2011-04-14 FCST: OK/KS/TX

[ChristianTerry]

Looking at the GFS for a possible setup in Southeast Oklahoma and Northeast Texas on Thursday. Seems like a disturbance will move into Southern Kansas and tap into some moisture, although im not to impressed at the amount the GFS is showing. A good amount of shear and a parcel of 2000 J/kg CAPE looks like it could pose at least an isolated threat in South Oklahoma and North Texas.

 

[Neil Robinson]

I think there's more than enough to initiate convection, and possibly sufficient directional shear to get things turning. The 00Z NAM has a well-defined DL bulge across the I35 around OKC at 00Z Fri, pushing into 65+ dps and generates 2000+ max CAPE - enough to develop a line of discrete cells on the composite ppn.
If I wasn't 3000 miles away I'd be thinking of taking some 'chasing leave' for Thurs afternoon, targetting just east of the I35 corridor around OKC/Ardmore.

 

[Mikey Gribble]

I'm just going to copy and paste the most recent post from my blog. This post was just on the GFS. I went over the NAM in a post earlier this morning if you want to read that. I was going to copy and paste that too, but this would be an enormous post if I did. Anyway, my primary concern right now is when the midlevel low is going to close off and it's effects on the shear profile. If it closes off fast like the GFS is showing we are screwed. If the NAM solution with an open wave Thursday afternoon verifies I think we are in good shape and have a good shot at a few tornadic supercells. The ECMWF is kind of in between, maybe leaning towards the NAM a little with the trough. I haven't forecasted a whole lot for this setup yet, but I'm leaning towards a compromise of the NAM and ECMWF where we keep more of an open wave or just starting to close Thursday afternoon. If the open wave solution can verify and we maintain our directional shear over the warm sector everything else looks okay (assuming moisture return works out).
Anyway, enough rambling. Below is my post after looking over the GFS. Again if you want to see my earlier post on the NAM just go to my blog (link in signature)...


The 12Z GFS is out and the problem I discussed in previous posts is becoming more apparent with the GFS solution. The primary difference between the GFS and NAM is that the GFS wants to close off the low and put a hard negative tilt on it (NAM favors open wave solution). The big problem with what the GFS is showing is that when a trough closes off like that (with negative tilt) it veers 850mb winds over the southern portion of the dryline and backs mid level winds over the northern portion of the warm sector. The result is virtually no crossover in the 850-500mb layer (unless you go way south where 850′s start to veer a little less). When you get poor directional shear like that the result normally isn’t good for tornadoes.
The NAM with the open wave solution would be much better for the tornado potential. The ECMWF is kind of in between the NAM and GFS solution (little closer to the NAM probably) and is just starting to close off the low at 00Z Thursday.
I’m not going to get into too much detail now. I already went over the 12Z NAM a little bit in my previous post if you didn’t already read it. I will post a more detailed forecast with a map when I get home later today. Overall this is looking like a pretty decent setup. The extent of any tornado threat is going to come down to what the trough is doing Thursday (I’m leaning towards the NAM ECMWF compromise on that) and moisture return. The models have been consistent with dewpoints in the 60′s into Kansas, but I’m still a little worried about moisture because of the relatively short window for moisture return.
I will update again later this afternoon.

 

[Jeff Snyder]

I'm having a bit of a hard time keeping my expectations and optimism in check. The 00z/13 NAM now holds the dryline back very near the I35 corridor by 00z Thurs evening (the 12z-18z/12 GFS has the DL a bit closer to the Tulsa area at 0z), with a classic synoptically-evident tornadic supercell pattern aloft. A beautiful negatively-tilted shortwave trough, with a strong jet streak upstream of the trough axis, and the target area nicely placed in the left-exit region of said jet streak. As a result, the wind profiles look very favorable for tornadic supercells E of the dryline, with southeastern winds at the sfc veering to >30kts from the S at 850, 35-60 kts from the WSW at 500 mb. Resulting hodographs show nice curvature between the sfc and 3 km AGL. The 00z NAM is slower with the primary vorticity max, with the stronger (>35 kt) 500 mb flow hanging back behind the dryline at 00z; the 12z/18z GFS has the stronger mid-level flow moving out above the moist sector by peak heating. Regardless, from a synoptic standpoint, I *always* look forward to these types of setups.

