seem to be possible as early as daybreak, although I'm hoping things hold until a little later

Overall a challenging forecast, and likely an even more challenging chase. I do expect we'll see a few tornadoes out of this event, perhaps even a significant tornado. The shear is just crazy strong as you get with these types of progressive negatively tilted systems.

As far as a chase target, I've reserved a hotel room up along the KS/MO border in Leavenworth, KS for tomorrow night. Where I end up will depend a lot on where the sfc low sets up.

 

[Jesse Risley]

The models continue to depict a broken line of semi-discrete storms all the way into IL with this system. While the one limiting factor may be the depth and breadth of available moisture, the theta-E ridge is sufficient enough, given the shear associated with this system, to produce an appreciable severe risk. Given the H5 environment aloft, there is potential for cold core play more proximal to the low on the nose of the best lapse rates. That risk aside, I'll be watching the progression of the stratus deck through the late morning into the early afternoon. With the low near OAX by early afternoon, the models are indicating the show starts early closer to the triple point, then progresses to ignite ESE along the axis of a pre-frontal line of forcing. Past experience indicates that SRH is enhanced INVO this corridor, and with the possibility of a semi-discrete storm mode, I do think tornadic potential is enhanced the first 3-4 hours of the event.

The instability evolution will be interesting to watch. While moisture is perhaps sub-optimal for the most appreciable type of outbreak, it is climatologically sufficient, even if the NAM is slightly overdoing the northward extent of the highest TDs. A cursory glance at actual observations last night further south indicated that northward progression of really quality, deep moisture might have been slightly overdone by previous medium-range model solutions. Nevertheless, as previously mentioned, the actual evolution of the stratus deck will probably be the key component, so paying close attention to regional vis sat models will be paramount. Another cursory review of lower level RH values on this morning's 12z NAM and 4km NAM-WRF runs indicate the potential for some dry air making it into the more kinematicallty favorable region of the warm sector, which probably factor into the more appreciable MLCAPE being depicted across portions of S IA and N MO early tomorrow afternoon. With that having been said, past experience has seen this going both ways, i.e., we may not know how much or little, or where, the stratus deck with erode until nowcasting time tomorrow. This probably holds the key for how the tornadic potential evolves.

The triple point is always a synoptically favorable region, but I also think there is a conditional threat of one or two photogenic, perhaps stronger tornado reports further south across portions of IA, MO and perhaps even west central IL INVO the pre-frontal forcing mechanics in the area of the best thermodynamic energy, as progged 0-3 KM MLCAPE values on the last several forecast skew-T diagrams have been rather impressive. Again, this will also depend on how long storms maintain any semblance of being quasi-discrete, but embedded mesovortex rotations are not out of the question tomorrow either, even as the main line of broken convection moves into central and NC IL and points eastward. It initially looks like a lower topped convective show where storms will be moving at speeds >50 kts, so actual long-term chasing may prove difficult, especially in this geographic region.

 

[Tim Paitz]

The models continue to depict a broken line of semi-discrete storms all the way into IL with this system. While the one limiting factor may be the depth and breadth of available moisture, the theta-E ridge is sufficient enough, given the shear associated with this system, to produce an appreciable severe risk. Given the H5 environment aloft, there is potential for cold core play more proximal to the low on the nose of the best lapse rates. That risk aside, I'll be watching the progression of the stratus deck through the late morning into the early afternoon. With the low near OAX by early afternoon, the models are indicating the show starts early closer to the triple point, then progresses to ignite ESE along the axis of a pre-frontal line of forcing. Past experience indicates that SRH is enhanced INVO this corridor, and with the possibility of a semi-discrete storm mode, I do think tornadic potential is enhanced the first 3-4 hours of the event.

The instability evolution will be interesting to watch. While moisture is perhaps sub-optimal for the most appreciable type of outbreak, it is climatologically sufficient, even if the NAM is slightly overdoing the northward extent of the highest TDs. A cursory glance at actual observations last night further south indicated that northward progression of really quality, deep moisture might have been slightly overdone by previous medium-range model solutions. Nevertheless, as previously mentioned, the actual evolution of the stratus deck will probably be the key component, so paying close attention to regional vis sat models will be paramount. Another cursory review of lower level RH values on this morning's 12z NAM and 4km NAM-WRF runs indicate the potential for some dry air making it into the more kinematicallty favorable region of the warm sector, which probably factor into the more appreciable MLCAPE being depicted across portions of S IA and N MO early tomorrow afternoon. With that having been said, past experience has seen this going both ways, i.e., we may not know how much or little, or where, the stratus deck with erode until nowcasting time tomorrow. This probably holds the key for how the tornadic potential evolves.

The triple point is always a synoptically favorable region, but I also think there is a conditional threat of one or two photogenic, perhaps stronger tornado reports further south across portions of IA, MO and perhaps even west central IL INVO the pre-frontal forcing mechanics in the area of the best thermodynamic energy, as progged 0-3 KM MLCAPE values on the last several forecast skew-T diagrams have been rather impressive. Again, this will also depend on how long storms maintain any semblance of being quasi-discrete, but embedded mesovortex rotations are not out of the question tomorrow either, even as the main line of broken convection moves into central and NC IL and points eastward. It initially looks like a lower topped convective show where storms will be moving at speeds >50 kts, so actual long-term chasing may prove difficult, especially in this geographic region.

For days with fast-moving storms like tomorrow, the better option is to point-intercept.

