2014-04-12 FCST: S KS/NW OK

[James Gustina]

Been keeping tabs on this day ever since Bob pointed it out in the "Descent" thread. GFS paints a somewhat strange scenario unfolding on the High Plains and further east this upcoming Saturday. A weak H5 impulse ahead of a pretty positively-tilted cutoff low looks to set up squarely over the OK PH. Unfortunately, modest winds at about 45-50 knots ruins the nice westerly component. The GFS has a broad sfc cyclone over SW KS into the panhandles with a dryline sharpening throughout the morning and marching east and extending almost directly down US 283 by 00Z. It looks blessedly sharper than the past few setups with lower-60F dews overspreading most of the warm sector immediately in front of it. Sfc winds around 5 knots could be better, but sfc winds backing with time over the area immediately off the dryline in western OK and southwest KS might make up for that. Almost due southerly H85 winds aoa 40 knots by 00Z immediately ahead of the dryline can only help but contribute to the overall low-level shear environment given the weak sfc winds. Progged deep-layer shear at 40+ knots is definitely nothing to sniff at. The overall shear environment looks great with pretty decent turning in the lowest level. I'm not inclined to trust the GFS' thermodynamic solution, but it's been throwing out SBCAPE values around 2500-3000 j/kg by 00Z across southern Kansas and into northern Oklahoma.

With that said, the biggest issue is the continual appearance of an almost thermonuclear cap and with questionable forcing at best, this day seems marginal as of right now. H85 temps at almost 20C is extremely concerning especially if there isn't something to initiate cooling in the mid-levels heading into the late-afternoon. I don't see sfc temps getting anywhere close enough to break an inversion that is that stout. I'll be interested to see what the NAM does with it tomorrow morning.

 

[Zack Hargrove]

I have also been watching this closely. A couple days ago, it seemed this setup was completely dead, but it has very slowly taken some very small positive steps. I want to believe in Saturday because its a weekend and any storms that do form would likely be isolated, but I still need a lot of convincing. Most of the concerns you mention, I also worry about. The last few runs have trended towards a weaker cap in south central/SW Kansas, and thanks to a bit of northern stream interaction (12z GFS), the deep layer shear there has looked substantially better. One positive note is that it seems like the 12z GFS was at least producing a storm after 00z in south central Kansas... that area has been pretty consistent breaking out some sort of precip over the past few runs. The weak upper level jet worries me (stronger upper level winds would likely deepen the surface cyclone more, helping with a trigger)... its still way far southwest, as well as the bulk of the mid-level jet. The 850s are decent but could be better. I love the directional shear, but the speed shear could be better, and some of the soundings show a subtle veer/back/veer pattern going up which is often a red flag. The 00z Euro from last night shows a similar solution, but the instability is further north and the low is slightly deeper. However, the Euro doesn't break out any precip on the dryline. Still, if we can get a little piece of energy moving over the right area of the dryline, there could be some dryline magic Saturday. I just worry that the timing is too far off.

The other thing to note is that last night's 00z GFS and 06z GFS today showed an interesting environment near a stationary/warm front in northern MO/southern IA... I have a hard time believing there will be enough moisture return that far north to produce the pockets of 1700-2000 J/kg CAPE in that area, but there isn't likely to be the same capping issue. On the other hand, it looks like whatever happens in that region is going to very probably be a convective mess but hodos looked pretty nice. Still, the 12z basically killed that threat.

Moving into Sunday and beyond, it looks like depressing crashing cold front garbage.

 

[Marcus Diaz]

I'll keep it simple.

NUCLEAR CAP

Haven't been impressed with anything the GFS is throwing about this setup for both days this weekend. Another likely setup I'll stay home on my ass both days.

 

[James Langford]

If the latest NAM is too be believed, Saturday in far NW OK could be a pretty decent play. Nice energy at 500 Mb, not too much cap, nice dry line bulge right along the KS border. I'll need to see some more continuity over the next few days but so far I am cautiously optimistic.

 

[James Gustina]

The shear profile on the NAM is a little less impressive but the capping issues are a little less prominent than they have been on the GFS. NAM seems to be more in line with the Euro as well, with decent low-level wind fields immediately ahead of the dryline in NW OK/SW KS. Overall better upper-level dynamics and higher H5 winds make me much more optimistic for this one. I'd still like to see a bit more cooling throughout the lower-levels to make capping a negligible issue but I'm not holding my breath.