The primary fly in the ointment, if you will, seems to be questionable moisture return. At 3z this evening, surface obs and RUC analyses indicate that the >60F Tds are along and south of the latitude of BRO. Unfortunately, although pressure falls and lee cyclogenesis will aid in stronger southerly low-level flow tonight and tomorrow across the southern Plains, it doesn't appear as though the 925 mb flow will be particularly strong across the western Gulf for most of the next two days (<= 20 kts). On the positive side, the surface pressure pattern across the southeastern U.S. looks very favorable for a deep fetch of moisture from the Caribbean, but I'm not sure the advection will happen quickly enough to provide us with the real, quality juice (>65 F Tds). That said, the 00z NAM has the 60 F isodrosotherm to near Wellington at 0z Fri, while the GFS has >60 F tds up farther into southeastern KS (and with a wider moist sector). Considering the rapid moisture return that will need to occur for such >60 F Tds to indeed be in place across far southern KS and OK by Thurs afternoon, it seems reasonable that low cloud cover (WAA-driven) may be an issue. Indeed, the GFS is keeping warm-sector temps down a bit as a result of saturation around 850 mb. Even with this, however, the relatively backed low-level flow (southerly at 850 mb, or maybe even south-southeasterly at 850 mb), appears as though it'll keep capping concerns at bay. In fact, CINH from both models is low by afternoon E of the dryline.

Looking at the 9z and 15z SREF guidance, the NAM does appear to be one of the most western solutions, as most of the other forecasts used in the SREF are farther east into the sticks of far eastern OK, southwestern MO, and adjacent areas of AR. For chaser-centric reasons, I'm obviously hoping for the slower solution, as a DL closer to I35 will result in considerably better chase logistics than a DL closer to Hwy 75 in eastern OK. In addition, I'm hoping that moisture doesn't end up being the "limiting reagent" in this atmospheric concoction the Mother Nature appears to be brewing up for Thursday.

 

[Mikey Gribble]

I agree with you for the most part Jeff, but I'm surprised you aren't more concerned about the low stacking more with the GFS and having veered 850mb winds along the dryline. Moisture return has been one of my chief concerns and continues to be, but I think the low stacking (like it does with the GFS) would be even more damning for tornado potential than poor moisture return. There is virtually no crossover in the 850-500 layer with the GFS. I can't get detailed enough charts for the ECMWF to get a good look at it, but just from going off the nation wide view COD offers it looks like it might be splitting the difference between the NAM and GFS on veering 850's and 850/500 crossover in the warm sector. I really don't think the badly veering 850's with the GFS will verify, but it still remains one of my biggest concerns at this point.
As you mentioned cloud cover and the extent of surface heating are more sublte concerns. The NAM is a little more agressive with surface heating and CAPE, with SBCAPE >2000 in tonights run. Either way CAPE/shear combinations should be favorable for supercells over a fairly large area. So with the cap not being a real concern at least we can go out Thursday expecting a decent storm. The big question mark for me remains the shear profile (and extent of tornado potential).
Like Jeff I am pretty optimistic about this setup and fully intend to chase on Thursday unless something changes dramatically between now and then. Should be a classic dryline chase in the plains.

I am just going to copy and paste my post from my blog, so I may repeat a couple things I already said above. I'm too tired to edit it out. Here's my post...


