2014-03-27 FCST: OK/KS/AR/MO

[chrisbray]

Well, I am by no means an expert at this but someone brought up tomorrow in the "descent to chase season" thread and I noticed no one had put a discussion up for it yet here, so here it is.

From what I am seeing, moisture is pretty lacking for this setup, but if somehow enough gulf moisture returns this would be a fairly big event.

NAM says temps in upper 60s/low 70s with dews in the low 50s to upper 60s, obviously the best found farther south. It has a more elongated low pressure system with winds either straight Southerly or veering southwest. GFS is showing better moisture, which I have come to expect. Dews of lower 60s are nosing almost up to Missouri, with surface temps of 70 nosing up to the missouri/kansas border. The Low is more compact but farther north in position.

For mid/upper air, both models seem to agree there will be a 70-80 knot jet streak from the WSW going through the fourish corners area that afternoon, but the lower level jet at 850 seems to be farther up into the Illinois/Missouri border where it won't be nearly as unstable

I'm not seeing great instability though, both models seem to show maybe 1500 cape in the areas of interest.

However, 0-1km Helicity is pretty good throughout the target area at 100-300 m2s2, and bulk shear around 60 knots in the area is definitely a positive. Plus, the cap seems to be very breakable between 18z and 21z.

Looks like a modest cape/high shear event over (from what I have heard, I have never been there) a not so great chase region.

Anyone want to add other thoughts/corrections?

 

[Skip Talbot]

The main forcing looked to be from a cold front. Winds are pretty veered near this boundary with big straight line hodos, which may limit the tornado and supercell potential. If storms can pop east of the boundary where the 1km helicity values are substantially higher, there could be some tornado play. I'm not biting given the location though. I'm watching the northern end of this setup for a local play, however. The instability axis is forecast to kiss I-72 in western IL. I'm not expecting anything significant all the way up here given the meager instability and low dews, but it's definitely an area to keep an eye on after our February 20 surprise.

 

[chrisbray]

Good call...I wanted to mention Illinois but I just couldn't see it happening with the models showing 50s temps/40s dews, but you're in a much more advantageous location than I am to take advantage of any surprises that make their way into Illinois

As for storms ahead of the Cold Front, it could happen with the jet streak racing overhead and the cap doesn't seem to be TOO terrible, but the winds are pretty veered the farther west towards the front you go.

 

[samuel stone]

in east kansas and western mo, linear forcing and mid-uper level winds too parallel for that type of forcing. further south in east Oklahoma and west Arkansas there could some discrete convection but likely not until near dark and in terrible chase country

its not worth it unles it right in your backyard and you dont have other obligations.

 

[Taylor Wright]

I get out of class at 12:15 in Lawrence tomorrow, so I'm hoping to get extremely lucky and catch something initiating close-by before the the jet streak runs away and things become linear. RAP not too bad at 18z west of Lawrence showing >1000 J of CAPE, an impressive LLJ, and decent instability despite the lack of moisture (LIs around -5). If that holds, there should be a small window of opportunity to see at least some decent structure. Definitely not an ideal setup, but if storms are close enough for 20-30 bucks in gas to cover, I'll be all over it. At this point I'd be fine with just seeing some lightning, really.

 

[chrisbray]

I get out of class at 12:15 in Lawrence tomorrow, so I'm hoping to get extremely lucky and catch something initiating close-by before the the jet streak runs away and things become linear. RAP not too bad at 18z west of Lawrence showing >1000 J of CAPE, an impressive LLJ, and decent instability despite the lack of moisture (LIs around -5). If that holds, there should be a small window of opportunity to see at least some decent structure. Definitely not an ideal setup, but if storms are close enough for 20-30 bucks in gas to cover, I'll be all over it. At this point I'd be fine with just seeing some lightning, really.

Looks like you are going to get your wish, SPC discussing a tornado watch over east Kansas/west Missouri. Looks like some clearing developing and moving into that area which may allow for some modest destabilization, and there is still a few hours for the higher dews/temps to advect north. Should be interesting to see if much happens

 

[Skip Talbot]

COD HRRR is plotting some impressive updraft helicity tracks across central Missouri:

Winds look pretty veered across the warm sector, but there is veering with height and with that extremely strong low level jet, helicity values are spiking pretty high. It's still going to be a difficult chase over bad terrain, with fast storm motions given the strength of the shear. Other ingredients remain pretty marginal including dews in the mid 50's and CAPE sub 1000 across much of the MO warm sector. The dynamics could make up for the lack of instability, but the chances of actually seeing something on this setup still look too low to put any real mileage into it to me.

 

[Mike Johnston]

Convective initiation! Convective initiation! ~ Lyndon, KS down to Burlington, KS. Storm tops approaching 30K feet. That dry line has been scooting along faster than anticipated, as seen by monitoring the Oklahoma mesonet this morning. Instability still modest, but a decent corridor of 1,000 j/kg through east central Kansas with higher values further south. Some good low-level helicity just to the east where the storms are headed. Maybe there's something here after all.

 

[Skip Talbot]

This is an interesting setup. Dews are struggling to make it out of the 40's across much of MO, but there's a thin ribbon of low 50's advecting from the SW out of OK, just ahead of the dryline creating a narrow instability axis that storms are stuck to. Moisture advection seems to be lagging a little from what it was forecast to be, and much of the warm sector looks completely socked in with clouds except for a thin stretch just ahead of the dryline. Instability is going to be really lacking as a result, sub 1000 J/Kg MLCAPE across the warm sector, and that's forecast to start waning after a couple hours when we lose our peak heating and the front starts to push through. Still though, impressive shear profiles with 400+ effective SRH. A decent updraft might be able to spin something up, but it's working with meager moisture on a thin instability axis. It's going to have to be soon though.

 

[chrisbray]

Some of the storms are organizing a bit just east of Kansas City. You're right though, this is pretty interesting, the storms have a very small window and right now they are squeezing through it. I am not sure how long it can be sustained though, as the moisture is not advecting very far north. I'm just not convinced there will be enough fuel here for tornados

 

[Tim Supinie]

For the record, just because the winds are veered doesn't mean the hodograph isn't curved. This is the 19Z RAP analyzed sounding just south of Kansas City. The wind profile on the sounding looks pretty veered, but the hodograph has some curvature to it.

http://www.twisterdata.com/data/tmp.../RAP_255_2014032719_F00_38.5000N_94.5000W.png
http://www.twisterdata.com/data/tmp...255_2014032719_F00_38.5000N_94.5000W_HODO.png

Other than that, pretty much what Skip said. Looks like these storms are forming in a very narrow band of surface-based instability. The leading edge of the surface-based CAPE has kept pace with the storms so far, keeping the storms rooted in the boundary layer, but I imagine they won't be able to too much longer. Also, there is some pretty decent elevated instability (~1500 J/kg, per the 20Z mesoanalysis) developing near the ArkLaTex region, and the SPC has issued a slight risk for hail in that region.