 

[Zack Hargrove]

LCLs are also a huge problem with the NAM because it's slightly less bullish with the moisture which is more realistic IMO. However, the 84 hour NAM doesn't exactly have a great track record.

Sent from my LG-LS980 using Tapatalk

 

[James Gustina]

LCLs are also a huge problem with the NAM because it's slightly less bullish with the moisture which is more realistic IMO. However, the 84 hour NAM doesn't exactly have a great track record.

Agreed, I'm not sure if it's necessarily indicative of the overall quality of moisture. The NAM has done this with some other setups up that way like May 25, 2012 (La Crosse) but that was also late-May with a much more dynamic system. I'm interested to see what the nested 4km WRF and other hi-res models say on Friday.

 

[Jeff Duda]

Moisture looks to be on the shallow side and mixes out within a few tens of miles of the dryline. That's probably why SBCAPE is so high with a cap. Looks like there is not a consistent focused upper level support for convection, and it's pretty warm in the mid-levels (up to 8 C at h7 in mid-April is pretty cappy, although surface temps in the mid-80s will certainly give parcels a run for that cap). Decent 500 mb flow despite the seemingly weak height gradient. It's possible something could happen from this, but it looks to be one of those 2%-type setups.

 

[Zack Hargrove]

Moisture looks to be on the shallow side and mixes out within a few tens of miles of the dryline. That's probably why SBCAPE is so high with a cap. Looks like there is not a consistent focused upper level support for convection, and it's pretty warm in the mid-levels (up to 8 C at h7 in mid-April is pretty cappy, although surface temps in the mid-80s will certainly give parcels a run for that cap). Decent 500 mb flow despite the seemingly weak height gradient. It's possible something could happen from this, but it looks to be one of those 2%-type setups.

The only way I would chase this setup is if I decided I wanted to give TX a shot Sunday (getting iffy with the terrain and just plain uncertainty front position wise), as well. Otherwise, its jut too much of a risk.

 

[Derek Weston]

The only way I would chase this setup is if I decided I wanted to give TX a shot Sunday (getting iffy with the terrain and just plain uncertainty front position wise), as well. Otherwise, its jut too much of a risk.

Agree it's a bit iffy for discrete cells during the day. To me it looks to come down to a well timed piece of energy hitting the area.

Sunday, though (other thread, I know) was looking a heck of a lot better on the ECMWF. Up into OK.

 

[Jeff Duda]

I also call the degree of moisture return seen on this morning's NAM and GFS into question. I think the NAM may be overdoing surface dewpoints by up to 5 F. Compare what the 9-hr forecast from the 12Z NAM says current dewpoints should be like compared to current analyses for case 1. Also, the RAP analyzed dewpoints over the Gulf are also a little overdone as of this moment when comparing analyzed Tds to buoy observations. Finally, all SREF members except those using the WRF-ARW say dewpoints should currently be in the mid-40s in Norman. The ARW members say it should be around 40. We're at about 38-39ish.

 

[James Gustina]

Just thought I'd throw this in here. Wow is that hard to watch:

 

[Jared Orr]

The way I see it, down south near the OK/KS border, cap is probably impenetrable considering the lack of forcing. NAM shows cap eroding in northern KS around 21Z, due partly to the high surface temps progged. GFS is showing a weakened, yet substantial cap as late as 00Z because of lower sfc temps...however, this also yields lower cloud bases, which would benefit tornadic potential. So both models have their pros and cons...but both models show late convective precip in central to northeast KS...probably due to this weakening inhibition and prefrontal forcing. However, I'm skeptical about the actual location of this precip if it were to develop...GFS has been pretty consistent showing a dryline bulge all the way up into central KS, which could serve as the focal point for some convection--if some parcels can muster up the audacity. Upper level support isn't stellar, but there is a decent amount of area under the hodo curve for central KS, and moisture return has been surprisingly sufficient. I may just go out since it's a weekend, but my target location could vary wildly depending on where the short-range models predict the most forcing and weakest cap.

One of my big questions is how the surface and 700mb temperatures will resolve, as it will dictate LCL and cap. Also, bulk shear is weaker than average for this time of the year, so that may present an issue.

 

[James Gustina]

Not overly enthused with the way this is starting to look on the 12Z NAM. Dang near 12C H7 temps with slightly less prominent turning in the lowest level. NAM is also backpedaling on the overall quality of moisture return/depth into Central Kansas making this day extremely iffy considering the lack of an appreciable trigger.