2015-04-24 EVENT: TX/OK/KS/AR/MO

[Russ Conlon]

Kind of surprised no one has talked about this one yet. ECMWF and GFS show 996 MB low parking itself over NW and NC OK between 18-00Z. Wicked looking 250MB subtropical jet stream looks to make it's annual introduction this time of year as it looks to swoop over OK and N TX . Mid to upper level winds turning to 70-80 knots at 500 MB and approaching 150 knots at 250 MB. Nice! Great looking moisture return ahead of the dryline with 70 degree dewpoints poking themselves into SC OK. The key here seems to be in particular the timing and speed progression of the dryline bulge as ECMWF and GFS differ on this. Temperatures and early convective initiation are also real concerns as this could limit CAPE. If convection holds off until mid afternoon and we get temps in the 80s, look out. Progression of low takes it across northern half of OK and southern KS which should further enhance already great shear in place, particularly in S Kansas on the NE side of the low. Will be very interesting to see the next run of ECMWF and the NAM once this day comes on line but with latest run showing placement of the features on Friday morning, models seems to be in reasonable agreement.

 

[Royce Sheibal]

Friday is really going to depend on what model you believe. The new NAM drops some heavy STP over SE KS and most of E OK. If NAM comes through, which it has lately, I'd be headed to SE KS where DPVA is going to be going wild and 850 Flow is still southerly and moist-ish.
GFS is another story. GFS says you better stay in eastern TX or you are boned. 850's will be coming out of the SW in KS and OK, drying and capping pretty hard. CAPE's are pretty pathetic and leftovers from nocturnal will ruin your day.

Right now let's call this one too unsure to call. If the GFS falls in line with the NAM, then we might see this turning into an enhanced or even moderate day. That latest NAM run is pretty sexy. Good luck down there, southern plains chasers.

 

[Russ Conlon]

Royce, 12z GFS shows a significantly slower eastward projection of dryline by 00Z falling more in line with the NAM than previous runs so that's encouraging. Got a sick feeling in my stomach when targets started saying eastern OK past Shawnee to Chekote and eastern TX. Terrible terrain to chase in. Timing of precip breakout and capping are all over the map on the models not to mention concerns of possible overnight Thursday into Friday morning convection. Classic boom or bust day shaping up. Hoping to see sunny skies and 75-80 degrees in central OK ahead of dryline by 18Z Friday.

 

[Royce Sheibal]

Nam and GFS solutions are getting closer as predicted. NAM 4km (my favorite so far this year) is saying to stick between Wichita and Ponca City, and it forecasting some nice UD helicity with cells between 21z and 00z. Normal NAM is favoring a little further E and S still. Either heading SE of Emporia or even down south of Tulsa. I'm typically one to favor the northern target which has better upper level support, but the NAM shows better low level shear on the southerly target. This is gonna be a tough call, Russ. You might have to wait till Friday morning to make your call. One the plus side, nocturnal convection looks like it will be long gone thanks to these crazy upper level speeds.

 

[Russ Conlon]

Royce, the northern target looks like the money target and either Wichita or Ponca City as you alluded to would be great targets to set up at. I'm thinking Shawnee as a southern target. Agreed on low level shear looking better on the southerly target (CAPE will be better too) as 40-50 kt southerly LLJ will come in between 19-21Z bending those hodographs nicely. When I first posted my main concern were the 850 mb winds and how much backing we might get out of them. This concern has lessened considerably in the last 24 hours of runs. NAM EHI looks great along a box traversing starting at I-40/Highway 177 junction, east along I-40 to US-69, then bend back SW on 69 toward Durant and then 177 northward back to I-40. Sig tor index confirms as well. Upper level support is the best I've seen so far this year. Both targets look good but the northern play would have the edge in being the better one.

 

[Brian McKibben]

If a storm gets going in central OK and moisture is decent, then watch out. Check out Hodograph from Seminole, OK

http://climate.cod.edu/hanis/model/fsound/index.php?type=18|NAM|SGP|850|spd|54|*150,114*|false

View media item 559

 

[Trey Thee]

Royce, the northern target looks like the money target and either Wichita or Ponca City as you alluded to would be great targets to set up at. I'm thinking Shawnee as a southern target. Agreed on low level shear looking better on the southerly target (CAPE will be better too) as 40-50 kt southerly LLJ will come in between 19-21Z bending those hodographs nicely. When I first posted my main concern were the 850 mb winds and how much backing we might get out of them. This concern has lessened considerably in the last 24 hours of runs. NAM EHI looks great along a box traversing starting at I-40/Highway 177 junction, east along I-40 to US-69, then bend back SW on 69 toward Durant and then 177 northward back to I-40. Sig tor index confirms as well. Upper level support is the best I've seen so far this year. Both targets look good but the northern play would have the edge in being the better one.

