2012-02-28 FCST: OK / KS / MO /AR /TX

[Jared Orr]

It's a conditional, early-spring setup right now. There's a healthy trough in place across the plains, with excellent speed and directional shear in all areas. IMO, the biggest issues will be the weak instability and the almost absent inhibition.
If sufficient clearing and daytime heating occurs, more discrete storms with updrafts strong enough to battle the 65 kt 500mb winds will have a tornado threat. But my fear is that we will end up with one of two scenarios:

1) Storms firing early due to weak cap...being blown apart or going multicell.
2) Clusters of supercells forming, weakening with stabilization of the atmosphere, and then turning into a linear clump very quickly.

My target, if I choose to head out, will probably be somewhere near the OK, KS, MO intersection.

 

[Trey Thee]

So great to see something in "Target Area" for my area. It's been a long time.

As a result I'm probably more excited about this then I should be, especially since the likelihood of me chasing is rather slim.

Jared, I think you touched on some key issues. It is definitely conditional and I'm not really sold on it at this point. But if things do come together I think we could definitely see a few late winter/early spring tornadoes. However, as of now the model data doesn't look overly encouraging because of some of the timing issues and just plain lack of instability. Helicity will be decent and hodographs don't look bad but then you've got the upper jet at 500mb that's going to topple a lot of the updrafts as you mentioned. Cape values might touch 1,500 or so, otherwise not much to go on...at this point it looks a bit more like a "crapvection" fest, perhaps a couple storms will go up, make it and do something?

We could have a few ingredients come together. Namely if moisture return is good and daytime heating turns out to be a bit more than forecast and if we can get some sort of a mild cap to prevent initiation until after 4pm we could see a few tornadic cells.

I'm not holding out much hope at this point but I could wake up tomorrow and change my mind? And I'm just glad we've got something to talk about at this point!

 

[samuel stone]

I'll be covering the northern target area here.

well its definently not your classic outbreak setup but it is right in my back yard so whats to loose. In central/northern Kansas and southern Nebraska initiation appears likey in the afternnon hours with a powerful vortmax begining to press through the area. Our upper level cold pool and sharp height falls press in over top sufficient instability in combination with an axis of insolation from the southwest by the afternnon. Obviously wind fields are favorable at all levels, this has improved the last couple days as 850mb winds have backed a little more and 500's have veered a tad more. the only issue here is gonna be velocities with the 0z NAM progging a 500mb jet max up to 100kt speeding through kansas by 21-0z. clearly this wont help chaseability of storm motions but also as stated above we dont exactly have a sturdy foundation of CAPE underneath that to balance and sustain any updrafts. This brings me to the big downfall. the NAM is progging anemic CAPE ans LI values across the Kansas and Nebraska warm sector. If that verrifies i dont much more than some small hailers and a couple weak tornadoes from low toppers just east of the 500mb low. However I do think the 0z NAM is slightly underdoing our CAPE values. but thats all going to depend on the stratus deck. NAM does decrease mid level relative humidities with some room to spare between the pacific front-dryline. We'll see what happens with our stratus deck through late morning but if it erodes a little earlier it could mean the difference for a couple more tornadoes to form out of the stronger updrafts on the pacific front. definently a long shot for chasers for the most part i would say though when you also throw storm motions in account.

I'll leave manhattan and head west on I 70 around noonish and play from there if things continue to look this way. might as well for only an hour and a half or so drive west to the PF-DL

Thoughts?

 

[Jason Persoff]

The rotational shear is beautiful, and I guess my $0.02 for what it's worth is that very warm, moist air is moving up Plains states courtesy of the strong sfc low (currently over Ogalla) with Tds already measured in the 50s in SW KS. Snow squalls are pushing off the mountains with high rates of speed currently in DEN/BOU region, and that suggests the possibility little inhibition will be present across the Palmer Divide east to GLD. Already satellite shows a line of Cu forming along the cold front.

