2012-03-02 FCST: IL/IN/KY/TN/OH

[Skip Talbot]

What looks to be a significant severe weather event is shaping up for this Friday around the Ohio River valley. Models are consistent in ejecting a very impressive 100+ knot midlevel jet with rapidly deepening surface low across the region. A 60 knot low level jet is forecast to rapidly advect 60+ dews as far north as I-72 in central IL. SBCAPE values are a modest 750-1250 across much of the region, but with 80 knots of bulk shear, 200 1km SRH, and significant low level instability and lapse rates, we should a have a favorable mix of ingredients for fast moving, tornadic minisupercells. NAM is hinting at initiation on the moisture axis, just ahead of the main cold front across central IL by early to mid afternoon where the little bit of inhibition that exists erodes first aided by convergence from the deepening surface low. Storms will track northeast at warp speed while building to the southwest along the cold front. I expect initial mode to be discrete low topped supercells given the hodos and low level instability. Strong forcing along the cold front will probably result in solid coverage across the boundary within a few hours, but the shear profiles and rich inflow are such that embedded supercells and tornadoes will probably still be a threat well after dark into IN/OH/and eastern parts of KY/TN. Uncertainty exists still in the exact placement of the low and surface features. The NAM is slowing down on each run, but that works out better for most chasers I believe as initiation occurs over the more favorable areas of central IL. Look for a MS river initiation if the slowing continues at this rate, however. I'm eyeing the i-57 corridor with a fast east west highway (i-72 or i-70 maybe) for a point intercept on a fast moving cell and a brief attempt trying to keep ahead of it, and then maybe playing down the line while I can stay ahead of it. Looks like the first chase of the year for me if the NAM is close!

An analogue for this event might be March 8, 2009: http://www.spc.noaa.gov/exper/archive/event.php?date=20090308

 

[Jim Parsons]

Latest NAM is still showing nice moisture return and instability into S/E IL combined with some decent wind profiles. I am also liking the little nub of EHI(18z) that is bumping back out to the N/W....Target IL, IN, KY border area for starters...Thoughts??

 

[cdcollura]

Good day all,

I am not on this one but I'll throw in my two cents. This appears to be an extremely energetic late-winter setup - Dominated by very high shear but modest CAPE.

Looking at both the GFS and ETA, a region of about 1000 CAPE appears likely from SW Ohio / SE Indiana down through the middle of Kentucky and into North-Central Tennessee. A powerful divergent jet max is also over this area from H5 through H25, two lobes of the speed max of the divergent jets are over this area, with the all-important northern side of the southern speed max over Northern Kentucky. Speeds at the H25 (250 MB) level are more than 125 knots, with 80 to 100 knots at H5 (500 MB).

A strong WSW flow at 700 MB also reaches the region by about 0z, with speeds of about 60 to 80 knots and a 0 C temp isotherm just N of the northern Kentucky border. 850 MB flow increases radically in speed and backs at around 0z from WSW to SW with a LLJ speed of 50 knots or so. Surface flow and just above (925 MB) has a 20 to 30 knot southerly to slightly SSW flow from Kentucky northward. A nice tounge of mid 60's dewpoints is also moving into this area at roughly 0z, with it's nose centered near the OH / IN/ KY tri-state borders. Temperatures should be in the low 70's.

Farther east, nearing the western slopes of the mountains (SE OH, WV, and E KY), there is a wedge of cooler air that may affect storms moving into those regions. At 0z, the surface cold front should be from the E Indiana border down through western-central Kentucky, with a warm front lifing N through central Ohio and sagging with the cool wedge of air over the mountains to the east (near West virginia).

At this time, a best target should be from south of Louisville to near Elizabethtown (along I-65) for starters. The tactic is to STAY AHEAD of the storms (especially the first ones) and allow the storm to come to you when mature. Try to be on the initial storms as well. The storm motions will be at least 50 knots to the NE. The storms will quickly become a squall line but most likely with embedded supercells threrafter / near dark. Another thing to not is that there is very little convective inhibition with this setup, with 700 MB temps over the target area a mere 0 to 2 degrees C (at 500 MB the temps will be from -15 to -20 C), so the cap will not be much of an issue.

As for terrain, Central KY to the OH / IN / KY border is the best you are going to get. This is mainly rolling hills, farmland, and trees - Similar to E Iowa / W Illinois (or even WI but not as bad as Arkansas - Still NOT great chase terrain). The major concern (besides trees) will be the Ohio River, so consider that if having to cross N out of Kentucky into Ohio or Indiana. Out of Elizibethtown you have some high-speed options (I-65 N-S and Blue Grass Pkwy 9002 SW to NE) to help race along with these storms.

Good luck on all those who head out!