I just got done glancing over the 00Z NAM and it looks pretty good. The NAM continues it’s trend of not stacking the low by Thursday afternoon (the GFS does), so again with the 00Z NAM it is showing good directional shear. That really is going to key to the extent of tornado potential with this setup. If the GFS verifies and the low stacks by Thursday afternoon the tornado potential will be decreased dramatically. The NAM has been trending towards the GFS a bit, closing the low by 00Z Thursday in the latest run (had been an open wave at 00Z Thursday with previous runs), but it still isn’t stacking the low and maintains good directional shear across the warm sector.
The 00Z NAM did back off on moisture return, which has been my other major concern. In previous runs it had dewpoints in the 60′s all the way up to the triple point. In tonights run 60 degree dewpoints are just making it into south central Kansas by 00Z Thursday. Surface temperatures are just approaching 80 along the dryline in north central Oklahoma and LCL’s are low enough for a good tornado threat so I don’t see why dewpoints in the low 60′s would be a problem. NAM forecast soundings across Oklahoma show the moisture is sufficiently deep too.
So as it stands now my two main concerns with this setup (moisture return, low getting stacked) are still looking okay with the NAM. I will check the GFS in the morning, but hopefully it will break its trend of stacking the low and killing any 850-500 crossover. If the GFS starts moving away from that I will feel a lot better about this setup.
I don’t want to comment on the extent of the tornado potential right now because I really do think the extent of directional shear will have a huge impact on the tornado threat, so without knowing what to believe on that it’s impossible to know what to think about tornado potential.
I think we won’t have to worry about breaking the cap and getting storms with this setup, which is a relief since that has been a problem more than once already this year. It appears as if we will get decent CAPE. The NAM is a little more agressive with surface temps and has higher CAPE than the GFS as a result, but with either model CAPE/shear combinations are favorable for supercells. So basically there is high confidence in a severe weather event taking place on Thursday, there just remains a lot of uncertainty regarding the extent of any tornado threat. Hopefully that will become more clear tomorrow morning.
My map is my best guess at where the best tornado potential will be Thursday. I don’t have much confidence in the extent of the tornado threat, but I am fairly confident that is the area where it will be highest Thursday afternoon.

 

[Jeff Snyder]

I agree with you for the most part Jeff, but I'm surprised you aren't more concerned about the low stacking more with the GFS and having veered 850mb winds along the dryline.

Mikey -- that's a valid concern. The 12z and 18z GFS do seem to show a veer-back-veer vertical wind profile in southeastern Kansas Thursday, implying good mid-level CAA, but yielding odd hodographs (ones similar to which I've had very little chasing success). However, a bit farther south, neared the base of the trough axis, you get away from the backed mid-level flow, and the GFS has a bit more classic wind profile and hodograph shape. If this looks to verify, I'll just pay more attn to the Oklahoma target. Heck, even if the NAM verifies, the hodographs in OK are very nice. Again, though, I'm not hot on the KS target area if the 12z/18z GFS verifies... The 00z GFS should be out to 48 hrs in 10-15 mins.

 

[Jacob Ferden]

00z GFS still showing veered 850s near the dryline, with more backing farther out into SE Oklahoma, western Arkansas, etc. I personally am trending more towards the NAM solution, because A. More often than not, the GFS has been too progressive this year. and B. I think the GFS is underdoing the forecasted CAPE.

As of now, I'm planning on chasing this one, as I have Thursday afternoons off and it might be pretty close to home.

 

[Jeff Piotrowski]

Per 0Z Nam run looking at tornado's from SC/NE-C-E/KS- eastern OK ahead of DL. Expect low top sup cells by 18Z north of I-70 tracking NW/N on the KS/NE border area.

Then farther southeast over central KS expect classic T-Storms some significant to form ahead of DL bulge from Salina-Wichita-NE/OK by 21Z.

Then the cap breaks from KS/OK border south ahead of DL after OZ to NE TX.

I also expect in the 21Z-6Z time frame across eastern Oklahoma for some long track tornadoic storms.

An upgrade to Moderate from SPS for the area is likely.

My take on the WRF, HRRR, NAM, GFS, GEM, ECMFW are the models are “TRENDING” to a local but intense outbreak of severe weather.

 

[Chris Vagasky]

One thing I've been noticing is the NAM continues to show more of a kidney bean shaped surface low...kind of a dual surface low configuration...and brings the dryline just to the west of the I-35 Corridor. 00z GFS has a bit deeper surface low (994 v. 996) and the dryline just east of the I-35 corridor (around 177?).

Hodographs and lapse rates across eastern Oklahoma look good for supercellular structures and large hail. Will be fun to watch what happens Thursday afternoon.

