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

[Mikey Gribble]

Just going to copy and paste the latest post I made on my blog. I have a map on there too if you're interested (blog link is in my signature). Basically I am liking the OKC area as a starting point. Everything seems to be on track for a good tornado threat tomorrow. Below is pasted from my blog...

The going forecast seems on track. The only notable change with the 12Z runs of the NAM and GFS are that both models made a very subtle move towards the other solution on 850mb winds. The GFS isn’t veering them quite as bad and the NAM is veering them slightly more, so I still think what will actually happen is 850mb winds will veer slightly immediately ahead of the dryline and then back 50 miles or so off the boundary. That will work out just fine.
Aside from the difference with 850mb winds and the GFS being slightly more progressive, the only other major difference between the two models remains the extent of surface heating and resultant CAPE. The NAM continues to be more aggressive with surface heating with temps across the Oklahoma portion of the warm sector in the mid to upper 70′s by 00Z. The GFS keeps surface temps about 10 degrees cooler. As a result the GFS has CAPE <2000 across Oklahoma and the NAM has it >2000 all across Oklahoma and even approaching 3000.
The cause of the temperature/CAPE difference between the models appears to be a result of the GFS keeping the warm sector sacked in with low level clouds through the day while the NAM begins breaking up the low level clouds and allows for partial clearing by early afternoon. This is very apparent if you compare the two models 850mb RH charts through the day.
I am thinking the NAM is correct and we will get partial clearing and good insolation during the afternoon. The GFS seems to over forecast the extent of low level clouds on a fairly regular basis. Plus the NAM typically does a decent job forecasting CAPE.
Both models are about on the same page with moisture return. They both have low 60 dewpoints nosing into Kansas by late afternoon with low to mid 60′s across Oklahoma. 60 degree dewpoints are just now nosing on shore in south Texas, so I’m still a little worried about that verifying, but even if moisture was slightly worse than forecast it wouldn’t be a big deal. There is room to spare with dewpoint spreads and LCL’s will be sufficiently low for a good tornado threat so the moisture question is inconsequential at this point IMO.
So basically everything is coming together quite nicely for a few tornadic supercells tomorrow. I am worried about the extent of forcing for a squall line over the northern portion of the dryline, but as you go south along the dryline storms will be more discrete, so again not a real issue.
I think the best compromise of expected convective evolution(mode), CAPE and shear is all setting up across central Oklahoma. I expect the best tornadic storms to fire along the dryline between Kingfisher and Ardmore Oklahoma. I plan on heading to just north of OKC tomorrow morning and I will fine tune the forecast from there and adjust as needed.
I expect at least a couple cyclic tornadic supercells to come off the dryline tomorrow. Any storms firing along the dryline in the area I mentioned above will pose a threat for a strong tornado or two as they move downstream into the northeast and east central portion of Oklahoma later in the day. I’d put the absolute highest tornado probability over the southern half of SPC’s moderate risk area in the latest Day 2 outlook.

 

[Brendon Lindsey]

I really want to share 12z NAM Skew-T for Henryetta, OK. It got me excited. The HODO is great looking. -10 LI , 0 CINH , 3600 SB CAPE , 100% Supercell Potential , LCL under 1000 m http://beta.wxcaster.com/cgi-bin/parse_skewt_trace.cgi?model=NAM&fcsthr=036&STATIONID=KF10

I like this site for deciphering the Skew T haha there is another one that has what to look for in every parameter for severe storms, but I dont remember that site.
http://theweatherprediction.com/severe/indices/

 

[Michael Riedl]

For the Northern part of the dryline:

Surprised no one is talking about the Warm Air Advection/Isentropically Lifted rain showers forecasted to be over much of SC KS most of the day. Temps are only about 60 degrees at 18z on Thursday. That will definitely be something that will limit the extent of the Warm Sector north. Also as Mikey noted the mid level winds wanting to wind up around the Closed Low at H5. LI's are quite a bit higher in this area for what its worth. Storm mode might be more clustered here than further south.

For the southern target: Things look pretty good here as directional shear is better and as a result Hodo's are more curved. 65 KNTS of Westerly deep layer perpendicular to the ground will provide more than enough forcing for discrete supercells to take off in the Mid Afternoon, as opposed to later in the evening as most setups have been this year. CAPE AOA 1500-2000 j/kg and Low LCL heights give me confidence in having one or two supercells produce along the dryline tomorrow, it just is a matter of where.