My heart tells me that there will be an isolated storm prefrontally in WC/NC KSNE borders near the triple point. I guess I'd favor a target just south of NE within the HLC-MCK lines. But I'm at work and don't have my road atlast to peruse the road network, but memory serves that this would be a good target.

I like your target, Sam. GL today!

 

[Mike Johnston]

Well, it looks like the cold front will be phasing better with a decently sharp dry line, the whole system seems to have slightly slowed down from what was progged by earlier models, and the the surface low pressure is on a bit more southerly trajectory. (The latitude of where these lee lows develop seems to be a wild card so often.) Goodness knows the low level helicity fields over western and central KS look very supportive. Moisture is still a bit lacking in an absolute sense, but the moisture advection looks to be proceeding as well as could be expected given the climatology. In general, it looks like a broad area of central KS holds some promise for severe later day. I know the SPC outlooks have tended to distinguish between a northern and southern target for today's setup, but I'm kind of intrigued by the area in between the two given the clearing trend and diurnal factor.

 

[Skip Talbot]

It doesn't look like the timing on the cold core end of the setup is working out. Right now is really the hour you want to be intercepting because you're often playing the steep low level lapse rates, and indeed there is strong heating nosing into the triple point and just behind the trailing boundary. The steep low level lapse rates look fantastic:
http://www.spc.noaa.gov/exper/mesoanalysis/s14/lllr/lllr.gif?1330457693970

The problem, is the cold air aloft is still well west. The -15 to -20C 500mb temps are making for almost stable mid level lapse rates ahead of the triple point:
http://www.spc.noaa.gov/exper/mesoanalysis/s14/laps/laps.gif?1330458143210

There just isn't much support in the midlevels for robust updrafts, despite low level lapse rates that are very favorable for spouts or mini sup tornadoes. The 50's dews aren't forecast to pool under the 500 mb cut off low with -20 to -25 C temps until well after dark. By then we've lost our solar heating and those steep low level lapse rates so the tornado potential may diminish as a result. Still, the lifted index spikes over eastern NE after dark with continued moisture advection at the surface under cold air aloft, so there may indeed still be some low topped storms and hail threat over this region.

I agree that it might be a little more interesting further south where there is better forcing along a well defined dryline bulge, with better upper level support.

Edit: And of course right after I post that, a couple nice looking cells flare up just ahead of the triple point. Cells like the one near Stockville, NE could be the play of the day as now is the time for a cold core intercept, and 50+ dews have cross the KS/NE border.

 

[Jason Persoff]

I need to bump my target slightly northerly...earlier I had stated HLC-MCK line, but I think this would need refinement to the MCK-LXN line looks really good. Latest sfc obs at LXN are 52/48 winds SE at 20. Latest satellite shows a pre-frontal line of TCu that look pretty discrete at the moment extending N from I-70 in KS into the SC NE area. Very narrow extension of moist air pooling in the prefrontal region with sharp Td drop off both east to the east. As Skip indicated, NOW is the time to chase, because linear mode seems probable a few hours from now.

EDIT: Looks like MCD up for the area too. It's my first 2012 forecast and I'm feeling good .

EDIT 2 @ 1430 MST: Prefrontal cells now firing along/south of I-70 in KS, also discrete for now. SRH is more than adequate in both places. And while CAPE is low, it is currently (per SPC) showing up as being in two areas: along my target above and also in C KS (both around 1000J/kg). Again, I prefer the SC NE play because moisture continues to feed into the area (3hr change +6 deg), closer to the triple point with more low-level backing, and something kinesthetic about pattern recognition...but that last one is not scientific.

EDIT 3 @ 1500 MST: ...I know that this is superfluous, but I just couldn't help crowing: TOR watch and isolated TOR warning in target area; nothing verified, but at least I'm feeling the springtime kicking in. Sorry, the rest of my post is relevant though .