 

[Mikey Gribble]

Above is the GFS (left) and NAM (right) 850-500 crossover and the difference between the two is significant. Like Jeff mentioned I have rarely had good luck with badly veering 850mb winds. Not that I am buying into what the GFS is selling. This wouldn't be the first time this year that the GFS was wrong with veering 850mb winds. As a matter of fact I think that might have been an issue with the last setup when we were 3 or 4 days out. If it wasn't the last one it was the one before that. Anyway, I am definitely leaning towards the NAM solution right now with regards to the shear profile. The ECMWF seems to be closer to that solution, but it's hard to tell given the poor charts I have access to. Plus I typically trust the NAM a little more than the GFS once you get inside 2-3 days.
Either way Thursday should be a severe weather event. I'm just uncertain on the tornado potential given the shear profile differences among the models. As long as 850mb winds don't veer badly, I think tornadic supercells are a good possibility Thursday. As things stand now, I'd target near or just south of OKC. I'm sure that will get tweaked slightly as we get closer, but I really like that central Oklahoma area. It seems to be the best compromise of cap strength, moisture, CAPE and shear.

 

[Jeff Snyder]

If it's any consolation, forecast hodographs from the 00z GFS look just fine farther south -- say, around the Red river. Essentially, you just need to get away from the backed flow aloft that the GFS shows closer to the OK/KS border. If that GFS forecast verifies, my eyes will be on the area between I40 and the Red, in perhaps questionable chase terrain. That GFS, being much faster to cut-off the trough / create a low aloft in the central Plains, seems to push the target area to the S compared to the NAM, but I like the environment in the target area (whether that ends up near the KS/OK border or in southern OK). The 21z SREF supports the forecast of the cut-off low occurring a bit later, more similar to the current NAM than the current GFS forecast.

 

[Trey Thee]

This is looking like the first real svr with tor probs for the Tulsa area this year. At this point I'd target the I35 corridor for initial convection and an area as far south as Pauls Valley and as far North as Ponca all appear to be in play. I'd setup just to the east of I35. Soundings look good as do the hodo's. As others have mentioned the veering still could be a potential issue but overall this system looks potent and I believe we'll have substantive moisture and resulting instability in place, especially south of the KS border.
As of right now the Tulsa area has little moisture but the south eastern portion of the state has winds out of the SE and moisture return beginning to take place.

 

[Doug Drace]

I normally have little to no interest in chasing E OK due to the poor terrain as well as road networks, but I must say 4/14 is even sparking some extra interest in my mind right now. Im off work at 11:30 tomorrow, so it may just be worth a chase in the sticks if things pan out as currently forcasted by 12z NAM. LCL's look really favorable in E OK at 1000 or even less from N to S, CAPE is as high as 3000 j/kg particularly in areas from I-40 to the Red River, and CIN is virtually non-exsistant throughout E OK into NE TX by 0z. Better LI's are N of I-40 near the OK/KS border. The Hodo's loop a little more in NE OK, however even in SE OK/NE TX they look pretty sweet as well...along with better Dewpoints from I-40 South. I wouldn't mind giving the southern end of the risk a shot, but the chase terrain is definately worse in SE OK vs NE OK. Currently im thinking about setting up somewhere around OKC to split the difference and go from there and see what happens. All of this is based on the 12z NAM, simply cause I trust the NAM a lot more than GFS within this time frame.

 

[Mike Smith]

I was just look at the 33 hr (21Z) forecast from the NAM (via Twisterdata) it looks very favorable. The surface low is just SW of ICT with very nice instability, profiles, and soundings ripe for initiation. Based on what I'm seeing now, I'd issue a tornado watch starting at 4pm Central along a 35 mi. either side of a line from 10 mi. west of Newton, KS to Pawhuska, OK.

 

[Chris Allington]

Based on the 12z runs this morning... I'll be targeting where ever the northern edge of the deeper moisture return makes it by show time. Likely somewhere in extreme SE KS near the Howard area by 21z. Shear profiles are better closer to the low and though I have some concerns about convective mode, I think there will be enough directional shear to keep things discrete atleast early before the linear forcing increases as the cold front overruns the dryline.