CAPE doesn't look that impressive Friday afternoon, I think that's driven in part by morning convection. There are definitely some positive dynamics in place but I'm not sold on Friday yet. I think the system will be fully onshore by 12Z runs tomorrow so we'll see if that changes much. Just not enthused about this yet.

 

[Zack Cooper]

Friday doesn't appeal much to me. Morning convection will lead to capping and instability issues for the rest of the day. Also there are some questions regarding the speed of the trough. However, if instability was greater and the axis wasn't so thin, I would be getting pretty excited. Hard to ignore wind profiles like the NAM has been showing along and just east of I 35 in Oklahoma. The 00Z NAM was even slightly less impressive in that regard, but previous runs had areas of >400 m^2/s^2 ESRH... pretty darn good.

I guess I'll keep watching this potential setup, but for now I just don't think it looks that solid.

 

[Russ Conlon]

Just yuck. Everything looks great on those 00Z NAM and GFS runs except showing AM precipitation breakout early Friday in SE Kansas and NE TX. Models are consistent showing this as well. Will still follow but I have to agree, lack of CAPE and resulting CINH issues seem to really gum this one up.

 

[Ben Holcomb]

After getting yesterday out of the way I've finally turned my attention to Friday again. A quick look at the 12Z NAM and all I can think is 'Nope'. I don't forsee myself even leaving home tomorrow unless something drastically changes. While we've got 80 knots at 500mb, which seems reasonable looking at water vapor today, with the california trough/low digging into the tropical jet.

80 knots at 500mb should make up for a huge disappointment in the instability tomorrow, but it still looks seriously messy. Overnight/morning convection is a huge concern with such a strong LLJ overnight.

I still know I'll find myself trolled out by a tornado watch for I-35 and east, but my hopes of seeing a photogenic tube are nil.

 

[Jeff Snyder]

The main issue I see tomorrow is the persistent forecast for morning and mid-day convection over southeastern OK and adjacent areas of AR and TX associated with a lobe of vorticity at 500 mb that moves through during the morning hours. This precip and cloud-cover bites a significant bite out of the forecast CAPE fields across most of the areas south of the OK/KS border. Perhaps associated with this, the NAM continues to show rather strong warming at 500 mb (+/- 100 mb) during the day tomorrow, with the 500 mb T jumping 4-5 degrees in areas of central and eastern OK. This, in turn, results in very poor lapse rates (4-5 C/km) above ~600 mb in some of the forecast soundings. The mid-level warming combined with low-level "not warming" (associated with precip, outflow, clouds, etc.) results in pretty marginal buoyancy profiles (with the EL well below the tropopause in some parts OK). Yuck.

This then leaves, for me, the option of heading N into KS to get closer to the sfc low. Some of the wind profiles near the low and warm front look pretty spectacular, but there may be issues with storm mode. The 12z NAM and 4 km NAM hold the dryline back compared to previous forecasts, which helps a bit. On the other hand, the 12z GFS lifts the front to the KS/NE border and mixes out dewpoints ahead of the dryline such that there's a very wide corridor where the Td gradually increases (that is, the dryline isn't much of a dryline). The GFS also shows widespread precip in OK east of I35 by 18z and into southeastern KS before 21z.


Not much more time to look at stuff this morning, so I'll leave this post at that.

 

[Chip Redmond]

Lots of uncertainty tomorrow, which typically I would thrive on. However, some big red flags are there for sure. Most have been touched on so I won't reiterate, but I will throw in the slight possibility for a bit more capping than models are hinting at. This just being the trend the previous few systems (pre-cut off low) to shift west/southwest and advect a bit more of that warmer air in the mid-levels to hold things back. Of course those systems had a bit different origin. Morning storms don't appear to be a huge issue across Kansas as they pull out of most the state by noon. Only issue will be how much convection further south hampers moisture return.