 

[Kelly Sugden]

Via NWSChat... looks like Mike Umsheid saw a tornado near Stapleton... sw of 92 and 83 in Nebraska. Mods, do we want a now then?

 

[Skip Talbot]

Via NWSChat... looks like Mike Umsheid saw a tornado near Stapleton... sw of 92 and 83 in Nebraska. Mods, do we want a now then?

Now and Forecast threads have been merged. Please continue the discussion in this thread.

It will be interesting to see what prompted that group of chasers to target that cell. Midlevel lapse rates are better further west with the cold air aloft, but marginally more so than cell now over Kearney that was tornado warned earlier. That cell with the report is much closer to the "cold core" play, sitting north of the low where the surface moisture is wrapping around colder air aloft. It's right on the fringe of the moisture and instability gradients though.

 

[Jeff Duda]

It will be interesting to see what prompted that group of chasers to target that cell. Midlevel lapse rates are better further west with the cold air aloft, but marginally more so than cell now over Kearney that was tornado warned earlier. That cell with the report is much closer to the "cold core" play, sitting north of the low where the surface moisture is wrapping around colder air aloft. It's right on the fringe of the moisture and instability gradients though.

With the exception of Mike Umsheid, every one of the chasers that were on spotter network on that storm are from CO. Thus my guess is they played that because it was closest to home. I think everyone has a bias like that to some degree.

I have trouble believing the SPC RUC mesoanalyses showing 1000 J/kg of nearly uncapped CAPE from SW KS through NW TX. With the amount of large-scale forcing and the surface forcing from the dryline, there's no way storms wouldn't have erupted there by now with that little CIN remaining.

 

[Jason Persoff]

With the exception of Mike Umsheid, every one of the chasers that were on spotter network on that storm are from CO. Thus my guess is they played that because it was closest to home. I think everyone has a bias like that to some degree.

Naturally they played it close to home--sfc analysis this am made things clearer, and early spring is very difficult time to forecast way in advance.

I would definitely like to hear how Mike had set himself up for this tornado today: what a catch...North of the low for the cold core seemed more conditional than south to the triple point. I definitely think Mike is the man when it comes to cold core events--I am delighted he caught a tornado today!

That said, I would have missed it were I to have been out. These cold core events are still a challenge to me. If I remember the sfc analysis and try to peg it close to where Mike was at the time, dewpoint depressions were pretty large (~55/40) with far less moisture and likely high bases with little room to the stratopause (LCLs around 1500kft). Notwithstanding, I would have been worried about hodographs that would have had shear from the sfc 090 and at H5 200 which feels like a more linear setup isolated cells (please someone set me straight if I'm wrong on this--i.e., the more higher level winds are at 180 degrees to sfc, the more likely a linear storm system will manifest).

So, I ask, triple point or north of the cold front about the low? What happened today?

 

[Jeff Duda]

The triple point has been pretty much colocated with the low today. The system hasn't begun occluding, so the low center is always going to have the strongest forcing since, by definition, it's synoptic scale upward motion that causes the low to form where it does and have the intensity it does. Basically, in situations like this, stick to the low and you won't be far from anything significant. It's also important to note that you can have convergence bands not associated with a front located away from the warm sector. Likely the one tornadic storm formed off of one of these. There just happened to be enough instability to squeeze a tornado out of things.

 

[Kelly Sugden]

The tornado location make sense to me as far as a ll boundary is concerned... warm front magic. Seems the upper level low/trof and sfc trough were fairly collocated and usually tornadoes occur within 200 miles from the pressure perturbation for cold core systems. What is interesting about this is that the 500 hPa temperature at LBF raob is not that cold (-23 deg C), imho.

 

[Mike Johnston]

In the latest tornado warning message for the cell near Hutchinson, warning text indicates mulitple tornadoes reported near Hutchinson. Not a classic velocity couplet, but definitely several areas of opposing SR velocities in close proximity and a few strong mesocyclone signatures indicated. As mentioned above, I thought central KS was looking pretty favorable for today's setup.