Positioning 100% correctly should not be too big an issue as you can get anywhere in the Warm Sector/Dryline pretty quickly.

Gonna Jet down I-35 when my prior engagements get done, because of this I am hoping some Supercells fire around the KS/OK border because of time constraints of getting to the southern target.

 

[Andrew Stoller]

I can't believe anyone hasn't mentioned the cold core nature of this setup, with a vertically stacked surface low through 500 mb. 500 mb temps are -10 to -15C across north central to northeast KS east northeast of the surface low where winds are due easterly. 700 mb temps are around 0 C. Something to consider anyways.

 

[samuel stone]

concerning cold core: if an axis of steep low level lapse rates can nudge in from the southwest into the are youve discussed andrew, then i beleive a number of low topped sups capable of producing tornadoes are likely. too me it all hinges on that. i think no ones talking about it cuz everyone is more interested in the strong possibily of more conventional supercell tornadoes further south. ill be headed south east from hutch on ks hgwy 96/ I 35 @ 2 when i get outta work. too tempting down there, probably wont be able to make it all the way to central ok by showtime (where id like to be) so ill be banking on the crapvection clearing outta sc ks nc/ne ok. the other problem not many have discussed it the completetely horrendous road network eats of the newkirk/ponca city are. already experinenced this one this year feb 27. so anyone targeting nc/ne ok may have to deal with this isse... thats another reason id rather be nearer to the I-40 corridor for showtime. but like i said thats not an option for me

 

[W. Grant Dade]

I am really liking central OK tomorrow afternoon. However due to my schedule I will be chasing the Red River Valley in North TX. I think there is still a good chance of an isolated sup here. PRX 12Z NAM sounding looks good for supercell and tornado development. The LCL may be a little too high but we shall see.

Interesting that the models are very similar to 4/9/09. There were quite a few long track tornadoes that day including a 35 mile long EF-3 along I-20. It also looks very similar to 4/02/82, the day of the Paris, TX F4 tornado and southern OK F5.

Everyone stay safe.

 

[Jeff Snyder]

Interesting that the models are very similar to 4/9/09. There were quite a few long track tornadoes that day including a 35 mile long EF-3 along I-20. It also looks very similar to 4/02/82, the day of the Paris, TX F4 tornado and southern OK F5.

Everyone stay safe.

Tomorrow does have some resemblance to 4/9/09 (see the 4/9/09 page in the Severe Thunderstorms Events database), though tomorrow looks like it'll be farther north (take 4/9/09 and shift northward). In the end, I hope the result isn't the same, however, since I just drove around far northeastern Oklahoma in a quasi-linear convective mess. As you noted, though, there were some tornadic supercells farther south. On the other hand, I think tomorrow's setup looks very different from 4/2/82 (see maps here). We won't have 65-70 F dewpoints, and the upper-level pattern looks quite different.

 

[Trey Thee]

After reviewing the models in more detail tonight, I think SPC will probably stick with the MDT, at least for now. The shear profiles and hodo's do look good but coverage and moisture return may keep it from being a high risk day. Moisture return will definitely be good, but not sure it will be fantastic. In the event they go high risk I would expect that with the noon update tomorrow or the 3pm update. The hail threat does appear to be very significant.

 

[Mikey Gribble]

The 00Z NAM is throwing a kink in my plans. I was pretty sure I wanted to target central Oklahoma, but the northern portion of the dryline is looking very good now. The warm sector over south central Kansas is about the perfect width by late afternoon for storms to mature and then begin moving into the very impressive low level shear along the boundary. I think there will be a window along the warm front where conditions are quite favorable for a strong tornadoes. Plus this is set up pretty well for stair stepping south to new storms as they cross through that window of greatest tornado potential along the warm front. The whole stair stepping thing always sounds like a good idea and easy to pull off, but it rarely works out that way so I am a little hesitant to get cute and try it, but it just seems like the best play right now. Anyway, that is my plan for the moment. Since this is close to home I will have plenty of time to look things over in the morning before picking a final target.
BTW I posted a map on my blog. I as going to post it on here, but I'm retarded and can't figure out how to make the image appear instead of showing up as a link. Anyway, here is the link to my latest forecast map

 

[Doug Drace]

I've noticed on the 0z NAM a small area south of I-40 pretty much over I-35 from a general line south of Purcell to Ardmore, which by 7pm a small hole opens up in the CIN, LI's as low as -10 and LCL's possibly in the 1000 or lower range. IMO, if a storm could fire in that environment, it would have a very low updraft base, and since it doesnt look like too many storms would develop south of the Red River, it wouldnt have to compete with anything else. A pretty sweet looking area that could produce a significant tornado east of I-35. Im really starting to like the Pauls Valley area to set up shop, and generally near the Ada area and points ENE for a strong tornado. Shear is still quite impressive south of I-40 to the Red River.