Will be interesting to see where the warm front sets up (see ensemble spread below). My hopes are somewhere along the I-70 corridor, but I bet it is further south and west. Regardless, will likely poke around the southeast side of the low and hope something can develop ahead of any mess that develops along the dryline. It will likely be a "stay way out ahead of the storm, let it come to me, lose it in the Flint Hills, and wave good bye as it hauls east/northeast" kind of day with 40mph+ storm motions. Maybe, just maybe we can get it to turn into mean flow and slow down a bit!



Chip

 

[Ben Holcomb]

Digging deeper provides more questions than answers. The 12Z NAM didn't seem to initilize well if you look at 500mb and 700mb RH vs water vapor. It's showing N TX and OK pretty dry, but that's far from the truth judging from WV. Part of our CAPE problem seems to be really crap lapse rates that Jeff touched on from about 700mb up. Not sure I buy that scenario now. What would bring significant warming?

 

[Andy Berrington]

What would bring significant warming?

Influence from the sub-tropical jet advecting warm air in the mid levels from the eastern Pacific is my initial thought.

 

[Jeff Duda]

Ugh. I'm really not a fan of "front-loaded" (really probably just positive tilt) troughs where the jet is on the lee side. Those systems just lift as they fly northeast rather than dig at all, meaning the good lift is usually limited to the far northern aspect of the target, possibly leaving areas with great thermodynamics completely capped off. Frankly I'm surprised we're not looking at a crashing cold front with this, but given it's located deep in the subtropical jet and is rather shallow in latitudinal extent, that probably explains the absence of really cold air at the low levels flying in behind this thing. However, I do think the shape of the wave is highly influencing the height patterns at the low levels, which frankly do not have me excited given the wind direction they indicate (see two paragraphs below).

I share the concerns of others who have posted on this thread. I don't think that any of these models has adequately captured all the necessary details to lock in the 36+ hour forecasts as gospel. However, I doubt we're going to see much change in the strength, shape, or location of the upper-level wave for this thing.

With that said, what bothers/frustrates me the most is the lack of backed flow in the low levels. I see little indication of any negative u-wind component just ahead of the dryline, even at the surface. Couple that with little veering to the SSW behind the dryline to result in only weak convergence at the dryline, which itself does not look to have much of a decent moisture gradient. Dryline setups tend to underperform when the good moisture doesn't make it right up against the dryline. This is probably the result of massive dry advection being progged at 850 mb throughout the day by both the NAM and GFS, which to me is the most disgusting aspect of this setup. The models have tamed this tendency a little over the past few days, but actually the 12Z NAM has a more westerly component to the 850 mb winds than the 12Z GFS over Oklahoma, and even drier air as well, which is a tendency in the wrong direction. This not only reduces moisture depth but also changes the shear profile by allowing some mixing of momentum down to the surface, causing slightly veered surface winds. The drying also probably mostly explains the general lack of tight moisture gradient along the dryline given the west-east gradient of moisture depth as dry air moves in from the west over decent surface moisture. This also results in faster storm motions, which are a concern to me. Not fun chasing 50+ kt storm speeds.

All of that uncertanity/discussion may be futile, however, if the forecasts for early-day convection across the southern portion of the target area verify. One big lesson I learned some years back when I was based out of Iowa and rarely chased southwest of Emporia was that early day convection south of your target area (even if by several hundred miles) almost certainly kills your target area to the north, for a few reasons:
1) Unless moisture is already in place before the southern convection develops, it blocks moisture return.
2) Unless you are lucky enough to get crystal clear skies for many hours during the day, it blocks warm air advection at the low levels.
3) Convection means clouds. Mesoscale convection means a widespread area of thick clouds which will almost certainly spread far enough north to reduce insolation and severely inhibit or reduce destabilization, making the first two points also pretty much pointless in this case.

I hope against hope at this point that there is some major detail that I either have wrong or that ends up being incorrectly forecast by the models. However, if these details verify, there looks to be only a very narrow window right along the warm front or triple point near I-70 in Kansas. At least that area is north of the 500 mb jet core, which would result in slower storm speeds (and less shear). But given the reduced CAPE, less shear may actually be a good thing in this case. Of course, see (3) above. Even if this is all that's left, I don't think it would be worth it to me to make the trip.

TL;DR: another crappy setup.