 

[Bob Hartig]

"I also think there is a conditional threat of one or two photogenic, perhaps stronger tornado reports further south across portions of IA, MO and perhaps even west central IL INVO the pre-frontal forcing mechanics in the area of the best thermodynamic energy, as progged 0-3 KM MLCAPE values on the last several forecast skew-T diagrams have been rather impressive. Again, this will also depend on how long storms maintain any semblance of being quasi-discrete. . . ."

That's my thinking. 0-3km CAPE is topping 400 J/kg in northern MO--just about half of the total CAPE profile--and 4km NAM breaks out pre-frontal cells ahead of the main line well into the event. Low-level shear is crazy. My hunch is, there'll be plenty of game left to the east for those who, like me, live way east of this thing and don't want to drive all the way to the KS/NE/IA border. Of course, there's the matter of daylight, but 21Z looks good for the central MO/IA border area.

 

[adlyons]

Per WV imagery vort max over Western Nevada and Northern California should continue to slink south as the jet streak to the west begins to round the base of the shortwave. As shortwave tightens up closed low should from in vicinity of the 4 corners region as the associated short wave takes on a negative tilt. Trough moment looks on par with current model thinking and timing. Trough should then eject rapidly to the North East as a surface lee cyclone rapidly develop over SE Colorado. 12z NAM continues to show a quickly deepening low which reaches sub 1000 mb by this evening. Nam also continues to be bullish with moisture showing a deep at least 70-100 mb layer of 60s dews. I dont see quite that much based of the current 12z observed. Moisture looks thinner, but should probably be sufficient. Our winds here in Norman Switched to southerly last night so the return process has begun. Coastal Texas soundings had dewpoints in the upper 60's with FWD showing a clear moisture max just off the surface correlating with the LLJ. Current think is moisture in the form of upper 50's to may 60 will make it to the Iowa border by sunrise tomorrow. Given the cold temps aloft, lapse rates in the lowest 3km of the sounding will be steep enough to generate some cape. 0-3km cape i have seen have been in the sweet spot from 300-400 j/kg which should enhance updraft acceleration and vertical stretching. Shear wise, immediately ahead o0f the dryline/ preforontal convergence zone, low level shear is excellent and should favour small mesocyclone development. Aloft, 0-6km bulk shear on the order 70-80 knots should favour supercell structures and healthy well ventilated storms. Going along with that, NAM Q vector shows strong convergence aloft which suggest strong lift will be in place. This is matched by beginnings of a deformation/diffluence zone in WV imagery. I expect semi discrete cells initiating on or Just west of the KC metro by about 16z. These should remain semi discrete for about 3-4 hours and have a potential tornado threat. I wouldnt rule out 1 or two strong tors either.

 

[Jesse Risley]

That's my thinking. 0-3km CAPE is topping 400 J/kg in northern MO--just about half of the total CAPE profile--and 4km NAM breaks out pre-frontal cells ahead of the main line well into the event. Low-level shear is crazy. My hunch is, there'll be plenty of game left to the east for those who, like me, live way east of this thing and don't want to drive all the way to the KS/NE/IA border. Of course, there's the matter of daylight, but 21Z looks good for the central MO/IA border area.

Just from perusing 12z NAM and 4km NAM-WRF data, and taking a glance at some point forecast soundings, there are some fairly impressive 0-3 km CAPE profiles that extend from the I-35 corridor east to the MS River, basically from SC IA into N MO. I thought the progged dry punch in the 700 mb looked a bit more pronounced on the 12z NAM, which is encouraging for the possibility of formidable stratus deck erosion, and this parallels the CF eastward into IL, spasmodically, from 18z - 00z/12. Once storms mature and start "rocketing" ENE, I do agree that NE MO, SE and SC IA and perhaps far WC IL will have an appreciable risk for an intercept for those who don't want to travel closer to the NE border area for initiation, and models continue to indicate a semi-discrete mode into early evening.

 

[Jeff Duda]

Today's 12Z NAM has fewer MAULs than previously. However, in all of the higher CAPE regions it still has them. I still doubt that much CAPE will actually be realized.

 

[Royce Sheibal]

For those of you heading to SE NE for the cold-core threat, welcome to your post! I expect initiation between Beatrice, NE and Falls City, NE shortly after 9am. This is under the assumption that NAM has overdone WAA aloft and cloud cover, and that we'll see mid-level dry slot clear things out before sun-up. If it doesn't clear out, we'll probably still see initiation, but likely no severe until afternoon on the IA side.

Indexes for a cold-core setup are all about as perfect as can be, and the forecast soundings are textbook. BRN's are down near 3, which indicates a very high shear to cape ratio needed for cold-cores. 0-3k SRH is good, but isn't totally relevant due to the theory that cold-core cells can initiate cyclonic motion and tap vorticity from as high as 6k. That would knock our 200 0-3k SRH up to about 1000 0-6k SRH, which helps explain why cold cores can be violent despite low cape values and small meso-diameter. Not to mention the smaller size absorbs less latent heat and covers less real estate, allowing for numerous and rapid cell development, sometimes in close proximity.

I'm probably going to pick a point just north of the initiation line (which i expect to form NW to SE along the nose of the best lapse rates) and wait for a storm to track NE toward me. Perhaps Unadilla or Nebraska City will be my target. For those of you looking to chase across the river in Iowa, beware the lack of crossings on the Missouri, and the maze of passable roads on the IA side for the first 40 miles going east. Good chasing and drive safe!