 

[Skip Talbot]

While still favorable for widespread severe weather across the OH river valley, this setup teeters on the edge of chaseability. I'm not really considering anything south of I-70 in IN or south of I-64 in IL as an option given the excessive storm motion and terrible terrain. The position of the triple point and available instability at the triple point seem key at this point. We had a string of nice runs yesterday that hinted at a slower progression of the trough and northerly position of the triple point, and a 700 mb dry slot that would clear the way for some sunshine and destabilization over the flat and paved road grid of central IL/IN. The 12z run indicated lingering junk on and south of the warm front and pushed the dry slot down to the OH river, resulting in the bulk of the necessary instability showing up over unchaseable areas. The 18z NAM is back on board with a nice triple point play from Terra Haute, IN at 3pm to north of Indianapolis. Given that the NAM seems focused on IN at this point, I'll probably be eyeing the I-65 corridor now for a point intercept on warp speed mini supercells. I was hoping for an I-57 play as the terrain is a bit better, there's less traffic, and the traffic is faster (pokey Indiana drivers on I-65 and heavy Chicago-Indianapolis traffic).

Huge curving hodographs and decent low level instability would favor tornadic supercells across portions of southeast IL and southern IN. Further south, instability is higher but the winds veer substantially and go parallel to the cold front which may favoring training lines with embedded supercells. My target is probably between Terra Haute and Crawfordsville, IN at this point for a brief intercept on a fast moving, low topped cell. I do not expect to be able to effectively keep up with any of these storms so the chase will be a short one. I'd also recommend leaving anything south of there to the local spotters. It's not going to be worth it to tangle with the storms speeds and terrain.

Cherry picked severe parameter highlighting the triple point play:
http://wxcaster4.com/nam/CENTRAL_MESO-ETA212_ATMOS_STP_27HR.gif

 

[Dan Robinson]

I agree with Skip on this being more of an 'intercept' day than a 'chase'. It will take very dangerous vehicle speeds to even get close to keeping up with any single storm. At this point I'm planning on choosing an east-west highway, likely I-64 or I-70 (or a suitable parallel two-lane for more pull-over options). The river crossings (Wabash and Ohio) will be a major factor to keep in mind. There are few crossings on the Ohio between Paducah and Louisville. There are a couple spots where some map versons may show bridges that are actually ferries (like at Cave-in-Rock). These ferries may not be operating if severe weather is in the area.

 

[wfrogge]

Nashville to Bowling Green... Not the most ideal chase terrain but dont think I will have time to get much further north before the event starts (leaving Memphis at 9:30 AM). The only positive here is that since we will have to wait for storms to come to us vs chasing (due to the speed) it should give chasers time to get into an ideal spot with a view.

 

[Matt Hunt]

I'm with you on that, Skip. I don't really wanna go further south than I-70 due to the poor terrain. Also consider I-69 as an option IF it pushes far enough to the north. It can get a little backed up between Indy and Anderson (don't even bother if it's rush hour), but if you're north of Anderson it should be pretty clear. For me it all depends on when I get off work, but I do like the better directional shear near the triple point. If initiation hasn't happened by the time I'm off, I'll probably sit right at home and monitor conditions! Depending on all of that, I'll likely either play I-65, US 31, or I-69.

 

[Chip Redmond]

Skip, I agree, I think best tornado potential is along the triple point/low that will track from Miss River NE through south central IL, central IN, and western OH. The best hodos are in the in the typical place, southeast from the low and the best opportunity for a storm to have a small chance to stay isolated and perhaps even find that warm front.

Instability definitely isn't an issue anywhere. The cold front will be hauling insanely fast and therefore I think many places to the south will not be able to break the cap farther south from the low. Winds out of the SW at the surface and especially 850 will limit turning with height and unidirectional hodographs result in these regions as well. A 110kt 500mb jet is just insane and with any downdrafts with this mixing down, straightline winds will be a huge issue across much of the region, more so than the tornado threat which I feel may be a bit over-zealous at the moment. Either way it is a definitely a dangerous situation with those winds and I would definitely tie down my lawn gnomes!

If I were chasing I would definitely do as I have done several times with these setups. Get on a good direction road to the NE and haul to stay in front. Punching these were usually pretty fun if you can get back out of the storm and see what wind speeds you can record in the process. E/W highway like 70 would be ideal (especially with higher speed limits in IN).

Chip

 

[Mike Johnston]

That cold front today draped across the southern states stalled about 3-4 county-lengths north of originally progged, and now it looks like the boundary is advancing north with a vengance. Projecting that to tomorrow's setup, it looks like southeast IN and southwest OH might be the prime areas. In this regard, it's kind of similar to the 4-3-74 setup (no, I'm not saying we'll have another Super Outbreak.) Surface winds tomorrow look to be veering horribly. The overall speed shear looks very supportive, though. The idea that we might see 2 or 3 "waves" of severe convection over the target area is also similar to the 4-3-74 event.\

EDIT: hmmm, might have to take back what I said about the veering surface winds. By the 00z NAM run, looks the the surface low might be compacting and there's some chance of surface winds actually backing over the target.