 

[Adam Simone]

I'm still a rookie at this forecasting stuff but I'll give it a try. I'm also going to play the northern part of the threat area. The main reason is I work till 2:00 in Kansas City and probably won't have time to drive to central or eastern Oklahoma so I'm going to target the Chanute, KS area for now. Looking at the 0z NAM, I like the wind shear in this area and there looks to be enough moisture return with dew point levels >55. If I need to go west from there I should be able to but as of now thats where I'll be heading tomorrow afternoon. I drew up my threat area early tonight based on the 18z NAM

 

[Jeff Snyder]

Still some significant differences between the 00z NAM and 00z GFS, primarily in regards to the midlevel flow pattern. The GFS is still showing some backed midlevel flow (e.g. southerly 500 mb winds) N of I44 at 0z tomorrow evening, which creates S-shaped hodographs in far NE OK and SE KS. In fact, if the GFS looks like it'll verify, I'll seriously considering north-central Texas. Yes, Texas. The longitudinal width of favorable chase terrain is wider in N TX than in S OK, and the hodographs from the 00z GFS are just fine down there. The NAM has the midlevel low a bit weaker, and keeps the midlevel flow veered more in SE KS and NE OK, creating more favorable shear profiles. In addition, there seems to be a possibility of tor sups S of I40, but the "doable" chase terrain narrows progressively between I40 and the Red River. In general, along and E of US 75, the chasing gets a bit more difficult; E of US 69, the chasing is very difficult, by and large. As such, to get E of the longitude of US 69, I'd want to be N of I44. Otherwise, S of I40, I'd want to be W of US 75 (and certainly W of US 69), which narrows the region of favorable chase terrain. That is, until one gets S of the Red River.

One other brief note -- the NAM indicates some weakening at 850 mb along and just E of the DL at 00z, which results in straight-line hodographs and unimpressive 0-3km SRH (<150 0-3km) W of US 75 (or even W of 69). There is a local max in 0-1 km SRH in central OK ahead of the DL, but the best low-level shear is shifted farther eastward. Of course, much caution should be given to 0-1 and 0-3 km SRH forecasting 24 hours in advance, since SRH is can be very sensitive to changes in wind speeds and directions over relatively small depths... All that said, the 00z 4km EMC WRF has a supercell near/over the OKC area at 0z.

 

[Derek Weston]

Given what I'm seeing on tonights NAM run... I'd play the northern extent of the good moisture return into KS. Love the easterly surface winds. Trick will be finding just enough veering at 500. Per 21Z... we get that in an area between Wichita and Joplin. Rather nice large looping hodographs.

 

[Mikey Gribble]

I agree Jeff. The differences in the shear profile betwen the GFS and NAM is still huge. I'm really surprised they've both stuck to their guns for this long. With the NAM I think the dryline over south central Kansas is the best play. I've called it a warm front, but I don't know if the warm front should really be placed their or farther north. Regardless the area where surface winds back (eastern edge of instability axis) hodographs look very impressive with large curvature in the lowest 3km (as Derek mentioned). With the GFS though shear profiles are not good over the northern portion of the dryline. They really aren't good anywhere, but you have to go south if the GFS pans out to where you at least have a little 850-500 crossover.
I pretty much gave up on trying to sort out which model is right and have decided to just go with the NAM. The differences between the two are too significant to try and compromise between them. The best tornado threat is basically a state apart from each other with the two models (really don't like the tornado threat with the GFS). It should become apparent tomorrow morning which model is telling the truth.
And yeah that lone supercell over central Oklahoma is nice with the 4km WRF.

 

[Stan Rose]

06Z NAM is moving in line with the GFS--suggesting a further S target. Id still split the difference and stick with central OK--theres been good consistency for pressure falls over OKC.