 

[Jared Orr]

I really really like the PVA, wind profiles, and forcing at the triple point. If tomorrow's models show any promise of substantial instability as far north as E-central IL or southern IN, I will find those locations extremely appealing. Obviously, starting out far enough downstream is going to be important with the already mentioned "warp speed" supercells. If storms do find instability at these locations, I think the less segmented structures would be much better for chasing...I wouldn't want to end up chasing a 60mph line down south with random embedded tornadoes. That's why the cold front would be a last resort for me...if I was chasing this event. Stay safe tomorrow folks.

 

[John Farley]

This certainly has the look of an outbreak scenario to me. Shear, forcing, low LCL, and not huge instability but certainly enough - the ingredients are all there. I can't chase this setup, and I'm not sure whether I would given the combination of insane storm speed and poor chase terrain. That said, from what I can see on this evening's NAM and GFS runs the best combination of parameters - ignoring the effect of terrain on chasability for the moment - would suggest setting up somewhere along a Louisville-Bowling Green, KY line. Initation becomes a little more uncertain as you go south, so purely based on meteorology, somewhere around Louisville would probably be a good starting point. But poor terrain, the Ohio River, urban congestion, and insane storm speeds make that target virtually unchaseable. So if I were actually chasing, I'd probably set up somewhere near Terre Haute and hope to track something along I-70 - at least there I would have a route that might allow me to stay ahead of the storm for a while. The instability there is less, but shear at least as good and you might catch some warm front magic. The terrain there is a little better, though not great. So based on what I'm seeing now, that's where I would probably go if I could - but with these storm speeds and fair terrain at best, it won't be easy even in that corridor. If you head out tomorrow, chase with care; it won't be an easy chase but could be rewarding if you're in the right place at the right time.

 

[Andy Wade]

I wrote a paper for Intro I on the Super Outbreak ('74) and I just wanted to throw out a few similarities and differences I see. (I'm not in any way suggesting that this could even approach the Super Outbreak, but because of the geography, it's bound to get comparisons.) The surface low in 1974 was a good bit stronger--about 980 mb, I think--but was also located farther northwest, moving from KS through NE to IA. The upper trough was negatively tilted; this one's positive. Due to that negative tilt, there was a lot of divergence over the Mid-South with the subtropical jet. That shouldn't be so prominent Friday. The jet streak propagating from the MS Valley up across the OH Valley, however, is common to both, making me think chasers targeting the triple point area may have a good day. The forecast of multiple lines of convection is reminiscent of April 3. The question for me is whether these could actually be multiple lines of discrete supercells simultaneously producing tornadoes, as in the Super Outbreak. My guess is no, if surface winds don't back any more than expected. The early MS Valley initiation possibility is another connection. In 1974, that first round cleared the outbreak area with incredible speed, as a squall line. One source I found speculated that a bore or something like that may have been responsible for strengthening it and moving it out so rapidly. Will the first line Friday get itself out of the way quickly enough for a second, more intense round, as then? Expected storm motions suggest it could.

Here's the one similarity that's jumping at me right now--insanely fast low-level moisture advection with a 40+ kt LLJ. The night of April 2, 1974, the 60-degree isodrosotherm was draped across central MS-AL. By mid-morning on April 3, it was north of the Ohio River at points. That's almost exactly what's forecast to happen overnight, though the best moisture may not reach quite as far north as it did then, according to SREF and others. One difference: the 1974 LLJ was more southerly, whereas this one has a notable westerly component.

 

[Trey Thee]

If the GFS moves in the direction of the NAM I believe we'll see a categorical high risk upgrade at noon. The instability and shearing environment over central TN mid afternoon looks impressive on the NAM at 3000j/kg and LI's of -9. The area would cover much of central TN and southern KY. If the NAM backs off a bit they'll probably stick with their MDT. Moisture return is impressive at this point and I'm a bit worried the GFS may trend towards the NAM as far as instability goes. It also looks like (as mentioned yesterday) that we could see two or three rounds of SVR move through some of these areas today.
Storm motions still look impressive and some areas of the now broader MDT are looking quite veered but overall this setup is looking potent. I've emailed some friends/family in the area to stay alert. Warning times will be cut significantly by the storm speed.

 

[Dave Gallaher]

Tor-warned cell moving through north Madison County in AL at 9:30am ct. Couplet has held up well through several scans. Secondary couplet forming behind the first atm.

 

[Clayton Fain]

Below is a link to the UAH ARMOR radar which could be of good use today. Already plenty to see obviously. Nice hook continues just north of Huntsville.

http://www.nsstc.uah.edu/ARMOR/webimage/